Effect of austenitic state on microstructure and mechanical properties of martensite/bainite steel

Various heat treatments and thermal simulation with different austenitizing temperatures and austenite deformation were applied on a bearing steel to obtain various austenitic state. The effect of austenitic state on microstructure of martensite/bainite (M/B) dual phase steel and its mechanical property has been investigated via microstructure observation and kinetic analysis. The results show that the M/B steels austenitized at 900 and 950 °C have better comprehensive performance compared with the steels austenitized at 850 and 1050 °C. The refined microstructure can be obtained after deformation, and the heavy deformation and low deformation temperature are useful for refining the microstructure. The bainite lath is longer and has well-directional arrangement at high austenitizing temperature with the same deformation. Furthermore, austenite deformation can improve the nucleation ratio, reduce incubation process, and affect the kinetics of bainite transformation significantly.