Nitriding

From GAWDAwiki

Nitriding is introducing nitrogen into the surface layer of a solid ferrous alloy by holding at a suitable temperature in contact with a nitrogenous material, usually ammonia or molten cyanide of appropriate composition. Quenching is not required to produce a hard case.^[1]

References

1. http://www.corrosionsource.com/handbook/glossary/mn_glos.htm#topn