某核电厂不锈钢螺栓发生开裂，采用光学显微镜、扫描电镜和透射电镜等方法对开裂螺栓的组织形貌、断口形貌和位错结构进行观察，分析螺栓开裂的原因。结果表明：断口存在明显的疲劳条带特征，疲劳条带间距很小，断口附近区域组织错密度较大，并有大量的驻留滑移带形成，远离断口区域组织位错密度较低，没有驻留滑移带形成。结合螺栓的服役条件推断该螺栓的主要失效原因为高周疲劳断裂。

Some stainless steel bolt cracked in a nuclear power plant. The microstructure, fracture morphology and dislocation structure of the cracked bolt were observed by optical microscopy, scanning electron microscopy and transmission electron microscopy. And the reasons for cracking of the bolt were analyzed. The results show that the fracture surface displayed obvious characteristics of fatigue striation, and the space between the fatigue striations was quite small. In the microstructure near the fracture, the dislocation density was high, and lots of persistent slip bands (PSBs) were formed; while in the structure far away from the fracture, the dislocation density was low, and there were no PSBs formed. Considering service conditions of the cracked bolt, it could be concluded that high-cycle fatigue fracture was the main failure reason of the bolt.