FEM modeling of dynamical recrystallization during multi-pass hot rolling of AM50 alloy and experimental verification

The microstructure simulation during the multi-pass hot rolling of AM50 alloy was studied by DEFORM-3D. The excellent agreement with the experiment observations shows that the present modeling and user routine are feasible for the reproduce of the hot rolling process. The multi-pass hot rolling contributes to the achievement of a uniformly recrystallized microstructure with fine grains in the rolled sheet. The sheet temperature before the finish rolling strongly affects the final grain size, but hardly affects the grain size distribution. This modeling and the user routine also have a potential to be applied in the researches of the other multi-pass hot deformation process.

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.

Three-Dimensional Thermo-mechanical Coupled FEM Simulation for Hot Continuous Rolling of Large-Diameter Mandrel Bar

Based on the important boundary conditions of rolling simulation including friction, heat conduction and interactionsof the workpiece and rolls, the hot continuous rolling processes of large-diameter mandrel round bar (200 mm indiameter) in 6VH-stand hot tandem mill are successfully simulated by three-dimensional coupled thermomechanicalelastoplastic finite element method (FEM). The distributions of stress, strain, temperature and the rolling force andtorque for the two-pass and four-pass continuous rolling are calculated respectively. Thus, the two and four-passroll schedules are verified, respectively. The simulation results show that it is safe to produce 200 mm round barby the two-pass (oval pass and round pass) continuous rolling on the existing equipment compared to the four-passcontinuous rolling. There are concave surfaces and increased widths occurring at the end of rolled billet due touneven deformations between the outside and inside of the workpiece as well as the free spreading close to the rollgap of the final pass.

Three-Di mensional Model for Strip Hot Rolling

A three-dimensional model for strip hot rolling was developed, in which the plastic deformation of strip, the thermal crown of rolls, roll deflection and flattening were calculated by rigid-plastic finite element method, finite difference method, influential function method and elastic finite element method respectively. The roll wear was taken into consideration. The model can provide detailed information such as rolling pressure distribution, contact pressure distribution between backup rolls and work rolls, deflection and flattening of work rolls, lateral distribution of strip thickness, and lateral distribution of front and back tensions. The finish rolling on a 1 450 mm hot strip mill was simulated.

Analysis of the thermal profile of work rolls in the hot strip rolling process

A 2-dimension axisymmetric model was developed by the finite-differencemethod, which can be used to predict the transient temperature field and thermal profile of workrolls in the hot strip rolling process. To demonstrate the accuracy and reliability of the solutiondeveloped, the calculation results were compared with the production data of a 1700 mm hot striprolling mill and good agreement was found between them. The effect of strip width and roll shiftingon the thermal expansion of the work rolls was studied. It is found that the strip width has markedeffect on the efficient thermal crown. Initially, when the rolling strip changes from narrow towide, a bigger efficient thermal crown can be quickly achieved; afterwards, when the rolling stripchanges from wide to narrow, not only the influence of uneven wear can be reduced but also theexcessive efficient thermal crown can be avoided. It is also found that the work roll shifting has adeterminate but not obvious effect on the reduction of the efficient thermal crown, and will makethe strip shape unstable without being used properly.

Adaptive threading strategy based on rolling characteristics analysis in hot strip rolling

In order to improve the threading stability and the head thickness precision in tandem hot rolling process, an adaptive threading strategy was proposed. The proposed strategy was realized by the rolling characteristics analysis, and factors which affect the rolling force and the final thickness were determined and analyzed based on the influence coefficients calculation process. An objective function consisting of the influenced factors was founded, and the disturbance quantity was obtained by minimizing the function with the Nelder-Mead simplex method, and the proposed adaptive threading strategy was realized based on the calculation results. The adaptive threading strategy has been applied to one 7-stand hot tandem mill successfully, actual statistics data show that the predicted rolling force prediction in the range of +/- 5.0% is improved to 97.8%, the head thickness precision in the range of +/- 35 mu m is improved to 98.5%, and the threading stability and the head thickness precision are enhanced to a high level.

Temperature field analysis and its application in hot continuous rolling of Inconel 718 superalloy

A coupled thermo-mechanical model containing metal flow and temperature field for calculating temperature variation has been developed on fourteen-pass hot continuous rolling of round rod for Inconel 718 alloy using 3D elastic-plastic finite element method （FEM）. The temperature of characteristic analysis points in the intermediate cross-section of the workpiece has been simulated at initial temperature ranging from 960 to 1000 ℃ and initial velocity in range of 0.15-0.55 m·s^-1. Based on finite element analysis and microstructural observation in cylindrical hot compression experiments, the appropriate hot continuous rolling technologies have been designed for rod products with different diameters. For a real rolling practice, the simulated surface temperature was examined and is in good agreement with the measured one.

Thermal Behaviors of Work Roll in Finishing Trains of Hot Rolling

In order to analyze the thermal field and thermal contour of work roll in finishing trains of hot rolling in rolling process, a quasi two-dimension implicit finite difference model is developed. To improve the calculating speed and precision, some special solutions are introduced, including the development of this model, the simplification of boundary conditions and the computation of heat transfer coefficients. The results show that these solutions of thermal behaviors of work roll are very much efficient and the model can be used as an on-line profile and fatness control model of large industrial mills.

Complete Mill Simulation of the Rolling Process of 1660 mm Hot Strip Continuous Mills

The three-dimensional plastic deformations of strip are analyzed using the stream surface strip element method, the elastic deformations of rolls are analyzed using the influence coefficient method, the analyzing and computing model of shape and crown of 4-high mill was established by combining them, and the rolling process of 1660 mm hot strip continuous mills was simulated. The simulated results tally well with the experimental results. The modei and the method for simulation of shape analysis and control of hot strip mills were provided.

Stream Surface Strip Element Method and Simulation of Three-Dimensional Deformation of Continuous Hot Rolled Strip

A new method,the stream surface strip element method,for simulating the three-dimensional deformation of plate and strip rolling process was proposed.The rolling deformation zone was divided into a number of stream surface(curved surface)strip elements along metal flow traces,and the stream surface strip elements were mapped into the corresponding plane strip elements for analysis and computation.The longitudinal distributions of the lateral displacement and the altitudinal displacement of metal were respectively constructed to be a quartic curve and a quadratic curve,of which the lateral distributions were expressed as the third-power spline function,and the altitudinal distributions were fitted in the quadratic curve.From the flow theory of plastic mechanics,the mathematical models of the three-dimensional deformations and stresses of the deformation zone were constructed.Compared with the streamline strip element method proposed by the first author of this paper,the stream surface strip element method takes into account the uneven distributions of stresses and deformations along altitudinal direction,and realizes the precise three-dimensional analysis and computation.The simulation example of continuous hot rolled strip indicates that the method and the model accord with facts and provide a new reliable engineering-computation method for the three-dimensional mechanics simulation of plate and strip rolling process.

FEM analysis for hot rolling process of AM60 alloy

<正>The rolling of AM60 sheets for 50%reduction was analyzed with DEFORM to investigate the hot deformation process. The simulated results show that the sheet velocities at the entrance(21 mm/s) and at the exit(37 mm/s) are less and larger than roll velocity,respectively.From the entrance to the neutral point,the velocity at the sheet surface is greater than that at the middle point of sheet in thickness,while that from the neutral point to the exit shows the opposite pattern.The effective strain of the sheet increases from the entrance to the exit due to the continuous reduction in thickness.In addition,the effective strain at the sheet surface reaches to 1.0 and is larger than that of 0.8 at the middle point of sheet.The difference of effective strain in thickness direction has a much stronger effect on the recrystallized fraction than on the recrystallized grain size.The minimum temperature of 347℃is obtained at the surface contacting directly with roll and the maximum temperature 388℃at the middle point of sheet in thickness.

Work roll thermal contour prediction model of nonoriented electrical steel sheets in hot strip mills

The demands for profile and flatness of nonoriented electrical steels are becoming more and more severe. The temperature field and thermal contour of work rolls are the key factors that affect the profile and flatness control in the finishing trains of the hot rolling. A theoretic mathematical model was built by a two-dimensional finite difference to calculate the temperature field and thermal contour at any time within the entire rolling campaign in the hot rolling process. To improve the calculating speed and precision, some special solutions were introduced, including the development of this model, the simplification of boundary conditions, the computation of heat transfer coefficient, and the narrower mesh along the edge of the strip. The effects of rolling pace and work roll shifting on the temperature field and thermal contour of work rolls in the hot rolling process were demonstrated. The calculated results of the prediction model are in good agreement with the measured ones and can be applied to guiding profile and flatness control of nonoriented electrical steel sheets in hot strip mills.

Research on Single-Side Long Edge of Hot Rolled Strip Caused by Asymmetrical Stiffness of Mill Stand

To analyze and solve the problem of single-side long edge of hot rolled strip in certain domestic factory, the asymmetrical deformation of rolls and strip in asymmetrical stiffness mill stand based on slit beam model, the strip profile and rolling force distribution at the exit of asymmetric stiffness stand mill were calculated using influence function method. Considering the character of in-site equipment and technology, a scheme of adjusting load distribution in finishing mill was made and the experiment was applied. Comparison of strip profile between new load distribution and the old one shows that the method can solve single-side long edge problem well.

A new method--the inverse strain method(ISM)for preventing welding hot cracking of high strength aluminium alloy LY12CZ

In this paper a new method for preventing welding hot cracking—the inverse strain method(ISM)is developed on the principle of welding mechan- ics.Effectiveness and feasiblity of method in preventing welding hot cracking of high strength aluminum alloy LY12CZ by synchronous rolling during welding (SRDW)along both sides of the weld at a suitable distance behind the welding arc are examined.Experimental resulte indicate that welding hot cracking of LY12CY can be effectively prevented and the mechanical properties of welded joint can also be improved by the method.It is an important new solution for preventing hot cracking in welding of sheet metal.

基于核偏最小二乘法的热轧板凸度预测

以某2160 mm热连轧生产线为研究对象,结合生产数据和数据驱动算法,提出并建立基于核偏最小二乘法和偏最小二乘法的热轧板凸度预测模型,并对模型的参数进行调整和优化。结果表明:偏最小二乘法模型的预测值与实测值误差为-25~30μm,88.74%的板凸度预测值绝对误差小于10μm;核偏最小二乘法模型的预测值与实测值误差为-25~25μm,91.57%的板凸度预测值绝对误差小于10μm。因此,优化后的核偏最小二乘法模型具有更好的预测效果。

基于混合多阶集成模型的非平衡热轧带钢凸度智能诊断

为了提升带钢热轧加工过程的智能化水平,基于数字孪生(DT)和信息物理系统(CPS),文本采用数据驱动方法以诊断热轧带钢凸度。因为热轧工艺具有遗传性、非线性和强耦合性的特点,因此带钢凸度诊断是一个决策边界不明确的非平衡问题。现有回归方法倾向于从多数类样本学习信息,而忽略了少数类的缺陷凸度。为了解决这一问题,本文提出了一个混合多阶集成模型(HMSEN)分类带钢凸度。首先,提出了一个新的采样方法,该方法结合了自适应采样(ADASYN)和重复编辑近邻样本(RENN)以强化对缺陷凸度的关注。随后,基于增加的数据,建立了一个多阶集成模型以提升分类精度。同时,通过分析不同基分类器的组合确定了最佳性能的混合多阶集成模型。实验结果表明,相比于其它采样方法,本文提出的采样方法更适合凸度数据集。此外,混合多阶集成模型的性能要优于现有回归方法和机理模型。因此,对于非平衡热轧带钢凸度智能诊断,本文提出的混合多阶集成模型是一种有效且鲁棒的方法。

热连轧过程机架间运动板带动特性研究

研究了热轧过程机架间运动板带动力学特征及其影响因素。基于热轧过程板带张力形成机理,考虑机架间板带张力建立了动态张力模型;同时,考虑热轧机活套辊对运动板带的支撑作用,基于Hamilton理论建立了运动板带等效运动梁模型,并基于四阶Galerkin截断法对偏微分方程进行离散化,得到系统四阶常微分方程组。仿真分析机架间板带张力、速度和活套辊支承刚度对运动板带动力学特性的影响,以及运动板带在辊系振动引发的速度摄动下振动特征和影响规律。结果表明:张力、板带速度和活套支撑辊刚度均影响板带动力学模态特征,且活套辊支撑作用可降低板带振动幅值;在热轧工艺范围内,调整板带张力和速度对运动板带的稳定性影响不大;辊系振动造成板带运动速度呈摄动特征,且摄动频率和幅值与板带振动强度关系密切。该研究对热轧过程机架间运动板带稳定性分析和活套控制设计提供参考。

热轧带钢镰刀弯产生原因与控制

热轧带钢是重要的钢铁产品,热连轧是热轧带钢生产的主要方式之一,其中带钢镰刀弯是热轧产线的一个重要指标。实际热轧带钢生产中,成品带钢头部和尾部都会产生镰刀弯,对后续的卷取工艺造成不利因素,对成品质量也起到了重大的影响,同时易导致轧制跑偏产生的废钢事故。本文主要对热轧生产中出现的镰刀弯的原因和相应控制手段进行阐述,为进一步提高轧制的稳定性和产品质量,积累一定经验。

Analysis of Strip Temperature in Hot Rolling Process by Finite Element Method

The program was developed by finite element method to calculate the temperature distribution in hot strip rolling process. The heat transfer coefficients of air cooling, water cooling and thermal resistance between work roll and strip were analyzed, A new heat generation rate model was proposed according to the influence of source current density, work frequency, air gap and distance to edge on induction heating by finite element method （FEM）. The heat generation rate was considered in the thermal analysis to predict the temperature distribution in the induction heating. The influence of induction heating on the strip temperature was investigated for different slab thicknesses. The temperature difference became more and more obvious with the increase of thickness. The strip could be heated quickly by the induction heating both in surface and center because of the thermal conductivity and skin effect. The heat loss of radiation has important influence on the surface temperature. The surface temperature could be heated quickly by high frequency when the strip is thicker.