风力发电机组用变桨轴承外圈在使用一段时间后发生断裂，通过宏观检查、化学成分分析、力学性能测试、断口形貌和显微组织观察等方法分析了断裂原因。结果表明：轴承外圈断裂性质为疲劳断裂；螺栓孔内表面在腐蚀介质作用下产生点蚀坑，形成应力集中点，在较大外力作用下，在应力集中明显的点蚀坑处萌生裂纹并诱发疲劳断裂。

Outer ring of a pitch bearing in a wind turbine generator fractured when used for a period of time. The reason for the fracture was analyzed by methods such as macro-inspection, chemical composition analysis, mechanical property test, fracture morphology and microstructure observation. The results show that the bearing outer ring fractured in a fatigue mode. Pits on inner surface of the bolt hole were generated by corrosive mediums, resulting in stress concentration points. By a relatively large external force, the cracks originated at the pits where existing obvious stress concentration, and consequently led to fatigue fracture.