通过宏观分析、显微组织和断口形貌观察以及硬度测试等方法对40Cr钢汽车半轴的断裂原因进行了分析.结果表明:汽车半轴断裂的主要原因是半轴凸缘与杆连接的轴台阶处表面存在脱碳层,在高的扭转疲劳剪切应力作用下形成裂纹源;40Cr钢含有较多的大尺寸非金属夹杂物,另外热处理工艺不当,造成材料综合力学性能达不到要求,使表面萌生的裂纹在应力作用下迅速扩展,造成汽车半轴发生疲劳断裂.

Using macro analysis,the observation of microstructure and fracture morphology and hardness testing,the failure analysis of breaking of 40Cr steel automobile semi-axle was analyzed.The results show that the crack was mainly caused of the decarburized layer on the surface of axial bench connected half shaft flange and rod,the crack initiation was formed under the high torsion fatigue shearing stress.The 40Cr steel contained more non-metallic inclusions,and its mechanical properties could not reach the request as the improper heat treatment process.The fatigue crack formed on the surface extended rapidly under the stress,which resulted in the fatigue fracture.