Study on Effects of Heat Treatment on Microstructure and Mechanical Properties of Ultra-high Strength 20Mn2CrNb Automotive Steel

The effects of heat treatment processes on the microstructure and mechanical properties of 20Mn2CrNb ultra-high strength automotive steel were investigated. The results show that the controls of microstructure and mechanical properties can be achieved when the experimental steel is austenitized at 950℃ followed by cooling in different ways or holding at different temperatures. After quenching treatment, the experimental steel is mainly martenitic, with a strength of 1690 MPa, elongation of 9.7%. After austenitic treatment and 300℃ insulation, the strength of the experimental steel reaches 905 MPa, and the elongation reaches 19.4%. There is almost no residual austenite in the steel after heat treatment. The Cr and Nb-rich particles in steel are the main means to regulate the mechanical properties of the steel.