某电厂核级手动截止阀阀杆(材质为17-4PH马氏体不锈钢)运行约6 a后，发生断裂，通过宏观检查、化学成分分析、力学性能测试等分析了失效原因。结果表明:基体材料晶界粗化，在海水系统中，阀杆表面出现较多点蚀坑，点蚀和晶间腐蚀的共同作用最终导致阀杆断裂；材料在海水环境中不耐蚀以及热处理工艺不当是引发阀杆断裂的主要原因。

The stem of a nuclear-grade manual globe valve in a power plant (made of 17-4PH martensitic stainless steel) was broken after running for about 6 years. The reasons for the failure were analyzed through macro inspection, chemical composition analysis, and mechanical performance testing. The results showed that the grain boundaries of the matrix material were coarsened, and in the seawater system, more pitting pits appeared on the surface of the valve stem, and the combined action of pitting corrosion and intergranular corrosion eventually led to the fracture of the valve stem. Inadequate corrosion resistance of the material in seawater environment and improper heat treatment process were the main reasons for valve stem fracture.