不均匀组织对高速动车组车轮踏面剥离损伤的影响

Influence of Non-Uniform Microstructure on Shelling Damage of Wheel Tread for High Speed EMU

针对某型动车组车轮踏面出现的剥离损伤,利用光学显微镜、扫描电子显微镜以及透射电镜观察踏面剥离损伤处的组织形貌,发现损伤处存在不均匀组织的特征;借助显微硬度、纳米压痕仪和俄歇探针分别对不均匀组织的微区性能和组织成分进行研究,分析不均匀组织对踏面剥离损伤的影响。结果表明:车轮踏面的剥离属典型的滚动接触疲劳损伤,疲劳裂纹的萌生及扩展主要发生在踏面不均匀组织处;不均匀组织中除存在珠光体和铁素体构成的基体组织外还存在上贝氏体组织,其硬度、弹性均高于基体组织,但塑性小于基体组织;在轮轨接触应力的作用下,使上贝氏体组织与基体组织交界处产生应力集中,进而诱发并促进车轮踏面疲劳裂纹的萌生及扩展,最终形成滚动接触疲劳剥离损伤;不均匀组织的形成是由于车轮中C和V元素偏析所致。

Aiming at the shelling damage of the wheel tread for a certain type of EMU, the morphology of tread shelling damage was observed by optical microscopy, scanning electron microscopy and transmission electron microscopy. It was found that there were non-uniform microstructures in the damage area. The properties and composition of non-uniform microstructures were respectively studied by microhardness tester, nanoindentation instrument and Auger probe, and the influence of non-uniform microstructure on tread shelling damage was analyzed. Results indicate that the shelling of wheel tread is the typical rolling contact fatigue damage. The initiation and propagation of fatigue cracks occur mainly in the non-uniform microstructure. In addition to the matrix microstructure composed of pearlite and ferrite, upper bainite microstructure exists also in the non-uniform microstructure, and its hardness and elasticity are higher than those of matrix microstructure, while its plasticity is lower than that of matrix microstructure. Therefore, stress concentration occurs at the junction between upper bainite and matrix microstructures under the action of the contact stress between wheel and rail, which induces and promotes the initiation and propagation of fatigue cracks on wheel tread, and the rolling contact fatigue shelling damage of wheel tread is finally formed. The formation of non-uniform microstructure is caused by the segregation of C and V elements in wheel.