The correlation between rail rolling contact damage and surface hardening behavior under various curvature radius and axle loads: comparing pearlitic and bainitic rail steels

This study investigated the correlation between rail surface hardening behavior and wear/rolling contact fatigue (RCF) damage through a series of rolling contact tests under varying curve radii and axle loads. Three rail steels with different hardness levels were examined: U75VH pearlitic steel (396 HV0.5), 1250B and 1380B bainitic steel (433 and 499 HV0.5, respectively). Results indicated that rail wear increased significantly with decreasing curvature radius or increasing axle load, with a generally slight increase in both crack length and depth. Notably, U75VH with the lowest matrix hardness exhibited the lowest wear rate, while the bainitic rail steel 1250B with intermediate hardness demonstrated the highest wear rate, accompanied by a significant increase in crack length as curvature radius decreased or axle load increased. Further Pearson correlation analysis revealed that wear rate exhibited a more significant negative correlation with post-test rail surface hardness (-0.54, P<0.05), whereas no correlation was observed with matrix hardness (-0.0053), indicating that rail surface hardening behavior played a pivotal role in directly determining wear resistance. The difference in hardening degree was related to the varying microstructural deformation of rail steels. The 1250B with the lowest hardening level was characterized by a discrete granular structure near the surface, in contrast to the fibrous structure seen in U75VH and 1380B rail steels. These findings highlight the importance of considering not only bulk mechanical properties but also surface hardening capability in rail material design.