Abstract: When high-speed electric multiple units were overhauled after driving for 12×10⁵ km, it was found that cracks appeared in the joint of the non-transmission end caps and the shell of the sensor. The causes of cracking were analyzed by means of macroscopic observation, X-ray examination, residual stress test, fracture macro and micro analysis, energy spectrum analysis, metallographic examination, chemical composition analysis, tensile test and so on. The results show that the end caps were overheated during the solid solution heat treatment process, and the intergranular cracking was caused by the later processing stress. Finally, some suggestions on process improvement were put forward.