42CrMoA钢制内齿圈在加工结束后产生了裂纹，采用光学显微镜、扫描电子显微镜和显微硬度计等对裂纹产生的原因进行了分析。结果表明：裂纹的形成是因感应淬火工艺不当造成的，同时钢中还产生了较大的热处理残余内应力，钢中的氢和环境氢会向应力集中严重的淬火裂纹尖端富集，形成局部氢浓度升高，使初始淬火裂纹在残余应力作用下又以氢致延迟性裂纹继续扩展；通过采用正确的热处理工艺，在淬火后及时进行回火以改善淬硬层组织可预防开裂。

The cracks were formed in the inner gear ring made of 42CrMoA steel after processing and the cause of the cracks was analyzed by means of optical microscope, scanning electronic microscope and micro-hardness tester. The results show that the initial cracks were caused by the improper induction quenching process, meanwhile the high residual stress by heat treatment was also produced in the steel. The hydrogen from the inner steel and the environment was accumulated to the quenching crack tips, and then the cracks continued to propagate as hydrogen induced cracks under the high residual stress. The crack prevention method was to adopt the proper heat treatment process of timely tempering after quenching to improve the microstructure of case-hardening zone.