某水电站水轮机制动器闸板螺栓发生断裂，通过宏观观察、断口微观分析、化学成分分析、金相检验及硬度测试等方法对螺栓的断裂原因进行了分析。结果表明：螺栓的螺纹表面存在折叠和微裂纹等加工缺陷，应力在该处集中；且生产过程中热处理工艺控制不当，螺栓显微组织不是调质组织，且存在魏氏组织，使螺栓力学性能下降；当受到较大冲击力时，裂纹从加工缺陷处起裂并迅速扩展，导致螺栓断裂。

The bolts for hydraulic turbine brake of a hydropower station fractured. The fracture causes of the bolts were analyzed by macro observation, micro analysis of fracture surface, chemical composition analysis, metallographic examination, hardness test and so on. The results show that there were some processing defects such as folding and micro cracks on the thread surface of the bolts, where the stress was concentrated. And the improper control of heat treatment process in the production process, the microstructure of bolts is not tempered micro structure, and there is Widmanstatten structure, which reduced the mechanical properties of bolts. When subjected to large impact force, the crack initiated from the processing defects and propagated rapidly, led to fracture of the bolt.