为探讨40Cr商用车前轴在装车后早期出现断裂失效现象,通过对断口进行宏、微观分析,确定该断裂属于典型晶间脆性断裂。结合金相组织检查、力学性能测试与应力分析探讨了断裂原因,一是由于前轴锻后淬火时,颈部截面心部冷却速度较慢,析出大量网状铁素体与粗大针状马氏体,并且该部位回火不充分,形成少量韧性较差的回火托氏体,不合理的热处理工艺导致颈部截面心部区域力学性能明显低于边缘区域;二是由于车辆行驶时,该处在交变载荷的作用下产生原始裂纹,当车辆制动时,此处实测剪切应力低于许用剪切应力,导致心部裂纹迅速扩展,最终边缘区域过载导致前轴断裂。 In order to investigate the fracture failure of 40Cr commercial vehicle front axle after loading, macroscopic and microscopic analysis of the fracture shows that the fault belongs to typical intergranular brittle fracture. Combining the metallographic examination, mechanical property test and stress analysis, the causes of fracture are discussed. First, when the front axle is forged and quenched, the core part of the neck has a slower cooling rate. A large amount of meshed ferrite and coarse needle- Body, and the tempering of the site is not sufficient, the formation of a small amount of poor toughness of the tempering, unreasonable heat treatment process led to the neck section of the core area of ​​the mechanical properties were significantly lower than the edge area; second is due to vehicle driving, the Under the action of alternating load, the original crack is generated. When the vehicle is braked, the measured shear stress here is lower than the allowable shear stress, resulting in the rapid expansion of the heart crack and eventually leading to the rupture of the front axle.