Martensite/austenite Multiphase Microstructure Control In Medium-thick Wear-resistant Steel

In recent years,the General Research Institute of Iron and Steel Research and Development has developed various martensite-based wear-resistant steel grades with good wear resistance by using quenching and tempering heat treament.However,the ductility of these grades is relatively low.The TRIP effect of the austenite phase in steel during friction and wear increases the surface hardness and the depth of the deformation hardened layer,thereby improving the wear resistance of the steel.Considering at the advantages and disadvantages of Ti wear-resistant steel and the role of austenite phase in the steel,a wear-resistant steel containing martensite/austenite multiphase structure(M/A)is proposed to meet the required wear resistance and good toughness as well as plasticity.The Q-P process makes the steel have better comprehensive mechanical properties due to the martensite/retained austenite(M/A)dual phase structure.In this paper,new medium-manganese-silicon alloyed medium-thick steel plates with different manganese and titanium contents were prepared,the composite structure of martensite/austenite wear-resistant steel was obtained by air-cooling quenching partitioning(Q-P)process.X-ray difractometer was used to quantitative analysis of the residual austenite content in the steel.Scanning electron microscope,backscattered electron diffractometer and transmission electron microscope were used to analyze and characterize the microstructure,and mechanical properties.The results show that:high volume fraction of retained austenite of the new developed medium manganese steel grades could be obtained by air cooling.It is speculated that as the austenite to martensite transformation progresses during the cooling process,the dynamic allocation of carbon atoms from transformed martensite to untransformed austenite occurs,resulting in the gradual improvement of austenite stability,thereby increased the final retained austenite.The quenching temperature affects the amount of primary martensite and then the final amount of room temperature austenite.The retained austenite content first increases and then decreases with the increase of the quenching temperature,and the maximum retained austenite fraction can reach 10.66%.The quantity of the retained austenite is directly proportional to the carbon content of the retained austenite.The maximum carbon content in the retained austenite can reach 1.33%.After Q-P treatment,the strength of Ti-free low-carbon Si-Mn steel can reach 1400 MPa,and the total elongation is 16%.The strength of Ti-containing low-carbon Si-Mn steel is 1500 MPa,and the total elongation is 15%.The strength of the test steel containing Ti is higher than that of the test steel without Ti.The plasticity is basically the same for the grades with and without Ti.Grain refine meat strengthening of Ti,the impact toughness is better than the test steel without Ti.