Rolling contact fatigue in relation to rail grinding

Spalling defects of a periodic nature are sometimes observed on heat-treated pearlitic steel rails. Defect properties suggest a relationship between maintenance grinding on a regular basis and the initiation of rolling contact fatigue (RCF). In this work, the effects of maintenance grinding are investigated experimentally for both standard and heat-treated pearlitic rails. Results show essentially different behaviour for both steels. On standard grades, friction-induced martensite (FIM) generated during grinding delaminates when in service. However, grinding induces severe top-layer deformation which coincides with that induced by train operation, thus yielding 'pre-fatigue' of the rail. On heat-treated grades, portions of FIM accumulated at groove edges during grinding are pressed into the deeper pearlitic matrix in combination with severe plastic deformation under tangential wheel-rail contact stresses. That process results in severe and extensive crack initiation. According to quantitative test results reported in the literature, this initial condition yields a reduction of the normal RCF life by roughly a factor nine, which is in accordance with both observations in the field and in the literature on rail spalling defects.