Effect of Tempering Temperature on Microstructure and Mechanical Properties of 35CrMo Steel

35CrMo steel was quenched at 860 ℃ and then tempered at different temperatures (450, 500, 550, 600 ℃). The effect of tempering temperature on microstructure, tensile properties and fracture toughness was studied by universal testing machine and scanning electron microscope. The results show that with the increase of tempering temperature, the carbides precipitated from supersaturated α phase and were sphericized, and the lath feature of martensite disappeared gradually. The tensile strength and yield strength of the tested steel both decreased,while the elongation increased with the increase of tempering temperature. The tensile strength, yield strength and elongation of the tested steel tempered at 600 ℃ were 1 014 MPa, 933 MPa and 16.8%, respectively. With the increase of tempering temperature, the fracture toughness of the tested steel increased, and the fracture initiation zone changed from rapid crack initiation and propagation characteristics to more obvious plastic deformation characteristics.