火电机组给水前置泵轴断裂原因分析

某火电厂4号机组B给水前置泵轴投运仅19h即发生断裂。经对断裂泵轴进行宏观分析、化学成分分析、常温力学性能测试、金相检验及断口扫描电镜分析，探讨并明确了泵轴断裂原因，同时提出了防范措施。结果表明：该给水前置泵轴断裂为疲劳断裂，在弯曲及扭转载荷作用下于变截面的应力集中部位的不连续及夹杂物处形成疲劳裂纹，同时大量夹杂物及沿晶分布的粗大a铁素体的存在严重降低了基体强度，使轴体所能承受的循环应力大大降低，即在较低的循环应力作用下疲劳裂纹不断扩展并最终断裂。

Causes Analysis on Cracking of Shaft of Water-feeding Fore Pump of Power Unit

The shaft of B water-feeding fore pump of a power unit fractured after operation only for 19 h. The fracture reasons of the pump shaft were studied by means of macro examination, chemical compositions analysis, room-temperature mechanical properties test, metallographic examination and fracture SEM analysis, and preventive measures were put forward. The results show that the fracture of the pump shaft was fatigue fracture. The fatigue cracks generated from the surface incontinuity and inclusions where stress concentration produced because of variable cross-section,when the pump shaft working under the action of flexural and torsional stress. In the meantime, the strength of the pump shaft was reduced greatly because of lots of inclusions and free α-ferrite. So fatigue cracks spread quickly in low cyclic stress condition and the pump shaft fractured finally.