It is a surface heat treatment based on a thermochemical diffusion on the surface of the piece. It is a simultaneous surface enrichment in carbon and nitrogen.
It consists of the maintenance of the pieces at a certain temperature in a liquid or gaseous medium capable of supplying carbon and nitrogen. Small amounts of carbon and nitrogen can be diffused into the steel maintained in a cyanide-cyanate nitriding bath, and in a cyanide-chloride case-hardening bath.
Carbonitriding can be carried out at low temperature (below A1 ~ 700 ° C) or at high temperature (below A3 ~ 730-900 ° C).
The carbonitrided layer provides high hardness, wear resistance and fatigue resistance. It improves friction conditions by reducing adhesion and improves corrosion resistance.
As a treatment performed at a lower temperature than case-hardening (due to the gamma nitrogen effect), the deformations of the pieces are smaller.