SWRCH22A钢螺钉在低于设计载荷下发生断裂，采用断口形貌、显微组织观察，硬度、镀锌层厚度测试及有限元仿真等方法，对其断裂原因进行分析。结果表明：该螺钉的断裂性质为氢脆断裂。热处理后螺钉形成了具有较强氢脆敏感性的回火马氏体组织；在后续镀锌或服役过程中，氢原子进入螺钉内部；在服役载荷作用下，螺头及附近螺纹根部产生应力集中，氢原子向应力集中处聚集，导致裂纹萌生和扩展，最终螺钉在应力集中最大的第一扣螺纹根部断裂。

SWRCH22A steel screws fractured below the design load. The fracture cause was studied by fracture morphology and microstructure observation, hardness and galvanized thickness test, finite element simulation, and so on. The results show that the fracture characteristic of the screw was hydrogen embrittlement fracture; A tempered martensite structure with strong hydrogen embrittlement sensitivity was formed in the screw after heat treatment. The hydrogen atoms entered the screw structure during the galvanizing or service process. Under effects of service loads, stresses were concentrated in the screw head and thread root, and hydrogen atoms gathered at stress concentration, leading to crack initiation and propagation. Finally, the screw fractured at the root of the first thread where stress concentration was the largest, leading to crack initiation and propagation, and finally fracture.