Rolling Contact Fatigue and Crack Propagation in Subway Rails – A Case Study on an Urban Subway Network

Rolling contact fatigue (RCF), particularly in the form of head checks, is a common and costly maintenance issue in heavily loaded subway systems. This study investigates the formation and propagation behavior of surface cracks in R260 rails within the subway network. Rails from selected track segments were removed and analysed using light microscopy after metallographic preparation. Crack angles, depths, and morphological characteristics were quantified and correlated with operational parameters and track geometry. The results show a distinction between crack initiation on the running surface and at the gauge corner, with the latter exhibiting lower crack angles and more pronounced plastic deformation. Average crack angles at the gauge corner were 25°, while cracks at the rail crown had angles up to 69°, indicating different dominant loading mechanisms. The penetration angle of 25° specified in EN 16729-2 applies exclusively to the gauge corner of rails in the subway network. It does not extend to surface cracks on the rail head. Additionally, transgranular crack growth along aligned ferrite lamellae and cementite lamellae was observed in plastically deformed regions. The findings highlight the significance of local loading conditions, braking and acceleration zones, and maintenance history for crack morphology and propagation direction. The results contribute to improved defect detection and a deeper understanding of anisotropic material behavior under real operational conditions. • Distinct crack propagation mechanisms observed for gauge corner and railhead surfaces • Gauge corner cracks show lower angles (~25°), while railhead cracks reach up to ~69° • Microscopic analysis reveals transgranular crack growth influenced by anisotropic microstructure • Findings highlight the need to adapt inspection standards for rail surface cracks