Influence of a decarburised layer on the formation of microcracks in railway rails: On-site investigation and twin-disc study

In the rail manufacturing process, the rail material is exposed to a high-temperature atmosphere, thereby causing decarburisation. It reduces the carbon content on the surface layer of the rails, which degrades the mechanical properties and hardness of the rails’ surface. Squat, a rail defect, results from rolling contact fatigue (RCF) due to the cyclic contact between a wheel and a rail. Generally, RCF initiates microcracks on the running band of a rail; then, when RCF accumulates, the microcracks grow deep below the surface of the running band and finally the squat is visually formed. This study aims to understand the effect of decarburisation on microcrack formation using twin-disc and site tests. Test pieces with and without decarburisation were compared during the twin-disc tests under the same test conditions. The results show that decarburisation affects the formation of microcracks and plastic flow. Furthermore, we investigated the effect of decarburisation on the formation of microcracks in the test pieces taken from the actual tracks. The comparison between the test pieces with and without a decarburised layer showed that the crack density of the ground rail was ∼2.7–5.7 times higher than that of the underground rail at a cumulative tonnage of 23 MGT. •An average decarburised depth of 30 new unused rails was 0.29 mm.•Confirmed decarburisation and plastic deformation with a twin disc tester.•The relationship between decarburisation and cracks was confirmed in the laying test.•The cracks increase from 2.7 to 5.7 times in the presence of a decarburised layer.•Cracks are formed by proeutectoid ferrite even without a decarburised layer.