Carburizing is a thermo-chemical process in which iron or steel absorbs carbon from a carbon-bearing material at processing temperatures between 850–1000°C, with the intent of hardening the metal.

Carbonitriding is a heat treatment process by which carbon and nitrogen (via ammonia gas) permeate the surface layer of steel components. The process involves temperatures of around 850°C followed by quenching in oil or gas solutions.

Nitriding is a heat treatment process that diffuses nitrogen into the surface of a metal to create a case-hardened surface. These processes are most commonly used on low-alloy steels. They are also used on titanium, aluminium and molybdenum.

Nitrocarburizing is a variation of the case hardening process. It is a thermochemical diffusion process where nitrogen, carbon, and to a very small degree, oxygen atoms diffuse into the surface of the steel part, forming a compound layer at the surface, and a diffusion layer.

The lower the dewpoint, the richer the endothermic gas, richer defined as having higher levels of carbon from the endothermic gas.