Analysis of wear debris in rolling contact fatigue cracks of pearlitic railway wheels

Artikel i vetenskaplig tidskrift, 2014

In the current study a severe subsurface crack network in a railway wheel has been studied and compared to typical rolling contact fatigue cracks found in the wheel tread surface. Microstructural characteristics, chemical composition and microhardness within the cracks and around crack faces were examined. While the two damage types are principally different, both showed similar crack characteristics, with short cracks branching along the main crack paths and a discontinuous sheared layer of wear debris and metallic flakes within them. Analyses of the wear debris showed that it does not originate from external contamination or being the result of corrosion primarily. Instead it has most likely been produced by shear deformation and wear mechanisms within crack faces caused by mixed-mode crack growth. Although microstructural appearance at lower magnification seemed to differ from the bulk material, at high magnification a lamellar structure was observed consisting of layers of deformed metallic flakes and particles of the base metal. Auger electron spectroscopy was used to analyze these sheared layers; higher concentration of oxygen was measured in between flakes, indicating the presence of oxides and flakes being of similar chemical composition as the base material. A possible explanation is that these layers are created due to high shear forces and friction between crack faces in the service of the wheel. With continued rolling the material being sheared by the cyclic relative motion of the crack faces disintegrates into smaller wear debris particles with concurrent oxidation.