Research On Deformation Characteristic And Quarter Wave Control Of Dual Phase Steel DP980 In Cold Rolling

Using high strength dual phase steel to make automobile stamping parts is an important way to improve automobile safety.In the automobile manufacturing industry,the proportion of high strength dual phase steel used in body in white is increasing year by year.The cold rolling production technology of dual phase steel with 1GPa tensile strength represented by DP980 has been mastered by more and more enterprises.However,the complex quarter wave problem of dual phase steel DP980 in the cold rolling process seriously affects the production efficiency and production cost of enterprises.At present,the research on the plastic deformation characteristics and cross-sectional shape inheritance of dual-phase steel DP980 during cold rolling is still insufficient.Therefore,it is impossible to clarify the generation mechanism of the quarter wave defect of dual-phase steel DP980 and the flatness control method of the quarter wave.Based on a 2130UCM tandem cold rolling mill(TCM),this paper takes the dual-phase steel DP980 as the main research object,and aims to find the evolution law of the cross-section shape of the strip during the cold rolling process and the quarter wave flatness control method.By establishing a multi-pass finite element model(FEM)considering the distribution characteristics of the transverse mechanical properties of the strip,the elastoplastic deformation behavior of the dual-phase steel DP980 during the continuous rolling process of each stand is analyzed,and the quarter wave defect flatness control method is studied,and the main achievements are as follows:(1)The multi-pass FEM of DP980 cold rolling was established.In order to reveal the influence of the difference of transverse mechanical properties of DP980 on the deformation behavior of cold rolling process,based on the transverse mechanical experiment of strip steel,a deformation resistance surface model was established to accurately describe the relationship between stress and strain at any position in the transverse direction of strip,and overcome the problem of low calculation accuracy caused by using the average deformation resistance curve to express the mechanical properties of strip steel.Based on the method of data transfer technology and model reconstruction technology between stands,a multi-pass FEM of DP980 cold rolling is established.By comparing with the measured data,the prediction deviation of rolling force of each stand is less than 4.5%,and the average thickness prediction deviation is less than 4.19μm.The multi-pass FEM has high accuracy.(2)The reason of the quarter wave defect caused by DP980 cold rolling is revealed.Based on the simulation and analysis of DP980 cold rolling process based on multi-pass finite element model,the important law of local thickness drop at the position 160mm away from the edge of S3 stand after rolling is obtained.Subsequent rolling passes could not eliminate the local thickness drop until inherited to the exit of last stand,showing a quarter wave defect.At the same time,the simulation shows that when the deformation resistance surface model has the sixth-order distribution characteristics similar to the mechanical experiment,the greater the decrease rate of edge deformation resistance,the smaller the high-order relative crown of the strip,which will increase the risk of quarter wave defect.When the deformation resistance is distributed in the shape of "W",it is more likely to cause the quarter wave.(3)The flatness control method of the quarter wave defect of DP980 cold rolling is proposed and verified by industry.Based on the evolution law of cross section shape of DP980 two-phase steel in cold rolling process,the flatness control effect of rolling force of each stand,working roll bending force and middle roll bending force on quarter wave was simulated and analyzed.Through industrial tests,it is proved that the quarter wave greater than or equal to 15 IU cannot be effectively eliminated by increasing the bending force of the work roll or combining the bending force of the work roll and the intermediate roll.On this basis,a work roll shape based on the bell membership function is proposed.The industrial test proves that the roll shape can reduce the average size of the quarter wave from 13.88IU to 2.07IU.