Multi-scale simulation for hot stamping quenching & partitioning process of high-strength steel

The quenching and partitioning process has proven to be an efficient way to improve the ductility of high-strength steel parts. In this study, two-step quenching and partitioning combined with the hot stamping process was investigated. A multi-scale coupling simulation was performed, in which the micro-scale carbon diffusion, interface migration and austenite domain were coupled into the macro-scale thermomechanical simulation by Abaqus user-defined subroutines. The effect of stress on martensite start temperature (Ms) was taken into account for calculating the retained austenite volume fraction after the first die quenching. The non-uniformity results caused by non-synchronous cooling and the effect of stress were evaluated with the coupled simulation. The carbon diffusion and interface migration were greatly affected by the loading history during the partitioning process. A careful comparison between quasi-static partitioning and dynamic partitioning results indicates that the heating history during the partitioning process cannot be neglected. Finally, a U–shape part was produced by hot stamping quenching and partitioning process to verify the multi-scale simulation. Initial martensite and fresh martensite were distinguished using scanning electron microscopy. The retained austenite volume fractions were quantitatively measured using X-ray diffraction and compared with predictions.