Abstract:
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.