Abstract: By performing the Gleeble-3500 annealing simulator, tensile testing machine and optical microscope, the effects of soaking temperature, slow cooling temperature and overaging temperature on mechanical properties and microstructure of 980 MPa multi-phase steel were investigated during the continuous annealing process. The results indicate that 980 MPa multi-phase steels are composited of typical ferrite, bainite and martensite. The contents of bainite and martensite increase with the rise of soaking temperature, enhancing the yield strength and tensile strength accordingly. The slow cooling temperature is related to the size of new ferrite and the content of martensite, which possesses the adjustability of mechanical properties. With the increase of overaging temperature, granular carbides appear gradually and can reduce the strength of martensite, which further improves the plasticity of multi-phase steels. From the view of multiple regulation on comprehensive mechanical properties of 980 MPa multi-phase steels, the optimal parameters are selected as soaking temperature of 800 ℃, slow cooling temperature of 700 ℃ and overaging temperature of 340 ℃.

Key words: multi-phase steels, continuous annealing, soaking temperature, overaging temperature, microstructure and properties