不均匀组织ER8车轮滚动接触疲劳性能研究

针对含不均匀组织ER8车轮服役过程中过早出现滚动接触疲劳(RCF)损伤这一实际问题，通过RCF试验，获得了车轮不均匀组织和正常组织的RCF极限；利用光学显微镜(OM)和透射电镜(TEM)重点表征了RCF裂纹萌生处的微观组织. 借助扫描电镜(SEM)和原位拉伸试验台测试了两种组织的弹、塑性能并原位观察了裂纹的扩展行为. 结果表明：车轮踏面不均匀组织的RCF极限低于轮辋正常组织，不均匀组织中除车轮正常组织应有的珠光体和先共析铁素体组织外，还存在大量的上贝氏体，上贝氏体的存在破坏了车轮正常组织的连续均匀性. RCF裂纹的萌生和扩展主要发生在上贝和正常组织的边界处，上贝氏体的硬度、弹性高于正常组织，但塑性小于正常组织，在相同接触应力作用下，两者弹-塑性变形的不协调是导致其组织边界处产生应力集中，进而诱发并促进疲劳裂纹的萌生和扩展，加速车轮RCF损伤出现的主要原因.Aiming at the practical issue that ER8 wheels with heterogeneous microstructures suffer from premature rolling contact fatigue (RCF) damage during service, RCF tests were conducted to obtain the RCF limits of both heterogeneous and normal microstructures of the wheels. Optical microscopy (OM) and transmission electron microscopy (TEM) were utilized to characterize the microstructures at the initiation sites of RCF cracks with a focus. Moreover, scanning electron microscopy (SEM) combined with an in-situ tensile testing platform were applied to test the elastic and plastic properties of the two microstructures, and to in-situ observe the crack propagation behavior. The results indicate that the RCF limit of the heterogeneous microstructures on the wheel tread is lower than that of the normal microstructures in the wheel rim. Besides pearlite and proeutectoid ferrite, which are inherent in the normal wheel microstructures, the heterogeneous microstructures also contain a large amount of upper bainite, and the presence of upper bainite disrupts the continuous uniformity of the normal wheel microstructures. The initiation and propagation of RCF cracks mainly occur at the boundaries between upper bainite and normal microstructures. The hardness and elasticity of upper bainite are higher than those of normal microstructures, while its plasticity is lower. Under the same contact stress, the incompatibility of elastic-plastic deformation between the two microstructures leads to stress concentration at their boundaries, which induces and accelerates the initiation and propagation of fatigue cracks, and is the primary cause for the premature occurrence of wheel RCF damage.

搜集汇总

背景与挑战

背景概述

本研究针对不均匀组织ER8车轮过早出现滚动接触疲劳损伤的问题，通过实验和微观表征，发现不均匀组织中存在上贝氏体，导致RCF极限低于正常组织，且裂纹主要萌生于上贝氏体与正常组织边界，因弹塑性变形不协调引发应力集中，加速疲劳损伤。