Carbonitriding is a modified form of carburizing that involves the introduction and diffusion of atomic nitrogen into the surface steel during carburization. This article discusses the composition, depth, and hardenability of a carburized case, and demonstrates how to control atmosphere in batch and continuous furnaces. It discusses the most important considerations in the selection of carbonitriding temperature. The article also describes the processing factors for minimizing retained austenite in the carbonitrided case. Hardness testing and carbonitriding of powder metallurgy parts, quenching and tempering of carbonitrided steel parts, and applications of carbonitriding are also covered in the article.

Carburization is the process of intentionally increasing the carbon content of a steel surface so that a hardened case can be produced by martensitic transformation during quenching. Like carburizing, carbonitriding involves heating above the upper critical temperature to austenitize the steel. This article introduces the fundamentals, types, advantages and limitations, and the complications of various forms of carburizing, namely, pack carburizing, liquid carburizing or salt bath carburizing, gas carburizing, and low-pressure (vacuum) carburizing. The related process of carbonitriding is also briefly described in the article.