Tribological behaviour of thermochemically surface engineered steels

A major purpose of thermochemical diffusion processes is to alleviate surface degradation. Wear resistance is not a simple property. There are many wear mechanisms. We show nitrided/nitrocarburized steels have good functionality in mildly oxidational environments at elevated temperature (up to 400°C); outperforming untreated, carburized and carbonitrided steels. ε-Fe_2-3N layers formed via nitrocarburizing, have specific advantage under lubricated high pressure (> 1GPa) rolling contact conditions. Borided steels exhibit anisotropic fracture behaviour and are too brittle being only suited to low contact pressures (< 100MPa). Conversely, vanadized steels (via the TD process) have sufficient hardness to resist abrasion by the hardest of abrasives and can best be exploited on very tough and very strong steel substrates. They maintain these properties up to 450°C.