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应用扫描电子显微镜、光学显微镜、直读光谱仪、硬度计和冲击试验机,对铁路用20MnTiB钢高强螺栓断裂件的断口微观形貌、显微组织、化学成分、硬度和冲击性能进行了检验分析。结果表明,高强度螺栓的螺纹齿底存在折叠缺陷,产生较大应力集中。在裂纹尖端形成的应力集中和露天工作环境的共同作用下,螺栓发生应力腐蚀开裂。同时,螺栓的热处理工艺不当,在螺纹表面产生增碳现象,促进了初始裂纹的萌生。建议螺栓生产企业改进热处理工艺和螺纹滚丝工艺,避免产生增碳现象和齿底折叠缺陷。
The fracture microstructure, microstructure, chemical composition, hardness and impact properties of 20MnTiB steel high-strength bolt were analyzed by scanning electron microscope, optical microscope, direct reading spectrometer, hardness tester and impact tester. The results show that there are folding defects in the tooth bottom of the high strength bolts, resulting in greater stress concentration. Under the combined effect of stress concentration at crack tip and open-air working environment, stress corrosion cracking occurs in the bolt. At the same time, the bolt heat treatment process improperly generated in the thread surface carbon phenomenon, and promote the initiation of the initial crack. It is suggested that the bolt manufacturers improve the heat treatment process and the thread rolling process to avoid the phenomenon of carbon increase and the tooth bottom folding defect.