Effect of desert sand on wear and rolling contact fatigue behaviour of various railway wheel steels

This work studies the effect of desert sand at the wheel-rail contact interface on two standard railway wheel steels (ER8 and CLASS C) and two upgraded steels (SANDLOS® S and SANDLOS® H) specifically designed for sandy environments. Rolling contact tests were carried out by means of a two-disc testing machine with and without sanding at the contact interface. The tests were performed for various durations in order to study the disc damage evolution. The response of the steels to the same contact pressure, rolling speed, sliding/rolling ratio and sand feed rate was evaluated in terms of wear rate, strain hardening and surface and subsurface damage. The ER8 discs performed worst, incorporating sand into the subsurface layer by extremely high plastic flow and were, therefore, subject to material detachment by rolling contact fatigue. The SANDLOS® H discs performed best, with a wear rate 2.5 times lower than that of ER8 discs, due to the steel having the highest mechanical properties, and thereby restricting the sand embedding mechanism to a thin surface layer. The sanding increased the wear rate of the wheel discs by a factor which varies from 1.4 for SANDLOS® H discs to 2.2 for ER8 and CLASS C discs. The damage mechanisms were qualitatively studied by finite element simulations, which recognised two different layers for the plastic strain. These layers are related to the dimensional scales of the disc-disc and sand-disc contact areas, respectively, and their influence on the total damage depends on the material cyclic yield stress.