Superhigh strength and ductile press-hardening steel produced by shortened austenitization of microstructure containing Mn/Cr-rich cementite particles

Abstract

We developed a novel Si/Cr-alloyed martensitic press-hardening steel (PHS), which has ultimate tensile strength (UTS) of 2280 MPa and total elongation (TE) of 10.9 % after a short hot-forming process, far superior to the present 22MnB5 PHS. Such an unprecedented mechanical combination is primarily attributed to the sufficient retained austenite (RA) grains with evenly distributed mechanical stabilities, which is realized by dissolving nearly 50 % volume percentage of Mn/Cr-rich cementite particles during the short soaking with the guidance of the numerical simulations. As a result, some RA grains have the C/Mn/Cr-enriched cores and other have the cementite cores that are neighbored with high C/Mn/Cr concentrations and steep gradients. This leads to the great heterogeneity in the mechanical stabilities of RA grains in a wide range so that these RA grains are able to provide a continuous TRIP effect for sustainably enhanced work hardening during deformation.