Run-out Table Research Articles

Online electromagnetic monitoring of austenite transformation in hot strip rolling and its application to process optimization

Online detection and monitoring of phase transformation using non-destructive electromagnetic system in industrial hot strip mill processing of steels are reported. The system renders wide range of possibilities for advanced control and fine tuning of the hot rolling and run-out table cooling parameters. These in turn allow for process modifications to better control the microstructure of hot rolled bands. In particular, such modifications can attenuate the adverse effects of uncontrollable cooling of hot band coils that leads to severely non-homogeneous hot band microstructure. An example of application is given demonstrating how reducing the non-homogeneity of hot band microstructure with the aid of online hot strip mill electromagnetic system can help eliminating the off-thickness defects in advanced high strength steel full hard strips thus contributing to lowering the production costs and increasing the yield.

Effect of Inclination Angle and Flow Rate on the Heat Transfer During Bottom Jet Cooling of a Steel Plate

The heat transfer that occurs during bottom water jet impingement on a hot steel plate has been investigated in terms of the effect inclination angle and flow rate. This research was carried out to develop quantitative knowledge of the heat transfer, which occurs on the runout table, a crucial component in the hot rolling production of advanced high strength steels. Industrially produced hot-rolled steel samples were instrumented with numerous subsurface thermocouples installed close to the quench surface. The experimental measurements were used in conjunction with an inverse heat conduction (IHC) model to quantify boiling characteristics as well as heat extraction histories for the different nozzle inclination angles and flow rates. It was found that, as nozzle inclination angle increased, the degree of asymmetry of the cooled region on the surface of the sample was increased and the overall rate of heat extraction decreased. The angle of inclination had a significant effect on overall heat extraction; a vertical nozzle was the most efficient from a perspective of heat transfer under the nozzle. As expected, as flow rates increased, the amount of heat energy extracted increased for all the conditions studied, regardless of the nozzle inclination.

Thermal, Microstructural and Mechanical Coupling Analysis Model for Flatness Change Prediction During Run-Out Table Cooling in Hot Strip Rolling

Non-uniformity of temperature distribution across strip width direction is the ultimate reason why the flatness defect occurs on the strip after cooling process although the strip is flat at the exit of finishing mill. One thermal, microstructural and mechanical coupling analysis model for predicting flatness change of steel strip during the run-out table cooling process was established using ABAQUS finite element software. K Esaka phase transformation kinetics model was employed to calculate the phase transformation, and coupled with temperature calculation using the user subroutine program HETVAL. Elasto-plasticity constitutive equations of steel material, in which conventional elastic and plastic strains, thermal strain, phase transformation strain and transformation induced plastic strain were considered, were derived and programmed in the user subroutine program UMAT. The conclusion that flatness of steel strip will develop to edge wave defect under the functions of the differential thermal and microstructural behaviors across strip width during the run-out table cooling procedure was acquired through the analysis results of this model. Calculation results of this analysis model agree well with the actual measurements and observation.

Fast algorithms for phase transformations in dual phase steels on a hot strip mill run-out table (ROT)

The hot rolling of dual phase steel, alloyed with 0.064% C, 0.05% Al, 0.48% Cr, 0.93% Mn, and 0.41% Si, was simulated by a deformation dilatometer. To model the ferrite transformation behaviour on the run-out table, the rate law approach proposed by Leblond and Devaux was employed. It models the ferrite transformation kinetics as a function of holding temperature and austenite conditioning, which is achieved by varying the austenite grain size and retained strain. Its transformation kinetics during cooling to the coiling temperature was investigated by varying the carbon content of the remaining austenite. The martensite transformation kinetics was also modelled by Leblond and Devaux's approach with a parameter coupled to the Koistinen–Marburger model. The modelling shows that this alloying concept allows a large process window for both temperature and austenite grain size. Finally, a selected set of processing parameters was chosen and transferred to a pilot rolling mill. The mechanical properties of the rolled sheets are satisfactory.

Dynamic temperature control with variable heat flux for high strength steel

We propose a dynamic temperature control (DTC) scheme for high strength steel to obtain the desired temperature and properties of steel in the run-out table (ROT) process. A control model with variable heat flux is developed to reduce the temperature deviation from the actual temperature of the strip, the temperature drop due to water cooling. The control concept uses field data and a timetemperature transformation (TTT) diagram. A ROT dynamic simulator (RoDys) with four simulation modes using the control model is developed to achieve the desired steel properties. The effectiveness of the proposed control scheme is verified from simulation results under a disturbance of the rolling speed. Using a hot strip mill field test, we show that the performance of the temperature control is significantly improved by the proposed control scheme.

Effects of TMCP Parameters on Microstructure and Mechanical Properties of Hot Rolled Economical Dual Phase Steel in CSP

Effects of chemical compositions, finish rolling temperature, isothermal temperature on runout table and coiling temperature on microstructure and mechanical properties of economical dual phase steel produced on CSP line were investigated. Experimental results showed that martensite volume fraction could be enhanced and banding microstructure could be reduced by controlling Mn, Si contents and applying proper finish rolling temperature. Optimized processing-parameters were obtained for DP580 production on CSP line of Wuhan Iron and Steel (group) Co (WISCO) in China. Optimal microstructure and mechanical properties could be achieved when the strip was finished rolling at the range of 790 to 830°C, isothermally holding at 680 to 740°C and coiling below 250 °C.

Advanced run-out table cooling technology based on ultra fast cooling and laminar cooling in hot strip mill

In order to meet the severe requirements of market and reduce production costs of high quality steels, advanced run-out table cooling based on ultra fast cooling (UFC) and laminar cooling (LC) was proposed and applied to industrial production. Cooling mechanism of UFC and LC was introduced first, and then the control system and control models were described. By using UFC and LC, low-cost Q345B strips had been produced in a large scale, and industrial trials of producing low-cost dual phase strips were completed successfully. Application results show that the ultra fast cooling is uniform along the strip width and length, and does not affect the flatness of strips. The run-out table cooling system runs stably with a high precision, and makes it possible for the user to develop more high quality steels with low costs.

Non‐Circular Hydraulic Jump on a Moving Surface due to an Impinging Circular Free Surface Jet of Water

AbstractLiquid jet impingement has many industrial cooling applications such as metal manufacturing and steel cooling on run‐out tables (ROT). The development of the wetting front around the impingement point of a jet is central in jet impingement cooling. In this paper, the effects of moving target surface and jet Reynolds number on wetted zone and on the formation and location of hydraulic jump (HJ) are explored through a series of industrial‐scale experiments of an impinging circular free surface long water jet with high Reynolds number of 11 000–50 000 and industrial jet parameters. The moving test surface impacts the radial evolution of circular wetted zone in all directions and alter the circular HJ at the wetting front into a non‐circular contour that depends on the jet Re number. The limited relations in the literature do not represent these measured shapes and do not appropriately predict radii of HJ in industrial scale. A new correlation for radius of non‐circular HJ has been derived in this study that compared more accurately to the experimental data. Numerical simulations of radial impingement flow on moving surface were performed using a variant of k–ε turbulent model and results are compared to the experimental data. The computational results for the wetting front were found to be close to the experimental data indicating the appropriate performance of the turbulent model.

Experimental study of heat transfer coefficient on hot steel plate during water jet impingement cooling

Experiments were performed, under transient conditions, to investigate the heat transfer phenomena of stationary hot steel plate under multiple top circular jets on run-out table. Based on inverse heat conduction model, a two-dimensional finite difference program was developed to calculate the local surface convective heat transfer coefficients and corresponding temperatures. The cooling water jet flow rate was varied from 15L/min to 35L/min and its effect on the convective heat transfer coefficient and surface temperature was analyzed. The results show that heat transfer coefficients are nonlinear functions of surface temperature. The cooling flow rate has no effect on heat transfer coefficient and surface temperature at stagnation point. Within 70mm distance from stagnation line, heat transfer coefficient ratio changes slightly from 0.87 to 0.97. Beyond surface temperature of 350°C, heat transfer coefficient ratio decreases with increasing distance from stagnation line.

다공질 자용성 합금 피복에 의한 열간 압연용 런-아웃 테이블 롤러의 내구성 향상에 관한 연구

본 연구목적은 열간압연용 런-아웃 테이블 롤러 표면의 기계적 성질을 개선하기 위해 다공질 자용성 합금으로 피복하는 방법을 개발하는 것이다. 열간압연에서 런-아웃 테이블의 롤러 내구성을 높이기 위해서는 고온에서 롤러표면의 경도를 높게 유지해야 하고, 내마모성, 내식성, 내열성, 내소부성 및 내응착성의 향상을 유지하여야 한다. 또한, 고온의 열연 강판을 안정적으로 이송할 수 있도록 하기 위해서는 롤러표면에 적절한 마찰계수를 유지하도록 하여야 하고, 롤러와 강판 사이에 미끄럼 발생이 없어야 한다. 본 연구에서는 자용성 합금에 텅스텐카바이드를 첨가시켜 서메트화하여 롤러의 내마모성을 증대시켰고, 미세 철분말을 롤러표면에 피복하여 다공질을 만들어 마찰계수를 높이고 붙잡음성을 향상시켰다. 그 결과, Ni-Cr 피복 롤러에 비하여 다공질 자용성 합금 피복 롤러는 피복층에 철분이 5 ~ 10 wt%로 많이 함유되어 재용융 공정에서 전기로로 가열하여 일부분만 합금화되고 나머지는 산화 및 용해에 의해 탈락되어 다공질로 나타나 강판과의 붙잡음성을 향상시켰다.

FEM analysis for residual stress prediction in hot rolled steel strip during the run-out table cooling

With the increasing demand of higher quality hot rolled strips, flatness defects occurred on the strips during the cooling process on the run-out table have received significant attention and should be considered in the online shape control model. Non-uniform temperature distribution and cooling across the strip width are the main reasons why the strip becomes unflatten after cooling process although the strip is rolled flat at the finishing mill. A thermal, microstructural and mechanical coupling analysis model for predicting flatness change of steel strip during the run-out table cooling process was established using ABAQUS Finite Element Software. In this model, Esaka phase transformation kinetics model was employed to calculate the phase transformation, and coupled with temperature calculation by means of the user subroutine program HETVAL. An elasto-plasticity constitutive model of the material, in which conventional elastic and plastic strains, thermal strain, phase transformation strain and transformation induced plastic strain were taken into account, was derived and realized using the user subroutine program UMAT. The conclusion that the flatness of the steel strip will develop to edge wave defect under the functions of the different thermal and microstructural behaviors across strip width direction during the run-out table cooling procedure was acquired through the analysis results of this model. The calculation results of this analysis model agree with the actual measurements and observation, therefore this model has a high accuracy. To better control the flatness quality of hot rolled steel strip, the shape compensation control strategy of slight center wave rolling is proposed based on the analysis result. This control strategy has been verified by actual measurements, and applied in actual production.

Extrusion of AlCuMg Alloys with Simultaneous Solution Heat Treatment

Extrusion of AlCuMg Alloys with Simultaneous Solution Heat Treatment In the work, the experiments on extrusion of high-strength aluminium alloys (2014 and 2024) with solution heat treatment on the press were performed. The experimental study describes extrudates microstructure and mechanical properties in dependence on alloy chemical composition, mode of homogenization treatment and temperature-speed extrusion conditions. The optical microscopy and SEM/EDS characterization were supported by DSC analysis, enabling to determine the solidus temperatures of the alloys. The investigations revealed that minimal contents of the main alloy additions (Cu, Mg), high-temperature homogenization and increased extrusion temperatures contributed to achieving high solutioning ratio of the alloys, guarantying improved mechanical properties of the extrudates. The high-temperature homogenization allowed achieving uniform microstructure of ingots with fine particles of intermetallic phases. The significant increase in solidus temperatures of the homogenized alloys enabled more effective solutioning on the run-out table. The maximal permissible metal exit speed was increased and the extrusion force was reduced in comparison to the conventional extrusion technology. The proposed solutions will allow for industrial producing AlCuMg extrudates of improved mechanical properties in the shortened technological cycle with heat treatment on the press.

Potential of Hot Rolled Dualphase Steel from Compact Strip Production CSP<sup>®</sup> in Automotive Applications

Industrial thin slab casting and direct rolling processing started in 1989 with the world’s first CSP® plant at Crawfordsville (USA). Since this time CSP® and competing thin slab casting and direct rolling concepts have been developed to a standard process for hot strip production [1]. Typical features of the CSP® process are the homogeneous structural and mechanical properties all along the strip. Direct hot rolling of thin slabs may be followed by a well defined cooling pattern to produce hot strip from high strength multiphase steel, like dualphase (DP) grades, on the runout table. These steel grades are characterized by a favorable combination of strength and ductility based on hard martensitic particles embedded in a ductile ferritic matrix. This paper highlights the mechanical properties of hot rolled DP steel from CSP® production. To this purpose, multiple tests and modeling have been applied to determine e.g. r-values, forming limit curves and yield locus. In addition, forming simulation as well as laboratory and industrial deep drawing tests have been performed.

Fountain Pyrometer for Strip Temperature Measurement in Cooling Banks of a Hot Strip Mill

Sumitomo Metal Industries, Ltd. (SMI) has developed a new temperature measurement method (Fountain pyrometer) and an associated control system, for hot strip cooled by water in cooling banks.High tensile steel is seeing increasing use in lightweight cars to improve fuel economy and reduce CO2 emissions. Reliable material quality of hot strip products, including high tensile steel, requires good temperature control on the run-out table. The conventional control method is not good enough because the temperature of a hot strip cannot be accurately measured in the cooling banks, where the cooling water interferes with thermal radiation from the hot strip surface.SMI has developed the Fountain pyrometer, which uses a water purge to stabilize the passage of thermal radiation from the hot strip surface. Experiment confirms that Fountain pyrometers can reliably measure hot strip temperatures above 360 degrees Centigrade even in cooling banks with a great deal of cooling water. The response time of Fountain pyrometers is 10 or 20 ms. SMI has also developed a new control system using Fountain pyrometers, a combination that allows very precise temperature control of hot strip on the run-out table.

Effect of Cooling Patterns on Microstructure and Mechanical Properties of Hot-Rolled Nb Microalloyed Multiphase Steel Plates

The effect of the run-out table cooling patterns on the microstructure and mechanical properties of Nb microalloyed steel plates was investigated by hot rolling experiment. The results showed that the mixed microstructure containing ferrite, bainite and significant amounts of retained austenite can be obtained through three kinds of cooling patterns on the run-out table under the same hot rolling condition. Three kinds of cooling patterns possess different austenite transformation kinetics, which leads to variations in microconstituent characteristics. The yield strength increases, the tensile strength decreases and the total elongation tends to increase as the cooling patterns I, II and III were applied respectively. The yield strength, the total elongation and the product of tensile strength and ductility reach the maximum values (547 MPa, 37.2% and 28 384 MPa · %, respectively) for the steel plate processed by cooling pattern III.

Effect of phase transformation latent heat on prediction accuracy of strip laminar cooling

The cooling of hot-rolled strips is of great importance due to its effects on the mechanical and metallurgical properties of the final product. In this paper, the effect of phase transformation on accurate prediction of strip temperature at the run-out table is investigated. For this purpose, a model is developed for the heat transfer and phase transformation in hot-rolled strips during the cooling process. The model is capable of calculating strip temperature and the volume fraction of steel phases during cooling at the run-out table under the two different situations of “regarding phase transformation latent heat” (RPTLH) and “disregarding phase transformation latent heat” (DPTLH). Actual data from a hot rolling line were used to evaluate the accuracy of the model. The model was used to predict strip temperature under the above two scenarios. Comparison of actual and predicted values in the two DPTLH and RPTLH cases revealed that disregarding the released heat would lead to considerable errors in temperature predictions. The results for different steel grades predicted by the model also showed that the higher the carbon content of the steel, the higher the error due to disregarding phase transformation latent heat.

Application of a Three-Dimensional Microstructure Evolution Model to Identify Key Process Settings for the Production of Dual-Phase Steels

During the production of dual-phase (DP) steels, many transformation phenomena occur, each of which may significantly influence the final properties of the product. In the continuous annealing line, recovery, recrystallization, carbide dissolution, austenite formation, ferrite formation, and martensite formation may all occur. These processes can strongly influence each other. Furthermore, these processes may overlap. This metallurgical complexity makes both establishing the root cause of property variations and the design of new chemistries experimentally expensive and time consuming. With the recent introduction of a computationally efficient three-dimensional (3-D) microstructure evolution model that describes all transformation processes that occur during the processing of DP steels, a tool has become available to study in detail the effect of individual process parameters on the final microstructure. The model has been applied to study the transformation processes on the run-out table of the hot strip mill and in the continuous annealing line. In this study, emphasis has been placed on the role the hot-rolled microstructure plays in the final DP microstructure. Therefore, the model was extended to include the influence of manganese segregation on band formation. Details of the model and findings on the relation between the final microstructure and process settings are presented.

Influence of chemistry and runout table parameters on hot coil collapse in C–Mn steels

The key metallurgical parameters affecting the incidence of coil collapse (soft slump) of C–Mn steels has been investigated using industrial data and laboratory simulation. Runout table (ROT) cooling/coiling simulations were performed on a Gleeble 1500D to study transformation before and during coiling of thin strip. For low C (<0·07%) grades, coiling temperatures above 650°C coupled with high nitrogen contents decreased the transformation end temperature Ar1 and increased collapse. Coiling temperatures above the Ar1 for ROT cooling increased both dilation and the time to complete transformation during coiling. These effects correlated with industrial conditions where a high frequency of coil collapse was observed.

열연 고강도강의 비정상부 온도제어를 위한 LBCC 개발

In this paper, a LBCC (Latter Bank Cooling Control) for the high strength steel is proposed to obtain the desirable temperature and the property of the material along the longitudinal direction of the steel on the ROT (Run-Out Table) process. A cooling valve is modeled to analyze the response of the ROT banks. The control concept is derived from a field data, a valve model considering the valve response and a TTT (Time-Temperature Transformation) diagram. The proposed control is verified from the simulation results under the various carbon quantities. It is shown through the field test of the hot strip mill that the deviation of the CT (Coiling Temperature) is considerably decreased by the proposed temperature control.

Application of Advanced Cooling Control System for Plate Mill

Based on the new generation TMCP technology, The State Key Laboratory of rolling and automation, Northeastern University(RAL) developed an advanced cooling system(ADCOS-PM). The system was combination of ultra-fast cooling (UFC) equipment with the advantage of high cooling intensity and homogeneous cooling and traditional accelerated cooling equipment(ACC). The UFC equipment was composed of jet impingement cooling device with high-pressure water and the ACC equipment was composed of laminar cooling device with good controllability. The control object of ADCOS-PM control system including finish cooling temperature and cooling-rate of every stage was controlled by adjusting the parameters such as the run-out table speed, state of active and inactive jet, flow rate of active jet. The temperature profile of plate was completed on the run-out table so that the product with fine microstructure and good mechanical properties was produced. The ADCOS-PM was built in 4300mm plate mill of Anshan Iron and Steel Co., Ltd. in 2010 and the recycling products with high-performance were produced.