某油井在施工过程中，27/8" Y8变31/2" Y8的悬挂短节发生了断裂。采用宏观观察、化学成分分析、力学性能试验、金相检验、扫描电镜及能谱分析等方法对悬挂短节的断裂原因进行了分析。结果表明：该悬挂短节由于材料热处理不当，显微组织异常，在外部应力的作用下发生了早期疲劳断裂。

During the work process of an oil well, the hanging sub joint of 27/8" Y8 changing 31/2" Y8 fractured. The fracture causes were analyzed by means of macroscopic observation, chemical composition analysis, mechanical property test, metallographic examination, scanning electron microscope and energy spectrum analysis and so on. The results show that the microstructure of the hanging sub joint was abnormal due to improper heat treatment, so early fatigue fracture occurred under the action of external stress.