起落架40CrNi2Si2MoVA钢螺桩断裂分析

起落架40CrNi2Si2MoVA钢螺桩在安装一段时间后发生了断裂。为确定螺桩断裂的原因，对断裂螺桩断口宏微观形貌、断裂螺桩及对比件的氢含量、材料的性能以及表面损伤等因素进行了检查，并对电镀工艺进行了评定。结果表明，裂纹主要起源于第一螺纹根部的机械损伤部位，源区以沿晶断裂特征为主，断裂件含氢量较高。综合分析认为。螺桩断裂性质为氢致延迟断裂，表面机械损伤对氢吸收和扩散的促进作用和40CrNi2Si2MoVA钢材料高强度所致的高氢脆敏感性是导致断裂的主要原因。

Fracture Analysis on a Landing Gear Dowel of 40CrNi2Si2MoVA Steel

A 40CrNi2Si2MoVA dowel fractured after assembly. In order to find out the fracture reason, mechanical property testing, macro and micro inspection of the fracture surface, hydrogen content testing of the fractured and contrast dowels and inspection of the surface damage were carried out. Qualification test of the electric plating process was also conducted. The results show that the crack mainly initiated from the surface mechanical injury region at the bottom of the first screw thread. The crack propagated along the grain boundary in the source region; the hydrogen content of the fractured dowel is higher than that of others. It is concluded that the fracture mode of the dowel is hydrogen induced delayed fracture. The main causes for hydrogen brittleness are the promotion of the surface mechanical injury to the absorption and diffusion of hydrogen and the high hydrogen brittleness sensitivity of 40CrNi2Si2MoVA steel.