The effects of deep cryogenic treatment in different holding times combined with the traditional HSS heat treatment processes on the microstructure and hardness of M42 HSS were investigated with metallurgical microscope, SEM and Hervey hardness tester. The process included: quenching+deep cryogenic treatment, quenching + deep cryogenic treatment + tempering and quenching + tempering + deep cryogenic treatment. The results have shown that deep cyogenic teatment in 24 h after quenching can obviously refine grain size, improve the hardness of M42 HSS,and significantly promote the transformation of retained austenite to martensite and the precipitation of dispersion distribution carbide, and meanwhile result in the change of the shape of martensite which is different from the conventional heat treatment. Deep cryogenic treatment before tempering can reduce the temperature of secondary hardening, where the peak temperature declined to 450 ℃ compared with 525 ℃ of the process without the deep cryogenic treatment. The hardness of secondary hardening peak is 998. 2HV,which is 5% higher than that of the process without the deep cryogenic treatment. The effect of deep cryogenic treatment after tempering on the micro-structure and the hardness of M42 HSS is not obvious.%采用金相显微镜、扫描电镜及硬度仪,研究了-196℃深冷处理与常规热处理工艺组合对M42高速钢微观组织及硬度的影响,所采用的组合工艺包括:淬火+深冷处理,淬火+深冷处理+回火,淬火+回火+深冷处理.结果表明:淬火后深冷处理24 h的工艺能明显细化晶粒,提高M42高速钢的硬度,促进残余奥氏体向马氏体转变及碳化物析出并弥散分布,并改变了马氏体的形态.在回火前对M42钢进行深冷处理可降低二次硬化回火温度,峰值温度由525℃降至450℃,硬度值为998.2 HV,较未深冷处理提高了5.0％.回火后深冷处理工艺对M42高速钢组织及硬度的影响不明显.
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