某电厂磨煤机运行过程中40Cr高强螺栓发生断裂。通过化学成分、硬度和金相检测对螺栓进行了失效分析,并采用扫描电子显微镜对断口形貌进行了观察。结果表明,螺栓断裂属于疲劳断裂,裂纹起源于螺栓头杆结合的R处;螺栓中Cr元素的含量和螺栓硬度均低于标准要求;金相组织中铁素体含量偏高,且螺栓心部的铁素体含量明显多于边缘,说明螺栓的原始热处理未达到要求。 40Cr high strength bolts break down during the operation of a coal mill. The failure analysis of the bolt was carried out by chemical composition, hardness and metallographic examination. The fracture appearance was observed by scanning electron microscope. The results show that the fracture of the bolt belongs to the fatigue fracture, and the crack originates at the R joint of the bolt head and rod. The content of Cr and the hardness of the bolt in the bolt are lower than the standard requirements. The ferrite content in the microstructure is high, Ferrite content was significantly more than the edge, indicating the original bolt heat treatment did not meet the requirements.