某电厂一台给水泵发生轴断裂事故。通过断口宏观及微观分析、化学成分分析、力学性能测试及金相检验等，对水泵轴断裂的原因进行了分析。结果表明：断裂泵轴存在魏氏组织、网状铁素体以及沿晶界分布的屈氏体等组织缺陷，材料的强度和韧性不足，使其在密封槽应力集中区产生裂纹；在交变应力的作用下，泵轴发生疲劳开裂；给水泵在运行时出现气蚀，也加速了泵轴的断裂。

A fracture fault occurred to a water pump shaft in a power plant. The fracture reasons of the water pump shaft were analyzed by methods of macroscopic and microscopic analysis of the fracture surface, chemical composition analysis, mechanical property testing, metallographic inspection and so on. The results show that:the microstructure defects, such as widmanstatten structure, reticulate ferrite and troostite distributed along the grain boundaries, existed in the fractured pump shaft, and the insufficient strength and toughness caused cracks in the sealing groove where the stress concentrated; under the action of alternating stress, fatigue cracking occurred to the shaft; the cavitation of the water pump accelerated fracture of the pump shaft during use.