某车辆差速器行星齿轮在运行过程中发生早期断裂。采用宏观观察、化学成分分析、硬度测试、金相检验和断口分析等方法分析了行星齿轮断裂的原因。结果表明：齿轮内的黄铜衬套与齿轮内壁发生摩擦，导致齿轮内壁磨损擦伤，擦伤区域产生应力集中使齿轮发生疲劳断裂。建议加强检查齿轮的润滑状况、安装过程、齿轮与黄铜衬套之间是否有异物卷入，以避免齿轮发生异常摩擦。

An early fracture occurred in the differential planetary gear of a vehicle during operation. The causes of planetary gear fracture were analyzed by means of macroscopic observation, chemical composition analysis, hardness test, metallographic examination and fracture analysis. The results show that the brass bushing in the gear had friction with the inner wall of gear, resulting in wear and abrasion of the inner wall of gear, and the fatigue fracture of gear was caused by stress concentration in scratch area. It is suggested that the abnormal friction of the gear should be avoided by checking the lubrication condition of the gear, the installation process, and whether there was foreign matter involved between the gear and the brass bushing.