某公司生产的水泵叶轮轴在服役半年多后发生断裂，采用宏观观察、化学成分分析、低倍检验、扫描电镜分析、金相检验、硬度测试等方法分析其断裂原因。结果表明：该叶轮轴在制造过程中的调质处理工艺不符合要求，使叶轮轴表面形成大量脆性较大、硬度较低的贝氏体组织，加上断裂源位于叶轮轴工艺退刀槽处，而退刀槽已经将淬硬层全部车削，进一步降低了轴的表面强度，在退刀槽处容易形成应力集中；叶轮轴在运转时受较大的扭转力作用，其表面容易形成疲劳裂纹，随着裂纹扩展，水泵叶轮轴最终发生断裂。

The impeller shaft of a water pump produced by a company broke after more than half a year of service. The causes of fracture were analyzed by means of macroscopic observation, chemical composition analysis, macroscopic examination, scanning electron microscope analysis, metallographic examination and hardness test. The results show that the quenching and tempering treatment process of the impeller shaft in the manufacturing process did not meet the requirements, so that a large number of bainite structures with high brittleness and low hardness were formed on the surface of the impeller shaft. In addition, the fracture source was located at the retreating groove of the impeller shaft process, and the retreating groove had turned all the hardened layer, which further reduced the surface strength of the shaft and was easy to form stress concentration at the retreating groove. The impeller shaft was subjected to a large torsional force during operation, and fatigue cracks were easy to form on its surface. With the crack propagation, the pump impeller shaft finally broke.