深冷处理对渗碳齿轮钢微观组织和硬度的影响

Effect of cryogenic treatment on microstructure and hardness of carburized gear steel

通过金相显微镜、X射线衍射仪、EBSD、维氏硬度计等手段,对20Cr2Ni4A及17Cr2Ni2MoVNb两种渗碳齿轮钢渗碳层组织及硬度进行表征,研究了深冷处理对试验钢微观组织及硬度分布的影响。结果表明,-75℃冷处理后两种试验钢的渗碳层最高硬度增加较明显,经-196℃深冷处理后试验钢的渗碳层硬度进一步增加不明显。20Cr2Ni4A钢及17Cr2Ni2MoVNb钢渗碳层残留奥氏体含量经-75℃冷处理后从34%和25%分别下降至19%和20%,-196℃深冷处理后进一步分别下降至11%和13%。20Cr2Ni4A钢中大尺寸残留奥氏体更多,冷处理后残留奥氏体含量下降趋势更明显,大尺寸残留奥氏体对渗碳层硬度有显著影响。

Microstructure and hardness of 20Cr2Ni4A and 17Cr2Ni2MoVNb carburized gear steels were characterized by means of metallographic microscope,X-ray diffractometer,EBSD and Vickers hardness tester,and the effect of cryogenic treatment on microstructure and hardness distribution of the tested steels was studied.The results show that the maximum hardness in the carburized layer of the two tested steels increases obviously after cold treatment at-75℃,and it increases a little further after cryogenic treatment at-196℃.After cold treatment at-75℃,the contents of retained austenite in the carburized layers of the 20Cr2Ni4A and 17Cr2Ni2MoVNb steels are decreased from 34%to 19%and 25%to 20%,respectively,and they are further decreased to 11%and 13%after cryogenic treatment at-196℃.There is a more amount of large-sized retained austenite in the 20Cr2Ni4A steel,which is decreased more easily after cryogenic treatment.Large-sized retained austenite has a significant effect on hardness of the carburized layer.