某矿用卡车前悬挂油缸活塞杆在服役时发生断裂。采用宏观观察、化学成分分析、力学性能测试、断口分析以及金相检验等方法对该活塞杆断裂原因进行分析。结果表明：该活塞杆热处理工艺不当导致表面形成感应淬火裂纹，在恶劣的服役环境下，活塞杆表面裂纹尖端开始形成疲劳裂纹并向内扩展。当疲劳裂纹扩展到一定程度时，活塞杆所受载荷超过其承载力，最终导致其瞬间断裂。

The front suspension cylinder piston rod of a mine truck fractured during service. The fracture cause of piston rod were analyzed by means of macroscopic observation, chemical composition analysis, mechanical property test, fracture analysis and metallographic examination. The results show that the improper heat treatment process of the piston rod led to the induction quenching crack on the surface, fatigue crack was formatted from surface crack tip to interior when piston rod worked under hostile service condition. When the fatigue crack propagated to a certain extent, the load on the piston rod exceeded its bearing capacity and eventually led to its instantaneous fracture.