Influence of Bainite Isothermal Temperature on Microstructure and Mechanical Properties of TRIP980 High Strength Steel

The phase evolution of TRIP980 steel and the effect of heat treatment on its microstructure and mechanical properties were studied. The phase transition process in thermodynamic equilibrium state was calculated by Jmat-Pro software.The phase transition law at different cooling rates was tested by Gleeble3500 thermal simulation tester and the CCT diagram was drawn. The mechanical properties of steel were tested, and the microstructure of metallographic, SEM and EBSD were observed. The results show that bainite can be formed at 0.5 ℃/s cooling rate of TRIP980 steel. The bainite isothermal section of 380-420 ℃ increases with the temperature, the yield strength of the steel is improved, the tensile strength is reduced, the elongation and the strong plastic product are increased. The maximum strength plastic product reaches 19750 MPa% under the constant temperature process of 420 ℃/120 s. The occurrence of bainitic transformation and the existence of stable retained austenite at room temperature are the key factors for plastic lifting of steel.