Microstructure and mechanical properties of a 2000 MPa grade ultrahigh strength boron steel

Press hardening steels (PHS) with very high strength are current key materials for lightweight engineering solutions and corresponding CO2 savings. In the present study, the microstructure and mechanical properties of a 2000 MPa grade ultrahigh strength boron steel for hot stamping were reported. Microstructure evolution experiment revealed that the microstructure of the 2000 MPa grade PHS only consisted of martensite when the cooling rate increased to 20 °C/s. The prior austenite grain size was about 6.8 μm when the sample was austenitized at 900 °C for 300 seconds. The appropriate isothermal quenching process should be austenitized between 900 °C and 950 °C during hot stamping because there is an abnormal grain growth of austenite grains at 950 °C. Following the optimal hot stamping condition, the 2000 MPa grade PHS alloy demonstrated yield strength in excess of 1300 MPa and ultimate tensile strength in excess of 2000 MPa together with a total elongation of about 7%.