某核电厂安全喷淋泵外筒体与底板连接螺柱在安装完成后断裂，采用宏观观察、化学成分分析、力学性能测试、金相检验、扫描电镜和能谱分析等方法对该螺柱的断裂原因进行分析。结果表明：断裂螺柱氢元素质量分数高达0.000 46%，其室温下屈服强度和抗拉强度分别为970 MPa和1 200 MPa；断口洁净且较平齐，无明显塑性变形，断口表面呈结晶颗粒状，启裂区有沿晶特征，晶面上有爪状纹，断裂性质属于典型的氢致延迟断裂；金相检验发现断裂螺柱心部存在偏析缺陷，导致氢元素在缺陷处扩展和聚集，加快了螺柱的断裂速率。

The connecting stud between the outer cylinder and the bottom plate of the safety spray pump of a nuclear power plant fractured after installation. The fracture causes of the stud were analyzed by means of macroscopic observation, chemical composition analysis, mechanical property test, metallographic examination, scanning electron microscope and energy spectrum analysis. The results show that the mass fraction of hydrogen in the fractured stud was as high as 0. 000 46%, and the yield strength and tensile strength at room temperature were 970 MPa and 1 200 MPa, respectively. The fracture was clean and relatively flat, without obvious plastic deformation. The fracture surface was crystalline granular, the crack initiation zone had intergranular characteristics, and there were claw-like lines on the crystal plane. The fracture property belonged to typical hydrogen-induced delayed fracture. Metallographic examination showed that there were segregation defects in the core of the fractured stud, which led to the expansion and aggregation of hydrogen elements at the defects and accelerated the fracture rate of the stud.