Experimental and numerical investigation on the wear behavior of high performance railway wheel steels paired with various brake block materials under dry sliding conditions

Sliding wear tests were carried out with a pin-on-disc machine to study the tribological behavior of EN ER7 and AAR CLASS B wheel steels paired with cast iron and organic composite brake block materials. The contact stress was 0.61 MPa and the sliding speeds were 0.52 m/s and 0.62 m/s. The wear behavior was related to the friction coefficient recorded during the tests, the specific wear rate calculated at the end of the experiments and the microhardness profile obtained on the cross-section of the wheel pins. The worn surface and cross-section of the pins were analyzed by optical and scanning electron microscopy to investigate the main damage mechanisms. A stationary finite element model was proposed to estimate the contact temperature of the pin. The test results showed the same damage mechanisms for both steels, such as oxidative wear, delamination, abrasive wear and material transfer from the brake disc to the wheel pin, which led to adhesive wear. Overall, ER7 steel performed better when paired with the composite material as the pins showed lower specific wear rate; on the contrary, CLASS B pins had lower specific wear rate when the counterpart was cast iron. The tribological behavior of both steels was not influenced by the sliding speed. The simulations showed that the contact temperature was always higher when the disc in composite material was used, regardless of the pin material. Furthermore, ER7 steel demonstrated lower contact temperatures than CLASS B due to the lower friction coefficients in the experiments.