Abstract：A company uses Φ150mm specification 20CrMnTiH to produce rear axle driven gear，after using 1～2 months，batch of fracturing damage occurred to the gear. In order to find the cause of gear failure, the failure gear is analyzed. Through the analysis of chemical composition, hardness, metallographic structure, non martensitic structure, effective depth of carburizing and hardening layer and fatigue fracture of different parts of the gear，the failure reason of the gear is that the depth of carburizing hardening layer and non martensitic structure do not meet the standard requirements，decarburization is found around the teeth，the stress caused by the difference of microstructure between decarburized part and non decarburized part and the quenching stress of steel form cracks and cause crack propagation. There are problems in the heat treatment process of the gear, resulting in cracks and fracturing damage to the gear.
2022, Vol. 29 