高强度螺栓断裂分析

Analysis on High-strength Bolt Fracturing

10件35CrMo钢高强度螺栓在使用过程中全部断裂。对断裂的螺栓进行了宏观检验和化学成分分析,检测了表面和截面硬度及微观组织。结果表明:螺栓的化学成分和硬度均符合要求,但螺纹根部存在滚压加工时产生的折叠,且螺纹表面有因热处理不良造成的16~20μm厚的脱碳层,正是这些缺陷导致螺栓疲劳断裂。

10 high-strength bolts made from 35CrMo steel all broke in service.The broken bolt was subjected to macro-examnination,chemical composition analysis,surface and section hardness measurements and microstructuresurvey.The results demonstrated that the chemical composition and the hardness of the bolt were conformed with the requirements,however,folds which dev eloped during thread rolling were present in the thread root,and there was decarburized layer as thick as 16 to 20μm which arose from fault in heat treating in the thread.It is these defects that cause the fatigue fracture of the bolt.