The bolt of tower crane was suddenly fractured after operating for one year. By analysis the chemical composition,mechanical properties, microstructure, impurity and pattern of fracture, the analysis shows that the grade of impurity exceeds the application criterion, the finish of the bolt face is not good, heat treated technology is irrationality, dehydrogenization treating could meet the technology require, these lead the bolt broken under the al-ternate load. At the same time, the relevant improving measures are put forward.%某塔吊服役仅一年,塔吊螺栓就发生突然断裂.通过对断裂螺栓的化学成分、机械性能、金相组织、夹杂物及断口形貌等方面的分析,表明螺栓的夹杂物等级超标、表面光洁度较差、热处理工艺不合理,以及没有很好地去氢处理,造成了塔吊螺栓在交变载荷作用下的脆性断裂.同时也提出改进意见.
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