Study of wear regime transition in steels for railway wheels by rolling-sliding tests

Wear tests were carried out in rolling-sliding condition by a bi-disc machine on specimens made by two railway wheel steels, coupled with the same rail steel. Contact load and sliding speed were varied from mild to very severe working conditions. The weight loss and coefficient of friction were monitored throughout the tests. At the end of the tests, the surface state was evaluated by roughness measurements obtained by an innovative laser distance sensor. Microscopic analyses of the subsurface strain state and wear debris were performed on some specimens to identify the wear regime. The results showed that, with increasing load and sliding speed, there is a sudden transition of wear from mild or severe to catastrophic. This is correlated with both parameters, but the sliding speed showed a stronger effect on the wear regime, whereas the contact load affected especially the thickness of the plasticized depth. The roughness at the test end was strongly correlated with the sliding speed. The SUPERLOS® steel showed a better performance than the ER8 one. To assess the wear regime, the correlation between the Archard wear number and various existing wear models (T-gamma, p-gamma, shakedown map), based on the working condition parameters, was evaluated, but it proved unsatisfactory. Therefore, a new model, named “p-vs2”, was introduced to better approximate the effect of the sliding speed: it showed an overall good correlation with the wear number, appearing as a promising model for predicting the wear regime up to very severe working conditions.