A 2000 MPa grade Nb bearing hot stamping steel with ultra-high yield strength

This study reports a novel 2000 MPa grade ultra-strong hot stamping steel, which contains lath martensite, nanometer-sized film-shaped retained austenite and precipitates. The yield strength significantly increases with increasing tempering temperature as the precipitation strengthening, grain refinement strengthening and reducing microstructure residual stress. Multi-strengthening mechanisms (i.e. grain refinement strengthening, precipitation strengthening and transformation-induced plasticity effect) work together to improve the strength and plasticity at the same time. The yield strength reached 1600 MPa, together with an ultimate tensile strength of 1939 MPa and total elongation of 9.14% when tempered at 573 K. Compared with commercial 22mnB5 steel, the tested steels have remarkable improvement in mechanical properties.