2020 Volume 61 Issue 9 Pages 1750-1759
We investigated the microstructural changes in carburized steel due to high stress rolling contact fatigue (RCF) in this study. The changes consisted of the formation of white bands (WBs), including the low angle bands (LABs) and high angle bands (HABs), following the formation of a dark etching area (DEA) in the bearing steels below the contact surface. Although several studies have analyzed the characteristics of WBs, their formation mechanism has not been sufficiently elucidated. We analyzed the orientation of the crystal constituting the WBs and investigated their relationship with the direction of the shear stress generated by the rolling contact. The morphology of the WBs as a function of depth from the surface was studied using an optical microscope, and the crystal orientation was analyzed using scanning electron microscopy–electron backscattering diffraction. It was found that the LABs and HABs respectively formed at a depth where the principal and orthogonal shear stresses were at their maximum. The results of the crystal orientation analysis revealed that the crystal were rotated under the principal shear stress at a specific depth, resulting in the formation of textures such as {111}〈211〉 and {122}〈411〉 in LABs and HABs, respectively. Thus, the WBs were revealed to be a type of shear band. The WB formation behaviors of the specimens with varying amounts of initially retained austenite (γR) were compared to elucidate the sub-surface initiated spalling life improvement mechanism of the γR. However, the WB formation behavior showed no difference regardless of the amount of initial γR. This suggested that the WB formation was not directly related to the sub-surface initiated spalling life.
This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 83 (2019) 388–397. The captions of Fig. 1–10, 12–16 are slightly changed.
