Effects of Heat Treatment in Bainite Region on Microstructure and Property of Martensite Matrix TRIP Steel

The water quenching and subsequent intercritically annealing and isothermal treatment in bainite region for low carbon Si-Mn experimental steel were carried out.The microstructure at different heat treatment was analyzed by OM.The mechanicai properties of experimental steel after heat treatment were tested through the tensile experiment. The change of content of retained austenite before and after tension was detected using the analytical method of X-ray diffraction.The results show that low carbon Si-Mn experimental steel is multi-phase microstruture after heat treatment,which is mainly made up of ferrite,bainite and retained austenite,the volume percent of retained austenite presents extreme point with the increase of constant temperature and the prolong of constant time in bainite region, which reaches maximum value holding 5 min at 400℃ and has maximal strength,plasticity and product of strength and plasticity.