Investigation on WEA fatigue spalling of U71MnG rail material subject to laser quenching surface treatment

Abstract

In this study, the fatigue spalling process and mechanism of the white etched area (WEA) caused by the laser quenching surface treatment of U71MnG rail material were investigated. The results demonstrate that the surface pearlite is visibly deformed under normal stress and creep force during the initial wear stage, whereas the WEA is not deformed. Discordant plastic deformation results in the formation of cracks at the contact between the initial position of the WEA and the substrate, which then propagates into the WEA. As the number of rolling cycles increases, the formation and propagation of cracks gradually shift into the middle of the WEA and branch cracks form, which eventually intersect and cause spalling. The substrate's plastic flow covers the WEA terminal position surface; the WEA edge fracture is formed due to bending under normal stress. Plastic deformation enhances the surface hardness of WEA. The substrate's apparent plastic deformation beneath the WEA suggests that the WEA flows under the influence of creep forces.