在断路器1 000～2 000次机械操作试验中，30CrNi3合金钢渗氮轴销发生断裂。通过化学成分分析、断口分析、低倍检验、金相检验、力学性能测试的方法，对轴销的断裂原因进行了分析。结果表明：该轴销的断裂性质为双向弯曲疲劳断裂；轴销材料渗氮层存在脉状氮化物，内部存在疏松、大尺寸夹杂物和气泡缺陷，降低了材料的力学性能；在周期性旋转弯曲力作用下，轴销表面缺陷处出现裂纹并不断扩展，最终导致轴销疲劳断裂。

The 30CrNi3 alloy steel nitride axis pin fractured during mechanical operational testing of the breaker for 1 000-2 000 times. The fracture reasons of the axis pin were analyzed by chemical composition analysis, fracture analysis, macro examination, metallographic examination and mechanical property testing. The results show that:the fracture property of the axis pin was the biaxial bending fatigue fracture; veined nitrides existed in the nitride layer of the axis pin material, and interior defects such as porosity, large-scale inclusions and bubbles also existed, which reduced the mechanical property of the material; under the action of periodic rotating bending force, cracks appeared on the position of surface defects and constantly extended, and finally resulted in the fatigue fracture of the axis pin.