经过高频淬火的活塞杆在使用中发生了早期断裂，通过断口的宏观微观分析、化学成分分析、显微硬度分析及显微组织分析，对活塞杆的早期断裂原因进行了分析。结果表明: 活塞杆断裂属于疲劳断裂，表面没有感应淬硬层降低了活塞杆的抗疲劳性能；次表面微裂纹的存在造成了应力集中，从而形成了疲劳源；活塞杆未进行调质处理，心部硬度和强度偏低加速了活塞杆的断裂。

The fracture of the piston rod under high frequency quenching treatment was occurred in the early use. The fracture cause of piston rod was analyzed by means of macroscopic and microscopic fracture ananlysis, chemical composition analysis, micro-hardness analysis and microstructure analysis. The results indicate that the fracture mechanism of the piston rod was fatigue fractue. Without the induction hardening layer, the fatigue resistance of the piston rod was reduced. The stress concentration was induced by the existence of micro-cracks in the subsurface. Thus the fatigue source was formed in the subsurface. Without tempering treatment, the fracture of piston rod was accelerated because of low hardness and intensity of the core area.