Abstract: Effect of quenching temperature on the mechanical properties and microstructure of 2200 MPa ultra-high strength steel was studied by means of mechanical properties test,optical microscope (OM),transmission electron microscope (TEM),X-ray diffraction (XRD) and other analysis methods.The results show that the optimal quenching temperature of the tested steel is 1025 ℃,so the subsequent heat treatment can obtain the best strength and toughness match:the tensile strength is 2244 MPa,the yield strength is 1836 MPa,the U-notch impact absorbed energy is 59 J,and the fracture toughness is 57.7 MPa·m^1/2.When the quenching temperature is low,coarse primary carbides appear in Mo-rich M₆C carbides,which seriously affect strength and toughness.As the quenching temperature increases,the primary carbide gradually decreases until it completely disappears at 1000 ℃.When the quenching temperature is higher than 1025 ℃,the grains are significantly coarsened,and the grain size becomes the main negative influencing factor.

Key words: 2200 MPa ultra-high strength steel, quenching, mechanical properties, microstructure, M₆C