11th International Rolling Conference - IRC 2019 | Schedule

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Usiminas Steel Plant in Ipatinga installed an accelerated cooling device named CLC (Continuous On-Line Control) in the year 2011, enabling it to supply steels produced by TMCP technology. There are various gains in terms of quality and productivity associated to the application of such technology. However, the flatness control becomes crucial because large thermal stresses may be generated due to thermal heterogeneity during the fast cooling when the austenite phase decomposes mostly into ferrite and bainite. In literature there is lack of knowledge regarding a full understanding of the relation among cooling conditions and plate flatness. Therefore, this work has focused on the effect of the cooling strategy for API steels, aiming at optimizing flatness and keeping the mechanical properties within the specified ranges. The starting point was dilatometer tests, where cooling conditions such as start cooling temperature, SCT, finish cooling temperature, FCT, and cooling rate, CR, were changed in order to evaluate their effect on microstructure and hardness. Those laboratory conditions supposed to give the best results were transposed to industrial scale, so as to produce experimental lots of plates with five different cooling strategies. It was shown the possibility to find a cooling profile that guarantees the balance between mechanical properties and flatness requirements. The influence of cooling strategy on flatness was explained by the varied heat transfer regimes occurring from hot steel surface to the ambient.

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The situation of the steel industry is still challenging. Worldwide overcapacities have an impact on profitability. More than ever, the point at SMS group is to provide the steel industry with flexible and profitable technologies and systems over the whole process chain. One example for that is the thin slab casting and rolling technology and, in particular the CSP® technology (Compact Strip Production), being well established for hot coil production. From its introduction in 1989, CSP® technology has been continuously further developed. Today, on a CSP® plant, the full range of high-quality steel grades can be produced with tightest geometrical and metallurgical tolerances under optimal economic conditions. With the introduction of semi-endless rolling and, as a further step, the endless rolling process, the product range for thin and ultra-thin products has been further enlarged, allowing for the production of hot rolled coils with a thickness of 0.8 mm for low carbon steel grades. Also high-strength steel grades may be produced with gauges below the minimum product thickness that can be achieved in a conventional-type hot rolling mill. Another step in the further development of CSP® technology is digitalization. In December 2016, the CSP® plant of Big River Steel (BRS), located in Arkansas, USA was put into operation. It is the first learning steel mill in the world. The CSP® plant of BRS comes with innovative technologies, providing impressive operational results right from the beginning.

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as the customers demand new, more resistant and dimensionally challenging (thinner and/or wider) steel grades, actions have been carried to improve thickness performance and reduction of internal losses while still meeting the more restrict tolerances booked by the customers. This paper presents the recent evolution of thickness performance, the reduction of internal losses and the main actions deployed.

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The necessary time to launch a vehicle has been reduced year by year due to, among other factors, softwares improvement that can predict forming process and application performances. The material behavior is one of fundamental issue to guarantee accuracy in numerical simulations. The relationship of the stress-strain determined by uniaxial tensile test is an information required in forming softwares. The strains obtained in stamping process normally are higher than those reached by tensile test. Therefore, it is necessary to extrapolate of the tensile data to predict the steel plastic behavior under biaxial stress state. This implies the development of new constitutive models or better application of old models. Among the models already known, this study makes use of the following constitutive equations: Hollomon, Ludwik Swift, Hockett-Sherby and Voce in the uniaxial tensile behavior of the steel. The results showed that the Swift, Hockett-Sherby and Voce equations, in general, present good fit to the experimental data. The initial (near of yield strength) and final (near of tensile strength) part of the stress-strain curve was best fitted by the combination of the Swift and Hockett-Sherby plastic models.

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This work reviews the new version of GB1499.2-2018 Chinese national standard and specifications governing production of high-strength reinforcing hot rolled ribbed bars. In addition, it discusses the main concerns from Chinese rebar makers that might affect production and application of Nb-bearing rebars, like reheating temperature required to dissolve given niobium additions, the promotion of bainite microstructure and continuous yielding, as well as Nb strengthening effects. Through extensive investigation involving both thermomechanical simulation tests and industrial trial, the existing state and effects of Niobium along the reheating, rolling and cooling are illustrated. At the end, optimum processing conditions has been established to produce high strength rebars for the specified requirements. That reflected in an amount of about 20.0 million tons of Nb-bearing rebar being produced in China in 2018 with required tensile properties and microstructure, and helped rebar makers to reduce production costs considerably. Based on production data, Niobium demonstrated positive strengthening effect for high strength rebars, in particular for small size rebars with earthquake resistant performance. What is more, the results of the research enrich the knowledge of the application of Niobium in steels under no TMCP rolling conditions.

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In recent years, several studies have been developed on the use of Nb micro-alloyed steels with low Mn content in the controlled rolling of heavy plates. This unprecedent concept of alloy leads to some peculiarities in its thermomechanical processing. For example, its very low levels of C and Mn promote an increase in the temperature at the beginning of the ferrite formation (Ar3), while its Nb content raises the non-recrystallization temperature of austenite (Tnr). This restricts the proper temperature range at which the finishing phase of controlled rolling should be performed. Lower Mn contents should lead to the acceleration of the NbCN precipitation kinetics during rolling, leading to a reduction in the soluble niobium content in austenite that delays by dragging the recrystallization of austenite. This fact, plus the heavy and fast passes applied under virtually isothermal conditions in a heavy plate rolling mill with high power, increases the risk of partial recrystallization during the finishing phase of the controlled rolling mill, since the strain hardening of the austenite becomes significant and the interaction between precipitation and recrystallization of austenite is increasingly delayed due to the greater reduction in the dissolved niobium content that results from the intensification of its precipitation. The objective of this study was to analyze the evolution of the average values of mean flow stress during the finishing phase of the controlled rolling mill in these Nb microalloyed steels with low Mn content, in order to better understand the metallurgical mechanisms acting during the thermomechanical treatment of this specific steel.

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The effect of the cooling conditions on the microstructure and hardness of a Dual Phase hot-rolled steel 800 MPa strength was investigated. Simulations of the cooling conditions using a dilatometer were carried out from samples of a hot rolled coil with variations of the intermediary temperature from 620 to 740°C, isothermal holding time between 1 and 10 s and coiling temperature between 50 and 400°C. In addition, two CCT (Continuous Cooling Transformation) diagrams were developed to evaluate the effect of the isothermal holding time on the phase transformations of the remaining austenite. It was observed that the intermediary temperature has a strong influence on the kinetics of the phase transformation, as well as the isothermal holding time influences the amount of ferrite formed and, consequently, the final microstructure and hardness of the material. The coiling temperature did not cause significant changes in the amount and morphology of the ferrite, but a gradual replacement of martensite with bainite was observed, which, in addition to the self-tempering effect, contributed to the hardness reduction.

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Many hot rolling mills worldwide face nowadays bonding zone fatigue problems before reaching scrap diameter of the work rolls. This phenomenon is nowadays known to occur in reversing roughing mills both in stainless steel and in carbon steel rolling. The phenomenon can be explained through longer rolling campaigns, inadequate backup or work roll maintenance, harder steel grades or increased throughput by reduced amount of passes to achieve the same thickness. In order to help users in optimizing the roll use, we developed a numerical tool to evaluate and optimize roll maintenance. This paper will review the influence of roll geometries on stresses generated at the roll surface but also at the bonding zone. We will also show how roll geometries can decrease contact fatigue damages by modifying crowning and chamfering procedures, shell thickness, material design or campaign length.

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Nowadays, due the development of new hot rolled strips at USIMINAS, established the necessity of realizing studies to define new parameters for the welding machine of new pickling line, in order to improve the results of mechanical and metallurgical properties relation of these materials. This study, that was designed for study of weldability of high strength low-alloy steel with low boron content that overcomes 600 MPa of tensile strength, there was analyzed the influence of energy input and preheating temperature on mechanical properties of hot rolled strips at three distinct thickness (2, 4 and 6 mm). To evaluate the welding results, there were made tensile test, micro-hardness, metallography (micro and macro examination) and scanning electron microscopy analysis. Through the analyzing of the mechanical and metallographic tests, a better welding performance was verified, increasing the welding energy and the preheating temperature.

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The innovative methodology developed by the author allows the elaboration of an Angle Roll Pass Design based on the practical observations of the rolling process and applying mathematical criteria supported by Advanced Excel tools (Achieve goal, Procv-Proch, Macros) and AutoCad. The development of the calculation had as initial basis the survey of the spread factors for angles previously studied by using Ekelund that is an empirical formula. The previously shown, the factors presents wide variation depending on the rolling conditions, the geometry of the grooves, the degree of free spread in the groove and the set-up of the guiding system among others. There are enormous dimensional varieties of angles of the covered products, with linear mass from 0.6 up to 60 kg / m. Depending on the angle dimensions and technical characteristics of the rolling mill, angles they could be rolled from two to eleven passes. There are at least four types of roll pass designs (currently used): • Butterfly with one straight leg • Butterfly with two straight legs • Butterfly with Intermediate Edger pass • Butterfly with opened pass • Finally Special roll designs. For the beginning of the project, it is necessary to define the initial draft, the number of passes and the reduction in each pass, the roll design method to be used, the spread factors, the finishing speed and the initial temperature. As explained initially, these calculations are performed through Excel and for all passes are inputted the entering date in the spreadsheets. The whole calculation by the Ekelund formula is carried out as flat passes and at the end, these flat passes are transformed into shaped passes. The height reduction of the passes are scheduled out and simultaneously, three heat transmissions types are calculated: (1) Heat loss by conduction from the bar to the rolls, (2) Heat gain by the deformation work and (3) Heat loss by radiance between exit time of the stand and the entering in the next pass. The temperature loss from contact with the cooling water is not taken in consideration once it is too low. The sum of these losses and gain generate the input temperature in the next pass. Then each item is calculated for all the passes: Bite Angle, Spread, Section Reduction, Separating Force, Torque, Power, Temperature and others. At the end of the calculation, it is checked if the desired size of the angle leg has been reached and otherwise it is necessary to adjust the initial stock or the spread factors. If this dimension is OK, we check the stand and if it is necessary, we adjust the initial draft, the reductions or the amount of passes. The last step is to transform the flat passes into shaped passes. For all the components of the grooves are parameterized according to the number of passes and the type of roll design chosen. These parameters form the skeleton of the pass and the thickness of it is calculated so that this pass has the same section of the rectangular flat pass generated in the calculations. With these parameters, the grooves are drawn in AutoCad and the final dimensions are checked with the calculated values. THE METHODOLOGY CAN BE USED IN THE OPPOSITE WAY: FROM AN EXISTING PASS DESIGN IT IS POSSIBLE TO CALCULATE ALL THE PARAMETERS OF THE STANDS AND PASSES AND CHECK IF ANY ITEM IS OUT OF ORDER AND CORRECT IT. THIS METHODOLOGY WAS ALREADY USED FOR THE DEVELOPMENT OF NEW PROJECT AND ALSO TO EXISTING ONES, WITH COMPARISON OF THE RESULTS AND HAS SHOWN TO BE RELIABLe.

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The application of thermo-mechanical control processing (TMCP) in hot rolling of steels has become a common routine since the last 60 years. The understanding of the physical metallurgy behind TMCP played a major role in the early developments. Physical and numerical simulation works are performed firstly to derive the fundamental metallurgical knowledge and secondly to conceive existing TMCP practices. In this paper, a summary TMCP techniques is presented. The occurrence of dynamic transformation of ferrite in the austenite region is shown by means of synchrotron light diffraction methods. This phase transformation mechanism is taken into consideration and its effects on TMCP are proposed in an exploratory way.

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Driven by market trends, increasing environmental accountability, government regulations and fostered by the Company’s strategic plan, ArcelorMittal Tubarão has developed new steel products to deliver better solutions to fit each customer’s needs. This often translates in higher strength, more complex and dimensionally challenging (thinner and wider) steels to attend a broad array of goals, such as reduction of vehicles fuel consumption and carbon emissions, increase in fatigue performance of heat treated parts, higher load capacity per net weight in vessels or wagons and lower supplying lead time as ArcelorMittal Tubarão establishes itself as a domestic option for so far imported grades. Based on the annual Product Development Plan, a structured workflow involves technical discussions from an operational point of view about safety issues, metallurgical project, steel grade family definitions, offline simulations prior to field trials, deformation resistance and process parameters adjustments and scheduling strategy. As a result of the increasing synergy between the areas, the share of new materials developed in recent years has been sustainably increased up to 15% in 2018, adding value to the final product without impact on hot rolled coil output and with a low cobble index.

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The influence of the coiling temperature after hot strip rolling on the microstructure and on the tensile and hole expansion properties of a 800 MPa multiphase steel was investigated. For the temperatures between 150°C and 600°C the microstructure consisted of a ferritic matrix with a dispersion of fine martensite-austenite (MA) and regions of degenerated upper bainite. In all cases the ferrite presented a heterogeneous mixture of polygonal, quasi-polygonal and acicular grains. The yield and tensile strengths showed a tendency of decreasing with the increasing coiling temperature, probably because of the larger fraction of MA particles at lower temperatures and higher fraction of quasi-polygonal ferrite at higher temperatures. The elongation was not significantly affected by the variation of coiling temperature. The average hole expansion ratio showed a maximum of 80% for the material coiled at 400°C and fell below 50% only for the coiling temperature of 150°C, probably due to the larger hardness difference between the ferrite matrix and the MA particles.

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As a low alloy wear-resistant steel with the highest strength, NM600 has been gradually applied in mining machinery, construction machinery, agricultural machinery and railway transportation. However, due to its high tensile strength and Brinell hardness, its elongation is generally less than 7%. The subsequent processing and forming methods are limited, which limits its application fields. The influence of reduction rate of austenite recrystallization on deformed austenite was studied by Gleeble-3500 thermal simulation test machine, and the continuous cooling transformation curve was measured. The grain size and shape of deformed austenite were controlled in the range of 15-25% secondary reduction rate in the elongation rolling process of austenite recrystallization area. At the same time, the grain size and shape of deformed austenite were set after final rolling according to the continuous cooling transformation curve Ar3 and Ar1 temperatures. Relaxation time, starting cooling temperature, cooling rate and other key parameters can control martensite morphology and lath bundle size in final service state. The average width of martensite lath bundle of NM600 is 1.0-4.6 um and the elongation of product is more than 8.5%. The contradiction between high strength, high hardness and high elongation of NM600 in iron and steel industry is solved.

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The competitive scenario of steel industry requires studies and developments to improve manufacturing processes focusing on increasing productivity and reducing costs. The practice of coating rolls for cold rolling with the chrome aims to increase the rolling campaign, reducing their wear by increasing the surface hardness, which guarantees a greater homogeneity in the surface of the rolled products. The present paper presents a study on the effect of the chromium coat on a forged steel rolls on the wettability of a SkinPass solution. The hardness of the coated layer and the contact angle were measured for two concentrations of solution on two types of surfaces, comparing the coated and uncoated surfaces. The results show that there is an influence of the coating on the wettability of the fluid when comparison are made with chrome coated and uncoated materials, being verified through tests in Goniometer. The productivity of the coated rolls showed higher productivity than the uncoated ones

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A CMnSiAl transformation induced plasticity (TRIP) steel was used to study the effect of retained austenite on room-temperature mechanical properties. The steel plates with retained austenite were obtained by hot rolling, cold rolling and subsequent continuous annealing. The starting and finishing temperature of hot rolling are between Ac1 and Ac3. Reduction ratio of cold rolling is 75%. The continuous annealing is carried out at different intercritical temperatures. The relationship between work hardening exponent and retained austenite was discussed. The results show that, the Ac1 and Ac3 were much high because of the alloy elements, and the temperature range between them was wide. Due to the high hot rolling temperature, the grains was hereditarily refined as a result of dynamic recrystallization. Annealing at intercritical temperature of 930 ºC, retained austenite with relatively high stability reached a maximum volume fraction of 25%, a maximum total elongation of 30.2% and a best ultimate tensile strength × total elongation of 20.1 GPa•%. Instantaneous work hardening exponent reflects strengthening mechanisms at different strain stages. The TRIP effect of retained austenite is the main mechanism during deformation. With retained austenite of sufficient amount and high stability, continuous work hardening was observed in the tensile specimen of 930 ºC.

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Circular steel is an important structural tool steel, it is widely used in the production of bolts, mechanical parts, seamless steel tubes and so on. The problem of finished product size is the main problem in the production of round steel.This paper analyzes the factors that influence the size of finished products in the actual production of various specifications and varieties of round steel at the price of 20mm~ 70mm for he steel xuansteel，the control method of finished product size in round steel production is summarized from the aspects of temperature, material type, looper tension control, pass design and operation specification.

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Aiming at greatly increasing efficiency and saving budget, higher strength and larger-diameter pipes have been developed and applied for constructing long distance pipeline projects in China. At the same time, in order to produce pipeline steel with high strength, high toughness and excellent DWTT performances, it is critical to refine austenite grain by static recrystallization rolling. Therefore, this paper focuses on the brief introduction of development of pipeline projects in China and also on the basics research in the field of static recrystallization during austenite processing of Nb-bearing steel.

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In this presentation, a 444-type heat-resistant ferritic stainless steel containing 0.05wt% Ce and 2wt% (Mo+W) was used as an experimental material and a study was carried out on the effect of rolling processes on the microstructures and texture evolution as well as on the mechanical properties and formability. The rolling processes contain hot rolling at different hot rolling finish temperatures, annealing after hot rolling, cold rolling and subsequent annealing. As for the hot rolling process, two hot rolling finish temperatures, 1133 K and 1043 K, were adopted, and their influence on the microstructures and mechanical properties was comparatively studied. The results showed that the microstructures after hot rolling and subsequent annealing could be refined by lowering the hot rolling finish temperature. The resultant microstructures after cold rolling and annealing were hereditarily refined. Lowering the hot rolling finish temperature can weaken the ALPHA-fiber texture in hot rolled or cold rolled ferritic stainless steel strip. However, the BETA-fiber texture was homogeneously strengthened by annealing the cold rolled ferritic stainless steel strip. Enhanced mechanical property and formability in terms of strength and average plastic strain ratio could be obtained by lowering the hot rolling finish temperature of ferritic stainless steel.

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The energy efficiency of reheating furnaces is a continuous challenge, as these equipment consume a representative portion of the total fuel of an integrated steel plant. Therefore, any investigation and implementation which brings improvement in this figure become an important issue for the mill competitiveness. In the case of production delays due to external factors (the condition addressed in this work), whether predicted or unforeseen, the slabs remain inside the furnace with high temperatures in order to avoid production delay during the production restart, elevating the specific consumption and scale formation. This work increased the energy efficiency of the two ArcelorMittal Tubarão’s walking beam reheating furnaces, by reducing the consumption of mixed gas during production delays (either scheduled or not) lasting less than 3 hours. The objectives were achieved through improvements, among them, tuning of Level 2 automation system parameters, automatization of procedures and operational training. The work resulted in a 34.4% fuel gas consumption reduction during the delays.

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The present study was developed in the Hot Strip Mill area that has a Steckel Mill in use. This equipment is a four high reversible stand that has four rolls that are assembled one on the other in the horizontal. The center rolls are known as work rolls, and these are of smaller diameter. There are two other rolls, known as backup rolls, which are of larger diameter. The work rolls that were analyzed in this study have 900 mm of diameter of the work table and weigh 18 tons. They are used in the hot rolling process and are responsible for the reduction of the cross section of the steel plates that arrive in the mill at temperatures around 1250ºC, transforming the steel plates into steel coils. Due to the direct contact of the heated plate with the work rolls, the same are heated and cooled during the process. After the rolling process and the finished campaign, they are with temperatures on the work table around 60ºC. In order to be regrinding and return the quality conditions of the surface, the rolls must be at temperatures of up to 30ºC. Thus, a system of cooling the rolls was provided, consisting of two pipes with holes that can project water on the surface of the rolls. About 90 minutes of forced cooling is required to meet this parameter. The creation of a new rolls cooling system composed of two piping arrangements with heat extraction nozzles was focused by this development. Some data was collected on the cooling time of the rolls, as well as temperature measurements from all the rolls. The new system was able to reduce the forced cooling time satisfactorily, which impacted the total cycle time of the roll and had greater availability of this input. We also had a very significant environmental impact because, due to the shorter time, we consumed a smaller volume of water.

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The quality of flat rolling process depends highly on multiple factors such as applied forces, materials involved for both strip and rolls, roll geometry and its positioning. To calculate the strip shape, a mathematical/numerical model can be applied, showing the final product and how the equipment behaves when changing some parameters. This is usually a time-consuming task for both user and computer, especially when it involves thin and hard strips. By coupling a quick rolling load calculation method as Bland-Ford and Finite Element Method (FEM) for roll stack deformation, it is possible to create an accurate and user-friendly rolling simulator. This paper presents the improvements done in the 3D FEM/multi-slab method and its actual capabilities by simulating two cases of a 6-High rolling mill. Different analysis in this equipment can be easily done in about 10 minutes by using the developed an electronic spreadsheet program interface and the folder generated with relevant results and logs. An operation manual and a commercial FE program plugins were made to aid construction of a completely new model. The code was created in a modularized way to assist the application of this simulator for other operational conditions.

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In this work we present a study of optimization of a new inhibitor for turbulence pickling line. The efficiency of inhibition was measured and the weight of loss was evaluated in four different materials to optimize the dosage of the inhibitor. In seven months we had 8.7% of reduction in pickling losses.

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The challenge The customer was planning to produce a 5" angle in a rolling mill designed to roll up to the 4" size. Initial studies indicated that this product required a 160mm billet and the replacement of a gearbox of the roughing train. The customer informed the need of a roll pass design using 150mm billet, which is the current size of the Melt Shop, besides not replacing the gearbox, which would represent an extra investment and demand a long implantation time. The mill's staff reported not having historic of breaking this gearbox and no overload on the heavier products. The project An innovative pass design was developed by the author, using the W Method, which increases the spread of the first four passes, thus reaching the desired angle leg dimension. The project of this angle is usually done with eight passes. This design was done with eleven passes in order to have low section reductions and consequently generating torque and power compatible with the mill characteristics. As this method is not used in any other known mill, thus not having a reference of its technical feasibility, a FES (Finite Element Simulation) and a FEM (Finite Element Modeling) was done through the Research and Development Department(R & D) of the customer that demonstrated the project viability. It was done calculations for spread, temperature loss, separating force, torque and power. The rolling mill team provided end-of-life rolls to machine the grooves, guides and accessories were manufactured and four months after the beginning of the project, it was possible to successfully test the first six passes in June/2018. The results From July 3 tests were done with the three angle thicknesses (5/16"- 3/8" - 1/2"), producing 700 ton of good quality products without difficulty of set-up. The rolling mill team carried out this project at a very low cost and in a very short time. The torque of the motors was between 40 and 60%, without overload of the equipment. The calculated roll efforts were compared with the real data showing the correction of the methodology. The shears, cooling bed, straightening machine and stacker processed the new product without problems. For the new rolls to be machined the pass design was revised, mainly for the 1/2” thickness, whose leg widths was close to the maximum of the tolerance, the grooves weren´t completely filled and with very low section reductions. For this size, were reduced two passes and created four specific grooves with smaller width in order to have a better control of the leg sizes. Conclusion This innovative project proved to be fully feasible, with low implementation costs, generating good quality products and without equipment overload.

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Major costs in the production of both flat and long commodity grade structural steel products include alloy, labor and energy. Flat and long commodity grade structural steels such as ASTM A36, ASTM A527Gr50, S235, S275, S355 and other equivalent world societal standards represent over 500 million annual tons worldwide. These simple commodity grades consist of a minimum of three base common alloying elements, carbon, manganese, silicon and then can be supplemented with microalloying elements of either vanadium or niobium. Since 2016 raw material costs for two of the five alloying elements in these commodity grade structural steels, FeMn and FeV, have risen significantly. For steel plants producing hundreds of thousands and in some cases over a million tons annually of these common structural steel grades because of the significant alloy cost increase for Mn and V alloy additions has squeezed profitability of these grades. These grades typically represent the base loading for cost controls in most all steel plants and hence a significant cost increase in two of the five elements used for these grades has a negative effect on overall production costs. However, with a proper strategy for alloy designs working in conjunction with the mills existing processing capabilities to achieve the desired end metallurgy/mechanical properties, alloy costs and operational efficiencies can be realized. Cost savings of US $2/ton to US $20/ton or in some cases higher in a mill producing typically from 200,000 tons up to 1 million tons annually can represent cost saving in alloy of US $400,000 up to US $20 million annually. Because of the significant opportunity for cost savings going to the financial bottom line, potential opportunities for alloy optimization is something that cannot be ignored and must be explored. Many worldwide commodity flat and long products structural steel producers have already taken steps in alloy optimization of their production and have realized significant cost savings. An understanding of what creates strength and ductility for any given structural steel microstructure is what is needed to achieve these cost savings. Strength and ductility for any structural steel are obtained from three metallurgical mechanisms or “building blocks”: a) grain size refinement, b) solid solution and c) precipitation. If better engineering of these contributions from the three metallurgical “building blocks” can be realized for a mill processing capabilities, alloy costs can be minimized resulting in significant annual cost savings. The correct use of these factors brings in addition process/mechanical property stability resulting in corresponding reductions in yield losses and additional operational cost savings. Use of practical metallurgical modeling tools along with mill data to determine process control capabilities can also assist in alloy designs for cost optimization.

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The objective of this project is to increase the hot charge by increasing the productivity of ArcelorMittal Tubarão's Hot Strip Laminator by the sequencing process of the Hot Strip Mill with the automation of the slabs relocation /process (reduction of time and movements in the hsm's slabyard ) that will evaluate exchange of cold slabs by hot slabs available after schedule process, every x hours automatically (without human interface). The work began with the revision of metallurgical rules for material relocation, definition of the definition criteria (hot / cold), groupings of material without evaluation and change of priorities in the reallocation of slabs. With the process / system is expected to achieve a potential 5% increase in slab hot charge index in slabs reheating furnaces, reduction of fuel consumption of the furnace and increase of productivity of the ArcelorMittal Tubarão Hot Strip Mill.

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Q&P steels undergo continuous multiple processes, including hot rolling, intermediate heat treatment, cold rolling and continuous annealing etc. The inheritant effect of initial microstructure could affect the final microstructure and mechanical properties of Q&P steels. In this work, effects of different hot rolled microstructure/texture on the final microstructure and properties subjected to Q&P process were investigated in Fe-0.38C-1.58Mn-1.6Si system. Different initial microstructures were generated combing different TMCP and cooling strategies. The microstructure and texture of hot rolled materials were characterized in detail. The hot rolled material was subsequently processed by intermediate annealing, cold rolling and continuous annealing. The comparison reveals great effects of the initial hot rolled microstructures, i.e. inheritance effect. The faster reverse transformation would lead to more sufficient austenitization and it would greatly weaken the inheritant effect of the initial microstructure. Although the difference of final phase fraction for different initial microstructures was not significant, the inheritance effect was mainly reflected in the effect on austenite morphology. For the mechanical properties, no obvious difference in strength was shown for the samples with different initial microstructures after Q&P heat treatment, but there was fluctuation in elongation.

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This study, which was applied in the coil storage yard of the Hot Rolling Mill area, aimed at optimizing the process of making decisions of the operator during transport and storage of steel coils. The coil storage yard is a strategic area that, besides storage, has the function of sending the coils directly to the customer, and it also monitors the temperature, so that part of the coils is sent to the Temper Mill. These coils arrive in the patio with temperatures up to 600ºC. The ideal temperature for the rolling process in the Temper Mill is 80°C. This patio has the capacity to store 650 coils on two levels. According to the initial project, the crane operators inside the operating cabins should receive information only from where they should stock each coil. The decision to release the coil is from the floor controllers. Those are responsible for measuring the temperature of each coil, making the decision and communicating by radio to the crane operator. This measurement used to be done through a portable optical pyrometer. In order to optimize this process, a portable thermographic camera was acquired. Knowing the temperatures of coils stored in certain regions, the controller can quickly define the best place for cooling. The images of the thermographic camera will be transmitted to the tablet of the controllers, allowing its rapid analysis due to the possibility of checking a larger number of coils in each measurement. Through the new form of measurement, it is now possible to speed up this process, increase the level of precision during the activity, guarantee the process parameters and, more importantly, reduce the exposure of the floor controllers near the coils at high temperatures, which makes the activity safer.

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In this work, we investigated the effect of the rolling process (warm-rolled or cold-rolled) on microstructure evolution and mechanical properties of 9Mn steel. After intercritical annealing at 670°C for 10min, both cold-rolled and warm-rolled microstructures are composed of ultra-fined austenite and intercritical ferrite. The austenite in warm-rolled sample includes two types of morphology, namely equiaxed and lamellar, which exhibits a wide distribution of grain-size. The incomplete recrystallization or recovery behavior of ferrite in warm-rolled and annealed sample results in higher yield strength and shorter yield point elongation. Moreover, the warm-rolled and annealed sample extends the TRIP-related work hardening over a broad strain range, resulting in a better combination of ultimate tensile strength and total elongation.

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This paper presents the project of Tangshan’s new no. 2 Cold Rolling Mill Complex (Pickling Line Coupled to a Tandem Cold Mill, Continuous Annealing Line and Continuous Galvanizing Line) dedicated to high-end markets such as the automotive industry. The project included equipment delivery, line start-up and Through Process Optimization Know How package to bring steel production and plant organization robustness and cover new steel grades especially AHSS. Combination of Primetals Technologies expertise in equipment, process and Know-how, associated to Tangshan experience in steel production brought a fast success already recognized on Chinese market and the certification dedicated to the most valuable products.

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The modeling of austenite evolution during the hot rolling of steels is covered in the literature for a wide range of chemical compositions, although mainly for carbon contents below 0.20%. In addition, most of the investigations on this topic are oriented for processes that are characteristic of flat products. In these cases, hot rolling is well-defined in two zones: a roughing stage, where deformation temperatures are usually above 950ºC, and a finishing stage, that is usually performed at temperatures below this range. Compared to those processes, the hot rolling of bars for structural applications presents considerable particularities. First, in bar rolling, together with dimension changes, the cross sectional shape is modified through each pass. This results in dimensional change through width that cannot be neglected as in flats, leading to a more complex state of deformation. Second, as structural bar rolling is strongly driven by high production output, the process is performed at high speeds and the rolling temperatures remain practically above 950ºC during the whole process. Considering the deformation parameters, these particularities result in (i) strain values that are considerably higher than those applied in flat rolling, usually above 0.45, (ii) much shorter interpass times, usually of fractions of seconds during the last stages of the rolling, and (iii) much higher strain rates, as great as 1000s-1 depending of final diameter. Regarding the thermal profile, rolling is performed with an overall variation of only 100ºC, with final temperatures usually above 950ºC. Consequently, the rolling window has less room for modifications. All these particularities affect the austenite microstructure evolution. On the one hand, it is well-known that the application of high strains at high temperatures can activate dynamic recrystallization. Therefore, post-dynamic softening mechanisms can play an important role in microstructure evolution. On the other hand, if the steel is microalloyed with elements such as Nb, strain-induced precipitation can take place during rolling and can interact with these dynamic and post-dynamic softening mechanisms. The aim of this work has been to develop an austenite microstructural evolution prediction program, MicroSim-Bars, which takes into account all the above mentioned singularities. In the program, the input information is the composition and data from industrial schedule. This is converted to nominal deformation conditions following the approach proposed by Lee [1 ]. Different types of torsion tests have been performed in the laboratory to develop austenite microstructural equations suitable for the steel compositions and deformation conditions usually employed in bar hot rolling, as well as to understand the interaction between the individual microstructural evolution mechanisms at these conditions. The equations have been implemented in the program, and both torsion and industrial microstructural data have been used to validate the model. 1) Y. Lee, S. Choi, P.D. Hodgson, Analytical model of pass-by-pass strain in rod (or bar) rolling and its applications to prediction of austenite grain size, Materials Science and Engineering A336 (2002) 177–189

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To meet the requirements of high-performance steel plates, while reducing manufacturing costs and saving energy, the advanced cooling system for plate mill (ADCOS-PM) with functions of accelerated cooling (ACC), ultra-fast cooling (UFC), and direct quenching (DQ) was researched and developed by the State Key Laboratory of Rolling and Automation (RAL). Since 2003, several sets of ADCOS-PM device were developed and implemented in industrial practice. To fully utilize the ADCOS-PM technology, the combination of various strengthening mechanisms was promoted by NG-TMCP technology and low-cost, high performance plates were produced such as pipeline steels, and high-strength construction machinery steel.

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A customized version of the Microsim-PM software for one Steckel rolling mill was built and adapted for specific mill parameters. The focus of this study is to use this model, which predicts the austenite grain size distribution evolution during rolling, to understand and quantify metallurgical issues happening during hot rolling. This will allow the steel mill to optimize the rolling process and chemical composition before the first industrial trial. Materials rolled for final thicknesses of 4.75; 6.30 and 12.5 mm of a carbon manganese steel and a microalloyed steel were selected to tailor the equations used by the model and to accurately reproduce the reality of the Steckel mill. This paper analyses the results from the customized model and compares them to mill data and final microstructure. Measured and predicted Mean Flow Stress (MFS) values are compared. After rolling, the material is subjected to accelerated cooling using laminar cooling. These cooling curves obtained from mill data are also considered to analyze the final microstructure characterized for all the cases using EBSD. The quantification of the microstructure allows for a better understanding of the relationship between chemical composition, process parameters and mechanical properties.

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The aim of this research is to be able to predict the grain size of steel during the hot rolling process. A rolling simulation system has been previously developed to calculate the deformation, stress, strain, and temperature fields by using a novel meshless method. Initial size of the billet, bloom or slab and the geometry of the grooves at each rolling stand are completely user defined. This prediction model may be applied to any of the roll pass designs. The information obtained by this rolling simulator has been considered in the one way coupled grain size prediction model. First the critical strain for dynamic recrystallization is being checked. If the calculated strain is higher than that, considering also the time for meta-dynamic recrystallization, dynamic or meta-dynamic grain size calculations are carried out. If the stain is too low then only the static recrystallization is considered together with its required time. Finally, austenite grain size and ferrite grain size are calculated respectively as the steel cools down. A further model of yield stress and ultimate tensile strength predictions, which requires chemical composition of the steel, may also be included as well. The solution procedure of hot rolling is based on cross sectional slices as computational domains which are aligned towards the rolling direction. For each slice position, the exact time and effective strain field are known from the simulation results. These two are the crucial variables of a successful grain size prediction system. The current prediction model is based on collection of empirical relations found in literature. The user is free to choose or create the model he wants with his own parameters. The simulation is capable of simulating up to 12 consecutive rolling stands and results may be visualized for each slice separately. The simulation system has been coded as a user friendly computer application for an industrial use based on C# and .NET framework and runs on regular PCs. The computational time for a rolling simulation is usually less than one hour. Because of this, it can be easily used for the optimization of the rolling mill design.

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The classical application of Nb microalloying in the development of thermomechanical processes for flat products has been related to its suitability to enhance strain-induced precipitation and get a pancaked austenite prior to transformation. As new steel grades or new lay-outs are being developed, more complex metallurgical conditions need to be evaluated. In this context, Nb microalloying, alone or combined with other microadditions, needs to intervene in a more controlled way in additional steps of the thermomechanical process, besides its conventional strain-induced precipitation role. For example, the hardenability enhancement associated with Nb to properly achieve lower temperature transformation products, demands a proper balance of the Nb amount precipitated during rolling and the one remaining in solid solution. Similar effects are also sought when the final available Nb is used to increase strength through precipitation hardening. This manuscript evaluates how changes in the rolling strategies affect the interaction between Nb(C,N) precipitation and austenite recrystallization at different steps of the rolling process. As the possible interactions between parameters intervening simultaneously are quite complex, the application of microstructural models helps to properly define the best austenite conditioning combined with the convenient amount of Nb in solution, as a function of the final property requirements. Along the manuscript, several strategies will be discussed for the case of hot rolling of flat products comparing both normal and coarse initial austenite grain sizes.

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ArcelorMittal's pickling and cold rolling line has been demanded to increase production since the installation of equipments in 2015. In addition to the improvement in productivity related to these new equipment, one of them the automatic surface inspection system (SIAS), work has also been developed in other equipment seeking improvement of production indicators. The present article exposes the actions and gains that were achieved with actions on two equipments in the same section as the Side Trimmer. The first one deals with the optimization of time gains with sequencing adjustments without financial contribution, using only internal labor seeking reduction of unproductive times by adjustments of the side trimmer in the cold strip mill. The second item discussed demonstrates the actions and the gains generated due to the availability of new resources (installation of SIAS equipment), the optimization of these resources seeking a focus on the reduction of ruptures in the tandem cold mill, configuring the same in the aid of the identification of critical defects and also in the automatic speed reduction action of the tandem cold mill in defects considered serious. In both cases the intention was to improve production, seeking to improve the results of the section and the line.

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The Pickling Line and Tandem Continuous Mill (PLTCM) at Ternium Pesquería Facility with a Five Stands, Six High configuration started in 2013. Manufactured by PRIMETALS, to produce steel for exposed automotive market, Turnkey project, with supervision of best practices from Nippon Steel. The main equipment that the process has are; Laser welding machine, 3 loopers, Scale Breaker, jet Pickling tanks, Inspection Station and COGNEX System Side Trimmer (flying width change), Type of Mill: UCMW(S) Carrousel, 2 Tension Reels. The principals goals are, Simulate production programs, validate materials for thin thicknesses before processing, low Re-welds, optimization use Cognex, good performance in Thickness, flatness and productivity.

Abstract:

In the process of wire rod production, the rolled wire products must be cooled from the red-hot state to the normal temperature state. How to cool the wire rod after rolling is one of the key links of product quality control in the whole wire rod production process. In this paper, combined with the closed-loop transformation project of controlled cooling temperature of Xuanhuan iron and steel group co., LTD., the closed-loop related controlled cooling equipment (including water cooler, valve table, etc.), nozzle layout and process layout of water tank, and closed-loop software control system of controlled cooling temperature of high-line are analyzed and designed. Closed-loop system design USES temperature of cooling water cooling and water cooling two temperature closed loop regulating circuit, through temperature feedback and feedforward to achieve the uniformity of temperature adjustment, in order to prevent occur due to temperature closed loop control function with the phenomenon of a steel before and after the temperature difference is bigger, system Settings have "absolute temperature regulation" and "relative temperature regulation" selection mode. The system has a self-learning mode, which can modify the temperature feed forward formula. In addition, this paper takes the hard wire 82B rod as the test object, and studies the process parameters and the comprehensive mechanical properties of the rod before and after the water cooling system reform. The research results show that the temperature closed loop system, can ensure the rolled piece temperature control precision of plus or minus 10 ℃, enhances the stability of wire rod cleaner performance. It can reduce water consumption by about 186m3/h and improve the utilization rate of cooling water.

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The control of the recrystallisation during hot rolling of steel, is of paramount importance to manufacture products with ultrafine microstructure able to possess both high strength and high toughness. However, during conventional hot rolling, the recrystallisation process promptly takes place when the material is deformed and therefore, very fine microstructures cannot be achieved in the final product. The combination of thermomechanical controlled processing (TMCP) and the addition of niobium to steel, has proven to be a functional way to prevent the recrystallisation and subsequently refine the microstructure. A relatively new type of steel known as HTP (high temperature processing), was developed to manufacture the grade API 5L X80 used in transmission pipelines, this grade contains low carbon and high niobium level (around 0.10%) and can allow for controlled rolling at high rolling temperatures. The effect of Niobium on recrystallisation of steel in TMCP has been widely studied, however, the understanding of the effect of the strain induced precipitation on the retardation of recrystallisation over the final finishing passes has not been investigated systematically, particularly in microalloy steels with high contents of Nb such as the HTP alloy. This research investigates an HTP concept steel composition, utilising plane strain compression testing (PSCT) to replicate commercial finishing passes and subsequent accelerated cooling. The aim of this work is to study diverse variables (strain, strain rate, deformation temperature, number of passes, holding time between passes and cooling rates) in a TMCP to simulate rolling routes able produce steels with ultrafine grain size. Simulation and modelling of the interaction between the recrystallisation and precipitation at different strains and temperatures was carried out, the results showed that recrystallisation can be supressed even at substantially higher temperatures than those in the conventional rolling methods, the strain induced precipitation of Nb(C,N) played in fundamental roll in retarding the recrystallisation and consequently, unrecrystallised microstructures with highly elongated grains in the direction of the deformation where produced. An optimal austenite conditioning during rough and finishing rolling was achieved, it was shown that it is possible to perform series of deformation passes plus holding times without triggering the recrystallisation process. Another set of experiments to produce micrometric ultrafine ferrite by TMCP was designed, when the HTP steel alloy was deformed at temperatures below Ae3 but above Ar3, abundant ultrafine ferrite was dynamically transformed during the deformation, analysis in SEM and SEM-EBSD were performed and it was observed that the size of the ultrafine ferrite ranged from about 0.5 to 2 microns.

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The objective of this study was to determine the effects of an eventual slab central macro-segregation in microalloyed steels with low Mn content (0.80%) and high Nb content (0.08 to 0.10%) on the kinetics of recrystallization of austenite during its rolling, on its critical temperatures, that is, of non-recrystallization (Tnr), start Ar3 and finish Ar1 of ferrite transformation and its response to a simulated industrial thermomechanical processing. The determination of the austenite recrystallization kinetics was made through isothermal double compression tests using a dilatometer, while the critical temperatures were determined through hot torsion tests in a Gleeble® 3800. It was found that austenite recrystallization kinetics, Ar3 and Ar1 temperatures did not present significant changes for the samples extracted both at ¼ of the thickness and at the core of the plate, indicating that, as expected, the central segregation in this type of steel was not intense to the point of affecting this phenomenon. The Tnr values determined for the samples extracted in the core of the plate were, on average, 30°C lower than those obtained from specimens extracted at ¼ thickness, which suggests that a significant portion of the carbonitrides present in the core of the slab are eutectic and coarse, not having completely dissolved during the reheating of the specimens. This occurred despite the fact that the austenitization temperature adopted in this treatment theoretically leads to the total dissolution of Nb, as seems to have occurred in the case of specimens extracted at ¼ of thickness, where carbonitrides have a finer size.

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SINCE THE BLAST FURNACE OF USIMINAS CUBATÃO WAS SHUT DOWN IN 2015, THE SLAB REHEATING FURNACE OF THE HOT STRIP MILL (LTQ2) STARTED TO USE NATURAL GAS AS DEDICATED FUEL TO HEAT THE SLABS. CHANGES IN MAINTENANCE OF THE BURNERS AND ALSO IN THE CONFIGURATION OF THE COMBUSTION SYSTEM WERE PARTIALLY DONE IN 2016, HOWEVER IT WAS NECESSARY TO CARRY OUT MAJOR MAINTENANCE IN THE FUEL GAS PIPES, REPLACE ALL CONTROL VALVES AND REPLACE PARTIALLY THE GAS LANCES OF THE BURNERS FOR NATURAL GAS. FROM JULY TO NOVEMBER 2018 THE ENGINEERING MODIFICATIONS WERE CONCLUDED AND IT WAS POSSIBLE TO ACHIEVE BETTER OPERATIONAL RESULTS, ESPECIALLY REDUCTION IN PRIMARY SCALE FORMATION AND FUEL CONSUMPTION AS REFERENCE TO THE HISTORICAL LTQ2 PERFORMANCE.

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MoO3 nanofluid was chosen as an alternative of MoS2 nanofluid for strip cold rolling to prevent the oxidative deterioration of MoS2. Pure MoS2 nanofluid, the mimetic oxidized nanofluids (hybrid nanofluids of MoO3 and MoS2 nanosheets) and pure MoO3 nanofluid were used as rolling lubricants to identify the influence of this oxidative deterioration on lubrication properties of MoS2 nanofluid. Cold rolling experiments were carried out by two-high rolling mills and both rolling forces of each rolling passes and minimum rolling thickness were measured. The tribological properties of different concentrations pure MoO3 nanofluid were tested by a four-ball tribotester. The worn surfaces were analyzed by means of scanning electron microscope (SEM) with energy dispersive spectrometry (EDS) and X-ray photoelectron spectroscopy (XPS). The results show that pure MoO3 nanofluid was confirmed to have similar lubrication properties to pure MoS2 nanofluid. With the application of MoO3 nanofluid, the surface smoothness was almost as fine as the surface lubricated by pure MoS2 nanofluid. An optimal concentration (0.4wt.%) of MoO3 nanofluid that could show best tribological properties was also proposed in this paper. Additively, the main lubrication mechanism of MoO3 nanofluid was obtained. A lubricating film of MoO3, MoO2 and organic reagents was considered to form on the strip surfaces due to the chemisorption and deposition of MoO3 nanosheets. Erosion corrosion was happened during friction process, MoO3 was transformed to MoO2 and iron was oxidized to ferric oxide. Simultaneously, part of organic reagents in the nanofluid was carbonized. The organic reagents can perform extra lubrication in the friction process.

Abstract:

Emulsions are frequently used for the cooling and lubrication of working rolls during the cold rolling. the fact that the lubrication and cooling are not separable makes the optimization of both functionalities difficult. the higher emulsion temperature decreases the cooling efficiency compared to cold water. heat transfer and fluid flow laboratory (czech republic), crm (belgium), tata steel (netherlands) and henkel (germany) cooperated on the increasing of a cooling efficiency during cold rolling. part of this research was focused on an influence of the emulsion composition on a cooling intensity. the cooling efficiency was laboratory investigated. the stainless steel sample with thermocouple was heated and then it was cooled by a nozzle. tests were performed with various emulsions and pure water. the heat transfer coefficient was computed from measured temperatures. the cooling intensity (heat transfer coefficient) of all tested emulsions was similar but an increase of the cooling intensity was found with water. further various emulsions concentrations were tested. results showed decreasing cooling intensity with increasing oil concentration. adding additives therefore is thought to cause a noticeable decrease of the cooling intensity.

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At various stages during their manufacturing processes – from casting to finishing before delivery – semi-finished steel and special alloy products must be cut and surface-treated as well. The requirements for the individual conditioning steps, however, can be quite different. For example, the workpiece can be hot, warm or cold. At any rate, the product must always be perfectly prepared for the next manufacturing step – reliably, in the shortest-possible time and at the lowest-possible cost. For cutting, AND grinding , BRAUN has developed Innovative technologies and highly flexible, tailor-made solutions which meet these requirements in the most optimal way. In particular, BRAUN’s cutting AND grinding technologies can also be used for large-scale products.

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The effect of soaking temperature in the reheating of slabs on the precipitates dissolution and mechanical properties of Ti-Nb microalloyed steel was investigated in pilot scale. It was verified, by means of transmission electron microscopy, a significant decrease in precipitates formed during the solidification of the steel as the soaking temperature increased from 1100°C to 1200°C. No significant changes in size and shape of the precipitates were observed with further temperature increase up to 1280°C. In line with the precipitates dissolution behavior, an increase in mechanical resistance was observed with the elevation of the soaking temperature up to 1200°C, due to the reprecipitation of (Nb,Ti)(C,N) during the rolling/air cooling. After reheating above 1200°C up to 1280°C, it was noticed a decrease in mechanical resistance of the rolled plates. This effect was credited to grain growth. The results were in agreement with Thermo-Calc and Dictra simulations.

Abstract:

The off-line simulation of the metallurgical process in an industrial line brings several benefits such as: evaluation of the influence of the main parameters that affect the results of the process, comparison between different set ups, greater assertiveness in operational adjustments, process optimization and reduction in the number of tests to develop new products. With this objective, a software for offline simulation of the hot strip mill process of Gerdau Ouro Branco was developed based on the logic of calculations implemented in the online model. The software results in important process variables such as mill pass schedule, load, torque, and power at each pass, temperature and the hot mean flow stress of the simulated material. During rolling the strip presents different temperatures and time between passes for different points along the length, which directly influences the hot strength of the product and consequently in the calculated variables, thus the calculations executed by the software were divided to three points of the strip , head, body and tail bringing the individual results to each of these positions. With the implementation and consolidation of this software for process simulation, a range of possibilities for process development is opened, allowing to add other functionalities and mathematical models to this tool that can help in the evaluation of alternatives to increase line productivity, and predictability of mechanical properties that will help in the development of new products and in the evaluation of microlalloying reduction contributing in the reduction of the cost of raw material, besides facilitating the dissemination of the technical knowledge of the process.

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The microstructure, properties, strengthening mechanism and work hardening mechanism of 600MPa grade high ductility hot-rolled sheet steel for automotive square tube were investigated by utilizing optical microscopy, scanning electron microscopy and transmission electron microscopy. The results show that the microstructures of low C-low Mn-Nb and Ti microalloyed steel (Steel A) and high C-high Mn-Nb microalloyed steel (Steel B) are composed of ferrite and a small amount of pearlite. Compared with steel B, the size of ferrite and pearlite of steel A is finer, while the size of the second phase precipitates is larger. The mechanical properties of the two tested steels are similar before tube forming, except that the yield ratio of steel A is higher. Steel A has/exhibits significant work hardening after tube forming; the yield strength and tensile strength increase by 45 MPa and 26 MPa, respectively, while the elongation decrease by 6.0 percent. The yield strength and tensile strength of steel B increase by 22 MPa and 10 MPa, respectively, and the elongation decrease by 4.0 percent. The grain refinement strengthening is the dominant strengthening mechanism, accounting for 52.9 to 61.8 percent of the total yield strength; the solid solution strengthening is the second strengthening mechanism, accounting for 17.2 to 25.3 percent, while the precipitation strengthening and dislocation strengthening contribute little to the yield strength. The dislocation strengthening increase by 82 MPa of steel A after tube forming, which is higher than that of steel B. Therefore, steel B has a low work hardening rate that is more suitable for manufacturing automotive square tube for secondary tube forming.

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A precise roll stack deformation model of a flat rolling mill is crucial for strip profile assessment as it depends strongly on the roll’s deformation. The need for more and more advanced products with stringent both geometrical and mechanical tolerances (e.g., Advanced High Strength Steels – AHSS), with thinner and harder steel strips, demands more advanced simulation models. The present paper addresses assumptions made in Finite Element Method (FEM)-based roll stack models on some important, yet barely discussed features: What is the impact on precision of the simplifications such as symmetry and anti-symmetry? Should roll neck boundary conditions in bearings be considered as fixed or simply supported? In this paper a hybrid model developed by the authors for a general flat rolling mill is used to assess those questions. This model runs much faster (100x in some cases) than a whole-FEM-modeled 6-high rolling mill with the elastoplastic strip deformation, thanks to its simplifications adopted. This model assumes a steady state rolling condition, and the roll stack is modeled with tridimensional finite elements, and the loads are calculated via a slab method adopting a plane strain state for the strip deformation (especially true for thin strips). An industrial 6-high cold rolling mill is modeled and results on the application of symmetries and different boundary conditions on the roll’s necks are presented. It is concluded that the application of symmetries and anti-symmetries for the 6-high rolling mill is possible for thin strips. And the way the necks are modeled does not impact on the final strip shape, though it influences the magnitude of the roll’s displacement. The coupling of the strip with the work roll applied assuming a symmetry plane of the arc of contact has little influence on the strip shape.

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Two major drivers for the use of newer steels in the automotive industry are fuel efficiency and increased safety performance. Fuel efficiency is mainly a function of weight of steel parts, which in turn, is controlled by gauge and design. Safety is determined by the energy absorbing capacity of the steel used to make the part. All of these factors are incentives for automakers to use Advanced High Strength Steels (AHSS) in order to replace the conventional steels used to manufacture structural parts in the past. Due to the great importance that surrounds the development and optimization of current and new steels, this work has proposed to optimize the metallographic preparation method for the quantification of retained austenite by Electron Backscatter Diffraction (EBSD) in AHSS steel. The Rietveld method applied to X-ray diffraction was used as a reference in the present study. Two different final polishing techniques were applied by immersion in colloidal silica: Vibration polishing using the Vibromet polisher and polishing using the Minimet polisher. For each of those methods, the polishing time was varied. The results indicated that polishing using the Minimet polisher was more efficient for this application. In addition, the EBSD method presented reliable results, close to the reference value, when the polishing method was efficient for the removal of the work-hardened layer by the previous steps of metallographic preparation.

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In bar and wire rod mills, rolling procedures featuring three- and four-roll technologies are state-of-the-art to produce high-quality long products. Therefore, the development of pass sequences for these processes plays an important role in the rolling industry. The assessment of a rolling process is bound to a reliable rolling model, which is suitable for the calculation of the force and power demands of the rolling process to ensure that limiting conditions of the rolling mill are not overridden. For rolling of long products, a suitable pass sequence has to be designed in order to meet the requirements of dimensional tolerance, as well as surface quality. While a rolling model for the three-roll process including an equivalent pass method was already presented by the author, pass design methods are dealt with in the current work. The geometry of the rolled product and roll grooves are described mathematically using functional contours, allowing geometric-numerical methods to be used for manipulation and deformation simulation of the rolled product. For a given pass, the output section is constructed using these methods. The very important spread calculation is based on the two-roll procedure and is adopted for the three- and four-roll processes with suitable correction functions. Here, also the temperature and material dependency of the lateral spread for a given material database is taken into account. The geometric calculation of each pass is carried out iteratively, as to satisfy the given boundary conditions of perfect contact conditions between rolls and rolled material, as well as the desired output material shape. Roll force, torque and rolling power are calculated using the mathematical rolling model presented before. Interstand tensions are discussed as influencing parameters on the force, torque and power demands, as well as on the section shape. A mathematical model for the influence of interstand tensions on lateral spread is incorporated in the model. To complete the pass design model, elastic mill stand feedback is considered in terms of a fixed elastic modulus for each rolling stand, the elastic feedback and therefore cross-sectional variation due to elastic mill spring being calculated iteratively from the roll force by application of the Gagemeter equation. The interaction of section height and width faults due to elastic mill spring and spread variations is analysed in detail and the consequences for the roll pass design are shown. The calculated results are presented in terms of an interactive software, where the roll pass designer or rolling mill engineer can check the calculated geometries and change the calculation parameters before recalculating the pass sequence, if necessary. Additionally, numerical output is given for all interesting deformation characteristics of the rolling procedure under consideration. The model is used to discuss different philosophies of pass design for the three- and four-roll rolling procedures. The different pass designs are compared to one another, dealing with different rolling conditions as varying rolling temperatures, rolling speeds and cross-sectional variations along the strand length. Pass designs for different purposes are compared, i.e. high reduction versus low reduction pass sequences for sizing purposes. The sizing possibilities of the considered processes are analysed by the mathematical model and detailed numerical results are presented.

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Structural steel final mechanical properties of strength and ductility are predominately generated by the final ferrite grain size/packet size and homogeneity of that ferrite grain size/packet size through the cross-sectional area. Forty to seventy percent of the strength components comes from how fine of a final cross-sectional ferrite grain size/packet size that can be realized. All the ductility properties of structural steels for a given microstructure are driven by how fine the final cross-sectional ferrite grain size/packet size AND how homogenous of a cross-sectional final ferrite grain size/packet size that can be developed. One key ductility property of structural steels used in construction and energy transmission applications is fatigue. Both low and high cycle fatigue can be realized in these end applications, however low cycle fatigue is typically the predominate mechanism. In construction applications the environment for fatigue is typically air, such as in wind towers or high-rise building construction. In energy applications, there is an interest in gaseous hydrogen as an alternative fuel source to fossil fuels. In these applications, economical transportation of gaseous hydrogen is typically done in pressure vessels or pipelines and requires operating pressures in the 800-3000 psi range. Various structural steel microstructures primarily related to API grade pipeline steels have been fatigue tested and published in both hydrogen and air over the past 10 years by NIST and other US National Laboratories. NIST in particular has developed a unique multi specimen fatigue testing device with capability for both air and high pressure gaseous hydrogen atmosphere hence allowing for capabilities to significantly increase productivity of the fatigue test. One of the microstructures fatigue tested by NIST is a production produced API X60 HIC Sour Service plate grade consisting of a predominately pure microstructure of polygonal ferrite with a low carbon (0.03%), higher Nb content (0.085%) allowing for higher temperature processing (HTP). This microstructure has performed well in both 800 and 3000 psi hydrogen pressure fatigue testing. However, one of the questions that has risen from this testing was while the overall microstructure performed well in fatigue testing what would happen to the fatigue performance if the same alloy design and same predominate pure microstructure of polygonal ferrite had variability in cross-sectional final ferrite grain size homogeneity. To study the fatigue performance of a common microstructure with different cross-sectional final ferrite grain size homogeneity, laboratory produced plate trials were developed duplicating the original API X60 HIC Sour Service alloy design but designing the rolling process to create two different cross-sectional final ferrite grain size/homogeneity situations in the laboratory produced plates. One design utilized a properly optimized rolling strategy to generate an optimum Type I Static Recrystallization behavior and Type II No-recrystallization behavior for the niobium content. The second rolling design strategy was a non-optimized strategy for Type I Static Recrystallization and Type II No-recrystallization behaviors. This “optimized” and “non-optimized” resulted in distinct differences in the cross-sectional final ferrite grain size and homogeneity. Since ductility properties are significantly controlled by high angle grain boundaries (HAGB, >15°), microstructural characterization of the laboratory produced plates of both low angle grain boundaries and high angle grain boundaries was performed. The goal of creating similar microstructures in the two laboratory plates with distinctly different cross-sectional final ferrite grain size/homogeneity was realized. The microstructure in both the optimized and non-optimized plates was predominately polygonal ferrite. The optimized produced plates had an average cross-sectional HAGB ferrite grain size of 3.2 µm with 20% of the cross-sectional HAGB > 8.5 µm. The non-optimized produced plates had an average cross-sectional HAGB ferrite grain size of 4.5 µm with 20% of the cross-sectional HAGB >16.5 µm. Both will be fatigued tested in air and high-pressure gaseous hydrogen to determine the effect the cross-sectional average and homogeneity has on final fatigue performance. This will be compared to the original production produced grade. In addition, austenite grain size evolution modeling with MicroSim® will be done utilizing the processing parameters from the laboratory rolling for comparison to the final polygonal microstructure characterized.

Abstract:

Mathematical models for rolling force calculation during hot rolling are crucial for both automatic mill operation and prediction of steel behavior and of mill capacity, especially for development of new steel grades and improvement of the existing ones. In literature, the models are based usually on the calculation of steel mean flow stress (MFS), firstly, followed by a force model based on MFS. This approach was applied to a large volume of industrial data of coils produced at Usiminas’ plant in Ipatinga, rendering unsatisfactory results. Then, the empirical model developed by Schultz was applied to calculate directly the force, with further fine tuning the model with a linear regression taking into account steel chemical composition. This approach led to force prediction capability better than the traditional models based on the binomial MFS-force presented in literature, markedly for plain CMn steels and IF steels. In such cases, more than 90% of force predictions were inside the ±10% error margin, considering the front stands of hot strip mill.

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Abstract: The corrosion behavior of three kinds of medium-Cr rolled steel pipeline steels in carbon dioxide collecting and transporting environment at different temperatures was studied. The results shew that the 5Cr sample was most affected by temperature. When the temperature rised from 30 °C to 90 °C, the corrosion rate increased from 0.1201 mm/a to 1.8698 mm/a, which was increased 15.6 times. The corrosion rate of 7Cr steel at 30 °C was similar to that of 5Cr steel. However, as the temperature increased, the corrosion rate rised slowly, which was increased 2.4 times at 90 °C. The corrosion rate of 9Cr steel was not obvious with temperature, and it was always below 0.06 mm/a. The thickness of the corrosion product film of the three samples gradually increased below 70 ° C, and suddenly increased above 70 ° C. This was related to the negative temperature coefficient of the solubility of FeCO3, and the thickening of the product film also affected the ion exchange of the cathodic reaction. An increase in the Cr content contributed to grain refinement and increased the proportion of the small-angle grain boundaries. More fine grains mean an increase in the total length of the grain boundaries, which could provide a diffusion channel for the free Cr element; on the other hand, the low-angle grain boundary structure was more orderly, with a lower free volume and lower interface energy. Under the combined effect of both, 9Cr steel and 7Cr steel had smaller micro-area potential difference and better corrosion resistance.

Abstract:

Optimized CAPEX, OPEX, yield and product quality and introducing of new products in new process equipment as well as by upgrading of existing facilities are the key factors for success and profitable operation. For this, innovation in processes and design is crucial. Danieli is supporting these customer and market demands by offering innovative and well-thought-out process equipment and upgrade solutions. In 2019, Danieli has put into operation a complete cold processing complex in Turkey, which includes a new continuous pickling tandem mill featuring latest generation of market oriented technologies. In this line, dedicated to run a broad range of size and grades (IF to AHSS as DP1000), the highly efficient Turboflo® pickling process was selected. This technology already proved its efficiency and ability in former applications handling ultra-thin gauges at speeds even exceeding 400 m/min in the pickling tanks. The 5-stand 6-high OSRT tandem mill features important developments, like actuators to improve significantly strip flatness and a special air knife arrangement on the tandem mill exit side to generate perfect strip surface cleanliness. Fast startup and thin gauge rolling already short time after production start are further proves for the technological superiority of this innovative mill design. In dis-continuous operating rolling mills, the Danieli Yield Boost technology is the right answer to significantly increase material yield with limited CAPEX. As an example, the usual way to operate a cold reversing mill for strip threading and tail-out is to open the roll gap. Danieli developed a method for already partial strip thickness reduction during threading in and tail out phases. Operating results at a two-stand reversing mill show an impressive increase in material yield. Depending on specific conditions, this technology can create annual savings in six or even seven-digit US Dollar figures. In the last 10 years, Danieli has supplied most of the worldwide construction and high speed galvanizing plants. In those lines, the zinc pot is the most effective area to reduce costs in operation and consumables and increase the product quality. Danieli has spent significant efforts in developing most advanced technology for the wiping process. A fully integrated system solution has been designed to perform a wiping process with high quality, economy, accuracy and productivity. Center part is the newly developed X-Jet / Compact X-Jet air knife. Its innovative design creates highly stable static pressure with direct impact on the shear effect, and extremely accurate pressure along the strip width. The new generation electromagnetic stabilizer is cutting down strip vibrations and improves strip flatness, leading to further increase in wiping process. Robotic systems are supporting to reduce human intervention and health risks in the zinc pot area. These technological packages are ideal also for upgrade of existing lines, typically generating a return of investment in less than 1 year, proven in latest revamp installations. On top, Danieli has developed advanced automation systems including L2 and L1 controls to achieve outstanding product performances.

Abstract:

The steel sheets coated with Zinc and their alloys are widely used in the automotive industry due they exhibit excellent corrosion resistance, together with good performances of formability and weldability. The corrosion resistance property is acquired through the galvanizing process; the coating layer protects the metal against direct contact with the corrosive environment. Among the largely range of steels in the market, the most important are galvanized, called GI. The GI coating can be divided into two main layers, the first composed of intermediate intermetallic phases of iron-aluminum-zinc, called the intermetallic layer. Its formation and composition may vary according to the characteristics of the substrate used (steel grade and surface texture), the chemistry of the zinc bath and the process parameters used during its production. The second layer is formed mainly by the zinc itself. The characteristics and properties of the GI coating have a direct relationship with the intermetallic layer formation, which is responsible for providing a dial between the metal substrate and the zinc layer, affecting the anchoring of the zinc layer itself. Thus, the intermetallic layer characterization becomes extremely important to the final characteristics of the total GI coating layer in the set. The study aims to present differentiated metallographic preparation techniques used to characterize intermetallic layers in steel samples of GI coated produced by hot dip. The samples were collected at coils produced with two different steel grades. The different chemistries studied were: IF (Interstitial Free) and TRIP780 (Transformation Induced Plasticity) steels. Due a significant difference in their chemical composition (addition of alloying elements), this grades were chosen for evaluating the substrate composition influence of the intermetallic layer formation. The TRIP steels present higher complexity chemistry due to the addition of high levels of alloying elements, such as Si, Al, Cr and Mn. The intermetallic layers were characterized for their morphology using different techniques of dissolution of the zinc layer. For the surface analyzes, it was used the immersion process in different chemical solutions, ultrasonic cleaning and metallographic procedures. For the section analyzes, were employed techniques based on different positions and angles during the bakelite preparation, providing greater amplitude of the field of vision of the interest region. The images were analyzed using a scanning electron microscope, and their chemical compositions were obtained by the energy dispersive X-ray spectrometer (SEM / EDS).

Abstract:

Reinforcing steel bars are usually specified based on mechanical properties with flexibility in chemical composition and processing. Most developments, in these steels, are usually focused on alloy and process design to reach minimum cost and conformity to specification. Processing routes using quenching and self-tempering (QST) and accelerated cooling are the most common. Microalloying with V and Nb have been used in rebar. When acicular constituents must be avoided, a combination of Nb microalloying with judicious control of cooling is one of the preferred options. Niobium can contribute to improvement in tensile properties through austenitic grain size control during hot working, precipitation hardening due to carbonitrides or clusters, and hardenability increase. In the present work the alloy design and development processes of a Nb microalloyed steel for rebars are presented. The designed steel has fulfilled the required specification and is under regular production. Austenitic grain size refining – when comparing with the “basic composition” normally used was observed, even without any change in the thermomechanical processing cycle. There are indications that precipitation hardening may also occur. Results indicate that Nb is a good alternative as a microalloying element in rebars.

Abstract:

The benefits of using the controlled rolling process followed by accelerated cooling (TMCP), currently used in the main rolling mills in the world are already well known and metallurgically based. The need to obtain mechanical properties with a high degree of homogeneity means that in some situations the ends of the rolled material are discarded, negatively affecting the metallic yield of the process. Therefore, this work focused on the determination of the mechanical properties variation at the ends of thick plates processed by TMCP of steels for application in oil and gas pipelines, in order to map the extent of these differences and to correlate them with the microstructure obtained, the profiles of temperature and cooling rates in these regions. To perform the work, two slabs of the studied material were rolled, and the temperature profile was recorded along the plate in the controlled rolling and accelerated cooling processes. The ends of the material were sampled in sections at every 100 mm and subjected to tensile test, hardness and the Charpy V-notch impact test, as well as dilatometry and microstructure evaluations. For the used process conditions, the results indicated the formation of a banded microstructure, basically consisting of polygonal ferrite and bainite, occasionally containing small fractions of perlite. The mechanical properties in the top and the base were higher than the values found in the plate middle, justified by the microstructure found. The work allowed understanding the relationship between the mechanical properties, microstructures and process conditions at the ends, helping the team to improve the process in order to result in a high degree of homogeneity of the product and, thus, lead to optimization of the metallic yield.

Abstract:

Gearbox Stand Mill LF 02 Pass 1 presented failures of internal components, such as bearings and gears. In order to determine its root cause, a dynamic evaluation of the Gearbox before process variables was performed. Thus, the following engineering tools were applied: Vibration Analysis, Operating Deflection Shape – ODS and Numerical Simulation by Finite Element Method - FEM. Vibration and ODS highlighted excitation frequencies, operational modes, which in these frequencies caused relative movements. Results obtained by Vibration and ODS were correlated to simulation, allowing to calibrate FEM model. Also, during simulation, Component Modal Synthesis technique was used, allowing evaluation of the fatigue life internal components. Based on field and numerical results obtained in this study, recommendations were: to verify alignment conditions, machine geometry using laser systems, and also application of the structural modifications on the support of gearbox to eliminate a resonance condition.

Abstract:

The deformation behaviors under both tensile and compressive forces and microstructure evolutions of cast SA508-4N steel were investigated at elevated temperatures. True stress-strain data were obtained from hot deformation experiments performed on a Gleeble-3500 thermal-simulator under different temperatures (750-1200 ºC) and strain rates (0.001-10 /s). The reduction of area decreases as a function of temperature from 750 ºC to 900 ºC and then increases. At 1200 ºC, the reduction of area reaches more than 99% with the strain rates of 0.5 /s and 1.0 /s. The dynamic recrystallization under compressive stress occurs at 800 ºC under low strain rate and a complete dynamic recrystallization can be observed when the temperature reaches above 1100 ºC. The value of the thermal deformation recrystallization activation energy is 407.34 kJ. A “two-stage” flow stress constitutive model concerned with dynamic recovery and dynamic recrystallization was established based on the true stress-strain data. This model shows good agreement with experiment results. Moreover, a dynamic recrystallization model was developed to predict dynamic recrystallization fraction and grain size using thermal processing parameters.

Abstract:

Currently, continuous implementation of safety and CO2 emission standards in automotive vehicles has driven the search for weight reduction and safety enhancement solutions. In this context, the development of steels of high mechanical strength has been presented as the most applicable. Due to the strong elastic return after the stamping operations, parts that have geometric complexity and require greater mechanical strength are generally produced by hot stamping. The steels employed have addition of boron, such as 22 MnB5. Parallel to the development of steels, researches related to the development of metallic coatings capable of withstanding mechanical stresses and heat treatment have been carried out. During the process of manufacturing the steels for the hot stamping process some control points become extremely necessary. These points are distributed throughout the production chain, ranging from the control of the chemical composition, either by the elements responsible for temperability (C, Mn, B, etc.), as well as to the cold rolling and subsequent annealing and galvanizing processes. In the present work, a study was carried out on the effect of the process parameters of a continuous annealing and application of metal coating by hot immersion in the mechanical and microstructural characteristics of 22MnB5 steel for the hot stamping process. The samples were subjected to dilatometry simulations with fast cooling by helium injection.The results obtained by simulation were compared to the results obtained in industrial processing, being evaluated by tests of microhardness, uniaxial traction and metallographic analyzes.

Abstract:

Automobile manufacturers are developing Electrified Vehicles with light steel body structure designs that reduce mass and therefore greenhouse gas emissions over the vehicle’s entire life cycle. This raises the demand for the production and development of Advanced and Ultra High-Strength Steels (AHSS / UHSS) and Electrical Steels with increased permeability and reduced core loss to improve energy conversion efficiency. To meet this requirements the steel market is tending towards new generations of AHSS with improved formability (3rd generation AHSS) and high-silicon steels with higher strength and thinner products. Therefore, facilities are required to produce these products in higher volumes and under stable operating conditions to achieve the desired high product quality. With this growing demand for advanced high-strength steels and electrical steels, producers are faced with a unique and interesting challenge in producing materials that strain or exceed the capabilities of existing mill equipment and automation designed to produce low- to medium-carbon sheet. While specialty steel producers have known for decades how to process special high-strength steels and thinner gauges, this equipment typically does not offer the yield and productivity desired by the market, necessitating innovation in re-engineering existing equipment to meet the market demands more economically than new construction. In the case of cold rolling, this can be supported through variable roll geometries, more effective roll-gap lubrication technologies, application of strip heaters (Warm Rolling) to reduce risk for edge crack propagation and strip breaks as well as continuous rolling managed by state-of-the-art automation technologies. The major lever to improve rolling capability of existing mills is to reduce the work roll diameter especially in the middle stands of a tandem cold rolling mill. This paper contains a historical review and outlook of work roll diameter evolution with respect to harder and thinner steels and introduces two new solutions for the production of AHSS / UHSS and high-Si electrical steels, continuing this history into the future. For cold rolling heavy reduction of hard materials such as grain oriented or high-grade non grain-oriented electrical steel advanced 20-high cluster mills with very low work roll diameters are applied. A further lever to support rolling of AHSS / UHSS and high-Si steels is to improve and optimize the roll-gap lubrication, which is of particular importance for hard and/or thin steel products. A new roll-gap lubrication technology allows a flexible adjustment of oil film thickness independent of the rolling speed. This leads to significant advantages for rolling high-strength grades. The trend to harder and thinner gauges poses more risk for unwanted mill vibrations. To overcome this risk a solution to eliminate gauge chatter supports a high-productivity production of AHSS / UHSS and high-Si electrical steels.

Abstract:

Boron steel is used in the industry due to its great wear and impact resistance. During the hot rolling production of 15B29 steel flat bars it is a recurrent problem that the bars will present warping while on the cooling bed. Control this phenomenon is an opportunity to have better productivity, preventing metallic losses. Through the observation of the macro and microstructure samples produced with different reheating temperatures and cooling rates, it was found the presence of residual stresses and cracks on warped bars macrostructure. The residual stresses appearance suggest that the material cooling is too fast. Billets temperature on the reheating furnace of 1230°C reduced to 1100°C and the production pace slowed down. Bars temperature when arriving the cooling bed was reduced from higher than 670°C to 625°C. The results obtained made it possible to produce the material with better quality, reducing the warping effect at the cooling bed. The major influence on the materials warping was identified as the cooling rate at the cooling bed and the reheating furnace temperature was adjusted to provide a homogeneous temperature along the bars.

Abstract:

Abstract: Flatness control is an important issue during the manufacture process of wide and thin plate. It will inevitably lead to uneven cooling of edge and middle parts, which will lead to uneven stress distribution and eventually lead to shape problem. In this paper, the evolution law of steel plate stress during rolling process is analyzed, and the thermal expansion experiment of the steel 45 Mn2V is carried out. The thermal expansion rule of 45Mn2V is obtained. In order to make micro center waves after rolling stage, the influence of bending force on plate crown is calculated，the shape of plate is adjusted by roller bending control, and counteract the non-uniform fiber length caused by different temperature drop. In this way,when the steel plate is cooled to room temperature, the steel plate turned to straightened again.By this method, good results have been achieved in batch production of wide and thin steel plates.

Abstract:

Rolling mill should have high operational reliability to avoid unscheduled shutdowns, since it significantly affect production. During the operational process high levels of vibration in certain production velocities were observed, causing Chatter Marks. In order to understand the dynamic behavior of these equipment in different conditions, and consequently to propose actions avoiding such events, field testing and numerical simulation were performed. Field testing highlighted vibrational problems caused by failures in internal components, as well as operational deflection forms related to each excitation source due to these events. Correlation of results with those obtained numerically showed their impact on the quality of the material produced. Vibrational levels and resulting problems were attenuated after application of suggested recommendations.

Abstract:

In the process control system of hot strip mill, rolling force model is the core algorithm of the whole automatic control system. Rolling force is the main factor affecting thickness control and looper stability. Improving the accuracy of rolling force calculation is the key research direction of hot rolling strip. With the development of computer technology, machine self-learning algorithm has been widely used in big data analysis. Based on the method system of applying big data analysis in this paper, a new intelligent rolling force model is established based on XGBoost deep self-learning algorithm, which select eigenvalues based on influencing factors of rolling force. At the same time, the prediction accuracy evaluation system is established. Comparing with traditional rolling force model, the new intelligent rolling force model improves the accuracy of rolling force prediction. At present, it has been successfully applied to the control system of the hot strip mill production line. The stability of the system and the precision of the product are improved. It promotes benefit to the manufacturer.

Abstract:

Cold rolled high strength steel are playing a very important role in reducing automobile weight for energy saving and environment protection. In recent year, more and more high strength steel were manufacturing in steel company. But there are some problems in the cold rolling process for high strength steel products. Periodic thickness deviation especially in strip head or tail is an important one in these problems. In this paper, the reason of periodic thickness deviation was analysed and a new AGC algorithm called Property FFC for high strength steel in tandem cold rolling was developed. The application of this new algorithm shows that it can reduce the thickness deviation.

Abstract:

The annealing and pickling line n. 1, responsible for the production of stainless steel 3xx, 4xx and 430A in thicknesses from 4 to 0.4 mm, has two vertical strip accumulators. These are intended not to let the material exceed the determined time in the furnace and in the pickling, and consequently do not cause defects like burning and excessive pickling. Strip accumulator n. 1 avoids the line from stopping during welding execution of the the coils in the welding machine. In sequence, the strip accumulator n. 2 avoids the line from stopping at the end cutting of the tips, and in the coils removal from the pickling. The strip accumulators have a roller table that during the strip accumulation moves vertically downwards while its counterweight moves vertically upwards, and do the inverse movement when the material is released. On December 12th 2018, the failure occurred in the strip accumulator n. 1, where it was verified that the axis of one of the pulleys had been fractured by high-cycle mechanical fatigue, which was characterized by alternating bending. With the fracture of the axis, occurred the unevenness of the counterweight that damaged the guides. Failure analysis of this occurrence was based on the PDCA methodology, when was verified a weld between the axis and the pulley. The analysis of the microstructure transformation in the molten zone, in the heat affected zone and in the base metal was carried out in an optical microscope, and no abnormality was observed. It was also carried out the END test by penetrating liquid, finding an inadequate weld in its geometry, as well as longitudinal trunks along the center of the weld bead. But after a huge investigation of the causes, it was found that the failure was triggered by an inadequate design of the pulley axis. It was also verified that the axis had an open measure, inadequate for the operational context. After the analysis, action plans were drawn up based on the FMEA methodology to inhibit the failure recurrence.

Abstract:

Niobium-microalloying technology has been increasingly applied in a wide range of steel applications over the past half-century, to increase strength, control microstructure, and enhance different application-specific properties. To achieve desired performance levels, thermomechanically processed microalloyed steels are widely supplied by the steel industry for high volume applications in hot-rolled plate, sheet and structural steels. However, in steel long products and forgings, the final properties are often generated by downstream users, after heat-treatment, surface hardening, forging or wire drawing This presentation highlights advancements associated with Nb-microalloying employed either individually or sometimes in combination with other elements, to enhance microstructures and properties developed during thermomechanical and/or downstream processing. Selected examples include the use of Nb as a solute or in precipitates for austenite grain size control in carburizing, and more recently for induction hardening, as well as recent work using Nb in high-carbon drawn pearlitic wire.

Abstract:

Development of industries in recent years, reveals the essential need to the microalloyed steels with high strength and good ductility. APIX60 steel belongs to high strength microalloyed steel group. It has a high mechanical strength based on API-5L standard and is regarded as a main steel in manufacturing of gas and oil pipes. The manufacturing process of this steel is controlled rolling (CR) with accelerated cooling (ACC) considered as TMCP treatment. One of the most effective and least costly methods to enhance spontaneous reinforcing strength and toughness in such steels is to refine austenite grains in recrystalization zone through a thermomechanical process. Microstructural studies and recrystallization behavior of API5L X60 microalloy steel were done by applying a hot compression device using single-hit (dynamic) test. The flow curves were analyzed at various temperatures and strain rates. The results showed that dynamic recrystallization occurred more easily at higher temperatures and lower strain rates. Observation of a single peak in stress-strain curve during the single-hit compression test, confirmed the occurrence of dynamic recrystallization in the temperature range of 950-1100 °C. According to the results of metallographic experiments, the smallest average grain size of initial austenite was 22 μm at 1000 °C and at strain rate of 0.1 S-1.

Abstract:

Intercritical heat treatments are used during the processing of many steels. The possibilities associated with the partitioning of carbon between ferrite and austenite and the formation of different austenite decomposition products on cooling has been the reason for the wide acceptance of these treatments. However, the result of the intercritical treatments may deviate from equilibrium predictions. Treatment temperature, heating (or cooling rate) to the treatment temperature, and holding time at temperature are known to have significant effects on the resulting microstructure at the end of the intercritical treatment. Different approaches have been used to model these transformations and better understand the related phenomena. Equilibrium and para-equilibrium calculations have been used, diffusion model with different degrees of complexity have been applied and phase field modeling has also been used. In this work we compare the results of intercritical treatments performed in different steels to the predictions that can be obtained using common computational thermodynamic tools: equilibrium, para-equilibrium and diffusion controlled transformation. As a result of this comparisons we highlight how computational thermodynamics can help in understanding and design intercritical heat treatment of steels and, to some extent, alloy design of these steels. Furthermore, the current limitations of the technique are discussed and further work to improve it, where justified, is suggested.

Abstract:

The automotive industry’s interest in galvannealed (GA) boron steel for hot forming processes application has been steadily increasing due to its excellent surface quality, galvanic protection provided to the parts, good paint adhesion and better weldability in relation to other coatings for this application. In this study, samples of 22MnB5 galvannealed steel were heat treated and hot stamped on a water cooled die in laboratory scale. Influence of heat treatment on stability of coating and steel was assessed by using heating rates 10.0ºC/s and 15.0ºC/s. Microstructural evolution of galvannealed coating and structural integrity of steel during hot forming were investigated by scanning electron microscopy with energy dispersive spectroscopy analysis (SEM/EDS), glow discharge emission spectroscopy (GDOES) and X-ray diffraction (XRD). It was possible to quantify the Fe-Zn phase evolution during hot forming, to understand the effect of these transformations on the product properties and to establish an optimized heat treatment for hot forming of these steel, achieving greater operational flexibility and final products free from surface defects or cracks in the substrate.

Abstract:

In this paper, the interactive effects of Si-Cr-Mo alloy elements on interfacial oxidation characteristic in dual-phase steel are studied. Thermal simulation, scanning electron microscopy (SEM) and electron probe analysis are carried out, and the influence of different alloy elements on hot coil surface quality under industrial production conditions is also discussed. Results show that the oxidation resistance of Si - Cr steel is higher than Si - Cr - Mo steel, because the interface oxidation of Cr element under high temperature. Compared with steel only adding Si element, the primary scale of the Si-Cr and Si-Cr-Mo steel is easier to remove, owing to the reduction of anchor scale structure at the interface between scale and substrate. However, Si and Cr element will form dense oxide film under 1100 ℃ at the interface, which increases the difficulty of finishing descaling. Mo is mainly enriched at the surface, and it reduces the activity of Si and Cr, blocks the diffusion channel of Si and Cr elements, and weakens the formation Si-Cr oxide film at the interface. Therefore the surface quality of Si-Cr-Mo steel is significantly improved under industrial production. This work can provide useful guidance for production of this kind of dual-phase steel.

Abstract:

Rolling stand xx (LTx) of long steel, installed in the company A, Piracicaba - SP unit, had presented high levels of vibration, which affected its internal components, such as: shaft, gears and bearings, generating downtime. To evaluate this equipment a study was proposed by the following engineering techniques: Conventional Vibration Analysis, Operational Deflection Shape (ODS) and numerical simulation by the Finite Element Method (FEM). In the Conventional Vibration Analysis, high levels of vibration were observed during manufacturing process, especially when the material reaches the equipment. Impacts generate high values in acceleration, on average 80 m/s² peak to peak. At the moment of impact, misalignment of internal components was observed by ODS. Field results were correlated to those obtained by the Finite Element Method, which allowed to calibrate FEM model. Thus, the most effective structural modification already evaluated numerically was implemented in the system. Afterwards, new measurements by vibration and ODS technique were performed, and the attenuation of the vibrational levels and the operational mode, which overloaded the internal components rolling stand, was verified.

Abstract:

Leveling is a standard process in the rolling mill to eliminate flatness deviations. The process layout is based on models and the leveling result depends on the accuracy of the material parameters in these models. Even small deviations from the correct assumptions can have a major effect on the final flatness. Thus, after leveling the products may look optically flat, but subsequent to a final cutting process springback occurs due to residual stresses. The objective of this work is to analyze the influence of material parameters and gravity on the flatness after leveling. To evaluate the sensitivity of the process, an FE parameter study is exerted that reveals the influence of fluctuations in material properties in the case that the leveling setup is fixed. Gravity is neglected to not conceal flatness deviations. Examples of this study are rerun in a further step under consideration of gravity to also analyze its influence on the resulting flatness and residual stresses. Finally, to analyze the consequence of the residual stresses, all information of the plate from the previous step are transferred while gravity is suppressed to prompt springback. This study revealed that slight deviations of the material properties can lead to uneven plates in simulations where gravity is not considered. If gravity is taken into account, the unevenness is concealed and the plate seems flat. A springback simulation of the same plate shows that strong residual stresses are still present and would lead to unevenness if e.g. the plate were cut.

Abstract:

The Cutting and Sampling Line (CSL) is a line for process of cut and sample in hot rolled coils. It was designed to meet a demand for mechanical testing requirements in materials above the thickness capacity of the Hot Skin Pass Line (HSPL) and Dividing Line (DL) in order not to increase the occupation of the HSPL or DL. In the near past, ArcelorMittal Tubarão had to rethink their CSL process because of the following situations: SAFETY - Reduction and control of risk for manual handling. Occurrence of an accident in December 2016; PRODUCTIVITY - Increase productivity in the CSL by 50% in order to reduce the operating period, with gain in reduction of effective labor force; HSPL or DL AVAILABILITY - Reduction of occupancy rate for sample withdrawals in the DL and HSPL to increase the lines productivity. QUALITY - Reduction and elimination of the cost of non-quality generated by manual slitting of the sample, with effective record of customer complaints and possible loss of Market Share. COSTS - Reduction of current and future costs (in service centers) when the demand for coils processing generated by the demand for CSL is greater than DL idleness. The implementation of the new CSL was defined and authorized on an exceptional basis, through OPEX (without additional budget), as an attenuating action taken mainly to the occurrence of the personal accident reported above. Therefore, ArcelorMittal Tubarão Hot Rolling & Finishing Products, Supply and Engineering Management teams had to face enormous challenges. These challenges summarize in the short term, the reduced costs of design, acquisition and implementation of the new line. Currently, new opportunities are being developed for the CSL, aiming at the production of steel sheets through the reuse of process discards.

Abstract:

Gas-fired pusher furnaces are commonly used to heat steel slabs before hot rolling. Temperatures well above 1000 °C combined with an oxidizing atmosphere containing H2O, CO2 and O2 result in rapid oxidation of most steel grades. The resulting oxide scale and the chemistry of the metal-scale-interface are major determining factors for the occurrence of hot rolling defects. To better understand these phenomena, lab-scale trials were performed with two different steel grades in an electric tube furnace in the temperature range 1000-1250 °C, using an atmosphere of about 20 % H2O, 7 % CO2 and 3 % O2. Humidification of the gas was achieved by evaporation, using a custom thermostat with standard laboratory glassware. The resulting samples were prepared metallographically, using cold mounting under vacuum with taper section angles, and analyzed using light microscopy and SEM/EDS. The scale structure of the Si alloyed steel was highly dependent on the oxidation temperature due to the formation of eutectic liquid phases of FeO, Fe2SiO4 and FeAl2O4. Below the eutectic temperature, the scale of the Si steel appeared to be made up of three distinct areas: The external scale consisting solely of Fe oxides, the internal scale containing Fe2SiO4 and FeAl2O4, and an internal oxidation zone with SiO2 and Al2O3 in a mostly plain Fe matrix. Comparisons of the experimental results with simulations of the internal oxidation showed good qualitative agreement.

Abstract:

A work roll thermal crown model has been developed for a wide range of hot and cold rolling mill applications. The model is extremely fast, robust and accurate to determine the evolution of thermal crown all along the rolling campaigns. It has also ability to consider work roll shifting, multiple segmented cooling zones along the length and circumference of the roll as well as composite rolls properties (e.g. different thermal properties between mandrel and core of the roll). Moreover, the model includes simultaneously fast and slow temperature evolution calculations, respectively near roll surface (skin area) and at a certain distance below the roll surface (bulk area). This gives to thermal crown predictions a higher accuracy than conventional thermal crown models from literature that consider only the slow temperature evolution regime. An optimization procedure together with roll surface temperature and roll thermal profile measurements have been used to tune the model. The tuned model applied to hot rolling conditions has shown a significant influence of roll shifting and composite rolls properties on the prediction of roll temperature distribution and thermal crown during rolling. The tuned model applied to cold rolling conditions highlights the importance of mill operators practices to modify cooling distribution across roll barrel length with the segmented cooling zones to adjust the thermal crown and to get better strip shape control

Abstract:

Chatter is a widely studied vibration phenomenon that affects most cold mills around the world and its impact on these lines are tremendous: from productivity and quality losses to mechanical equipment damage. The investigation of its origins and how to minimize the occurrences and their impact on the equipment require special instrumentation and algorithms in order to have a detection of the vibrations as soon as they start. This paper presents three methods of identification of chatter on a Tandem Cold Mill and the actions to leave the vibration frequency range before its amplitude achieve catastrophic values.

Abstract:

Softening heat treatment of CHQ alloy steel (Cr-Mo Steel) is a bottleneck process that requires 90% or more of the entire manufacturing process. In order to reduce the property deviation between edge and center and remove the low-temperature structure problems, CHQ products is heat treated by customers. This technology comes from the idea to solve the problem by applying the concept of “In-line isothermal transformation through initial quenching + heat source addition. Consider the stability of field operations, durability from high ambient temperature and fall of scale, Instantaneous heating and cooling control was required for the conversion of slow cooling and rapid cooling products. An electric heater system was applied to the underside of Stelmor air-cooling nozzle. Using the Scan Pyrometer, the feedback control was performed and fine temperature control was performed through the thermocouple by zone. Through the this technology, it is possible to develop and expand products that can be shortened or omitted by the heat treatment process of customers.

Abstract:

Recently, the demand for ultra-thin steel plate with high hardness and strength has been increasing in various industries. In order to satisfy this requirement, steel company designs the chemistry with low CEQ and obtains the required characteristics through quenching and tempering process. Especially, these steels are accompanied by low temperature tempering as a necessary process. Unlike ordinary high temperature tempering steels, it is impossible to improve the flatness after low temperature tempering. Therefore, shape control in the quenching process is very important for securing the excellent quality flatness. In order to obtain flatness in the quenching process, uniform cooling inside the plate should be accompanied. However, the quenching process has limitations in estimating the temperature behavior during cooling because the plate temperature is lowered to room temperature. In this study, a thermocouple was installed inside the actual quenching plate to measure the temperature behavior during cooling and to establish the manufacturing conditions of the quenching plate to ensure excellent flatness quality.

Abstract:

The highly competitive business environment of the metals industry in the world is moving to the demands for more cost effective operation of steel making facilities, rolling mills, and strip processing lines. Achieving stable operation is vital for the steel industry to produce high quality products constantly and productively. In recent years, advances in computer processing speeds, data acquisition rates, and data storage capacity gradually enable industrial applications using new technologies of Big Data, analytics, IoT, and AI for control system designers and process engineers. “Smart Rolling Mill” in the hot strip mill is proposed by our group, and the goal of “Smart Rolling Mill“ is a sophisticated, state of the art, and automated steel rolling mill. It has various solution engines that improve process stability, increase the performance of mill equipment, and provide improved process control. These solution engines are based on extensive knowledge of the rolling process and associated control system. Especially, among these solution engines, the diagnosis system for rolling condition and product quality contributes to cost effective operation and minimizing of yield loss. In this paper, we focus on especially the diagnosis system for rolling condition and product quality in the hot strip mill. Advanced information technologies using Big Data analytics and Machine Learning are applied to real-time data collected from automation system which controls operation and process of rolling. We have developed diagnosis solutions of rolling condition and product quality. The solutions contains predictive and clustering diagnosis. Predictive diagnosis is able to detect a change in the state of facilities or rolling condition, and to avoid a risk of serious trouble. Clustering diagnosis is able to classify fluctuation patterns in the trend chart of product qualities, and to provide effective tuning guidance in order to improve the product qualities. The paper describes these applications with several examples.

Abstract:

The aim of the present work was to study the influence of temperature in the grain refining process from severe plastic deformations through the simulation of Accumulative Roll Bonding (ARB) by torsion tests at temperatures lower than the end of the austenite-ferrite transformation in micro-alloyed steel. The assays were performed to simulate the ARB at three different temperatures of 550 ° C, 625 ° C and 700 ° C with 5 torsion cycles with equivalent deformation of 0.8 per cycle at a rate of 0.1s^(-1), totalizing an accumulated deformation of 4.0. Samples of the annealed steel and of each deformation temperature were analyzed by optical and scanning electron microscopy to measure the final grain size of the process. Thus, after 5 cycles of deformation, grain refining was achieved in the material. The analysis of the stress and strain graphs revealed the occurrence of dynamic recrystallization during the deformation stages, which resulted in grain refining at three temperatures reaching the mean size of 2*10^(-6)m in the 550 ° C test. At the temperature of 625 ° C there was the grain refining of the material for the average size of 5*10^(-6)m and at the temperature of 700 ° C for the average size of approximately 6*10^(-6)m. Vickers hardness tests were also performed on the annealed test specimens and those obtained at the end of the process. In addition to grain refining, the Vickers hardness increased by 68% from 119HV in the annealed sample to 175HV in the deformed sample at 550 ° C. In the deformations at 625 ° C and 700 ° C the value of 130HV E and 150HV respectively was obtained. Based on the obtained results, it can be affirmed that the severe plastic deformations in microliged steel, carried out at temperatures lower than the end of the austenite-ferrite transformation, produce refined grains of the order of 2*10^(-6)m and consequently the increase of the mechanical strength of the material.

Abstract:

This study combined with the actual production, from analysis of the occurrence rule and the mechanism , the black spot is the cause of emulsion residue.At the same time , this study analyzed the effect of through extreme pressure properties and oxidation resistance properties emulsion in the roll gap, purging device, emulsion dripping isolation device, rolling mill, concentration of emulsion, emulsion ion state, emulsion formula, the pressure, the mechanical structure and other factors, then made the control measures of emulsion residue.

Abstract:

Steel strip manufacturing ever reinvents proposing new grades, requiring to tackle technical limitations of production systems. Primetals Technologies breaks through strip welding by expanding the welder LW21L “Asolid” technology used on low gauges for high-end market such as automotive CAL/CGL. Addressing the usual drawbacks in maintenance, operation and safety of current welding system based on mechanical cutting and CO2 laser welding, the newly developped LW21H “Asolid” technology processes thicker strips up to 7 mm with solid-state laser cutting and welding. This new welder is brought to reality through a scale 1:1 pilot developed, manufactured and tested in Primetals Technologies workshop.

Abstract:

Hot-rolled seamless steel pipe is a kind of irreplaceable and important steel products. The hot forming process of hot-rolled seamless steel pipe successively experiences high temperature piercing, rolling and sizing process. The piercing at high temperature and lacking of controlled cooling technology for circular and hollow shape lead to be short of effective methods for microstructural control of hot-rolled seamless steel pipe, which results in mechanical property development depending on adding alloys elements and additional heat treatment. This brings many adverse effects on high quality pipe development, production cost, manufacturing efficiency and energy consumption control. Based on the research and development of circular section uniform cooling mechanism, the authors developed controlled cooling technology for hot-rolled seamless steel pipe. Meanwhile, for high temperature piercing process, the second phase particle that could be steadily existed at high temperature was introduced, such that nucleation rate of intragranular ferrite was greatly improved. At present, a good research progress has been achieved. Second phase particle inducing fine grain combining with controlled cooling will fully realize on-line microstructural control during forming process of hot-rolled seamless steel pipe, and lay a foundation for effective on-line microstructural control and further develop comprehensive properties of hot-rolled seamless steel pipe.

Abstract:

In recent years, the market for thick plates has been highly competitive, in this scenario the plates quality is a critical success factor. In this process, the quality of the cut in thick plates is one of the important requirements for the customers, by the visual aspect as well as the technical aspect of the plate application. In the shear line, the cutting is done by shearing to trim tips, subdivide plates, trim side edges, remove samples, eliminate defects, etc. The cut is obtained by the penetration of the upper knife in the plate, causing plastic deformation in a certain region and hardening. If the clearance between the knives is adequate, the cracks will be close to the center of the plate thickness and will result in a good cut quality. This work will present the theory of cutting of thick plates, the types of shearing, the quality of the edge in the cut, the types and the main characteristics of the knives.

Abstract:

Temperature, microstructure and dimensions are the main material parameters to be controlled during hot rolling of steel. Although thermal mathematical models have long been developed and applied for hot strip rolling, each Hot Strip Mill (HSM) must have its own model adapted to its facilities. Thus, a mathematical model for temperature and scale evolution during rough rolling has been developed for the Usiminas HSM at Ipatinga Plant. The model achieved a high level of accuracy, which was assessed by comparing measured values of temperature at the hot strip mill entry with the calculated ones, the difference ranging from 10° to 18°C. Application examples have shown that the slab can be occasionally stopped before start of rolling for as long as a couple of minutes without compromising its further processing. On the other hand, if the transfer bar stops after rough rolling even for short time, further processing in the HSM can be hindered, due to excessive temperature drop. In case of such abnormal line stop, the model can be used as a tool for decision-making to either continuing the planned rolling schedule or to change the route, thus improving the overall rolling process.

Abstract:

In this presentation, a low carbon high strength steel microalloyed with Nb and Ti was processed by thermo-mechanical controlled process (TMCP) containing two stages of controlled rolling. The austenite with various grain sizes was obtained by austenitizing this hot-rolled steel at different temperatures. And the effect of austenite grain size on bainitic transformation was investigated in a dilatometer to reveal microstructural change. The results showed that the microstructure of the hot-rolled steel was mainly composed of granular bainite, lath-like bainite, and martenite/austenite constituents (M-A constituents). With increasing the austenitizing temperature, or increasing the austenite grain size, the microstructure was changed from granular bainite to lath bainite. When the steel was reheated to a lower temperature of 860 ºC, a relatively higher start temperature (Bs) was measured for bainitic transformation. This was mainly caused by the formation of solute-depleted region in the austenite and the promotion of the granular bainitic nucleation. The highest reaction rate occurred at austenitizing temperature of 1000 ºC with fine grain size, while the coarse austenite grain can lead to a sharp increase in the amount of bainite. An analysis was made on the kinetics of bainite transformation which was controlled by the volume diffusion of C atom.

Abstract:

SORM 3plus (SORM = Superfast Optical Roughness Measurement) is a system enabling online measurement of roughness parameters during continuous strip processing. Increased requirements for new materials and more complex components call for ever increasing process safety. The roughness parameters are important quality features of uncoated and surface refined strips. The traditional method of measurement involves using a mechanical stylus based instrument. For this purpose the operator must stop the production line or samples are taken from the end of the coil and measurements are made offline in the lab. SORM 3plus, however, is a non-contact, online surface roughness measurement system that can be used for metallic and many non-metallic surfaces at strip speeds of up to 2400 m/min. The surface roughness data are stored in the system computer, displayed to the operator and if needed are fed into a higher-level network. The operator is alerted, if the limited values preset by him are exceeded or if any changes within the line will jeopardise the production process. SORM 3plus calculates the roughness parameters as defined in the standards, such as the arithmetic average roughness (Ra) and the peak count (RPc).

Abstract:

Rheorolling is a novel technology to manufacture metallic strip. This process saves energy because the material is formed in semisolid state demanding less power from the rolling mills, i.e., no robust equipment is required and many stages of traditional rolling can be suppressed. The typical coarse cast structure of ingoting and continuous casting products is refined by hot rolling. On the other hand, rheorolling processing refines microstructure by the high heat transfer during processing of the strip. Furthermore, during forming of the semisolid state, shear stress acts degenerating the dendritic morphology. Thus, globular structure occurs increasing the mechanical properties. The rheorolling requires minor separation force between the rolls in comparison with the traditional forming processes. Al-Si A413 alloy is usually processed via die casting. This alloy is not suitable to obtain metallic strips by forming because of the brittle Si particles, in such a way that rheorolling process can become this viable. In this work, Al-Si A413 alloy was melted and poured at 680 ºC on a cooling slope to obtain the semisolid material feeding the ceramic nozzle (150 cm³) at the lower roll. The two rolls of the roll stand are separated with a gap of 1.5 mm, have approximately 105 mm in diameter and are made of carbon steel. The chill/columnar layer formed at the lower roll drags the metallic slurry at a rate of 0.2 m/s to be formed by the upper roll, obtaining a metallic cast strip with a thickness of 2 mm, approximately. Three conditions were applied to test the continuity of the process: 1) Roll stand without any mechanism to reduce the pressure on the metallic slurry; 2) Roll stand with springs attached on the upper roll in order to reduce the separation force between the rolls; and 3) The upper roll as modified with springs and the lower roll internally cooled by soluble oil in order to increase the heat transfer. The first situation did not work properly due to the sticking of the strip onto the lower roll. The second condition was successfully performed obtaining a continuous metallic strip. The last condition failed due to complete solidification of the melt alloy between rolls and at the ceramic nozzle. This indicates a lack of fluidity of the metallic slurry promoting premature solidification in the processing.

Abstract:

The development of a 600mm U-Pile was done in Gerdau’s Ouro Branco Heavy Section Mill in order to feed the local market with a product the was imported from Europe and USA due to the non-existence of South American producers. The focus of this study is to show the developmental process which the Mill went through until it was prepared for hot trials. All roll pass and guide designs were developed by our own team. Analytical tools like Finite Element Analysis and reduced scale lead trials will be shown and how these tools impacted on the development timeframe and accuracy of the final results on steel. The final results on the steel product, the rolling parameters such as separating forces, trust forces, torque, product behavior, spreading, elongation, and others will be compared to results predicted by the tools and how to interpret them.

Abstract:

The Gerdau Ouro Branco Mill, three years after the implementation of its new plate mill, has started to develop high complexity products. The plate mill’s learning curve has been increasingly challenging since products are being developed to their highest grades. This work aims to present the first results of the development of steels of the strength class of 510 MPa produced by TMCP (Thermomechanical Controlled Processing) followed by accelerated cooling. These results show the potential and advantage of the accelerated cooling process regarding to obtain products of high mechanical strength and high toughness, associated with a low equivalent carbon.

Abstract:

Electromagnetic based (EM) sensor technology has been shown to detect changes in the magnetic permeability of steel strip travelling down the run out table after rolling. Measuring below the Curie temperature, these changes can be interpreted in terms of the phase transformation from austenite (paramagnetic) to ferrite (ferromagnetic). These real time measurements provide a detailed insight into the changes in the structure at high temperature providing the steel producer with feedback on quality control, product consistency and product development. However unlike mill microstructure models, the sensor measurement provides a point reading at a distance through the cooling course. To map the transformation in more detail, a sensor array is required along the length of the Run Out Table i.e. to measure points on the austenite to ferrite transformation curve. This paper describes the process and metallurgical factors that should be considered in the optimum design of a sensor array, i.e. the number and location of the sensor heads. Examples of cooling strategies for different steel grades e.g. low carbon, structural and dual phase steels are used to demonstrate the importance of sensor location. In addition, the effect of variability within typical industrial parameters e.g. cooling speed, on the sensitivity of sensor output and location will be considered.

Abstract:

Impinging water jets promote high heat flux extraction rate. Steel industry widely employs the process for accurate temperature control to improve the microstructure and to ensure adequate mechanical properties. The range of surface temperatures, heat fluxes and cooling rates are very large, which makes it important to obtain an accurate value of the heat transfer coefficient. This paper presents an experimental and numerical study of the heat transfer behavior of a high temperature (450°C - 900°C) steel plate cooled by a water jet at 20°C to 70°C. High-speed imaging (up to 20,000 fps) within water jet impingement zone allowed the characterization of the boiling regimes in the early stages of cooling. The effects of initial temperature, water jet temperature and velocity and on the heat transfer coefficient were analyzed by inverse heat conduction method that predicts the heat flux and temperature on the top surface from temperatures measured with thermocouples inserted in test plate. Heat transfer is strongly affected by the initial temperature of the hot steel, water jet temperature and, less intensely, by jet velocity. High cooling rates start when liquid water is in direct contact with surface temperatures above 700°C.The results will contribute to the enhancement of the temperature cooling control on the runout table and cooling model employed at Usiminas Hot Strip Mill.

Abstract:

TOday, there are good solutions extensively described by various OEMs & steel makers to optimize CAPEX & OPEX for small capacity Cold Rolling Mills (CRM) as well as for high capacity CRM. A good solution for small capacity CRM is to start with a single stand reversing mill (up to 400 ktpy, depending on product mix), which can be expanded in the future into a twin stand mill (up to 900 ktpy, depending on product mix). The main drawbacks in conventional practice are the off-gauge length in single stand configuration and the stoppage time of the mill, which is quite long for erection of the second stand. For higher productions CRM, it is recommended to go directly for a new PLTCM, with a high CAPEX which is common practice. But…. what is in between? How to start with limited output and limited CAPEX but without jeopardizing final ultimate expansion goal (1.2 to 2 mtpy) for which PLTCM is the best technico-economical choice? Today there are no solution, and CMI has therefore developed an integrated solution which will limit the CAPEX in the first phase, without penalizing the future by an easy and economically viable expansion up to a PLTCM, without a long production stoppage. The solution consists to install first a twin stand mill, which can be expanded into a tandem mill by a smart layout of the line. Therefore it’s possible to have a first project phase up to 900 ktpy (for which single stand can be installed first, then second stand later), and an second phase with a conversion into PLTCM for a production from 1.2 to 2mtpy, depending on the market evolution and financial capacities. Therefore CMI has developed a smart new layout in reversing phase combined with totally new rolling strategy to optimize productivity and limit off-gauge compared to conventional solutions (patents pending). In addition the layout enables an easy conversion to tandem mill without high over investment compared to conventional purchase of PLTCM from the beginning. Long stoppage times for capacity extension which could be detrimental to this approach phase by phase is also avoided. Technical and process description of the new layouts and rolling strategies together with CAPEX & OPEX description of the phasing are described in the paper.

Abstract:

The evolution of microstructure and texture of Ti6Al4V alloy developed by cold rolled followed by annealed treatment at thickness reduction ratio of 15%-70% were investigated by scanning electron microscopy and X-ray bulk texture measurement technique. It is found that during cold rolled deformation process, the grains were severely broken up and elongated, and the degrees of the mechanical anisotropy of the Ti6Al4V alloy were increased. For cold-rolled samples, recovery and recrystallization occurred during annealed treatment. After the thickness reduction ratio of 10% and 30%, the microstructure still retained the structural features of the cold rolled. When thickness reduction ratio reached 50%, the deformation band structure disappeared. This is related to the large residual internal stress in the microstructure under the condition of severe deformation. Compared to the cold rolled samples, the mechanical anisotropy of the annealed samples was weaker and it was mainly related to the texture components. The intensity of the {0001} basal texture and <10-10> fiber texture were strengthened by cold rolled, (0001)<10-10>, (-12-10)<10-10> and (11-25)<10-10> components dominated the texture of the cold rolled samples. Among them, (-12-10)<10-10> and (11-25)<10-10> texture components inherited the as-received microstructure and the intensity of that was increased with thickness reduction ratio increased. But the intensity and volume fraction of the texture (-12-10)<10-10>component rapidly increased and the intensity of the texture (11-25)<10-10> and (0001)<10-10> components were weakened by the annealed treatment. At high temperature condition, the elongated slipped region start recrystallizing faster and starts growth, the prismatic scatter grains have more severe deformation (higher stored energy) compared with the prismatic tilt grains and preferential nucleation may happen in the region having texture of prismatic scatter. This eventually leads to grain having texture component (-12-10)<10-10> orientation is gradually strengthened by consuming other scatted orientations. In addition, it can be found that an increase in the intensity and volume fraction of (-12-10)<10-10> texture component has a positive effect on improving the mechanical anisotropy of the Ti6Al4V alloy. So it can promote optimizing the process treatment of the Ti6Al4V alloy by studying characteristic of the texture components.

Abstract:

mandrel mill is a process used to manufacture seamless tubes. the process consists in 8 stands using 2 rolls in each stand reducing the outside diameter and one mandrel inside of the shell to keep the inside diameter. THE WALL THICKNESS of the tube IS the main result of this process. the pqf (premium quality finishing) has the same objective concerning wall thickness, but with high quality. vallourec has, in partnership with sumitomo, a pqf located at jeceaba. the mandrel from this process has the same material specification. an opportunity was identified to apply an excess of mandrel bars from pqf mill in mandrel mill. however, the hardness specified to Mandrel mill is higher than pqf mill due to surface treatment performed on mandrels surface in jeceaba (chroma). the challenge is to increase the hardness of x35 material homogeneously since the surface down to the core. focusing on increasing hardness in this 12 meters of round bar, a search was carried out to define the cooling process and partner to perform the treatment. oil was the most AGGRESSIVE way found in articles and suppliers datasheet. nevertheless, to treat this length is not usual and no partner was identified to carry out the treatment. so, An idea raised up from the technical team in charge of tooling. The idea was to carry out the heat treatment using the Q&T line for tubes located in the same plant. the vallourec team specified the heat treatment with internal know-how and technical information taken from suppliers datasheet. this work will show details of this heat treatment and comparison of microstructures in each phase of the treatment. penetrating liquid (non destructive test) was also performed once the cracks are critical and undesirable in the application on the mill.

Abstract:

Texture analysis is a method of process control to better understand the behavior of material properties throughout it. It is intrinsically related to the forming process and the material’s microstructure. Planetary Rolling Process is derived from Piercing Rolling Process and can be applied in the production of seamless copper tubes, replacing additional processes of reheating and drilling of the billet, as well as allowing for longer starting tubes. In this case study, there was a variation in the starting material for the tube production with capacity to reduce about 90% of initial thickness of the tube. The process used to feed a Pilger Mill with reheated extruded billets. Currently, the process takes place directly from the cast billet to feed the planetary mill. The planetary mill was temporarily fed with extruded billets as well, which led to a question as to whether this could modify the properties of the final product. By using texture as a process control variable, this study aims to catalog the textures by the planetary lamination process of seamless copper alloy 10300 tubes obtained by different starting structures, to analyze them, to compare them and to understand them within the process’ context. Texture analysis of external surface showed some variation for both the macrotexture and the microtexture of the same starting material. To macrotexture was mainly {200} and for microtexture was mainly {111}. It is possible that the layers could recrystallize at different times due to the different velocities and deformation temperatures that vary along the thickness of the tube. And then the transversal surface was analyzed and showed some {111} around outer surface and {100} at the bulk. This means that the deformation of the tube is so intense that the texture tendency may not be related to starting material’s characteristics. To prove that, further analyses should be performed as macrotexture of middle thickness surface and inner surface of the tube.

Abstract:

When austenite is deformed above the Ae3 temperature, partial amount of it transforms dynamically into ferrite by a displacive mechanism. After unloading, it retransforms back into the stable austenite by a diffusional process. This influences the rolling load which decreases under isothermal condition or does not increase with decreasing temperature as rapidly as expected. Plate rolling simulations under isothermal and continuous cooling conditions were carried out on a 0.09 wt.% Nb X-70 steel. Pass strains of 0.2 were employed together with interpass times of 10 s, and 30 s for the cooling conditions and 0.3 with interval of 10 s at 900 °C for the isothermal experiments; strain rate of 1 s-1 was used during the simulations. The mean-flow-stress (MFS`s) behavior of both conditions indicates that dynamic transformation and dynamic recrystallization were taking place during straining. The critical strains for the initiation of dynamic transformation fell around 0.06 while the critical strain for DRX was 0.12. It has been shown that ferrite is formed due to the applied deformation of roughing passes and increases its volume fraction throughout the finishing rolling stage. Under cooling conditions, the ferrite formation is also favored as the temperature approaches the Ae3 line. Such ferrite forms when the driving force for dynamic transformation is higher than the total free energy barrier preventing its formation. This obstacle consists of the free energy difference between austenite and ferrite as well as the lattice dilatation work and shear accommodation work. The addition of Nb retards the retransformation of the ferrite into austenite. Moreover, holding times after rolling increases the amount of austenite available for microstructure control on subsequent stages. The dynamic transformation (DT) mechanism can be used to design improved rolling schedules.

Abstract:

In the production of hot strips, one of the factors that may affect productivity is the possible occurrence of failure from the geometry of the strip at the exit of the rolling rolls, since the tip of the strip can turn-down or turn- up. This study had the objective of evaluating the behavior of the strip when leaving the working cylinders, through numerical simulation, aiming to know the influences of the main variables that govern the formation of the "turn-down". The methodology consisted in performing the computational simulation of the strip lamination and to vary the operational and geometric parameters that can influence in the process. The analysis of the results allowed concluding that the lamination of strips of HSLA material with final thickness varying between of 3 to 6 mm and a reduction of 6.6% to 11.0% in the last strip mill, tends to bend towards the cylinder with larger diameter, higher coefficient of friction, higher temperature and lower limit of material flow. It was observed that the variation in diameter is the factor that contributes most to the formation of the curvature of the strip tip. Based on these results, several measures were implemented in the industrial line, with a significant reduction in the occurrence of "turn-down".

Abstract:

The rolls are the first source of cost in a hot strip mill. To get a strip with good quality, a proper wear resistance and a resistance to surface degradation is needed. In the hot rolling process, the work-rolls undergo two types of fatigue solicitations. The most damaging one is the thermal fatigue. To reduce the industrial use cost (mainly roll price) and to have a good strip surface quality, we must master its degradation. The work-roll cooling can have a strong effect too. Therefore, a suitable and mastered work-roll cooling can avoid or delayed the roll degradation. To assess the work-roll lifetime or to optimize its efficiency, different ways of modelling are available. Currently, most of the thermo-mechanical models used are based on 1D thermal transient hypothesis. That kind of model allows us to predict the effects of design constraints on the cooling efficiency. For instance, different technical assistances are done to help mills to implement an anti-peeling system also knowns as skin-cooling, to study the effect of an addition or removal of cooling nozzles, to build parametric studies on the effect of each cooling headers etc. Nevertheless, that kind of model is too conservative and not adequate to determine a thermal fatigue criterion based on multiaxial solicitations as it is the case for the work-rolls. Consequently, a 3D model based on FEM (finite elements method) of the work-roll in the finishing mills is currently under development to have a better insight of the thermal field distribution within the work-roll. Afterwards, a mechanical analysis will be done to understand how thermal and mechanical stresses are created inside the work-roll. This study will help us to deepen our knowledge on work-roll cooling and work-roll degradation that can bring more reactivity to tackle plant's issues.

Abstract:

Due to the increasing demand for fuel efficiency and collision safety, Advanced High Strength Steel (AHSS) has been applied to vehicles. When AHSS is rolled at a high reduction ratio, the forward slip ratio in cold rolling tends to be lower than that of other softer strips like low-carbon steels and the work roll sometimes skids the strip. This skid causes defects on the strip surface. When the reduction ratio increases, then the bite angle also becomes larger. This large bite angle increase leads to a decrease of the inlet oil film thickness and the friction coefficient increases with the increase in the forward slip ratio. To identify why the forward slip ratio of AHSS at a high reduction ratio becomes smaller than that of low-carbon steel, the relationship between the reduction ratio and forward slip ratio was investigated by a rolling experiment. For this trial, a 4Hi laboratory cold mill was used. AHSS and low-carbon steel coils were rolled by two different rolls that set to be 0.3 and 0.6 μmRa in order to make two kinds of friction conditions. Furthermore, the rolling conditions were numerically analyzed to determine the influence of the friction coefficient and flow stress on the relationship between the forward slip ratio and reduction ratio. These experiments and numerical analysis revealed that the forward slip ratio was reduced with increasing rolling reduction ratio in a low friction state, on the other hand, it increased with increasing rolling reduction ratio in a high friction state. This feature was clearly seen when harder materials were rolled.

Abstract:

The study of asymmetric rolling on the AA 5454 aluminium alloy plates was carried out. The plates were taken directly from the industrial hot rolled sheet. They were cold rolled on the laboratory mill with different rotation speed of the upper and the lower work roller with the strains around 33 % and 44 %. To get closer to the industrial conditions the maximal dimensions of the rolled plates for laboratory rolling mill and the special industrial lubricant was used. After deformation the plates were annealed to the soft condition. This research was focused through all possible effects of asymmetric rolling: the reduction of rolling force, the increase of strain at same set roll gap, the bending of workpiece, the finer microstructure, the heterogeneous texture and as consequence of that the better mechanical properties. The asymmetric rolling with favourable mechanisms in the deformation zone created the material with the homogeneous hardness in the cross section and with the LOWER anisotropy, which is crucial for improvement of formability properties of aluminium work hardened alloys and get closer to properties of steels. In the presented paper the general impact and different effects of speed difference of rollers was investigated on cold rolled aluminium alloy. Obtained and analysed results explain the function of asymmetry in rolling process and the options to implement the asymmetric rolling in industrial plant.

Abstract:

TO EVALUATE THE POTENTIAL APPLICATION VALUE OF THE NEW STEEL, THE STRENGTHENING AND TOUGHENING MECHANISM OF GRAIN SIZE IN TENSILE PROCESS WAS STUDIED. THE MICROSTRUCTURE EVOLUTION AND MECHANICAL PROPERTIES OF THE FINE-GRAINED AUSTENITIC STAINLESS STEEL WERE COMPARED WITH THOSE OF COARSE-GRAINED AUSTENITIC STAINLESS STEEL DURING TENSILE TEST, AND THE INTERNAL RELATIONSHIP BETWEEN DEFORMATION MECHANISM AND AUSTENITE STABILITY WAS ANALYZED. IN THE PROCESS OF RESEARCH, MECHANICAL PROPERTIES OF AUSTENITIC STAINLESS STEELS WITH DIFFERENT GRAIN SIZES WERE OBTAINED BY TENSILE TEST AND PHASE ANALYSIS WAS CARRIED OUT BY ELECTRON BACKSCATTER DIFFRACTION (EBSD), THEN DEFORMATION STRUCTURE WAS OBSERVED BY TRANSMISSION ELECTRON MICROSCOPY (TEM) AND FRACTURE CHARACTERISTICS WERE OBSERVED BY SCANNING ELECTRON MICROSCOPY (SEM), FINALLY THE RELATIONSHIP BETWEEN MECHANICAL PROPERTIES, MORPHOLOGY AND GRAIN SIZE WAS STUDIED. IT IS FOUND THAT THE EVOLUTION OF MICROSTRUCTURE PLAYS A DETERMINED ROLE IN MATERIAL PROPERTIES DURING PLASTIC DEFORMATION. TRIP OR TWIP EFFECT WILL OCCUR IN METASTABLE AUSTENITE OF AUSTENITIC STAINLESS STEEL UNDER EXTERNAL STRESS, SO GOOD TENSILE STRENGTH AND HIGH PLASTICITY CAN BE OBTAINED. THE RESULTS SHOW THAT THE GRAIN SIZE OF AUSTENITIC STAINLESS STEEL IS REFINED FROM COARSE GRAINS， AND THE STRENGTH AND PLASTICITY OF FINE GRAINED AUSTENITIC STAINLESS STEEL ARE IMPROVED SIGNIFICANTLY. AT THE SAME TIME, FINE GRAINED AUSTENITIC STAINLESS STEEL OBTAINS EXCELLENT PLASTICITY MAINLY THROUGH DEFORMATION TWINNING (TWIP), WHILE COARSE GRAINED AUSTENITIC STAINLESS STEEL OBTAINS GOOD PLASTICITY MAINLY THROUGH STRAIN INDUCED MARTENSITE EFFECT (TRIP). THE DEFORMATION MECHANISM FROM DEFORMATION TWINS TO STRAIN INDUCED MARTENSITE IN THE COARSE-GRAINED STRUCTURE IS OWING TO THE INCREASED STABILITY OF AUSTENITE WITH GRAIN REFINING.

Abstract:

Austenitic stainless steel is widely used in various field because of the excellent corrosion resistance. However, intergranular corrosion is the most important limitation of austenitic stainless steels. Generally, it is believed that sensitization treatment of the stainless steels is the principal cause of intergranular corrosion in stainless steels. Due to the sensitization temperature of the heat treatment process, the Cr-rich carbides precipitate at the grain boundary. Chromium can ensure the excellent corrosion resistance of the stainless steel. The lack of chromium can explain the intergranular corrosion of stainless steels. In order to investigate the effect of sensitization temperature and time on the microstructures and properties of austenitic stainless steel, different heat treatment temperature（sensitization temperature） and heat treatment time was studied by using 204C2 austenitic stainless steel in this research. In this paper, the 0.3 millimeters-thick 204C2 austenitic stainless steel was solution-treated by the temperature of 1000℃ and the time of 30s. Water quenching was taken after the solution treatment immediately in order to gain fully austenitic structure without grain boundary precipitates. Whereafter, the 204C2 austenitic stainless steel specimens with heat treatment were sensitization-treated by the temperature of 500℃、600℃、700℃、800℃、900℃ and the time of 10s、20s、30s in order to gain different situation of precipitates. These sensitized stainless-steel specimens are the main subject of this study. Microstructure of them was investigated by means of optical microscopy (OM). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to observe the evolution of Cr-rich carbides zone with different sensitization temperature and time. Energy dispersive spectrometer (EDS) was also applied to analyze the chemical components of the precipitates. For mechanical properties investigations, hardness and tensile tests were carried out. The results showed that, due to the high chromium element content, 204C2 austenitic stainless steel is easy to separate out Cr-rich carbides precipitate during the low-temperature heat treatment. After the solution treatment by the temperature of 1000℃ and the time of 30s, the austenite grains are equiaxed without grain boundary precipitates. However, the chromium in 204C2 stainless steel decreased with the increase of sensitization temperature, meanwhile the carbon increased. Cr-rich carbides in network would be formed at the grain boundary of 204C2 stainless steel because of the free energy at the grain boundary is relatively higher. With the increase of the sensitization time, carbides would be increased. Serious intergranular corrosion would be induced by the decrease of chromium and the decrease of carbon. It is observed that the hardness and strength decreased with the increase of sensitization temperature, meanwhile the elongation increased. This is closely related to the precipitation of carbides.

Abstract:

Abstract:

The controlled rolling followed by accelerated cooling, known worldwide as TMCP, aims to increase mechanical properties without toughness deterioration. The process principle is to promote the plate cooling with water at fast speeds along the ranges of the transformation temperatures. The accelerated cooling process is only fully effective when controlled in an integrated manner, as it alone cannot ensure significant improvements in the final steels properties. The plate surface quality depends on some parameters that must be controlled before the plate initiates the accelerated cooling. Good flatness is essential to avoid irregular water accumulations during cooling. After the reheating process, the plate should have uniform temperature, uniform austenitic grain size and easily removable scale. The slab thermal and microstructural heterogeneities are inherited by the rolled plate and tend to increase further during the accelerated cooling. This results in flatness problems, high level of internal stresses and mechanical properties variation. The descaling strategy is an extremely important factor and must be determined with great caution. It is important that the scale thickness is uniform, to ensure a uniform cooling over the entire plate surface. Otherwise, there will be an uneven temperature distribution, which can cause serious problems of flatness, surface quality and mechanical properties.

Abstract:

The study of oxidation behavior of High Chromium Steel material used for surface layer of work rolls was carried out. Specimens taken directly from the roll were subjected to thermal fatigue in the temperature range between room temperature and 500 °C up to 700 °C by using thermo-mechanical simulator Gleeble 1500D. Our observation was focused on the impact of oxidation as a principal mechanism of degradation of the roll’s surface layer - mainly on the characteristics of oxidation propagation in relation to the test temperature and microstructure constituents characteristics of the material. Oxidation is considerably accelerated by certain characteristics of eutectic and primary carbides, i.e. their size (area), composition, morphology, orientation regarding to the water-cooled surface, etc. In the presented paper selected cases where emphasized oxidation takes place are investigated, analyzed and explained. Obtained results thus represent a contribution to explanation of conditions which lead to acceleration of oxidation behavior that in turn can lead to chipping or even early spalling of material from the roll surface layer.

Abstract:

IF-Skin Panel sheets require very strict surface quality (especially the exposed panel of automobiles).Tata Steel’s Cold Rolling Mill (CRM) in Jamshedpur, India had been facing heavy rejections on account of a new defect which appeared as small tiny particles scattered across the width and length of the cold rolled coil. We found that defects were created in the hot rolling process after detecting the scales under the defects by SEM analysis. Trials based on data analysis and metallographic evidence revealed the followings: 1. There is a good region, which falls approximately in the middle of the work roll campaign of the Reversing Roughing Mill, where the defects observed in the CR coils is the least. 2. Correct placement in the Finishing Mill campaign of Hot Strip Mill is mandatory for reducing the defects. 3. Two different makes of work rolls were used in the early Finishing Mill stands of the Hot Strip Mill. It was found that certain make of the work rolls lead to an increase of the defects by almost 5 times than the other make. 4. Pickling concentrations were found to play a very important role in elimination of scale before reduction in cold rolling mail. It was found that concentration of the first two tanks is very critical for this. Based on these analysis results, a series of countermeasures have been implemented. These include rigorous hot mill scheduling rules for placement of surface-critical automotive IF steel slabs within the campaigns of both the rougher work rolls and the finishing mill work rolls, and strict selection of hot mill work roll grade and make. As a result, we were able to eliminate the defects. Through the implementation of Through Process approach we were able to put in place process conditions which would led to a drastic drop in these defects. We were also, able to increase the overall Strike Rate of IF-Skin Panel to a new record level in Tata Steel.

Abstract:

The vibration system is a tool used to diagnostic possible fails in industrial processes, that are caused by mechanical oscillations that can basically compromise the productivity of a process and products’ quality. This paper presents cases studies of vibration analysis of the mechanical systems of a tandem cold mill, 5 stands and 4 high type. Through charts study of global energy and Fast Furrier Transforms – FFT charts, it was possible to create oscillatory identities of the origin of specific problems of mechanicals assemblies, as well as to know the influence of process variables in the vibrations curve of a rolling stand, differentiating it from the natural frequency of this set. Determining vibrations standards chart, these become the start of a predictive maintenance activity to later eliminate the root causes of the problem to eliminate emergency process stoppages and consequently improving the machine’s operational performance.

Abstract:

The high competition scenario pushes the steel producers business. Zero defect requirements from customers force the operators for additional efforts in process control and quality management. PQA® has been developed as an advanced process and quality management assurance solution. It is focusing on the analysis of process data, equipment information, inline quality measurement devices and trend analysis. The paper describes the structure of the advanced process and quality management assurance solution PQA®; it gives insights on the expert know-how, process and quality evaluation and points out the benefits like cost reduction, improvement yield and customer satisfaction increase.

Abstract:

steel industry is rapidly approaching solutions that integrate automation, robotics, machine vision and data management system, in order to be globally more competitive. Digitalisation is heavily entering in steel plants OFFERING opportunities TO IMPROVE Productivity, Quality, Safety & Security, KEY ELEMENTS manufacturing 4.0. SMART Robotics AND ADVANCED AUTOMATION PLATFORMS ARE useful tool for a new operator's role, the one of supervisor.

Abstract:

Since 2016 Gerdau Ouro Branco has been producing steel plates of various qualities and grades. However, it was not until 2018 that the first plates produced by accelerated cooling process were made available for external testing, in this case for large diameter UOE pipes manufacturing. Recent line pipe and OCTG specifications are showing that the oil and gas market still consumes regular API grades, such as X60, X65 and X70, however with increasing wall thicknesses, reaching values up to 1,5 inches. These specifications also demand longitudinal and transverse tensile guarantees and drop weight tear tests in temperatures as low as -40°C. Projects with these types of mechanical properties present process requirements as challenging as those necessary for higher API grades in lower thicknesses. This paper shows the steel design concepts and rolling routes for achieving the necessary properties for X70 steel plates in 28,15 mm. The microstructural features were also investigated and associated with the production process and the tensile and toughness results. Finally, challenges such as tensile anisotropy and DWTT abnormal fracture are presented.

Abstract:

Surface quality monitoring is primarily implemented in the last steps of steel manufacturing before shipment to the end user. However, an increasing trend for also addressing this topic in the upstream stages, such as hot rolling plant, is tackled by Primetals Technologies to give steel producers the key to a global optimized yield management, and efficient “lessons learned” processes. After the last developments of SIAS Next Gen platform, including High Resolution and Near Infra-Red, some site results will be exposed on the very specific high constraints lines such as ESP Endless Strip Production and Plate Mills, and highlights the related most interesting aspects for our customers.

Abstract:

A ultra-high strength medium Mn steel with good ductility was designed and manufactured via the combination of warm rolling and V alloying, which produced not only the extensive precipitation of fine VC particles in both ferrite and austenite but also the bimodal size distribution of retained austenite (RA) grains. A substantial increase of yield strength up to 650 MPa was achieved due to the addition of V without deteriorating ductility. The coarse RA grains firstly transformed to martensite during yielding at the much higher stress threshold, followed by a significant work hardening due to dislocations multiplication, twinning-induced-plasticity (TWIP) and transformation-induced-plasticity (TRIP) in the ultrafine RA grains. The best combination of strength and ductility included 1.5 GPa ultimate tensile strength and 28% total elongation. This was achieved due to the sustainable TRIP and TWIP effects in the later straining stage resulting from the ultrafine austenite grains, the latter were reversely transformed from the recrystallized ferrite grains.

Abstract:

During cold rolling of Cr-Mo alloyed DP steel, considerable oscillation of thickness may occur. The literature points out that such occurrence is due to non-uniform cooling of the coil after the hot rolling process. Since the austenite transformation in this steel continues after coiling, the microstructure and, consequently, mechanical properties are very susceptible to natural variations in cooling rates associated with distinct positions of the coil. The influence of coil cooling conditions on thickness oscillation during cold rolling was evaluated in this work by using both industrial experiments and dilatometer tests. It was verified that an industrial coil presented large variation of mechanical properties associated with its heterogeneous microstructure. Consequently, thickness oscillation occurred during cold rolling. Dilatometer tests simulating hot run-out table and coil cooling showed that the austenite transformation is very slow under small cooling rates that occur after coiling. Thus, the slow transformation rate makes the coil very susceptible to environmental conditions around it during its natural cooling and is responsible for variation in mechanical properties of the coil. To ensure the formation of a more homogeneous microstructure in the whole coil, it is necessary either to make use of technologies that improves the cooling uniformity or to adjust the steel alloy design. The latter alternative has been done with relative success by using conceptions with lower amounts of Cr and Mo.

Abstract:

Currently, continuous implementation of safety and CO2 emission standards in automotive vehicles has driven the search for weight reduction and safety enhancement solutions. In this context, the development of steels of high mechanical strength has been presented as the most applicable. Due to the strong elastic return after the stamping operations, parts that have geometric complexity and require greater mechanical strength are generally produced by hot stamping. The steels employed have addition of boron, such as 22 MnB5. Parallel to the development of steels, researches related to the development of metallic coatings capable of withstanding mechanical stresses and heat treatment have been carried out. The Al-Si coating composed of Al-Si-Fe multiphases has been strongly used. During the austenitization occurs to the formation of new phases by the inter-diffusion of Fe and solidification reactions defining the final microstructure. Samples of coated 22MnB5 steel (Al-Si) were treated between temperatures of 500 to 900 ° C. Through the analysis of microscopy (SEM) and GDOS it was possible to identify the diffusion of Fe along the coating layer. Based on the ternary phase diagram and the simulations, it was possible to propose a way of understanding the transformation of the Al-Si coating by the diffusion of the iron.

Abstract:

ULTIMA® are high performance, centrifugal cast, double poured (CC duplex) work rolls. This paper describes the principle of the ULTIMA® roll concept and its wide range of usability. The ULTIMA® concept provides a solution for rod and bar mills to increase performance and output, even under harsh rolling conditions. The main focus is on highly loaded mill stands that require both high wear resistance and resistance against thermal fatigue, like pre-dog bone, dog bone, slitter. Specific case studies of quite different mill configurations and rolled product mix prove the positive impact on production yield, mill and roll shop operations, and profitability in terms of TCO (total cost of ownership).

Abstract:

Gerdau Ouro Branco´s plate mill started the operation in 2016 with high level technology. Stands out the capacity to produce plates with different thickness in the same as rolled. Therefore allows special service for sectors such as building structures, bridges construction, shipbuilding and mechanical applications. The purpose of this study is to present the first results obtained in this innovative product in Brazil. Some slabs of SAE J403 1045 and EN10025-2 S355JR+AR steel were rolled and were evaluated the dimensional tolerances, mechanical properties uniformity, grain size, surface and internal qualities. In addition, a correlation was observed between slab and plate thickness reduction and internal plate quality. The results show that this technology can be used with adequate performance for these steel grades in the current market.

Abstract:

The purpose of this project is to increase the visibility of which will be daily produced on the hot strip mill (HSM). The forecast was performed through the implementation of an automated tool for weekly HSM production planning. The project was started with the definition of the weekly planning process, through the determination of the main business objectives, like as: priorities of service (customers and delivery date), definition of HSM’s rules and restrictions of operating resources. Using a sophisticated mathematical model, through the computational simulation is possible the experimentation of various production scenarios, allowing the visualization of volumes by type of sequence, clients / priorities, mix to be produced, cylinder change quantity forecast, better forecasting of the productivity of the HSM, consumption of utilities, within others. Main benefits: sequencing which production orders should be produced, reducing unforeseen stops due lack of material, improving the quality of the stock which allows the reduction of the aging of slabs in the slabyard and the vision of customer services. Computational simulation as a weekly planning tool achieve, with other benefits, to present alternatives for better decision making.

Abstract:

Over the two decades years, big achievements have been made for the development and application of high-strength and low-alloy steels with thermomechanically rolling and cooling in China, among which the most typical application case is the development and application of X80 coil and spiral welded pipe used for the Second West-East Pipeline trunk line. In order to increase deliverability from 30 billion cubic meter to 38 or 45 billion cubic meter annually, X80 welded pipe with higher thickness and larger diameter was required, and X80 welded pipe with the diameter of 1422mm and the thickness of 21.4mm was employed. However, almost all X80 welded pipes with such size for already constructed pipeline were supplied by X80 LSAW pipe made of plate, instead of X80 SSAW pipe made of coil. Based on traditional two-stage rolling experiences, some people thought it is impossible to produce 21.4mm thick X80 coil on commercial scale. In order to meet demanding requirements, optimized rolling and cooling schedule besides low carbon and high niobium alloy design made it possible to break the ceiling of 18.4mm in thickness. Up to now, about 500,000 tons X80 coil and spiral welded pipe with 21.4mm in thicknes have been produced and applied to China's section of Russia-China East line. What is more, burst test results demonstrated more excellent performance to resist crack propagation than that of longitudinal X80 welded pipe. In this paper, metallurgical design, production data and microstructure analysis before and after pipe making would be presented.

Abstract:

In temper cold rolling processes, roughness transfer remains one important quality aspect for sheet and tin plate steel products. An existing roughness transfer model [1] able to predict the usual roughness parameters related to peak height distribution (Rq, Ra, Rsk, Rku) has been completed in the present work with the prediction of peak counts distribution RPc (number of peaks on the strip/cm). This new modeling development is driven by the automotive industry that requires higher and higher peak counts RPc (> 75 peaks/cm) on steel sheets in addition to the usual average roughness Ra to maintain a good strip surface finish after painting. The model that is currently only valid for uncoated materials is based on the Monte Carlo method to generate randomly roughness transfer profiles on roll and strip. Two major mechanisms involved in the roughness transfer are considered: the asperity crushing mechanism (crushing roll into the strip) and the asperity plowing mechanism due to roll-strip sliding in the bite. Measurements of strip and roll roughness were carried out before and after temper rolling to calibrate the model and evaluate its ability to predict roughness evolution in various temper rolling conditions: new and worn work rolls, different strip elongations, hard and soft steel grades. Finally using the calibrated model, different process actuators were identified with the goal to maximize final strip peak counts (RPc) while maintaining average roughness (Ra) on the strip within customer tolerances. The work is concluded with the new developments needed to extend the model to coated steel sheets. References [1] Roughness Transfer Model for Cold and Temper Rolling Processes, N. Legrand, C. Counhaye, D. Oliveira, 10th International Rolling Conference, June 06-09 2016, Graz (Austria)

Abstract:

The development of advanced high strength steels (AHSS) is motivated by the automotive industry demands for higher strength steels with better formability and stretch-flangeability to avoid fractures during parts forming. In response to this, the new steel grades must have special microstructures in terms of constitution, morphology, distribution and hardness, which are strongly dependent on the chemical composition of the steel sheet and its processing, especially in the continuous annealing stage, in the case of cold rolled sheets. In this study the influence of the annealing heating rate and intercritical temperature (IT) on the microstructural evolution and the final hole expansion ratio of a cold rolled 980 MPa AHSS grade was evaluated. The annealing process was simulated using a Dilatometer and a Gleeble machine, and the microstructures were characterized using scanning electron microscopy, electron backscattered diffraction (EBSD) and nanohardness measurements. The increase of heating rate resulted in an overlap between ferrite recrystallization and austenite formation, changing the austenite morphology from a random to a fibrous distribution, while a higher IT resulted in more homogeneous microstructures and higher hole expansion ratios. This microestructural homogeneity, confirmed by nanohardness measurements, suggested that the difference in hardness between ferrite and the second phase affects the micro-void formation and crack propagation during the hole expansion test.

Abstract:

The (R)evolution in Metal Cutting: Inventors around the world have been successfully developing innovations for decades, but only some of these developments have had „GAME CHANGING“ potential. One of these innovations is the new developed saw blade LINCUT®, a patented changing system that paves the way for a fundamental reorientation of the entire saw blade industry worldwide through a simple and economical concept for rolling mills or heavy forging lines. Cost efficiency starts with the raw material: Circular saws equipped with a standard saw blade are expected to have a necessary 2 percent standstill per year due to required tool changing. LINCUT® technology reduces this unnecessary loss of production by more than 50%. The ROI can therefore be reached faster which immediately lowers your production costs. No matter what material, conventional carbon steel or highly alloyed stainless steel, the coating and shape of carbide plates is perfected for extended tool life up to 25% with increased performance. LINSINGER is running their own tool technology centre in Austria specialized in research and development of tools, constantly expanding R&D activities to achieve best (r)evolution in metal cutting.

Abstract:

Arcelor Mittal Brasil, through its commitment of improving the performance of the enterprise more and more, of sharing with the society its vision of being the most admired steel producer of the world and also of continuing to assure progress in every aspect of sustainability, has returned, since 2017, with its investments in the technical capacitation field, aiming to achieve continuous improvement of the company (6sigma). The market of steel is even more selective and strict nowadays, requiring a very meticulous analysis of each step in the production processes with the main goal of reaching high levels of accomplishment and quality. Since 2009, the Hot Strip Mill is upon a production increase procedure, with the startup of the second reheating furnace and overall improvement of the production process, going from 2,5 Mtons/year of production to the actual 4,1 Mtons/year, with an expected production of 4,5 Mtons/year in 2022. In the hot coils production process, the process rolls represent one of the main items regarding the cost of operation due to its high price, apart from being a factor of great importance in the quality, since the rolls are the tools in direct contact with the laminate. Therefore, the rolls manufacturers are in constant development, aiming to increase these tools wear resistance and dimensional metallurgical stability, factors combined with adequate mechanical resistance and fracture tenacity. In this scenario of increased production and because of the fact that the wear of the rolls affect directly the coils production cost, some statistical analysis were conducted with the 6sigma methodology, pursuing to verify and evaluate the working conditions of the rollers in the mill of Arcelor Mittal Tubarão. In 2018 it was initiated an work in the Rolls factory via blackbelt 6sigma, to study the tribology applied to the rolls wear, the operation conditions, the campaign and fatigue during its lifetime. This research has shown a great reduction in the rolls consumption (Work rolls, backup or vertical edge), increase in the mill production, reduction into the CAPEX of the rolls as well as in costs measured indirectly (energy, FTE, lubricants). Another important factor was the financial feedback (ebitda) to the company. About R$ 16 million less in CAPEX of the rolls, 32 hours of increased production in function of the rolls campaign improvement, as well as a dispended cost of R$ 18 million that would be required in order to afford a new grinding machine, wich would be necessary to attend the conditions of the annual production.

Abstract:

A point of great importance of the cold rolling process for automotive sheet is the cleanliness of the STRIP. This is particularly critical when batch annealing with poor efficient cleaning lines. in these specific cases, pollution of the strip surface could be prohibitive when rolling in the early stands of tandem mill with conventional forged rolls as ground: the strip cleanliness strongly deteriorates during rolling mainly with high roughness rolls and iron fines coming from the strip surface are progressively sticking on the sheet. it is well known that chrome plating the conventional forged rolls in the early stands delays the onset of strip cleanliness degradation during rolling. this paper summarizes the results of 3d surface roughness topography study on forged work rolls with and without chrome plating combined with sheet cleanliness measurement during rolling. it shows that a well determined topography has to be obtained on the work rolls used in early stands in order to roll in the mixed lubrication regime minimizing the friction coefficient and therefore optimizing the cleanliness of the rolled sheet. the main roughness parameters to take into account for that purpose are the roughness level SA and even more the kurtosis parameters Sk, SPK, SVK, SSK and SKU. THE IDEAL SURFACE MORPHOLOGY PROMOTES DEEP VALLEYS TO THE DETRIMENT OF PEAKS, LEADING TO A ROLL SURFACE CAPABLE TO RETAIN / TRAP Oil in the valleys while peaks are minimize reducing the abrasive effect in the roll bite and consecutively the amount of iron fines produced. To achieve such objective, new grinding wheel technologies are currently developed in partnership with wheel manufacturers to create such ideal morphology of roughness well adapted to forged HSS ROLLS.

Abstract:

Spring steels are usually classified as medium to high carbon low alloy steels with very high yield strength, enabling the part to return to its original shape regardless of significant bending or twisting. Despite the fact that plain carbon steels are suitable for small springs, larger and high performance springs usually requires alloy steels such as Cr-V or Si-Mn in order to achieve an even microstructure throughout the cross section. Clutch diaphragm spring is a high performance part that requires very good cleanliness and microstructure homogeneity, thus requiring an alloy steel. In this paper was studied, in an industrial scale, the process parameters and critical characteristics for the development of a Cr and V alloyed high carbon sheet steel for the production of clutch diaphragm spring. The steel was characterized throughout the entire process (casting, hot rolling, cold rolling + batch annealing and heat treated) using tensile test, hardness test, optical microscopy (OM) and scanning electron microscopy (SEM) to assess the mechanical and metallurgical properties of the studied steel. The results have shown the material’s microstructure evolution after each main stage of the process, from a ferrite-bainite/perlite based microstructure as hot band to fully spheroidized as cold-rolled/annealed and then fully martensitic as ready-to-use part.

Abstract:

Microalloyed steels have been intensely studied as an alternative to increase strength by grain refinement and/or precipitation hardening. Long steel products have a wide range of opportunities to apply well-defined principles of controlled rolling (CR) in order to increase strength and toughness with reduced costs. To evaluate the effect of microalloying elements as Nb and Ti with thermomechanical treatment, three conditions were tested: DIN 16MnCrS5 with hot rolling (HR), DIN 16MnCrS5 with Nb and CR and DIN 16MnCrS5 with Nb+Ti and CR. Austenitic grain size, obtained by direct quenching after rolling, has shown a decrease 32% with Nb addition, and 29% when Nb and Ti was added. Controlled rolling generated higher grain refinement and pancacked grains near the surface. When comparing ferritic grain size, controlled rolling plus niobium and titanium additions resulted in significant reduction of 35%. Yield strength increased 15% with microalloying and CR and more than 270% in impact toughness, even at -40°C.

Abstract:

iN this work, the mechanical and metallurgical behavior of titanium added ultra-low carbon (ULC-Ti) steel under hot and warm working conditions was studied by means of dilatometer compression tests. Double hit schedules were performed at temperatures between 700°C and 1000°C, inter-pass times of 0,5-100 s, and deformations of 0.5 and 0.3 in the first and second stages, respectively, with strain rate of 1 s-1. The analysis of the flow curves obtained allowed the evaluation of the softening characteristics of the steel. The softening and microstructure features indicate different restoration mechanisms depending of the temperature range. Static recrystallization with rapid microstructure restoration is observed at temperatures within the austenitic and intercritical region. Strain induced boundary motion and recovery mechanisms apparently control the restoration process in the ferrite region. In general, flow stress curves showed dynamic recovery behavior. Only the deformation in the intercritical region produced dynamic softening. Isothermal holding tests associated with single hit compression indicated the presence of dynamic strain induced transformation, accelerating the softening kinetics at intercritical region. ThE study provided insiGHTs to industrial warm rolling of the ULC-Ti steel.

Abstract:

The increase in customer demand for steels with higher surface requirements, associated with the need to increase ArcelorMittal Tubarão's HSM productivity, it was necessary the development of controls and actions to reduce scale losses within the scenario of high productivity. This article describes the path followed by the hot strip mill team in order to reduce the occurrence and severity of scales.

Abstract:

Checkered plate, which is also known as floor plate, has a raised pattern that provides excellent skid resistance for a wide range of applications, such as flooring, walkways, platforms, stair treads, covers, etc. As one of most common used products, carbon steel checkered plate needs high cost in corrosion resistance. Although stainless steel checkered plate meets the requirements of corrosion resistance, it is also hard to provide a highly comprehensive performance for its low mechanical properties, which mean higher thickness, higher weight, lower stability of structure. Combined the advantages of stainless steel and carbon structural steel, one kind of SUS316L-BDT01 or SUS304L-BDT01 roll-bonded clad checkered plate with high performance in skid resistance, high strength and corrosion resistant is developed. The metallography shows cladding interfaces are very good. The yield strength, tensile strength and elongation from tensile tests are significantly better than the other kinds of checkered plates. Both external and internal bending at room temperature can be done successfully done without any cracks. Therefore, roll-bonded clad checkered plate shows superior performance in microstructure, strength, ductility and workability. It will meet the requirements of modern factories and has a broad market prospect. Through a case of the application on a pulverized coal injection platform in an iron-making plant, the processing and installation of this kind of material were introduced. After two years tracking on the platform, the product shows high performance in corrosion resistance and mechanical properties.

Abstract:

One of the main factors that reduce strip cleanliness are iron fines, which are formed due to the abrasive interactions of the roll surface and the strip in the roll bite during cold rolling. They can cause a problem in fouling of the cold rolling mill as well as downstream processes. It has been repeatedly observed that chrome plating the work roll improves strip cleanliness. In the present work, scratch tests and reciprocating sliding tests were carried out under lubricated conditions to explore the influence of chrome plating on iron fines formation. Scratch tests were conducted to study the influence of chrome plating on iron fines formation at single asperity scale due to its intrinsic property. Reciprocating sliding tests were performed to study the influence of chrome plating a rough surface on iron fines formation, taking into account the initial roughness. The scratches made using chrome plated pins showed lower friction, generated less iron fines and exhibited lower material transfer. Reciprocating sliding tests done using the uncoated pins showed galling at different sliding distances depending on the roughness of the pin. On the contrary, reciprocating sliding tests with the chrome plated pins exhibited no galling irrespective of the roughness.

Abstract:

In this study, in order to achieve ultra-high strength without reducing plasticity, a novel heat treatment involving a pre-quenching process prior to conventional intercritical annealing (P-IDP) was proposed in a low carbon low alloy DP steel. It revealed that abundant fraction of banded structure was observed after conventional intercritical heat treatment (IDP) due to the inheritance of cold rolling deformation. However, the banded structure in novel heat treatment was eliminated significantly, whilst the refined microstructure was relatively more homogeneous with ultrafine ferrite grains. Moreover, obvious chain-networked martensite grains along the ferrite grain boundaries were obtained. The optimum mechanical properties with ultimate strength of 1238 MPa, total elongation of 17%, product of strength and elongation (PSE) of 21GPa% were obtained by P-IDP treatment, which was much higher than the values reported with similar composition. As to pre-quenching treatment, all of grain refinement, homogeneous distribution of martensite islands and precipitated strengthening of microalloyed carbides were beneficial to improve the final strength and ductility.

Abstract:

A new plant for special steel long products was commissioned in recent years at Dangjin, South Korea, for Hyundai Steel.Two multi-line rolling mills supplied by Primetals Technologies are capable to produce yearly 1 million tons of billets,straight and coiled bars,with dimensions from 5.5 to 350 millimeters.The products are used for manufacturing engine and transmission components used by Hyundai Kia Automotive Group.The processed grades include carbon,special alloy,spring,bearing and free-cutting steel.The demanding requirements posed by the automotive industry are met by the supplied state-of-the-art equipment and processes.Blooms coming from a 4-strand continuous caster,also supplied by Primetals Technologies,are rolled by the first mill (LBM) into finished large round and square products,as well as into intermediate billets.With a yearly capacity of 1,000,000 tons and an hourly productivity of 200 tons,the LBM processes continuously-cast blooms measuring 530x390 mm crosswise and 3.5-8 m lengthwise,which are hot charged to the re-heating furnace and descaled.A 2-hi reversing breakdown stand is followed by a hot-scarfing station,then by finishing and sizing trains,where CGA stands are equipped with under-load roll parting system for automatic gap control.After normal/slow cooling facilities,bars are made ready for dispatch.Shearing and sawing systems are provided along the mill for dividing and emergency operation.Beside finishing large rounds ranging from 80 to 350 mm in diameter,the LBM prepares billets with square dimension of 150 or 180 mm.The billets feed a second mill (SBM),which combines the lines of small bars,rods and bars-in-coil.The SBM has a yearly capacity of 800,000 tons and is designed to roll 160 tons per hour,a record value for a combination mill.After re-heating,the billets are rolled in a continuous rolling mill with 16 RedRing® Series 5 stands.The rod outlet further rolls the bar in two 2-stand prefinishing mills,followed by an 8-stand Morgan No-Twist® mill and a 4-stand Morgan Rod Reducing/Sizing Mill.Wire rod with a diameter from 5.5 to 26 mm is finished at a maximum speed of 110 m/s.A laying head deposits the rod rings onto an 11-zone Morgan Stelmor® conveyor for flexible cooling operation,which is followed by the coil forming station.Bars are finished at 18 m/s maximum speed by a sizing block,supplied by Kocks (Germany).A 102 m-long and 12.5 m-wide cooling bed is provided for straight bars with diameters from 16 to 100 mm,and followed by bundling and handling facilities.Bar-in-coil products with diameter from 16 to to 60 mm are coiled at the pouring reel station,which is followed by a conveyor for cooling according to the required temperature curves.A combined vertical pallet / horizontal hook handling system is provided to service coils from both the rod and bar-in-coil outlets.Several water boxes for thermo-processing as well as shearing and sawing systems for dividing and emergency operation are provided.The SBM is particularly designed for low-temperature rolling,to improve the metallurgical structure and mechanical properties of end products and enhance flexibility during the rolling operation.Advanced sensors and electronics integrate with mechatronic packages,thus implementing Industry4.0 tenets to ensure a consistently high quality of the products.Several customer's benefits are obtained,including optimized conversion cost,flexibility to meet market changes,high product quality,reduced floor personnel.

Abstract:

The technological integration of the process and physical metallurgical advancements of value-added niobium (Nb) microalloyed thermo-mechanical controlled process (TMCP) steels continue to be developed for more demanding end user requirements and cost-effective steel production. The market demand for reduced fuel consumption and CO2 emissions in the automotive and construction sectors have further increased the demand for these new and advanced higher quality microalloyed grades produced via TMCP. The reheat furnace process step has a profound effect on the TMCP performance, final hot rolled steel quality and mechanical property consistency during the production of hot rolled steels. The uniformity of heating applied across the entire width and length of the slab or billet is critical in the achievement of consistent customer properties regardless of the chemistry. The resultant ferrite grain size in the final hot rolled product is significantly governed by the initial prior austenite grain size. However, the transition from laboratory melted and TMCP hot rolled heats to the production scale is challenging. Aberrations in the reheating process step at the industrial furnace are often the root cause of mechanical property quality issues when the prescribed mechanical metallurgy TMCP practices are met. These combustion process metallurgy parameters connect directly to the resultant TMCP product quality and is defined as Combustion Metallurgy® (CM®). The quality and efficiency of the reheating process has a profound effect on the prior austenite grain size and uniformity of grain size along the entire length of the slab or billet. The resultant ferrite grain size in the final hot rolled product is significantly governed by the initial prior austenite grain size (PAGS). This reheating step in the steelmaking process often receives low priority in the evaluation of product quality and mechanical property performance. In laboratory studies, the furnace heating step is typically quite uniform resulting in a homogeneous and fine PAGS. Unfortunately, in industrial operations, it is much more difficult to control the uniformity of heating along the entire length and through the thickness of the work piece. Such inhomogeneity and efficiency of heating is highly influenced by several combustion process variables such as the air-to-gas ratio, furnace burner condition, furnace pressure and refractory condition. The optimum air-to-gas ratio of 1.10 yields the highest adiabatic flame temperature. Often in actual operations, cracked burner orifice plates, poor burner tuning, and inefficient combustion fan performance contribute to variations in the air-to-gas ratio. These situations have a huge effect on the optimal adiabatic flame temperature performance which translates into inhomogeneous austenite grain size and variations in mechanical properties in the hot rolled product. Mechanical property variations may result in quality issues involving the toughness, ductile-to-brittle transition temperature (DBTT), bendability, formability, yield-to-tensile ratio and drop weight tear tests (DWTT). CM® corrective actions and operational practice recommendations are presented to minimize inhomogeneous heating effects on product quality. Operational practice recommendations are presented to minimize inhomogeneous heating which results in inferior product quality, hot rolling model anomalies and toughness variations in the through-thickness-direction.

Abstract:

By applying high-end rolls with utmost performance and superior surface quality, hot strip mills can be further optimized. Operations in the mill have been also waiting for improved roll solutions that can minimize required roll changes which impact production efficiency. Limitations are usually due to the low performance and surface degradation of the rolls in the late finishing stands (F5 – F7). VICTURA is the most recent developed grade for rolls utilized in the late finishing stand at Union Electric Åkers (UEÅ). These rolls have been tested and applied in mills all over the world. A significant improvement over the enhanced ICDP rolls has been observed. Hot strip mills are realizing improved operating efficiency and Total Cost of Ownership (TCO) through the transition of their entire roll inventories to these break through products.

Abstract:

The reduction of carbon dioxide (CO2) to the environment is a worldwide concern due to its negative impact on global warming. One of the proposals of the automotive industry to reduce air pollution without affecting the production of vehicles is by using less fuel. This can be achieved by reducing the weight of the vehicle using lighter and stronger components in their structure. Advanced High Strength Steels are currently being used for the safety cage or B-pillars reinforcements where high resistance is required for passenger safety. Controlled thermomechanical processing is needed to produce the microstructure leading the required mechanical properties. Critical processing temperatures such as recrystallization-stop temperature (T5%) was calculated from double hit tests with different deformation parameters typical of industrial rolling conditions. Also, phase transformation temperatures were measured by dilatometry experiments at different cooling rates. The non-recrystallized elongated prior austenite grains were observed for deformation at temperatures less than T5%. Severely deformed austenite with high dislocation density and deformation bands increases the nuclei sites to start the transformation products. This microstructure along with a cooling strategy will lead to the success of increasing the final mechanical properties of the steel.

Abstract:

With increasing demands from customers to provide flat strip with tighter tolerances on material properties, particularly flatness of e.g. martensitic steel grades (M1500), it has become necessary to develop strategies to improve flatness without influencing the tensile properties for such hard steel grades. Usual skin pass mills are not capable to apply sufficient tension and roll force for these kinds of material to improve the flatness. Therefore alternatives have to be searched for. One option is to use Sendzimir rolling mills for skin pass operation (using small roll diameters), which are often not available in-house. A second option would be to invest in a major upgrade of the installed skin pass mill or even to install a new skin pass mill with increased roll force and tension capabilities (higher investment costs). On the other hand due to current production overcapacity tandem mills are not utilized to their full extent, which leads to additional outage times. Under such circumstances the idea was borne, why not to use a tandem mill during its additional outage time for skin pass operation of “high strength” steel grades. Through utilization of the tandem mill enough roll force and tension are available. Instead of applying a total reduction of up to 90% during normal rolling operation, the mill technological functions have to be modified for skin pass operation, where the total reduction is minimized down to 0.3% to 0.5%. Technological process and control strategies have to be adapted, like pass schedule generation and interstand tension control. This paper describes skin pass - / temper – rolling methods from the classical one to new alternatives in order to satisfy the demanding market of higher material properties and idle running mills in rolling plants.

Abstract:

The Pickling Line Tandem Cold Mill (PLTCM) at Ternium’s Pesqueria plant with a 5 stands, 6 high configuration started in 2013. At the time of the start up the work roll specification and grinding practices were stablished following a low risk policy to be able to sustain any start-up associated accident. Once a stable operation has been achieved both these policies are being modified to improve productivity and reduce costs. The specified hardness of the rolls has been increased and efforts are being made to optimize the grinding according to the rolling campaign length and materials. The fatigue damage in work rolls, after rolling and its removal by grinding was followed by hardness measurements made at the end of the rolling campaign and after grinding. Softening of the rolls after rolling was found mainly in final stands to be related to the averaged stress experienced during the campaign, the original roll hardness was recovered after grinding. Hardness evolution was also followed after each grinding step finding that the total amount of grinding could be reduced. The grinding practice was modified accordingly for the first stands and the yield of work rolls in them has improved.

Abstract:

In mid-2015 the steel industry faced a strong crisis due to the weak performance of the Brazilian economy and the persistent entry of Chinese steel into Brazilian territory. This situation demanded that Brazilian steelmakers seek to develop products to meet new export markets. Within the volume of exports possible are the rebars, where its applications are in the construction industry. One of the largest importers is Peru which has a large percentage of this export volume. This market demands as a priority requirement the surface quality of Blue Condition (low oxidation index) and mechanical properties normative. In order to meet the items required by the customer at a competitive cost, a vanadium micro-alloyed steel was applied to the hot rolling process without heat treatment after the last rolling pass. Where the great challenge was to achieve a high level of stretching without compromising the minimum limits of resistance and flow. Assuming that the steel used is the correct one interventions were made on rolling parameters such as set-point temperature, residence time of pieces in the furnace, linear mass and rolling speed. All the changes made were based on statistical tools and practical tests. Finally, with the execution of actions generated from the statistical analyzes and tests it was possible to reduce process losses by 96%.

Abstract:

In general, national and international plate markets are every day more rigorous about final product quality. Suppliers must be aware about dimensional accuracy, surface quality and flatness of the plates, independent of the quality standards. To guarantee the best service to this increasingly demanding and competitive market, it is extremely important to guarantee the original project conditions executing the right maintenance of the rolling mill main components. In order to maintain the product quality and avoid the production and maintenance cost increase, it is important to find ways to control the mill and the main process variables, through daily measurements of the equipment performance. This paper aims to present the influence of the main equipment variables that affect the mill operational stability and how to control and evaluate the mill performance.

Abstract:

Finite element method (FEM) is widely used to model the hot strip rolling process. Flatness defects e.g. front-end bending in multipass hot strip rolling is studied by authors using a finite element (FE) model with interactively operating automated controlling logic (ACL) [1]. However, industrial corresponding grade of accuracy in strip thickness subsequent to the rolling pass is not easily accessible in FE-model without separate calculation of significant rolling parameters and integrated roll gap control. In order to study flatness defects and optimize pass schedules the controlling and physics of the FE-model must correspond to the industrial process. For this need the automated controlling logic is upgraded by setup calculations to predicting roll force and work roll flattening. These predictions are utilized in setup positioning of a work rolls. Reliable setup calculation enables smooth multi stand rolling process without significant additional adjustment of roll gap clearance. State of art rolling technology requires above-mentioned setup controlling for the FE simulations to simulate different pass schedules without time consuming preparations. Operational setup calculations together with automated controlling logic of hot strip rolling enable simulation of new pass schedules and efficient problem solving.

Abstract:

Calendering is a mechanical formation process of great industrial relevance, since metal parts made out of this process – usually of tubular geometry – are applied in the fabrication of silos, eolic towers structure, tubes and plumbing of the construction sector etc. The present work has proposed to analyze the hardness and the microstructure of calendered metal parts of SAE 1020 and SAE 1045 carbon steels and the effects of heat treatments on these. The low carbon steel part – SAE 1020 – was annealed for tension relief, and the medium carbon steel part – SAE 1045 – was quenched and then tempered. The hardness of both metal parts was measured and compared for three different moments: before the calendering, after it and after the heat treatment. Likewise, the microstructure of the metal plates was observed in these three distinct moments. The results have shown that the calendered metal plates had a higher hardness, comparing with the plates in the initial stage. SAE 1045 steel has presented higher hardness after quenching and tempering, while SAE 1020 steel has suffered huge hardness decrease after the annealing, due to tension relief and grain growth. It is possible to conclude that the application of quenching followed by tempering is valid for the increase of mechanical resistance of calendered SAE 1045 steel parts. Regarding the low carbon steel plates, the annealing process has caused a huge decrease in its hardness. Therefore, it is possible to conclude that the annealing process is not valid for the SAE 1020 steel, since the tension relief comes together with an expressive hardness decrease, that makes the steel part inappropriate for many uses.

Abstract:

Tandem cold mill (TCM) is a process to obtain flatness as well as thickness desired by the customer by rolling hot-rolled coils continuously. The final stand of the TCM plays the most important role of flatness control, which usually uses the real-time measurement at the exit. However, as the material property increases, it is not easy to handle flatness with only the final stand. In order to overcome such a limitation, we propose a feedback control method to strengthen flatness control for non-final stands. The proposed method was tested in an actual production line, and the effect is proved for 45K or less steel grade

Abstract:

There are many installed cold single-stand or tandem mills, and all cold rolling producers face the challenge of extending their output and reducing the cost of production – new alloys, wider strip, heavier coils, higher throughput. This is necessary to achieve or maintain competitive advantage. Each mill line has its own limitations on maximum strip width and coil diameter, and torque available by stand. Changing these may need major investment. However, a line’s throughput is often held back by the time to change over from one coil to the next, or by the need to keep final coiling temperature low enough. These can be tackled on an existing line without huge investment. Reducing the dead time between rolling one coil and the next will allow greater throughput in the line. Clever combinations of automation and minor equipment upgrades, with operator training, can reduce the overall time needed. This gives a shorter cycle to decelerate and tail out the strip, remove a spool or pup coil and replace it with a new entry coil, take out the finished coil and place a new empty spool, and thread and accelerate the next strip. Maintaining the final coiling temperature below a certain limit, while keeping all mill stands running as close as possible to their speed or torque limits, optimises the line throughput. This is only possible by removing enough heat from the strip at the stand, or between mill-stands for tandem lines. Of course, increased rolling speeds will generate more heat in the strip and reduce the time to remove that heat. Therefore good design of cooling, for the work rolls and for the strip between stands on a tandem line, is crucial to achieving the best possible throughput. If this is combined with automation solutions, which can vary the reductions and rolling speed to keep the final coiling temperature within close limits, then the final properties of the cold rolled strip will be very consistent. Achieving these aims needs a combination of skills; mechanical and fluids engineering, Level 1 and Level 2 automation expertise, metallurgical and process knowledge and thermodynamics. This paper discusses how to address these challenges and possible solutions to optimise existing asset utilisation.

Abstract:

Stretcher reducing mill (srm) is a mill that defines the external diameter of tubes. it is composed by 24 stands and each stand uses 3 rolls. the final external surface quality is achieved in the srm and any undesirable external marks in this process is hardly recovered. a great analysis was developed to understand the mechanism of external marks. the first step was to check the rolls quality based on technical requirements of rolls. a characterization was performed to check not only the requirements in the specification but also the material integrity. an opportunity was identified about the specification of roll. based on results of characterization, next step was to communicate the main supplier about the result of characterization. The hardness was out of specification (lower) and an action was required. since the supplier did not accept the claim in a first view. The third step was to confirm in vallourec group all specification of rolls concerning hardness of rolls. It is an important and critical requirement of roll strongly linked with wear resistance. The majority of rolls in Vallourec group has the same range of hardness. therefore, the specified hardness was preserved and MORE COMPLETE SPECIFICATION was made taking ALL THE KNOWLEDGE GAINED IN the characterization phase. The fourth and hardest step was to develop a new supplier in an internal market with a low know-how in manufacturing rolls. the casting process was developed after some tentative and thermal treatment was also required to achieve the specified hardness. an unusual heat treatment was specified in partnership with an expert supplier chosen by vallourec once the partner of foundry was not able to heat treat the material without breaking the material. The vallourec partner developed a curve and process able to heat the material and achieve the hardness with very low variation. the last step was to apply a pilot batch to qualify the suppliers (foundry and heat treatment). The results were acceptable and the external marks were minimized when using the new rolls. However, srm uses lots of stands and many rolls with low hardness are still working. all suppliers were pushed to improve their quality issues. so, a new level of quality was established with main requirements for rolls. No thermal treatment and chemical analysis was specified in order to not limit the suppliers technology of materials.

Abstract:

Danieli Universal Endless (DUE®), the new flag ship within the QSP family, combines the advantages and the abilities of “universal” rolling modes, endless and coil-to-coil within one single plant configuration by making this plant a major technology innovation compared to the previous generation. This new approach can be seen as the natural evolution of Danieli’s thin slab route, namely the application of the vertical curved design thin slab caster and the separation of the rolling stands into high reduction units and finishing units. Recently, the first plant of this kind has successfully been taken into operation at SGJT in China.

Abstract:

Studies were carried out with samples of 430 stainless steel stabilized with niobium produced by direct reduction (just one cold rolled process) in order to evaluate the influence of grain size on material drawability. Recrystallized samples were heat treated in the laboratory promoting the growth of the recrystallized grain. Microstructural characterizations were done by X-ray diffraction with emphasis on the evaluation of crystallographic texture, optical microscopy and EBSD. The drawability was evaluated through tensile tests for the determination the planar (Dr) and normal (r) anisotropy coefficients. The increase in grain size promoted an increase in the intensity of the gamma (beneficial) fiber and reduction theta (damaging) fiber on the surface of material thickness. At the center of thickness it was observed that the gamma fiber intensity did not change significantly and the theta fiber intensity was reduced. The change of the crystallographic texture, promoted by the increase of grain size, increased the coefficient of anisotropy (r) in all directions analyzed.

Abstract:

The semi-HSS work roll has excellent wear resistance. The application of semi-HSS work roll in cold tandem mill was reserched. On the same condition, the rolling force and modulus of rolling mill using semi-HSS and Cr5 work roll were equivalent. Using semi-HSS work roll, the rolling tonnage was increased by 100%, the roughness retention was increased by 43%, and the millimeter steel pass was increased by 150%. The application of semi-HSS work roll, the roll consumption and abnormal strip of thickness were reduced, and rolling efficiency was increased. It has the value of promotion.

Abstract:

This article deals with a project to reduce the preparation time and threading the coils in the input section of a pickling line coupled to the cold strip mill (PLTCM) at ArcelorMittal Vega. The project developed serves for the detection and elimination of bottlenecks in the input section. The project was conceived by the philosophy of the Theory of Constraints (TOC) and Lean Six Sigma (6 sigma), here seen as sequencing serial / parallel in the preparation and threading the coils. In this context, a proposal to modify the automatic sequencing and reduction of interruptions due to failure of the automation / equipment confirmed its effectiveness reducing the total time preparation time and threading the coils in the entry section by 15%. This project was developed without investment costs, bringing gains on the order of US$613,769.00.

Abstract:

Graphitic HSS roll grades such as ESW’s brand VANIMO can be considered as the latest developments for the last finishing stands in hot strip mills. These roll grades are developed on the basis of the alloying concept of (Carbide Enhanced) Indefinite Chill work roll materials. During the development of VANIMO, the amounts and types of carbide forming elements were increased and adjusted into the direction of cast HSS roll grades. The microstructure of graphitic HSS roll grades therefore consists of tempered martensite, cementite and several different carbide types as well as a well-defined amount of free graphite. The main purpose of graphitic HSS roll grades is to combine the high surface quality of Indefinite Chill alloys as well as the high wear resistance of HSS roll grades. Several systematic steps were taken to increase the wear performance from Carbide-Enhanced Indefinite Chill grades to the more advanced VANIC grade and further on to the highest alloyed roll grade VANIMO. In every development step, the surface quality of the roll grades was carefully monitored. The decision to invest in new testing equipment at ESW’s plant was driven by the wish to see microstructural effects of different alloys in a macroscopically dimension. Usually samples are taken from cast rolls and investigation is done in comparable small size areas compared to the total surface of a roll. Rolling of strip is done with the total barrel, so effects of alloy and microstructure can appear anywhere in the barrel surface. To ensure better understanding and deeper knowledge about influences of alloying trials we decided to install the last version of LRI (Lismar Roll Inspection). LRI includes the latest technology of Eddy Current with an enormous resolution. Depending on the formation of carbide precipitations, carbide network as well as matrix and free graphite, the EC test can detect smallest differences. The possibility to analyze the different results of EC and UT surface wave inspection will be discussed. A few examples of surface effects in the mill application will be discussed and improvement strategies explained.

Abstract:

ArcelorMittal Tubarão HSM productivity has increased gradually and consistently over the last four years, based on increasing charging temperature, furnace efficiency, decreasing Roughing mill and Finishing Mill cycle times and tuning models for Mill Pacing Control and Slab Design. This paper will show the path which was followed by TUBARÃO HSM team to achieve more than a 20% productivity increase resulting in a hot coils year production more than 700 kt higher.

Abstract:

The Tandem Cold Mill is composed by stands with rolls positioned so that the rolling force can be transmitted to the strip being processed. Due to the mechanical stresses inherent in the process, the roll bearings are heated and have lubrication and cooling systems. Nevertheless, there is the challenge of continuously monitoring the temperature of the bearings, which would allow preventive intervention in case of overheating. This paper presents an in-house solution to temperature measuring system applied to the backup roll bearings of a continuous Tandem Cold Mill. The system uses Wi-Fi technology and is integrated with the main control system, allowing early diagnosis of bearing heating and proper intervention. Results and features of the system are discussed.

Abstract:

The Pickling Line Tandem Cold Mill (PLTCM) from Ternium Pesquería started in 2013. It is a line with 5 stands, 6 high; focused mainly on the exposed automotive market, with a wide spread of products with high quality requirements. In addition the operational continuity is very important, for this, one of the greatest challenges is to ensure operational discipline, the order of production, the quality of the input (hot band), operational interruptions, equipment failure, breakage of strip in the mill, among others. In relation to this, it has a strong impact on productivity, customer compliance, damage to equipment, rolls, safety, quality, reprocessing among others. Here is present the results obtained in the project "decrease of strip breaks" which focused on several fronts, discipline in the order of production, previous review of raw material in surface and dimensional defects with automatic inspection equipment in the hot mill, as well as in PLTCM, generation of logic in the redundant systems of alerts and prevention to avoid or minimize strip breaks that were high impact in the past. All these multidisciplinary actions led as a whole to a significant improvement in the performance indicators of the PLTCM, in productivity, compliance, reprocessing and quality in the cold rolled mill.

Abstract:

IN A STECKEL HOT ROLLING MILL PRODUCTION LINE, THE PRODUCTIVITY OF THE REHEATING FURNACE IS CLOSELY RELATED TO THE ONE OF THE ROLLING MILL, BECAUSE THE ROLLING TIME INCREASES AS THE DESIRED FINAL STRIP THICKNESS IS REDUCED. THE RESIDENCE TIME RANGES FROM 180 TO 300 MINUTES DEPENDING ON THE FINAL STRIP THICKNESS. HIGHER RESIDENCE TIME AT THE HOT OXIDIZING ATMOSPHERE INSIDE THE FURNACE INTENSIFIES THE OXIDE LAYER FORMATION ON THE SLAB SURFACE CAUSING LARGE STEEL LOSSES AS WELL INCREASING THE GAS CONSUMPTION. IN THIS CONTEXT, A POSSIBLE STRATEGY TO OPTIMIZE THE RESIDENCE TIME AND THE FURNACE PRODUCTIVITY IS TO INCREASE THE SPACE BETWEEN THE SLABS DURING THE CHARGING AS THEM MOVE FASTER AND ARE HEATED FOR SHORTER TIMES AT EACH HEATING ZONE. THE PURPOSE OF THIS WORK WAS TO EVALUATE THE BETWEEN THE SLABS IN A WALKING BEAM TYPE REHEATING FURNACE CONSIDERING THE ROLLING TIME FOR ACHIEVE DIFFERENT FINAL STRIP THICKNESS IN A STECKEL MILL, SEARCHING FOR OPTIMIZE THE SLABS RESIDENCE TIME AND ITS EFFECT ON METALLIC YIELD AND IN THE SPECIFIC ENERGY CONSUMPTION BEHAVIOR.

Abstract:

This study focused on the influence of reheating treatment on the microstructural evolution, dissolution/precipitation behavior of Nb and Ti, and their effects on the mechanical properties in a Nb-Ti microalloyed steel. The tested steel was rough rolled at 1050 °C, followed by the immediate reheating to 1150 °C on an endless thermomechanical processing route. The state of Nb in solution was analysed as a function of hold time at this isothermal reheat temperature. The microstructure and precipitation after reheating process were analyzed by scanning electron microscope (SEM), electron backscatter diffraction (EBSD), transmission electron microscope (TEM), and electrolytic dissolution and filtration tests. The results revealed that majority of the Nb and Ti dissolved into the matrix after the reheating process. Plenty of quasi-polygonal ferrite (QF) and granular ferrite (GF) formed during the cooling process due to the decreasing in the phase transformation temperature of γ→α. The average grain size of ferrite was eventually refined to 2.01 μm resulting from the combined effects of the chemical driving force and the volume strain energy. The dissolution of Nb and Ti during the reheating process, coupled with the deformation in austenite non-recrystallization zone during finish rolling, facilitated the strain-induced precipitation of large amounts of nano-sized M(C, N), which contributed greatly to the high strength of the Nb-Ti microalloyed steel by precipitation strengthen.

Abstract:

The demand for hot rolled strip is growing in multiple ways. To remain competitive, new and existing mills must meet arisen challenges in the best possible way. The production of hot strip is a key element of steel production. Since close to half of all steel produced is hot-rolled to strip, mills require maximum throughput and availability combined with geometrical precision and the ability to create optimum material properties. Today there is a clear trend in developing new steel grades with high-strength and improved formability, like 3rd generation AHSS (Advanced High Strength Steels), as well as a trend to produce thinner and wider gauges. This trend challenges hot strip mills because it requires new technologies which provide more flexibility in metallurgical treatment during the rolling process. In order to meet and promote these trends Primetals Technologies is currently working on different concepts and solutions. One example is the development of a new mill stand technology FLEX-HI HOT which allows to adapt the last finishing mill stands by efficiently switching from 4-high to a 6-high mode with small work roll diameter based on production needs. Another solution is to apply a permanent 6-high rolling stand at the end of the finishing train. A smaller work roll diameter allows to achieve higher specific thickness reductions and deformation rates resulting in significant thinner hot-strip gauges with valuable metallurgical benefits. The developed solution concepts with technological and metallurgical benefits will be presented in this paper.

Abstract:

Due to the increasingly stringent requirements and the needs of the automotive industry, galvanizing lines dedicated to automotive products have to be modernized and improved. Beginning of 2017, SEGAL, a Tata Steel CGL line located in BELGIUM and fully dedicated to automotive market, placed an order to CMI in order to increase the line capacity from 550kt/year to 600kt/year, to be able to process a wider range of steel grades and to improve the product quality according to automotive requirements. To achieve such a production, it was necessary to increase the loopers capacities, and to install a new inductor at the furnace, a new water quench and one BLOWSTAB® cooling box to increase the cooling capacity. To improve the product quality, a major revamping of the skin pass was necessary. The objectives were first to increase the work roll diameter from Φ560mm to Φ650mm in order to be able to transfer the required roughness with low elongation on soft material and second to increase the rolling force and tension to reach higher elongation on high strength steels. Existing mechanical elongation system has also been replaced by a completely new single AC motor with helical gearbox at each bridle roll. The request of the customer was very challenging regarding engineering, delivery time and shutdown time. Complete analysis and engineering has been done within three months with maximization of existing equipment reuse on a skin pass originally not supplied by CMI and with only paper drawings available. The complete motorization concept has been replaced, including modification of the rolls during the shutdown. For the skin pass mill, only the housing, auxiliaries inside the cellar and interconnecting piping have been kept. Indeed new roll force cylinders with increased diameter and tailor made design, new work roll chocks and new bending blocks have been supplied. All other mechanical subassemblies have be modified in order to avoid any interference with the increases 650mm work rolls, including among others work roll and back-up roll change, modification of work and back up rolls chocks and new anti-crimping. In order to limit costs and shutdown time, the modification of the housings has been avoided thanks to a smart engineering. CMI achieved such complicated revamping in a very short time since the shutdown started only 6 month after the contract signature. Moreover, the shutdown down schedule has been optimized with pre-erection works and the teams working 24/7 to implement all the changes. The complete skin pass section, as well as the other parts of this project (furnace, loopers) have been adapted during the only three weeks shutdown. Today the customer can use both 560mm and 650mm work roll diameters. Thanks to the use of the new 650mm work roll diameter, the customer is able to make the same elongation using a bigger roll force (average 20% more), which has strongly improved the roughness transfer to the strip and the removal of the defects. Today, Tata Steel SEGAL is really satisfied able to produce and supply higher quality automotive products to his demanding customers. CMI takes the opportunity of this paper to warmly thank SEGAL team for his thrust and his authorization to present and publish this paper in several conferences.

Abstract:

ArcelorMittal's pickling and cold rolling line has been demanded to increase production since the installation of equipment in 2015. In addition to improving productivity related to these new equipment, several additional jobs were planned and executed on equipment already installed has been carried out in order to improve the efficiency of the line. The present work exposes what was done in the scale breaker (tension leveler) to improve the availability results of the section and consequently of the line.

Abstract:

The design was developed to optimize the time of the shifting of the work rolls in the Hot Strip Mill. With this, the objective was to increase the availability of the mill, eliminating losses and increasing the annual volume produced. The main problem is focused on the time of movement of the rolls after the rolling process. This task is performed after a time about five minutes for each set of rolls and with the mill stopped. The cumulative loss for this time is very high during the month, with a potential gain of around one day of production of coils. This movement is accomplished through the crane and an exchange device (lifting tong) that attaches to the rolls to be transported from the Mill to the Roll Shop. The critical path of the project is to automate this lifting tong by allowing the operator to coupling the device through a remotely operated hydraulic system, enabling the operator to perform the activity at a safe distance from the load, thereby eliminating the need for consign the mill. An autonomous hydraulic system (UPS) was developed, remotely actuated by the operator, eliminating the need for manual coupling of the transport device in the rolls. With this improvement, we have eliminated the need to stop the mill to perform the activity. In the development of the work were used the Rapid Tool Exchange (TRF) and MASP methodologies to propose ideas solutions and analyze the feasibility and safety of the project. After the analysis, the PDCA methodology was used to develop and plan the execution. As a result, after the implementation of the project, there was no further occurrence of production stoppage due to the movement of rolls after the change. We eliminated about 17% of total minutes from the mill stoppage only for this special cause, which represents a production increase about 3% of tons of rolled coils per month. Another significant gain was with regard to the safety and ergonomics of the operators at the time of the exchange, where we reduced the human machine interface, repetitive efforts and the need of operators to be close to suspended loads.

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High-Turbulence Roll Cooling in Tata Steel IJmuiden Hot Strip Mill 2 Tata Steel IJmuiden Hot Strip Mill 2 (HSM2) is currently being upgraded, resulting in an increased rolling force and motor power capacity. With the current conventional spray cooling, a deterioration in work roll & strip surface quality performance is expected as a result of the increased mill capacities. In order to improve the strip surface quality, HSM2, in close collaboration with CRM Group (Belgium), decided to do a full-scale production trial with a prototype High-Turbulence Roll Cooling (HTRC) at the Finishing Mill Stand 2 (FM2) top work roll. HTRC is a relatively novel way of roll cooling, developed by CRM, using a high turbulent flow regime, operated at a high flow rate (up to 700 m3hr per HTRC unit) and at a low pressure (2-3 bar). HTRC is a cooling unit attached to the stand exit guide with a similar curvature as the work roll, which is positioned very close to the roll surface (5-15 mm). The water flow is going upwards, in the same direction as the circumferential roll speed, which is beneficial to prevent wiper water leakage and also to cool as efficiently and as closely as possible to the gap exit (minimal “wet angle”). Minimizing the wet angle is reducing the repetitive heat penetration into the roll as much as possible, which is believed to be beneficial for roll degradation and thus strip surface quality. Fluid mechanics tell us that a high turbulent flow regime and thus a high heat transfer coefficient, are achieved by high flow rates (to increase the Reynolds number (Re) values) in combination with perturbation of the flow regime. Therefore, the HTRC unit also has a specifically designed pattern of nozzles, which are creating the perturbation of the flow regime. Implementing the HTRC prototype was quite a challenge, but rewarding! The HTRC had to be integrated in an existing (spare) exit guide. High pressure pumps needed to be by-passed. Implementation must be possible within an 8 hours stop and fully reversible in case needed. Operationally, key aspect of the HTRC is close positioning to the roll, creating a narrow 5-15 mm gap in-between the HTRC and the roll surface. To prevent scratching the roll, the wiper nose at the bottom side and the blocks at the top side of the HTRC unit are used to maintain the gap distance. Pushing too hard to the roll, leads to (undesired) high wear rate of the wiper nose and the blocks. If the pressure is not high enough, the water will push the HTRC unit away from the roll, possibly leading to water leakage on the strip and a decreased cooling efficiency. In HSM2, lifetime of the wiper and blocks is currently excellent with no water leakage on the strip. HTRC has been implemented at the FM2 top work roll in August 2018. At the same time, the entry cooling has been blinded, providing opportunities to apply work roll lubrication (which otherwise would possibly be washed away by the entry cooling water). The percentage of rolls with a poor roll surface has dropped more than a factor of 10. In 2020 HTRC will be implemented in stands FM1-FM4, leading to savings on improving roll and strip surface quality. Shutting down redundant high pressure pumps adds significant savings on electricity costs.

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To a great extent, the successful production of the hot bands of consistent crown and minimal flatness defects depends upon the correct setup of the finishing stands of the hot strip mill. A mill shape setup model must accurately predict the roll stack deflection, which includes elastic deformation of the work and backup rolls of known dimensions and ground crown, their thermal expansion, and wear. If a roll stack model does not accurately account for the worn profile of the work and backup rolls, then roll bending and shifting references may not be adequate, thus resulting in deterioration of the hot bands flatness and in noticeable deviation of the actual strip crown from the target. Results of analysis of the effect of the roll stack wear on flatness and crown are discussed, as well as successful implementation of the roll stack wear models.

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The application of preheating before rolling on non oriented high grade electrical steel was studied in this paper. In order to investigate the influence of preheating temperature, the mechanical properties of normalized coils of high grade non-oriented electrical steel at different heating temperatures were measured by the high temperature tensile testing machine. And the results show that the tensile strength, yield strength and elastic modulus of high grade non-oriented electrical steel decreased with the increase of heating temperature. What’s more, the mechanical properties are obviously improved when the heating temperature is 70 °C compared with 20 °C; while the mechanical properties are not obviously changed when the heating temperature is 100 °C compared with 70 °C. The pre-rolling preheating device was applied to the tandem cold rolling mill and it could be seen that the rolling force of the first stand decreased significantly in the actual rolling, while the change is not significant from the second stand to the fifth stand. After the high grade non-oriented electrical steel was put into the preheating before rolling, the edge quality of the cold rolled strip was good and the rolling stability was improved.

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The Brazilian steel industry is dealing an adverse scenario with direct competition from global emerging markets. In this scenario, the need to improve operational performance of his assets, makes the diversified and complex studies involving technical knowledge and asset life behavior, become important tools to support decision making process considering the performance, costs and operational risks relationship. The Asset Management approach support these studies in order to observe the whole asset life cycle, understand value chain through all company process and optimize the asset economic life. In this context, this article aims to support asset management decision making regarding ArcelorMittal Vega cold rolling drive motors, through the motors fail behavior modelling and estimated the risks involved in asset management decision. In this context, the present technical work has the propose to support the decision making regarding the management ArcelorMittal Vega Cold Rolling Mill. Through the Reliability, Availability and Mantenability (RAM) analysis, simulations were performed considering the failure, repair and cost data of asset life cycle. Athwart scenarios simulations the risk of performing preventive and corrective maintenance becoming available and thereby build options to mitigate the risks

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The designed steel chemistry for API X56 Grade was a low carbon (~0.073 %) – medium manganese (~1.33 %) steel, micro-alloyed with chromium (~0.15 %), niobium (~0.04 %), vanadium (~0.025 %) and titanium (~0.019 %) and was rolled into 15.88 mm thick strips by adopting optimized Thermo Mechanical Controlled-rolling Practice (TMCP), when slab re-heating temperature was maintained at 1180 ± 10 C and rough rolling was performed in the temperature range of 1130 to 880 C, maintaining reduction per pass ~20% and higher. Finishing passes were performed within the temperature interval of 880 to 715 C, when reduction ratio was maintained at ~3.6. This rolling practice was followed by accelerated cooling of strips from 715 to 580 C at the rate at ~18 C/second. The microstructure thus evolved in the finished strips was composite in nature i.e. bands of fine ferrite and granular bainite, manifesting low YS/UTS ratio (0.82), evaluated along 45o to the rolling direction (typically, YS: 435 MPa, UTS: 533 MPa and % El: 40) with high toughness properties (Charpy V-Notch (CVN) test at 0 C: 430 Joules and shear area in Drop Weight Tear Test (DTWW) at 0 C: 100%). On conversion of these hot-rolled strips into Helical Submerged Arc Welded (HSAW) pipes of outside diameter: 2732 mm, the typical mechanical properties were YS: 418 MPa, UTS: 529 MPa, % El: 40. The observed marginal change in tensile properties of strips was due to imposition of nominal cold forming strain (~0.6 %) experienced by the material during fabrication into large diameter pipes and the final quality of HSAW pipes satisfied the specified requirements. The chosen chemistry for API X70 Grade plates and strips (thickness: 20.9 / 18.8 / 15.3 / 13.0 mm) was again a low carbon (~0.05 %) – high manganese (~1.55 %) steel, alloyed with molybdenum (~0.09 %) and chromium (~0.15 %) and micro-alloyed with niobium (~0.045 %), vanadium (~0.045 %) and titanium (~0.020 %). Adoption of such type of alloy was found effective in maintaining higher strength in plates / strips through combined effects of enhanced hardenability and formation of finer precipitates of NbCN particles in low temperature transformed phases like acicular ferrite / bainite, even under wide range of cooling rates (18-25 C / second). The optimum finished rolling temperature was 770 C and finished cooling temperatures were in the range of 545 – 574 C, depending on plate thickness. The tensile properties of plates / strips varied within a narrow range (YS: 540 – 545 MPa, UTS: 613-623 MPa, %El: 34-42 and YS/UTS: 0.87-0.88) and satisfied requirements of toughness properties (CVN test at -15 C: 395 Joules and shear area in DWTT at -10 C: ~100 %). The quality of finished Longitudinal Submerged Arc Welded (LSAW) pipes (outside diameter: 457 and 762 mm) were found in conformity to the requirements of customer with no loss in strength properties of plate during pipe forming.

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S460Q Carbon and Low-alloy High-strength Steel Plate possesses good weld ability features, high resistance to brittle cracking and good cold-forming properties. It is typically used for welded structures in shipbuilding and machine-building and for construction of bridges, steel structures and wind generators supports. S460Q structural steel was produced according to European standard structural steel of EN 10025-6. The steel is available in either Quenched and Tempered or thermo-mechanically rolled with Tempering condition. In this research, it has been tried to investigate and compare microstructural variations and mechanical properties of S460Q steel plates produced by two methods of hot rolling operation, including “As hot rolled with Quenching and Tempering” and “Thermo-mechanical control processing (temperature controlled rolling (TCR) with accelerated cooling (ACC)) with Tempering”. For this purpose, two slabs of S460Q steel grades were both provided from the same heat and dimensions then converted to plates with similar dimensions by two mentioned methods. Results were analyzed by mechanical tests and microstructures observations. Results of mechanical tests show that plates produced by two mentioned methods were matched with EN10025-6. Plate Tensile properties produced by TMCP with tempering were lower than as hot rolled with Quenched-Tempered method. moreover, the toughness in Quenched-Tempered method has been increased in comparison to the other one. Besides that metallugraphical observations repersent microstructure with bondings and abnormal ferrite grain growth in Plate produced by TMCP+Tempering method.

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Essar Algoma Steel, Canada, awarded Danieli Transimissions a strategic order for the upgrade of the main drive spindles belonging to the most loaded stands of the Hot Strip Mill, F1-F2, F5 and F6. Featuring special heavy duty design and advanced torque monitoring system, these spindles replace existing competitors’ grease lubricated design with the efficient continuous oil lubricated solution to withstand the tough working conditions, increase life expectations and provide room for a product mix extension. The first couple of spindles have been installed in September 2017 by the expert Service team and are showing already good and reliable performance. Progressively all the others are being installed.

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Stability of the hot strip mill rolling process remains a main topic when it comes to processing thin and hard materials. Strip steering especially at the end of rolling and tail out rips are a main source of unscheduled down times in a Hot Strip Mill. Main focus of this paper is new developments in this field of mill operation targeting at mill stability and quality. An overview of SMS group developments in the recent years regarding equipment and control strategies is given. The new side guiding system in the entry area of the finishing mill is introduced and explained with operational examples. The system provides reproducible conditions for the threading process and during rolling. Steering control has a direct benefit on availability of the mill. New developments of the roll alignment control strategies based on roll force and mill stand entry guide force measurement will be presented. Additionally a camera based measuring system is introduced that generates a direct process feedback of strip position. It provides together with the roll alignment control the necessary control parameters for adjusting the roll gap and guiding the strip correct centered through the mill. As a summary the SMS group system is explained combining all features.

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