AbstractNitrocarburising is outstanding for the profusion of proprietary names and claims it has attracted during its 40 year existence. It can be characterised as a low distortion treatment for ferrous materials where surface enrichment, predominantly by nitrogen, forms a hard surface layer ofεiron nitride, beneath which there is a nitrogen diffusion zone. The surface layer imparts wear and corrosion resistance and the diffusion zone increases the yield and fatigue strength, particularly in thin sections. Process developments have significantly enhanced the corrosion resistance and aesthetic appearance of treated components to make nitrocarburising competitive with electroplated finishes. Major commercialisation took place duringthe 1980s, and examples are given of a wide range of successful applications from wheel bearings to bumper armatures, which use combinations of the properties obtainable from the process to provide cost and weight savings. Advances in equipment and process materials offer a treatment which greatly reduces environmental pollution.