35CrMo汽车凸轮轴的综合检测与断裂失效行为研究

Study on Comprehensive Inspection and Fracture Failure of Automobile Camshaft

采用金相显微镜、扫描电子显微镜、拉伸力学性能测试等方法,对某型号汽车断裂凸轮轴进行了显微组织、断口形貌和力学性能检测,讨论了汽车凸轮轴发生断裂的原因。结果表明,断裂汽车凸轮轴的化学成分、室温拉伸力学性能和冲击性能符合标准要求;断裂凸轮轴的基体组织为回火索氏体+铁素体;凸轮轴在最后一次失稳断裂前已经存在3 mm深的疲劳裂纹,较大的应力作用和疲劳裂纹形成的尖端应力集中,是凸轮轴发生快速失稳断裂的原因;凸轮轴的疲劳裂纹起始于螺纹根部,超出材料疲劳极限的较大应力作用和螺纹表面存在加工缺陷,是导致凸轮轴从螺纹根部发生疲劳开裂的原因。

By means of metallographic microscope, scanning electron microscope and tensile mechanical property test, the microstructure and fracture morphology mechanical properties of the fracture camshaft of 35CrMo steel were examined, the reasons for the fracture of automobile bolts were inrestigated. The results show that the chemical composition, room temperature tensile mechanical properties and impact properties of the fracture camshaft meet the standard requirements. The structure of the fracture camshaftis is composed of tempered ferrite and ferrite. The fatigue crack about 3 mm exists before the last unstable fracture of the bolt, and the larger stress and the stress concentration of the fatigue crack are the reasons for the rapid failure of the bolt. The fatigue crack initiation of the camshaft is at the root of thread, the larger stress beyond the fatigue limit of the material and the processing defect on the surface of the thread are the causes of the fatigue cracking of the bolt.