某企业新氢压缩机组一级缸端盖螺栓发生断裂。结合螺纹加工工艺，对螺栓断口宏观形貌、材料化学成分、显微组织、微观形貌等展开分析。结果表明：螺栓材料内部和螺纹加工面夹杂较多，在冷滚压加工过程中导致螺纹加工表面产生开裂，齿根处微裂纹在交变作用力下引起疲劳裂纹扩展，最终导致整个螺栓断裂。

The cylinder cover bolt of a make-up hydrogen compressor in an enterprise suddenly fractured. Combined with the thread processing technology, a series of analyses were conducted on the cracked bolt, including macro morphology observation, chemical composition analyses, microstructural examination and micro morphology observation. The results showed that, due to the large number of inclusions inside the bolt material and thread surface, microcracks on the thread surface were generated during the thread machining process. The bolt final fracture was due fatigue extension of microcracks in root to caused by alternate stress.