卧式马弗炉带钢热处理的加热与冷却分析

针对电加热卧式马弗炉内的带钢光亮热处理，建立了简便的热处理数学模型，用它可定量地分析马弗管、加热壁的尺寸和表面黑度等因素对带钢加热与冷却的影响。     

热连轧轧辊瞬态温度场研究

考虑水冷、空冷、轧辊与轧件接触热传导等动边界条件，采用有限差分法，建立了热连轧轧辊瞬态温度场变步长分析计算模型。该模型能实现轧辊温度场的动态分析和精确计算，预测轧制时以及终轧后空冷的轧辊瞬态温度场。试验和仿真结果表明，所建立的分析计算模型考虑因素全面、合理，计算精度较高，计算值与实测值吻合良好，真实地反映了轧辊的温度变化情况。     

Two-Dimensional Transient Temperature Field of Finish Rolling Section in Hot Tandem Rolling

Comprehensively considering the factors such as descaling cooling, air cooling, watercooling, frictional heat and deformation heat in gap of every stand, heat conduction betweenwork roll and strip etc, a model of two-dimensional transient temperature field of finish rollingsection in hot tandem rolling was built with finite difference method to calculate the temperaturefields of strip and work roll. So two-dimensional accurate analysis and calculation of strip tem-perature were realized, and the theoretical basis for predicting and controlling strip temperaturewas provided. The simulated results show that the model is practical and reliable.     

板坯电磁感应加热的有限元分析

针对采用电磁感应方法对板坯进行补偿加热的情况,从理论上分析了工作频率的确定原则以及矩形截面板坯电流透入深度与工作频率的关系。利用有限元法分析了不同工作频率下的板坯电磁加热过程,结果表明随着工作频率降低,集肤效应显著性减弱。工作频率和板坯形状尺寸对感应加热过程有重要影响,工作频率较低时,温度最大点位于距对称轴一定距离的层面,该层面偏向表层,随着工作频率增加,温度最大值向板坯边角部移动。矩形板坯感应加热过程较为复杂,应该根据不同工艺要求选择合适的工作频率。计算了试验板坯的感应加热温度,并将计算结果和实测值进行了比较分析,结果吻合良好。     

Re-reddening on Strip Surface After Water Cooling

After water cooling,there is a big temperature difference between the center and the surface of strip,which leads to the heat transfer from the center to the surface,and the surface temperature can rise in a short time.The finite element method was used to simulate the phenomena of re-reddening on the surface of strip and to analyze the temperature field of hot rolled strip during laminar cooling,and the periodical variation curve of the cooling rate was obtained during water cooling and subsequent re-reddening.The results show that the critical line of the cooling rate is at 1/3 of the half-thickness from the strip surface.The regression model of the relation of re-reddening temperature,time,and distance from the surface was obtained in the re-reddening region.Re-reddening regularity on the surface of strip under the condition of different thickness and cooling rate was also studied.     

板坯直轧感应加热的有限元模拟

针对板坯连铸直轧过程中的感应加热技术进行研究,综合运用纵向磁通和横向磁通2种感应加热方式解决板坯补热问题。以板坯空冷温度场结果为基础,建立板坯感应加热有限元模型。通过 VB对 ANSYS的二次开发调用,实现板坯和线圈相对运动过程中感应加热的三维有限元模拟。结果表明：经过纵向磁通感应加热后板坯边角温度仍然偏低;横向磁通感应补热能有效提高板坯边角温度,2种方法的结合使用对于板坯直轧的实现有一定的指导意义。     

立式连续退火炉中带钢气体射流冷却数值模拟及温度场计算

气体射流冷却是立式连退炉内带钢快速冷却的主要方式,计算冷却过程中带钢温度场分布,对改善带钢连续退火工艺有着重要的指导意义。利用CFD模拟软件对冷却过程进行数值模拟,获得带钢表面换热系数分布规律。运用有限差分法,对带钢温度场分布进行数值仿真计算。研究了初始带钢温度对冷却过程中带钢温度场分布规律的影响。     

重轨端部淬火温度场与相变的计算机模拟

运用有限元法对U71Mn钢(%:0.65～0.76C、0.15～0.35Si、1.10～1.40Mn、≤0.030V、≤0.025Ti)重轨端部电磁感应加热55 s,空冷8 s,喷风冷却42 s,空冷至常温的热处理过程进行了计算机模拟分析,计算机图形学理论动态显示轨端内部任意时刻的温度分布、组织分布。模拟结果表明,在该冷却条件下淬火后端部横断面组织为细片状珠光体(索氏体+托氏体),无马氏体、贝氏体等组织,与实验结果相吻合。     

20CrMnTiH圆钢精轧后控冷过程温度场有限元分析

通过对20CrMnTiH圆钢精轧后控制冷却过程温度场进行有限元模拟以及现场温度实测,得出了Φ35 mm规格圆钢芯部、1/2半径处和表层温度的分布曲线。分析说明,轧后水冷却过程圆钢表层温度急速下降,而芯部温度下降缓慢,水冷时圆钢芯部与表面的最大温差约为115℃;水冷后的空冷过程使得圆钢芯部和表层温度逐渐一致。20CrMnTiH圆钢精轧后采用快速水冷并配合空冷工艺,有利于抑制奥氏体晶粒长大并获得均匀细小的轧材组织。     

层流冷却过程中带钢温度场数值模拟

分析了带钢层流冷却过程中的传热，并利用有限元法对层流冷却过程中带钢温度场进行了模拟计算。结果表明：随着轧件厚度的减薄，在带钢厚度方向上的温差逐渐减小；冷却速度不同时，带钢表面温度和中心温度的变化趋势以及波动幅度相应发生变化。在进行模型计算时，应合理考虑带钢厚度及内部热传导的影响。这对提高数学模型的精度，控制卷取温度，提高产品质量以及指导生产具有重要意义。     

Numerical determination of heat transfer coefficient for boiling phenomenon at runout table of hot strip mill

Abstract

The heat transfer coefficient during film boiling at the runout table of the hot strip mill is usually determined by experimental methods. Described in the present paper is a finite difference based model for analysis of the thermal behaviour of the strip during cooling at the runout table of the hot strip mill at Tata Steel, India. The model, developed for the prediction of strip temperature, is used to determine the heat transfer coefficient at the water/strip interface while water cooling occurs. A simple form of polynomial as a function of the strip surface temperature is proposed to describe the heat transfer coefficient at the water/strip interface. Good correlation has been found between model predicted temperatures considering the polynomial type heat transfer coefficient and the actual coiling temperature.     

Numerical Simulation of Temperature Field and Thermal Stress Field of Work Roll During Hot Strip Rolling

  Based on the thermal conduction equations, the three dimensional (3D) temperature field of a work roll was investigated using finite element method (FEM). The variations in the surface temperature of the work roll during hot strip rolling were described, and the thermal stress field of the work roll was also analyzed. The results showed that the highest roll surface temperature is 593 ℃, and the difference between the minimum and maximum values of thermal stress of the work roll surface is 1457 MPa. Furthermore, the results of this analysis indicate that temperature and thermal stress are useful parameters for the investigation of roll thermal fatigue and also for improving the quality of strip during rolling.     

New Method for Evaluating Thermal Wear of Rolls in Rolling Process

A new method was developed by a thermal wear machine to evaluate the thermal wear of roils in steel rolling process. The steel strip and rolls were simulated by upper and lower heating disks. The upper heating disk could he kept at a temperature of over 900 ℃ by induction heating. The pressure between the disks as high as 323.2 MPa could be achieved and the slipping rate could be 12. 7 %. The thermal wear of high speed steel （HSS） roll material, the wear rate of the HSS roll, and the SEM morphology of a worn HSS roll surface were investigated. This method was useful and could be employed to simulate friction and wear between strip and roll during the strip rolling process.     

热轧带钢三维温度计算与应用

温度是热轧带钢控制模型的基础,温度模型以加热炉抽钢温度为起点,充分考虑带钢轧制过程中经过的空气冷却、高压水冷却、形变升温等过程,按时序计算带钢全程温度变化。把带钢纵向切分成密集的多个截面,在截面上按宽度、厚度方向划分网格,计算所有截面二维温度分布后再进行截面串联,实现热轧带钢全长三维温度模拟计算。以三维温度计算为基础,结合宝钢1580 mm热轧产线实际情况,调整边部加热控制策略与机架间冷却水流量策略,完成精轧出口温度计算。结果表明,带钢整体温度分布更加均匀,三维温度模拟计算结果与带钢实绩温度分布基本一致。     

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.     

热连轧机轧辊热辊型及冷却制度研究

针对热带钢连轧机由于带钢规格变化(主要指窄料和宽料)导致轧辊热辊型的大幅度波动,对轧辊温度场、热凸度和冷却效应进行了分析。采用有限差分法对轧辊温度场和热凸度进行了数值模拟,计算值和实测值吻合较好。进而应用该模型根据来料规格、压下规程等因素来确定工作辊冷却水轴向分布,为热带钢连轧机工作辊冷却系统的改造提供了可靠依据。     

冷轧工作辊热凸度及其对板形影响

冷轧过程中工作辊的热凸度变化是决定带材板形质量的重要因素,研究分析工作辊的热变形及其对板形的影响对于提高带材质量有着重要的意义.以某厂1 450 mm冷连轧生产线为研究对象,运用大型有限元分析软件ANSYS与LS-DYNA分别建立四机架与五机架的工作辊二维热凸度有限元仿真模型和三维有限元轧制仿真模型,并将2个仿真模型相...     

Comparison of Austenite Decomposition Models During Finite Element Simulation of Water Quenching and Air Cooling of AISI 4140 Steel

An indigenous, non-linear, and coupled finite element (FE) program has been developed to predict the temperature field and phase evolution during heat treatment of steels. The diffusional transformations during continuous cooling of steels were modeled using Johnson–Mehl–Avrami–Komogorov equation, and the non-diffusion transformation was modeled using Koistinen–Marburger equation. Cylindrical quench probes made of AISI 4140 steel of 20-mm diameter and 50-mm long were heated to 1123 K (850 °C), quenched in water, and cooled in air. The temperature history during continuous cooling was recorded at the selected interior locations of the quench probes. The probes were then sectioned at the mid plane and resultant microstructures were observed. The process of water quenching and air cooling of AISI 4140 steel probes was simulated with the heat flux boundary condition in the FE program. The heat flux for air cooling process was calculated through the inverse heat conduction method using the cooling curve measured during air cooling of a stainless steel 304L probe as an input. The heat flux for the water quenching process was calculated from a surface heat flux model proposed for quenching simulations. The isothermal transformation start and finish times of different phases were taken from the published TTT data and were also calculated using Kirkaldy model and Li model and used in the FE program. The simulated cooling curves and phases using the published TTT data had a good agreement with the experimentally measured values. The computation results revealed that the use of published TTT data was more reliable in predicting the phase transformation during heat treatment of low alloy steels than the use of the Kirkaldy or Li model.     

Q345C钢连铸板坯热送热装过程中温度场和应力场模拟

考虑板坯钢种弹性模量、导热系数、比热容及线膨胀系数对模拟精度的影响,通过ABAQUS有限元分析软件对Q345C钢250 mm×1500 mm单块连铸板坯冷却过程应力场和温度场进行模拟,经处理得出应力（<20~148 MPa）、温度（769~1000℃）和时间（0~1200 s）三者的关联信息。计算结果表明,板坯空冷温度沿宽度方向分布不均匀,板坯表层边部降温速率0.46℃/s,板坯表层距边部200 mm以外,基本具有相同的温降速率（0.23℃/s）;铸坯堆垛空冷速度较低,约为15℃/h,和现场实测结果吻合。应将连铸坯从火焰切割机到板坯加热炉输送时间降到最短,以及增加保温措施,防止表面热应力过大而形成缺陷。     

Prediction of Microstructure and Mechanical Properties of Hot Rolled Steel Strip: Part I ‐ Description of Models

A metallurgical through‐process model is presented which describes the microstructural evolution and predicts the final mechanical properties of low carbon steel during hot strip rolling. Process models concern the thermal and deformation phenomena, which take into account the strain, strain rate and temperature distribution along the length of the strip. And the metallurgical models cover five modules, which are (i) austenitization of cast slab in reheating furnace, (ii) recrystallization of austenite in hot rolling, (iii) phase transformation of austenite‐ferrite in laminar cooling on the run‐out‐table, (iv) grain growth after coiling, and (v) final structure‐mechanical properties of products. Temperature is the main parameter and has dominant influence on the microstrutural evolution and the mechanical properties. The related temperature variation in hot strip rolling concerns air cooling, scaling, water cooling, heat transmission by roll contact, heat generation by deformation and friction. These complex factors are incorporated into the thermal models to simulate the temperature distribution along the length of the strip from the reheating furnace exit to the down‐coiler. A self‐learning algorithm is employed to improve the calculation accuracy and the computational temperatures are compared with the measured ones at typical locations. In the structure‐property relationships, two key process parameters (e.g., finishing exit temperature (FT7) and coiling temperature (CT)) are introduced in the model to consider the influence of morphology of microstructure on mechanical properties.