40Cr商用车前轴早期断裂失效分析

Early failure analysis of 40Cr commercial vehicle front axle

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 analysis the early failure phenomenon of 40Cr commercial vehicle front axle ,the failure model was identified through macro and micro analysis .Metallurgical structure examination ,mechanical testing and stress analysis were carried out to find out the cause of the fractured fragments .The results show that the fracture mode of the front axle is typical intergranular brittle fracture .The cooling rate in the center of neck section was slow when quenching ,and a lot of network ferrite and coarse acicular martensite precipitated .And the tempering in this region was not sufficient ,and little poor toughness tempered troostite was formed .The mechanical properties in center significantly lower than those in the edge of the neck section were caused by the unreasonable heat treatment .Also ,when the vehicle is traveling ,the original crack was produced in this region subjected to the alternating load .When the vehicle braking ,the shear yield strength is below the allowable shear stress in this region ,and the cracks expanded rapidly ,finally the edge region overload leads to the front axle fracture .