四辊平整机辊系与带材耦合变形有限元分析

 采用大变形弹塑性有限元法将辊系弹性变形与带材弹塑性变形耦合在一起建立四辊平整机三维模型。研究了不同宽度和厚度下工作辊弯辊力对辊系变形、辊缝形状及轧件出口厚度的影响规律。计算结果对平整机设备设计和生产工艺制定具有实际参考价值。所建模型也为轧制过程离线分析提供了一种有力的手段。     

Experimental and theoretical analysis of roll flattening in the deformation zone for ultra-thin strip rolling

For ultra-thin strip rolling, the conventional rolling force models are no longer applicable. To obtain accurate rolling force in the shape and gauge control process, Fleck proposed a new roll flattening model. In this study, experimental analysis, finite element simulation, and theoretical analysis were conducted to evaluate the Fleck model. The experiments and simulations show a clear neutral zone in the deformation zone with decreasing strip thickness. The finite element simulation results show that the proportion of the elastic unloading zone is small, when an elastic unloading phenomenon appears in the neutral zone. Thus, to simplify the rolling force model, the effect of an elastic zone could be ignored. Based on this finding, we develop a rolling force model with quick calculation speed, high precision, and convenient online application. Finally, the accuracy of the simplified model is verified by the measured rolling force.     

Finite Element Analysis of Flange Spread Behavior in H‐beam Universal Rolling

Flange spread is one of the most important factors in the production of H‐beams with the universal rolling mill. Although some prediction models for flange spread have been proposed, the constants in the model equations should be determined for each product size, which requires much experimental work. In this research, finite element analysis was carried out in various rolling conditions and a technique for deciding the model constants by the analysis was investigated. First, rolling experiments using pure lead were carried out to confirm the correctness of the flange spread model. Finite element analyses were then executed for rolling conditions corresponding to the experiments. The flange spread in the numerical analyses showed very good agreement with the experimental results, confirming the accuracy of the numerical simulation. At the same time, the possibility of determining the model constants by numerical analysis was demonstrated. Other related properties of universal rolling were also investigated with the data from the finite element analysis. Changes in the web and flange thicknesses after exiting the roll gap were quantitatively simulated. The cross‐flow behavior between the web and flange was investigated, and the effect of rolling conditions on the cross‐flow ratio was obtained. This research demonstrates that finite element simulation is a powerful tool for investigating and modeling deformation in H‐beam universal rolling.     

超高强钢冷轧过程轧制力计算的改进模型

 为了解决采用圆弧模型计算超高强钢冷轧过程轧制变形区轧辊压扁曲线误差较大的问题,充分考虑到超高强钢的轧制特点,通过分析不同压扁半径下轧辊压扁曲线的变化规律,构造出新型轧辊压扁曲线函数模型,给出了该函数中轧制变形区接触弧长特性参数与轧辊压扁曲线特性参数的求解方法。基于此,根据弹塑性理论中的变形与应力关系,推导了入口弹性变形区、塑性压下变形区以及出口弹性变形区单位轧制压力分布计算过程,建立了超高强钢冷轧过程总轧制力计算模型。并将其推广应用到某钢厂2030冷连轧机组,验证了该模型的计算准确度。结果表明,超高强钢冷轧过程轧辊压扁曲线用二次函数表示,更能准确反映轧辊压扁状态,其计算结果与实际值具有较高的吻合度。同时,为冷连轧机组生产超高强钢产品极限轧制能力的评估与轧制规程的制定提供了理论依据。     

板带轧制过程多参数耦合模拟系统的开发

考虑轧件和辊系间的接触力与变形协调关系，采用一种选代的方案，开发了一个分析三维板带轧制过程的计算机模型。它耦合了计算轧件变形的三维刚塑性有限元法，计算辊系变形的影响函数法和弹性有限元法。该系统可用来精确预报轧制压力横向分布，前后张力横向分布，金属横向流动，以及轧后板带的横向板厚分布，包括板凸度和边部减薄等，并且具有较高的计算效率。     

Study of New On‐Line Pre‐Hardening Technology of 3Cr2NiMo Plastic Die Steel

The thermal property parameters of 3Cr2NiMo plastic die steel were tested and the two‐dimensional finite element model was established in the paper. The temperature fields of 3Cr2NiMo plastic die steel plate with the thickness of 130 mm were calculated and analyzed under three quenching processes. The results showed that for all of the three processes the cooling rates could avoid the pearlite transformation zone when the temperature of the steel plate was more than 500°C. When the temperature was less than 500°C, the cooling rate of the third process was slower, and the temperature difference was effectively alleviated, which avoided large transformation stress appearance. For 3Cr2NiMo plastic die steel with the thickness of 130 mm, the third process was the best process. In the paper, the hardness and the microstructures were tested after the third process and tempering. After tempering process, the structures were all tempered sorbite, and the tempering hardness difference in the whole steel plate was less than 3HRC, and there were no cracks. The study provided references for on‐line pre‐hardening process formulation and optimization of large plastic die steel.     

Material Characterisation for Reliable and Efficient Springback Prediction in Sheet Metal Forming

In this paper, a novel experimental‐numerical methodology for an accurate prediction of springback after sheet forming is presented. An advanced phenomenological material model is implemented in the FE‐code ABAQUS. It includes the Bauschinger effect, the apparent reduction of the elasticity modulus at load reversal after plastic deformation, the strain rate dependence and the elastic‐plastic anisotropy and its evolution during the forming process. The required material parameters are determined from stress‐strain curves measured in tension‐compression tests. These tests are carried out with a special test rig designed to avoid buckling of the specimens during compression. The benefits of this procedure for springback prediction are demonstrated. Additionally, parameters for the phenomenological models are determined from texture simulations.     

Numerical Solution of Thin‐walled Tube Bending Springback with Exponential Hardening Law

The process of manufacturing thin‐walled tubes which show exponential hardening is investigated. The analysis is based on the feedback analysis of bending springback tests. The springback angle is calculated using a formula which is derived from numerical methods. The experiments and finite element calculations prove that the formula agrees well with the test results. However, for tubes with strong hardening characteristics, certain discrepancies exist. The springback angle increases linearly with the ratio of plastic and elastic modulus, and decreases nonlinearly with increasing hardening index. The larger the ratio of plastic and elastic modulus, the greater the amount of reduction as the hardening index increases. The amount of increment in the springback angle incurred by the increase of the normalized bending radius is greater for smaller hardening index values. For thin‐walled tubes, after unloading, the elastic component takes a higher percentage in the total deformation as the relative wall thickness increases, causing the springback angle to increase slightly. However, when the growth rate of the cross section inertia moment is greater than that of the proportion of elastic deformation, the springback angle tends to decrease slightly as the normalized wall thickness increases. The formula will be applied to promote the technical development in springback prediction, control and compensation.     

3D‐FE Modelling and Simulation of Multi‐way Loading Process for Multi‐ported Valves

Multi‐ported valves are widely used in the marine, sanitary, petrochemical and power industry. Multi‐way loading forming technology provides an efficient approach for integral forming of high strength multi‐ported valves, such as tee pipe coupling, high‐pressure cross valves, large‐scale complex valves, and so on. Since the multi‐way loading process is a very complicated plastic forming process due to the complexity of loading path, finite element numerical simulation is adopted to investigate the multi‐way loading process in order to predict and control the multi‐ported valve forming process. A reasonable model of the process is developed under DFEORM‐3D environment based on the coupled thermo‐mechanical finite element method. Then the reliability of the model is validated with respect to geometry development and forming defects. Numerical simulations of multi‐way loading forming for a tee valve and a cross valve have been carried out via using the developed model. Further, the forming processes of tee valve and cross valve have been compared. Moreover, the modelling method is also suitable for multi‐way loading processes of other complex components.     

Multistage High‐speed Compression Test to obtain Material Data for the Kinetics of Microstructure Change in Microscale analysis of Large‐strain Working Technologies

A new analytical model for predicting microstructure change is proposed, and the actual steel microstructure changes that evolve during multistage and single‐stage high‐speed compression are analysed by EBSP (Electron Back Scattering Pattern). Severe plastic deformation induces evolution of various microstructure changes. Prediction of the changes requires the micro‐scale analysis of large‐strain working technologies and accurate material data, which are usually collected by conducting experiments such as compression tests. The analytical model uses the residual dislocation density and austenite grain size as parameters, and can be used to analyse the ferrite nucleation and transformation inside the grains. The compression tests were performed using a newly developed machine that can realize multistage forming at high strain rates. The precision of the data from the tests can be expected to be higher than that from conventional tests. Through the investigation, it becomes clear that multistage high‐speed forming can produce ultrafine‐grain steel whose chemical composition is the same as plain carbon steel, when applying the kinetics of microstructure change shown in the analytical model.     

极薄带轧制变形区轧辊压扁试验与有限元模拟

 极薄带在轧制及平整过程中,工作辊的弹性压扁对轧制压力的分布有很大影响,传统的轧制力模型已经不再适用。为了在极薄带板形板厚控制过程中得到准确的轧制力,Fleck提出了新的轧辊压扁模型。针对Fleck模型进行试验研究,同时进行有限元模拟分析。试验过程中使用合金工具钢轧辊,轧制不同厚度的轧件,通过显微镜测量变形区各部位的厚度,得到变形区轧辊的近似轮廓形状。试验与有限元模拟结果表明,随着轧件厚度的减小,变形区出现了明显的中性区,但是很难出现Fleck模型中提到的弹性卸载区,因此计算极薄带轧制力时可以忽略中性区内的弹性卸载区以简化轧制力模型。     

三辊连轧管(PQF)的计算机仿真

针对影响连轧管产品质量的几大关键因素进行了三维弹塑性大变形有限元分析，建立了相应的各种分析模型，以动态图形形式的模拟了变形过程与壁厚变化规律，为产品工艺设计提供科学依据。     

板材冷轧残余应力的有限元分析

借助非线性有限元分析软件，采用弹塑性热力耦合有限元方法分析了板材冷轧后残余应力的分布情况，结果表明：压下量较小时，板材表层为残余压应力，内层为残余拉应力；压下量较大时，板材表层为残余拉应力，内层为残余压应力，且板材最大残余拉应力随压下量的增加而增大。     

A Newly Developed Upper‐Bound Approach for Calculating the Width Flow in Hot Rolling

This paper presents an investigation of the 3D metal‐forming process during hot flat rolling by an upper‐bound approach. The general aspects of this limit analysis refer to the volume deformation taking into account a polynomial propagation of the free side surfaces. In this approach the deformation region is limited by the roll‐gap entrance and exit with parallel planes. It is characterized by a non‐linear velocity field. A mathematical model of an upper‐bound calculation for the symmetrical flat rolling is developed in order to examine the influence of the most relevant functions, namely the velocity field together with the boundary conditions. A comparison of reasonable onsets is proposed. Therefore, the study can offer useful knowledge for better prediction of lateral flow.     

Springback Analysis of Two-Layer Strips in Clad Cold Bimetal Bending

Recently, multi-layer metallic materials are increasingly being employed in a wide variety of industrial applications in order to create materials with combined functions and higher performances. Based on a nonlinear finite element analysis, the present study aims to develop a model for investigating the effects of sheet thickness and position on the springback of a stainless-steel clad aluminum sheet. It addresses three different types of strain hardening models, namely isotropic, cyclic, and Johnson–Cook (JC). A purely empirical approach, JC considers strain, strain rate, and temperature in elastic–plastic deformation. Good agreements are seen between the obtained results and the experimental verification data, therefore it is concluded that the bending behavior of a bi-layer metallic sheet/strip can be accurately predicted by the proposed model.     

Effect of Lubrication during Hot Rolling on the Evolution of Through‐Thickness Textures in 18%Cr Ferritic Stainless Steel Sheet

Samples of a ferritic stainless steel sheet were hot‐rolled with and without application of lubrication. The effect of the different hot rolling processes on the evolution of texture and microstructure after hot rolling, cold rolling and subsequent recrystallization annealing was studied by means of macro and micro‐texture analysis and microstructure observations. After hot rolling, the sample rolled with lubrication displayed uniform rolling textures through the sheet thickness, while the sample rolled without lubrication showed shear textures in the outer layers of the sheet. The finite element method was employed to reveal the strain states during hot rolling with and without lubrication. The texture of the hot rolled sheet strongly influenced the formation of texture after cold rolling and final recrystallization and, therewith, planar anisotropy as well as the severity of ridging of the final gauge sheet. Hot rolling with lubrication was beneficial to the formation of strong recrystallization textures through the whole thickness layers leading to an enhanced planar anisotropy of the sheet. The recrystallized sheet hot‐rolled without lubrication displayed less severe ridging, however, which was attributed to a less frequent formation of orientation colonies in the outer thickness layers of the sheet.     

Micro‐scale Strain Distribution in Hot‐worked Duplex Stainless Steel

A modified microgrid technique has been applied to a laboratory‐made duplex stainless steel, to experimentally simulate the local state of deformation of the austenite‐ferrite microstructure of low‐alloy steels subject to intercritical deformation. A sample containing such a microgrid was deformed by plane strain compression at high temperature under conditions representative of hot rolling processes. The distortion of the microgrid after hot deformation revealed, in a quantifiable manner, the plastic flow of both phases and different deformation features. The micro‐strain distributions measured can be used to validate the models predicting the hot deformation of low alloyed C‐Mn steels during intercritical rolling.     

中厚板轧制过程中有限元理论的运用

本文介绍中厚板轧制过程中有限元理论的运用,通过MARC软件对中厚板轧制过程中塑性变形有限元分析模型的建立和边界条件的确定进行了详细的阐述,比较真实地反映轧制过程中塑性变形规律,对实际生产起到很好的指导作用。     

Optimum Temper Rolling Degree: Pre‐Set and Influencing Effects of Bending Deformations

The present article describes a research project concerning the influence of bending deformations on strip mechanical properties imparted by temper rolling and a strategy for mill pre‐set to achieve the selected temper rolling degree in as short a time as possible. Research results show that, during strip temper rolling, rolls involved in the process, for example deflector rolls and anti‐sticking rolls, introduce plastic bending deformations into the strip which can amount to more than 30% of the temper rolling reduction, depending on the effective bending radii. Bending tests involving strips made of low‐carbon steel in a tension roller system with an integrated bending unit demonstrate that bending deformations influence the mechanical properties of the strip in a manner similar to the temper rolling process itself. It appears necessary to take account of the bending effects when selecting the optimum temper rolling degree. The most accurate roll force pre‐calculation possible and its application at the mill stand are of major importance for pre‐setting the required temper rolling degree. Existing analytical methods have been unable to yield the necessary calculation accuracy. Combination of an optimised analytical approach with a data‐based model to create a hybrid model has led to significant improvements. The accuracy achieved in the pre‐calculation of the required roll force has helped to improve mill pre‐set of the investigated temper mill and to reduce strip head‐end scrap on average by around 6 m per strip. Based on the annual outputs stated by the plant operator, this makes it possible to achieve a cost saving of more than 200,000 € per year.