Abstract: The rod of the housing of the constant-velocity drive shaft fractured while a new car was tested. The chemical compositon, non-metallic inclusions, microstructure, hardness, residual stress, and fracture morphology of the fracture of rod were analyzed by macro and micro observation, metallographic examination, physical and chemical testing. The results show that the fracture of the rod is brittle fracture. The chemical composition, non-metallic inclusions, and microstructure of the rod are all in accordance with the technical requirements, but the surface hardness is overhigh. The analysis result indicates that the lower tempering temperature resulted in the greater residual stress in the part, and thus cracks initiated in the hardening layer under the effect of straightening stress. Finally, the rod fractured during testing. Accordingly, a temperature sensor was used to monitor the tempering temperature to ensure that the workpieces were completely tempered. In addition, the straightening process was improved to avoid stress cracking.