某热电厂低压转子次末级叶片在使用过程中发生断裂。运用宏观检查、化学成分分析、能谱分析、扫描电镜分析、金相检验和力学性能试验等方法对叶片断裂原因进行了分析。结果表明: 由于叶片进汽侧表面电火花强化层存在较多缺陷, 受恶劣运行工况的影响在应力集中的进汽侧圆角处萌生裂纹;叶片基体材料冲击韧度偏低, 缺口敏感性和脆化倾向高, 促进了裂纹从强化层到基体的扩展;裂纹在机组运行过程中受汽水冲蚀和其他应力作用加速扩展, 最终导致叶片发生疲劳断裂。

The second last blades of low-pressure rotor in a thermal power plant fractured during service. The fracture reasons of the blades were analyzed by means of macroscopic examination, chemical composition analysis, EDS and SEM analysis, metallographic examination and mechanical property test. The results show that there were a lot of defects in the inlet side blade surface electric spark strengthened layer, and cracks initiated from the stress concentrated inlet side leading edge position under the severe operating mode. The low impact toughness and high notch sensitivity and embrittlement tendency of the blade base material promoted the crack propagation from the strengthened layer to the substrate. And the steam flow impact and other stresses action accelerated the growth of the cracks during operation, which led to the fatigue fracture of the blades.