A process of case hardening in which a ferrous alloy, usually of special composition, is heated in an atmosphere of ammonia or in contact with nitrogenous material to produce surface hardening by absorption of the nitrogen without quenching. The alloys used for nitriding are known as nitroalloys. Several types are available, with ranges of composition as follows: aluminum 0.85–11.2%, carbon 0.20–0.45%, chromium 0−8%, Molybdenum 0.15–1.00%, Maganesen 0.4–0.7%, silicon 0.2–0.4%.