35CrMo钢螺栓在使用中发生断裂.为了揭示螺栓断裂的原因,对断裂的螺栓进行了化学成分分析、显微组织检验和力学性能测定.结果表明,螺栓的化学成分、显微组织、氢含量以及夹杂物含量均符合要求,拉伸性能偏低.由断裂螺栓的断口分析发现,大部分螺栓都存在疲劳裂纹,疲劳裂纹均起源于螺纹根部,裂纹端部应力集中是螺栓发生断裂的原因,与偏低的拉伸性能无关.此外,螺纹根部的机加工缺陷也是裂纹源,在周期应力的作用下导致螺栓疲劳断裂.%35CrMo steel bolts fractured in service.The fractured bolts were subjected to chemical composition analysis,microstructural survey,and mechanical property measurements to reveal the reason why the bolts fractured.The results indicated that the chemical composition,microstructure,hydrogen and inclusion contents of the bolts came up to the mark,and that their tensile properties were on the low side.From fracture analysis of the failed bolts it was seen that fatigue cracks that originated from the thread root were present in most of the fractured bolts,which brought about the bolt failure because of stress concentration in crack end,regardless of the lower tensile properties.In addition,machining defect in the thread root also was a crack source that resulted in fatigue failure of the bolts by the action of a cyclic stress.
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