三柱槽壳杆部断裂分析

在新车下线并进行驻车上坡测试时，等速驱动轴的三柱槽壳杆部发生断裂。采用宏观观察、微观分析、金相分析及理化测试分析等试验方法，对该三柱槽壳杆部断口的化学成分、非金属夹杂物、金相组织、硬度、残余应力、断口形貌特征等进行分析。结果表明：三柱槽壳杆部为脆性断裂，杆部断口的化学成分、非金属夹杂物、金相组织均符合技术要求，但其表面硬度值高于技术要求。分析表明回火温度偏低，三柱槽壳回火不充分，工件内部存在较大残余应力，在校直力作用下淬硬层萌生应力裂纹，导致三柱槽壳杆部在使用中断裂。采用温度传感器对回火炉内的回火温度进行实时监测，保证工件回火充分；并改善校直工艺，对校直量过大和校直次数过多的工件予以报废，避免引起应力开裂。

Fracture Analysis of Rod of Housing

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.