Hot-head strategy optimization based on rapid multi-physics coupling computational platform: a new perspective for shape defect control in high-strength steel coils

The post-coiling cooling process of DP980 dual-phase steel is investigated. A computational model for temperature and phase transformation was established using the finite difference method, while a stress model considering viscoplastic stress relaxation at high temperatures was solved using the lower-upper decomposition method. These models were coupled into a multi-physics rapid calculation model, and the accuracy of the computational results was validated using industrial field data. To address the issue of poor inner coil shape after post-cooling uncoiling in a certain hot-rolling production line for DP980 steel, the influence of different hot-head strategies on residual stress during the post-coiling cooling process is investigated. Detailed simulation analyses were conducted in three aspects: hot-head temperature, hot-head length, and transverse temperature gradient of the hot-head. Based on these analyses, an optimization strategy was proposed. The optimized process significantly improved the internal stress distribution of DP980 hot-rolled dual-phase steel, effectively reducing compressive stress at the coil edges and mitigating shape defects, such as inner edge waviness and warping. Statistical analysis showed an average increase of 6.4% in strip yield rate and an average reduction of 7.7% in rework rate.