Micromechanical characterisation of Indian rail steel

Railway transport dynamics cause rails in general to experience a time varying rolling contact load to add shear strain to that from traction and normal strain from the axle loads. These loading conditions together with the frictional heat at the contact interface alters the microstructure in the near-surface region of the rails and wheels. This paper presents the hardness and microstructural study of used Indian rail steel to expose the influence of load parameter active at the interface. Samples are prepared from the rail section taken from Dhanbad railway division. The hardness variation along the rail head cross-section and metallurgical variations of the test sample are presented. Microstructural examinations reveal existence of micro cracks near to the rail surface favouring formation of wear debris. Also, the presence of the pro-eutectoid ferrite and cementite phase at the grain boundaries of the pearlitic rail material is observed. The fatigue cracks are found to initiate across the grain boundaries containing the pro-eutectoid ferrite phase. This study will help to develop a better understanding of rolling contact fatigue (RCF) crack initiation and wear debris formation mechanisms on the rails. Thus, these results can be used to improve rail maintenance planning and risk assessments. (paper)