材料为ML30CrMnSiA钢的十字槽沉头螺钉在初次装配过程中发生批量断裂失效，通过宏观观察、化学成分分析、力学性能试验、金相分析、断口扫描电镜及能谱分析、氢含量测定等方法对螺钉断裂原因进行了分析。结果表明：螺钉头部的十字槽底部在冷镦或热处理过程中产生微裂纹，在酸洗、镀镉等工序中，氢沿微裂纹渗入基体，加之螺钉强度偏高，超过设计要求，从而导致螺钉发生氢脆开裂并扩展，实际承载面积降低，最终在装配应力作用下发生断裂失效。

Batch fracture failure happened to ML30CrMnSiA steel cross recessed countersunk flat head screws during initial assembly. The fracture reasons of the screws were analyzed by means of macro observation,chemical composition analysis, mechanical property test, metallographic analysis, fracture SEM and EDS analysis, hydrogen content determination and so on. The results show that micro cracks formed at the bottom of the screw head cross recess during cold heading or heat treatment. In the process of acid pickling and cadmium plating, hydrogen penetrated into the matrix along the micro cracks. In addition, the strength of the screws was higher than the design requirements. So hydrogen embrittlement cracking occurred. With the propagation of the cracks, the actual loading area of the screw decreased, and finally the screw fractured under the action of assembly stress.