Performance of wheels in heavy haul service: matching microstructures to service conditions

The requirements of wheels for performance under high wheel-rail loads and heat input from braking are examined, with consideration of recent investigations of rolling contact fatigue damage. While the use of higher hardness wheels with elevated carbon to improve the wear resistance can seem attractive, the wear rate needs to be sufficient to remove accumulated surface damage prior to the development of cracks. The presence of alloying elements to stabilise the structure under high thermal loads is also regarded as beneficial, to delay the microstructural damage caused by prolonged exposure to high temperatures, or under very high heat input, short duration conditions such as wheel sliding. The presence of carbide forming elements such as chromium and vanadium has proven effective in this regard. These and other effects of alloy design on the response under other combinations of thermal and mechanical loading are also briefly reviewed.