通过对发生断裂失效的给水三通阀阀杆进行宏观检查、化学成分分析、拉伸试验、冲击试验、金相检验和硬度试验, 分析了其断裂原因。结果表明: 阀杆断裂为疲劳断裂, 阀杆断裂的主要原因是表面渗氮处理增加了阀杆与阀芯表面相交处的脆性, 加上阀杆与阀芯表面相交的位置结构突变造成应力集中, 在流体的长期挤压和剪切力作用下, 便会在应力集中部位的渗氮层中形成裂纹源, 并在阀杆服役时的交变应力的作用下, 裂纹从渗氮层逐步扩展到阀杆基体, 最终导致阀杆断裂失效。

Macro examination, chemical composition analysis, tensile test, impact test, metallographic examination and hardness test were performed on a fractured water supply three-way valve stem to find out its fracture failure reasons. The results show that the fracture of the valve stem was fatigue fracture. The main reason for the fracture was that the nitriding process increased the brittlement of the changeable cross-section position of stem and stem core, and the structure change of stem and stem core caused stress concentration, thus forming a crack source when the stem was extruded and sheared with fluid. Under the action of alternating stress during service of the valve stem, the formed crack gradually extended from the nitriding layer to the valve stem base material, which led to the eventual fracture of the valve stem.