挖掘机用直线行走阀芯表面采用渗碳淬火工艺，服役一段时间后，阀芯中部油孔位置处发生疲劳断裂。通过宏观观察、扫描电镜和能谱分析、金相检验、硬度试验等方法分析了阀芯断裂的原因。结果表明：阀芯的失效形式为拉-压载荷作用下的低应力高周疲劳断裂；断裂主要与设计不当造成的油孔边缘棱角效应、异常打磨产生的表面损伤和渗碳不良形成的网状碳化物有关；通过有限元仿真计算发现，横向载荷对油孔处应力的大小和分布影响显著，边缘倒角可有效降低棱角处的应力集中程度和减轻尖角效应。

Surface of straight-line walking spool for excavator adopted carburization-quenching treatment, after service for a period of time, fatigue fracture occurred at oil holes. Through Macro observation, scanning electron microscopy and energy spectrum analysis, metallographic examination and hardness test and other methods, the reason for spool fracture were analyzed. The results showed that the failure form of spool was low-stress and high-cycle fatigue fracture under tension-compression load. The fracture was mainly related to sharp corner effect of hole edge caused by improper design, the surface damage caused by abnormal grinding and network carbide formed by poor carburization. Through finite element simulation, it was found that transverse load had a significant effect on the size and distribution of stress at circular hole. The edge rounding could effectively reduce stress concentration and reduce sharp corner effect.