针对某汽车变速箱输出轴断裂失效问题, 运用失效分析方法, 开展了宏观痕迹分析、断口分析、化学成分分析、金相检验, 硬度测试及氢含量测定。结果表明：汽车变速箱输出轴断裂为延迟断裂, 输出轴尾部螺纹处表面渗碳层较高硬度的回火马氏体组织为延迟断裂提供“必要条件”, 这与螺纹处局部处理工艺的控制不合理相关; 一定的外加静拉应力、自身残余应力和氢含量为延迟断裂的“充分条件”。最后提出了改进与预防措施。

Aiming at the fracture failure of an automobile gearbox output shaft, the failure analysis was done to the output shaft through macroscopic trace analysis, fracture analysis, chemical composition analysis, metallographic examination, hardness test and hydrogen content test. The results show that the fracture of the gearbox output shaft was a kind of delayed fracture. The tempering martensite structure with high hardness of the carburized layer in the threaded end of the output shaft provideds ‘necessary condition’ for the delayed fracture, which was caused by the inappropriate local processing of the screw thread. And a certain foreign static tensile stress, its own residual stress and hydrogen content provided ‘sufficient condition’ for the delayed fracture. Finally, some improving and preventive measures were put forward.