Nitridaatio

Nitridaatio, commonly called nitriding in English, is a heat treatment process that introduces nitrogen into the surface of a metal, usually steel, to form a hard nitride layer. The aim is to increase surface hardness, wear resistance, and often fatigue life while maintaining a tougher core.

The process is performed at moderate temperatures and can be carried out by several methods: gas nitriding (in an ammonia-based atmosphere), vacuum or plasma nitriding (ion nitriding), and salt bath nitriding (cyanide-based). Gas nitriding typically operates around 500–550 °C; plasma nitriding can be conducted in a broader range, often 300–520 °C. In all cases, nitrogen diffuses into the surface to form iron nitrides such as Fe2N, Fe3N, or Fe4N, depending on alloy composition, temperature, and time. The resulting microstructure comprises a hard surface nitride layer over a diffusion zone.

Nitridaatio is commonly applied to steels, including low- and medium-carbon steels and alloy steels containing elements such as chromium, molybdenum, or vanadium, which promote nitride formation. Case depths typically range from a few tenths of a millimeter to about one millimeter, depending on process duration and method.

Applications include gears, shafts, camshafts, fasteners, cutting tools, and other wear-critical components. Benefits include high surface hardness, excellent wear and fatigue resistance, and good adhesion of the nitride layer with limited distortion. Limitations include potential brittleness of the nitride layer if over-processed, the need for specialized equipment and handling of ammonia or salts, and, in some cases, post-treatment tempering.