Cr-enriched carbide induced stabilization of austenite to improve the ductility of a 1.7 GPa-press-hardened steel

Obtaining a desired quantity of retained austenite (RA) in press-hardened steels (PHSs) with a martensitic matrix is of great interest for the performance of safety critical components in vehicle bodies, as it improves the ductility/toughness without compromising strength. In this study, RA in a 1.7 GPa-PHS was stabilized via local chemical heterogeneity associated with Cr-enriched carbides. The Cr-rich carbide was introduced as a temporary reservoir of Cr and C into the pre-hot stamping microstructure by an annealing treatment. During the subsequent austenitization in hot stamping, the slow decomposition kinetics of Cr-rich carbide contributed to localized enrichment of Cr and C, which stabilized the austenite and resulted in a significant amount of RA with a core -shell structure after die quenching. Finally, sufficient RA ensured that the 1.7 GPa-PHS had a total elongation of-9.3%, which is about 43% higher than that of the 1.5 GPa-PHS grade 22MnB5 (-6.5%).