中文摘要：

某柴油机用30CrMoSi钢高强度螺栓在使用过程中发生断裂。通过化学成分分析、金相检验、断口分析、硬度测试等方法对螺栓断裂原因进行了分析。结果表明：螺栓断裂为早期疲劳断裂,螺栓螺纹根部存在加工缺陷以及螺栓材料中存在较多的非金属夹杂物是导致其疲劳断裂的主要原因。最后针对螺栓断裂原因提出了预防措施。

英文摘要：

High strength bolts with material of 30CrMoSi steel used for diesel engine fractured during service, and the fracture reasons were analyzed by means of chemical composition analysis, metallographic examination, fracture analysis and hardness test. The results show that the fracture of the bolt was early fatigue fracture, and machining defects at the screw root and more inclusions in the material were main reasons for the fatigue fracture. Finally, prevention measures were put forward for the fracture reasons.