Unlubricated sliding wear of pearlitic and bainitic steels

Sliding wear has a great influence on the performance of rail-wheel systems, especially because the wheel flange slides over the rail in a curve track. Since rail-wheel sliding introduces adhesive effects, high slip ratios strongly affect the rolling contact fatigue wear acting on the surfaces. Sliding wear tests were carried out in a pin-on-disk device to study the behavior of AISI 1070 pearlitic and AISI 15B30 bainitic pins sliding against AISI 1085 pearlitic disks. The sliding speed was 1 ms−1 for all the tests and normal loads of 10, 30 and 50 N were used. A bainitic microstructure was obtained after austempering the AISI 15B30 steel at 310 °C for 30 min, while the AISI 1070 samples were normalized in air, being the austenitizing temperature 850 °C for both materials. The wear resistance was related to the mass loss measured after the tests and the worn surfaces, as well as particle debris, were analyzed by optical and scanning electron microscopy. Micro-hardness profiles were also obtained to analyze strain hardening effects beneath the contact surfaces. The pearlitic steel showed higher sliding wear resistance than bainitic steel, due to the excellent strain hardening of pearlite compared to bainite. Oxidative wear regimes were observed in the pearlitic steel, while in the bainitic one adhesive wear was the main removal mechanism, leading to a much more accentuated damage of the surface. In fact, the wear regime for bainitic samples was always severe, even for the lower loads applied.