Deformation Resistance And Forward Slip Model Of High Strength Steel During Cold Rolling

With the development of automotive lightweight technology,the market demands for coldrolled advanced high-strength steel are increasing year by year,and the requirements for the thickness,shape and surface quality of cold-rolled sheet are becoming higher and higher.This paper takes the chance of "high strength automobile plate cold rolling process of high precision model development and application" research projects of the HBIS Group Tang-Steel Company.It focuses on two problems-the out-gauge and the negative forward slip in the mass production of the 1740mm cold rolling mill in Tangshan Steel Pickling and high strength dual phase steel.Based on the well-understanding of the production,the theoretical and the experimental studies are combined and this paper studies several aspects respectively from strain hardening properties of materials,the establishment of deformation resistance model,the analysis of the influence the forward slip and the phenomenon of "negative forward slip".The main conclusions of this thesis are as follows:(1)Study on strain hardening characteristics of high strength steel.Through rolling-tensile test,the strain hardening curve of three kinds of high strength steel DP590,DP780,DP980 are obtained.The result shows that "platform" occurs obviously when the deformation of three kind of high strength steel is about 30%,and this paper propose an explanation about the dislocation slip for the phenomenon.(2)Establishment of deformation resistance model for cold rolling.In the actual production process,the deformation resistance and coefficient of friction are difficult to determine,but the calculation accuracy of these two parameters directly affects the cold rolling process of the most important parameters-the rolling force of the preset calculation.Regression analysis of deformation resistance curve obtained by rolling-tensile test was carried out.By comparing the results of three different model structures corresponding to three kinds of high strength steel,the model structure with higher degree of agreement with the steel is selected,and the corresponding model of deformation resistance is established.(3)Verification of deformation resistance model.Based on the measured data of rolling process,an iterative algorithm for deformation resistance and friction coefficient is created.After several iterations,the stability values of the deformation resistance and the friction coefficient are obtained,this value is very close to the result obtained by tensile test,and it is consistent with the change of deformation degree.(4)The study of "negative forward slip".Through the comparative analysis between "the negative slip forward" and the before slipping mechanism that applies to the research of"negative forward slip".It is found that the key to solve this "negative forward slip" problem is to prevent slipping strip in rolling process.For this reason,the concept of slip factor is introduced,and the optimization method of cutting order is established to avoid slippage as objective function.(5)Research on "negative forward slip" of tandem cold rolling mill.Regarding to the particularity of cold rolling at the end of the frame,the resistance to end frame and elastic recovery,an elastic analysis for the exit of the deformation zone to the cold rolling has been carried out to find that the export elasticity longitudinal contraction caused by the rolling direction is the main cause for the negative forward slip in the end of the deformation zone.Therefore the correction has been made accordingly to find that the calculated values of the new model agrees well with the measured data on site.