Tribological Behavior of Two High Performance Railway Wheel Steels Paired with a Brake Block Cast Iron
Michela Faccoli, Nicola Zani, A. Ghidini, Candida Petrogalli
Abstract
The wear behavior of two steels for tread-braked wheels (ER7+ and CLASS B+) against the same brake block cast iron was studied through pin-on-disc tests to understand the phenomena at the interface and compare the steels. The contact stress (0.61 MPa) and sliding speeds (0.52 and 0.62 m/s) were set considering the UIC 510-5 (E) for technical approval of monobloc wheels. The friction coefficient, weight loss of both the steel pin and cast iron disc, and pin hardness were correlated with the damage of the pin. In addition, a preliminary thermal finite element model was proposed to predict the temperature of the pin contact surface. The experiments showed that material transfer from the cast iron disc to the steel pin and the subsequent detachment of the adhesion joints caused high friction coefficient fluctuations. The removal of the adhesion joints probably promoted the detachment of steel particles from the pin, which could explain the high weight loss and remarkable delamination of the pin in some of the studied conditions. In contrast, small friction coefficient fluctuations and red oxide formation due to the temperature increase were detected when the material transfer was very limited. ER7+ steel showed lower weight loss and less damage than CLASS B+ at the lowest sliding speed, in contrast to what was observed at the highest sliding speed. Finally, the simulation showed that the maximum temperature of the pin contact surface varies between 61 and 97 °C, which is consistent with the presence of red oxide.