Study on wear and rolling contact damage mechanism between quenched U75V rail and wheels with different microstructures

Most existing wheel/rail hardness matching studies have been carried out using pearlite steels with different hardnesses; no relevant wheel–rail hardness matching research has been carried out for other microstructure types such as bainite and other tempered materials. In this paper, a CL60 wheel (pearlite) was quenched and tempered to obtain wheel materials with a certain hardness gradient, and matching tests between different wheel materials and a quenched U75V rail were carried out to explore the influence of wheel microstructures on wheel–rail damage. The results showed that with increasing tempering temperature, the wheel microstructure changes from tempered troostite to tempered sorbite, with ferrite changing from a needle shape to a multilateral shape; additionally, the cementite particles grow obviously larger, resulting in a gradual decrease in wheel hardness. With the increase in the wheel/rail hardness ratio, the wear rate of the wheel and wheel–rail system first increases and then decreases; the wear rate of tempered sorbite is the highest. Wear surface analyses indicate that typical peeling appears on the wear surfaces of the CL60 wheel as well as the coupled rail. Tempered sorbite shows slight peeling; however, severe peeling and delimitation occur on the wear surface of its coupled rail. Moreover, severe peeling and serious material delamination are present on the wear surface of tempered troostite, and typical peeling appears on its coupled rail surfaces. The fatigue crack initiation and propagation behaviors of wheel and rail materials are closely related to their microstructures. The cracks in pearlite always initiate on the surface and propagate along the ferrite line. Short and shallow fatigue cracks appear on the tempered sorbite with a high wear rate, and the cracks in the tempered troostite easily expand into the centre of the samples, indicating poor rolling contact fatigue (RCF) resistance. Therefore, the pearlite structure shows better comprehensive mechanical properties for wheel service; moreover, more attention should be given to wheel microstructure when conducting research on wheel–rail matching.