某电站稳压器支承裙座锚固螺栓在安装一段时间后发生断裂，从力学和材料角度对该螺栓断裂原因进行了分析。对断裂螺栓进行了金相组织观察、化学成分分析、力学性能试验以及断口的宏观及微观形貌观察，发现螺栓断口附近组织异常，外部环状带晶粒粗大，硬度和抗拉强度偏低导致裂纹启裂，裂纹逐渐扩展引起螺栓整体失稳断裂；螺栓局部出现组织异常的原因为螺栓热处理过程中控温不当导致局部过热。

A fasten bolt of the stabilizer of a nuclear power plant was found fractured during the onsite inspection after installation. The fracture failure analysis was performed according to the examination of the material and mechanical properties of the bolt. The microstructure, chemical compositions, mechanical properties and fracture surface were examined to investigate the root causes of the failure. Abnormal microstructure was found near the outer side at the fracture initiation position with lower micro hardness and strength which resulted in the initiation of cracks, and the bolt fractured for the cracks propagation. The abnormal microstructure was caused by the local high temperature during the heat treatment process.