某柴油机喷油器的42CrMo合金结构钢螺柱出现早期断裂，通过宏观分析、化学成分分析、硬度测试、金相检验、工艺分析、再回火试验等方法，对螺柱断裂原因进行了分析。结果表明：回火温度过低，显微组织转变不充分，造成螺柱硬度、抗拉强度过高，氢脆敏感性增大，同时螺纹表面质量差加剧了应力集中，两者共同作用导致了螺柱的氢致延迟断裂。

The 42CrMo alloy structural steel studs of a diesel injector appeared early fracture. The fracture causes were analyzed by means of macroscopic analysis, chemical composition analysis, hardness test, metallographic examination, process analysis, re-tempering test and so on. The results show that the tempering temperature was too low, the microstructure transformation was insufficient, which results that the hardness and tensile strength of the studs were too high and hydrogen embrittlement sensitirity increased. At the same time, the poor surface quality of the threads aggravated the stress concentration. The combined action resulted in hydrogen induced delayed fracture of the studs.