Abstract:  The effects of tempering at 380 ℃- 620 ℃ on the microstructure and mechanical properties of the double-vacuum smelting secondary hardening steel were studied by optical microscope （OM）， scanning electron microscope （SEM）， X-ray diffractometer （XRD） and tensile test. The test results showed that when tempering at 380 ℃-620 ℃， the matrix of the test steel changes from tempered lath martensite to tempered sorbite with the tempering temperature increasing， while the austenite increases. The tensile strength and yield strength reached their peak value at 440 ℃， which may be related to the increase of the strength of the test steel caused by the precipitation of Fe3C during tempering. The tensile strength and yield strength gradually decreased when tempering at 440 ℃-620 ℃. Elongation and section shrinkage gradually increased. In addition， the fracture form of impact fracture changes from quasi-cleavage fracture to ductile fracture + quasi-cleavage fracture. The comprehensive test results showed that the test steel has the best mechanical properties when tempered at 496 ℃， and can achieve better strength and toughness matching.

Key words: Gear steel, Microstructure, Mechanical Properties, Tempering Temperature

摘要： 采用光学显微镜（OM），扫描电镜（SEM），JMat Pro软件以及拉伸试验等研究了380～620 ℃回火对双真空熔炼的二次硬化钢显微组织及力学性能的影响。试验结果表明，在380～620 ℃回火，试验钢基体组织随着回火温度的升高，由回火板条马氏体转变为回火索氏体，同时奥氏体增多；抗拉强度和屈服强度数值在440 ℃时达到峰值，这可能和回火时析出的Fe3C导致试验钢强度升高有关；在440～620 ℃回火时抗拉强度和屈服强度逐渐下降，伸长率和断面收缩率则逐渐上升。此外，冲击断口断裂形式由准解理断裂向韧性断裂+准解理断裂转变。综合试验结果发现，试验钢在496 ℃回火时，力学性能最佳，可以达到较好的强韧化匹配。

关键词: 齿轮钢, 显微组织, 力学性能, 回火温度