50Mn钢齿圈在使用很短时间后即发生断齿失效，为确定齿圈断裂的原因，对其进行了化学成分分析、宏观检验、硬度测试、断口分析、金相检验。结果表明：该50Mn钢齿圈的化学成分、外径面硬度等指标符合技术协议要求。齿部淬硬层可见多条裂纹，淬硬层深度和表面硬度不均匀，且不符合要求。齿圈齿部断齿是由淬硬层裂纹引起的疲劳开裂，失效原因与其齿部热处理工艺控制不当有关。

The 50Mn steel gear ring suffered broken teeth after a short service time. In order to find out the fracture causes, the gear ring was analyzed from the aspects of chemical composition, macro examination, hardness testing, fracture analysis and metallographic examination. The results show that the indexes of the 50Mn steel gear ring, such as chemical compositions, external surface hardness and so on, were up to the requirements of the technical agreement. There were many cracks in the hardened layer of the Gear. The depth and surface hardness of the hardened layer were not homogeneous, and not in accordance with the standard. The cause of broken teeth of the gear ring was the fatigue cracking caused by cracks in the hardened layer, which was related to improper heat treatment of the gear ring.