某核电厂核级手动截止阀阀杆在运行期间发生断裂。采用宏观观察、化学成分分析、力学性能测试、金相检验、扫描电镜及能谱分析、填料分析等方法，研究了该阀杆断裂的原因。结果表明：该阀杆的热处理工艺控制不当，造成阀杆的耐腐蚀性能变差；在运行过程中，该阀杆接触的填料腐蚀性元素含量较高，在长期承受较高拉应力的环境下，阀杆发生了应力腐蚀断裂。

The valve stem of a nuclear grade manual stop valve in a nuclear power plant fractured during operation. The fracture reasons of the valve stem were studied using methods such as macroscopic observation, chemical composition analysis, mechanical property testing, metallographic examination, scanning electron microscopy and energy spectrum analysis, and filler analysis. The results show that the improper control of the heat treatment process of the valve stem resulted in a deterioration of the corrosion resistance of the valve stem. During operation, the filler in contact with the valve stem had a high content of corrosive elements. Under long-term high tensile stress, the valve stem experienced stress corrosion fracture.