Abstract: Microstructure and mechanical properties of 22MnB5 steel were characterized by means of optical microscope (OM), universal tensile testing machine, scanning electron microscope (SEM), Xray diffraction(XRD) and electron backscattered diffraction (EBSD). The relationship between the volume fraction of retained austenite, the carbon in retained austenite and the mechanical properties of 22MnB5 steel treated by onestep Q&P process were analyzed. The results show that an ultrahighstrength 22MnB5 steel sheet with tensile strength over 1400 MPa and elongation over 15% can be obtained using the onestep Q&P process. As the quenching temperature is increased from 240 ℃ to 300 ℃, the microstructure of 22MnB5 steel can be changed from martensite to martensite+retained austenite complex, and the volume fraction of retained austenite in the specimen is increased gradually. With extending partitioning time at the same partitioning temperature, the volume fraction of retained austenite increases first and then decreases. The average carbon content in retained austenite under different heat treatment processes is 1.49wt%. The onestep Q&P heat treatment process can enrich carbon in the retained austenite, improve the stability of the retained austenite, and the product of strength and elongation can reach 22.14 GPa·%.

Key words: 22MnB5 steel, one-step Q&P process, retained austenite, product of strength and elongation, EBSD