Subsurface crack networks and RCF surface cracks in pearlitic railway wheels
Paper in proceedings, 2012
Subsurface cracks developed by rolling contact fatigue (RCF) are both a lifetime limiting factor for railway wheels and a safety issue. In the current study a severe subsurface crack network has been studied and compared to RCF cracks on the surface. Microstructural characteristics, determination of local chemical compositions with Auger electron spectroscopy and microhardness within cracks and around crack faces were examined. Both damage types showed similar crack growth characteristics, with small cracks branching from the main cracks. Continuous third body material resembling wear particles were identified in many cracks. The analyses showed that this material does not originate from external contamination or oxide inclusions but is produced by shear deformation and wear within crack faces by mode II and III crack growth. The third body material showed a higher hardness than the surrounding base material indicating a high shear deformation and work hardening. While microstructural appearance at lower magnification appeared different to the bulk material, high magnification revealed that the third body material mainly consisted of deformed flakes of base material, wear and oxide particles. Auger electron spectroscopy confirmed the theory that the third body consists of several layers of deformed metallic flakes covered with thin oxide layers indicated by the variation in oxygen content.