The microstructure of 10Ni5CrMoV steel was observed by optical microscopy and the effects of heating temperature, heating time and circular times on grain size were discussed after the steel was heated for different times at 930-1 030℃ and quenched for different circular times, and mechanical properties and fracture morphology before and after heat treatment of the steel were analyzed. The results show that grain size of the steel increased with prolonging of the heating time at different temperatures, the grain size was best when heating time was 100 s. The grain was coarse and heterogeneous when circular times were less than three times, and the refining effect was not obvious when circular times were more than three times. Raising the heating temperature, the grain size decreased and then increased, and it was finest at 950℃. The optimal process of grain refining was heating temperature of 950 ℃, heating time of 100 s and circular quenching times of three times, and the grain could refine from 253μm to 63μm. The strength and ductility could be raised obviously after quenching and temgering.%对10Ni5CrMoV钢在930-1030℃进行不同保温时间、不同次数的循环淬火，采用光学显微镜观察显微组织变化，并探讨了加热温度、保温时间、循环次数对晶粒尺寸的影响，对热处理前后该钢的力学性能和断口形貌进行了分析。结果表明：不同温度下随着保温时间的延长，晶粒尺寸逐渐增大，100S时最佳；循环次数小于3时晶粒粗大且不均匀，大于3时细化效果增加不明显；随加热温度升高，晶粒尺寸先降后增，950℃最细小；细化晶粒的最佳工艺为加热温度950℃、保温100s、3次循环淬火，可使晶粒尺寸由253μm细化至63μm，淬
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