Assessment of the factors influencing micropitting in rolling/sliding contacts

Micropitting is currently a significant failure mechanism in carburised steel gears, but the detailed mechanisms of crack initiation and propagation are not well understood. Experiments have been carried out using a twin disc machine, according to a factorial experimental design in order to assess the influence of seven factors: material, surface finish, lubricant, load, temperature, speed and, slide-to-roll ratio. In order to minimise time, the design adopted was a fractional factorial design 2(7-4). It has been found that load has the biggest effect on micropitting initiation whereas speed and slide-to-roll ratio have the biggest effects on micropitting propagation. Finally it is shown that micropitting is related to the phenomenon of martensite decay.