Shape stress evolution and control strategy of high-strength strip during the post-coiling cooling process

Abstract

This article focuses on the post-coiling cooling process of DP980 dual-phase strip. The temperature-phase transformation coupling model was solved using the finite difference method, while the elastic-viscoplastic constitutive relationship model, incorporating stress relaxation, was addressed through LU decomposition. These models are coupled into a rapid multiphysics calculation model, and the calculation results are verified against industrial field data for accuracy. This study focuses on a hot-rolling production line where DP980 strip coils exhibit shape defects after the coiling and cooling. The investigation examines the effects of two factors on the residual stress during the post-coiling cooling process: the temperature difference between the middle and edge of the strip before coiling and the degree of phase transformation prior to coiling. Detailed simulation analyses focused on two key factors: minimising the pre-coiling temperature difference between the middle and edge of the strip, and reducing the degree of phase transformation in the middle of the strip prior to coiling. Based on the results, optimisation strategies were proposed. The optimised process significantly improves the residual stress distribution of the hot-rolled dual-phase strip, effectively reducing compressive stress at the edges of the coil, thereby improving shape defects such as edge wave and buckling. The average yield rate increases by 6.8%, and the average repair rate decreases by 7.2%.