Nitriding (N)

Nitriding heats the steel part to 482–621 °C (900–1150 °F) in an atmosphere of ammonia gas and dissociated ammonia. The time the part spends in this environment dictates the depth of the case. The hardness is achieved by the formation of nitrides. Nitride forming elements must be present for this method to work; these elements include chromium, molybdenum and aluminium.

The advantage of this process is it causes little distortion, so the part can be case hardened after being quenched, tempered and machined.