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对断裂的起重机变幅油缸断口进行了宏观分析、扫描电镜观察,并对缺陷处和材料内部进行了组织分析和硬度测试。结果表明,表面存在的焊点使局部淬火得到马氏体组织,疲劳裂纹在此萌生;材料中粗大的魏氏组织促使疲劳裂纹快速扩展,最终导致疲劳断裂失效。
The fractures of crane luffing cylinder were analyzed macroscopically and observed by scanning electron microscope (SEM). The defects and the internal structure of the crane were analyzed by microstructure and hardness. The results show that the welded joints on the surface make the martensitic structure locally quenched, and the fatigue crack initiation occurs here. The coarse Widman’s tissue in the material promotes the rapid expansion of the fatigue crack and eventually leads to the failure of the fatigue fracture.