Abstract: In order to explore optimum heat treatment process of 30Cr16Mo1VN steel, the effect of quenching and tempering temperatures on the microstructure and mechanical properties was studied by impact and tensile tests, Rockwell hardness test, OM, SEM, XRD and TEM. The results show that the optimum austenitizing temperature for quenching of the steel is 1050 ℃, at which there are a small amount of M₂₃C₆ carbide and M₂N nitride to hinder the grain boundary migration in quenching, and the average grain size of prior austenite is 14.1 μm. However, most of the carbide and nitride are dissolved into the matrix, resulting in lowering of the Ms point and increasing the content of retained austenite up to 59.2%. After cryogenic treatment at -73 ℃, a large amount of retained austenite is quenched into martensite, and the hardness of the steel is increased to 57 HRC. After tempering at 300 ℃, the steel has a good match of strength and toughness, with the tensile strength and the area reduction up to 2030 MPa and 10.0% respectively. The tempering leads the matrix to recover and the dislocation density to decrease, while as the tempering temperature rises, the dispersed fine spherical carbide precipitates in the matrix to hinder the movement of dislocations and produce secondary hardening, and the hardness peak appears when tempering at 450 ℃. When the tempering temperature is lower than 500 ℃, the hardness is always greater than 55 HRC, the steel has good tempering resistance.

Key words: 30Cr16Mo1VN steel, quenching temperature, retained austenite, tempering temperature, hardness peak