Increase of surface carbon content to a defined depth (total or effective), followed by cooling at a controlled rate and tempering, usually, in order to improve mechanical properties such as hardness, resistance to abrasion, fatigue and torsion.

This diffusion process is used mostly on low carbon steels (0.10 to 0.25 % C) to maintain a good core ductility / toughness while improving mechanical properties where they are most required; at the surface.

Selective areas can be carburized when required.