不均匀组织ER8车轮滚动接触疲劳性能研究

Rolling Contact Fatigue Performance of ER8 Wheel Steel with Non-Uniform Microstructure

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.

To resolve the problem of premature rolling contact fatigue(RCF) damage to wheels with non-uniform microstructure arising in their service,RCF test was conducted to investigate the influence of the wheel tread nonuniform microstructure on the RCF of wheels. The tensile properties of uniform and non-uniform microstructure were tested using in-situ tensile test bench,and the crack growth behavior was observed by scanning electron microscope.Microstructural change at RCF damaged area of specimen with non-uniform microstructure was observed by optical microscope and transmission electron microscope. The result showed that the RCF limit of non-uniform microstructure was lower than that of matrix. In addition to the normal pearlite + proeutectoid ferrite(matrix),there were a large amunt of upper bainite in the non-uniform microstructure,which interrupted the continuity and uniformity of normal matrix.RCF cracks mainly initiated and propagated at the boundary between upper bainite and matrix. Both the hardness and the elasticity of upper bainite were higher than those of the matrix while the plasticity was lower than that of the matrix.Under the same contact stress,the incongruity of the elastic-plastic deformation resulted in the stress concentration at the boundary,and thus induced and facilitated initiation and propagation of fatigue cracks in wheel steel and accelerated the occurrence of RCF damage.