Evaluation of material deterioration of rails subjected to rolling contact fatigue using x-ray diffraction

Crystallite size and dislocation density in RCF (rolling contact fatigue) affected layers have been identified using x-ray measurements for the serviced rails and rail disk sample. The evaluation of crystallite size and dislocation density was based on the modified Williamson-Hall and Warren-Averbach analyses. This evaluation enabled to provide a quantification of the microstructural evolution in the RCF layer with the increase of accumulated loading as well as an identification of the most deteriorated locations in the RCF layer. In summary, the surface layer experienced the highest deterioration in all evaluated cases. Furthermore, the accumulation of loading (in terms of MGT-Million Gross Tonnes) increased the depth of the surface RCF layer. A (111) texture formation was observed in the subsurface RCF layer after some accumulated operational loading. Further conclusions from the study are that it is essential to consider the surface roughness in the contact patch in addition to the microstructural variations such as the refinement, the plastic flow, etc., since it enhances the deterioration of surface RCF layer. In addition, the dislocations induced by the RCF were mostly stemmed from the screw dislocations in the surface RCF layer. In contrast, they were mostly derived from the edge dislocations in the subsurface RCF layer. This difference is likely owing to the characteristics of dislocations, the tangential load, the applied shear stress, localized stress concentration induced by the surface roughness contact, etc