The role of deformed rail microstructure on rolling contact fatigue initiation

Metallurgical examinations are being used to validate progressive development of a mechanics model of contact damage in rail, with data from worn and fatigued rails removed from track and from SUROS twin-disc, lubricated tests, where standard grade rail steel discs were tested both to failure initiation (detected by eddy-current probe) and to proportions of fatigue life. This paper describes microstructural changes induced by compressive-shear, cyclic contact. Initial rail examinations indicated strain-partitioning between the pro-eutectoid ferrite phase at the prior austenite grain boundaries and the pearlite phase, with surface rolling contact fatigue (RCF) crack initiation primarily along the more highly strained, pro-eutectoid ferrite phase boundaries, therefore some rail discs were heat-treated prior to testing in order to alter the volume of pro-eutectoid ferrite. The SUROS results supported the rail examinations with regard to surface RCF crack initiation and the RCF life and the part-life results showed the development of strain-partitioning.