4. Nitriding steels

4.1 General

Nitriding treatments create a hardened layer by introducing nitrogen into the ferritic phase, at temperatures ranging from 400 to 575 C, without the need for final quenching.

Nitrogen can harden steel:

• by an interstitial solid solution effect. It then forms what is known as a diffusion layer in which, in the presence of suitable alloying elements (Al, Cr, Mo, V...), it is likely to precipitate finely in the form of nitrides, or even carbonitrides, precipitation which then provides additional hardening;

• by alloying with iron, it can form, at the extreme skin, a combination layer consisting of Fe ₄ N nitrides (