WEB Understanding the microstructural essence of damage development in rail steels subjected to rolling contact fatigue
Rails are subjected to complex loading conditions involving rolling contact fatigue, wear and sometimes severe dynamic loads. The service life of rails is predominantly determined by Rolling Contact Fatigue (RCF) damage which initiates at the microscale and is closely related to the steel microstructure. This microscale damage ultimately results in macroscopic defects like head checks and squats, which can grow into the rails and lead to the failure of rails causing safety threats to the passengers. The removal of macroscopic damages from the rail surface leads to high maintenance costs. Hence, detailed knowledge on the development of rail defects is of paramount importance for the maintenance, safeguarding of the railway system and prolonging the rails’ lifetime. In this study, a detailed understanding of microscale damage initiation and growth is established in pearlitic rail steels when subjected to Rolling Contact Fatigue. Furthermore, the stage in which microscopic damage develops into macroscopic head checks and squats is also discussed. In the initial stage of damage evolution due to RCF, microstructural changes are found to occur at the rail surface due to severe plastic deformation and temperature rise. These changes affect the damage initiation and propagation at the microscale. Ferrite-cementite interfaces and the interfaces of MnS inclusions with the matrix are primary damage initiation sites. Additionally, the damage is also found to be affected by the crystallographic orientation of the pearlitic colonies. Hence, the study also discusses the role of pearlite colony orientation on the damage initiation and growth.