Carbonitriding is a surface case hardening process that produces a thin, high hardness case and is a modified form of gas carburizing. This modification consists of introducing ammonia into the carburizing atmosphere to allow for nitrogen from the ammonia to be added to the carburized case as it forms. This thermochemical treatment diffuses both carbon and nitrogen into the surface of the component simultaneously.

Carbonitriding is typically carried out at lower temperatures with shorter cycle times, resulting in shallower cases than most carburizing processes. Carbonitrided case depths will typically range from .058 to .762 mm. The addition of nitrogen to a carburized case increases the hardenability of the carburized case. This allows plain carbon and lower alloy steels to be case hardened successfully with full transformation to martensite in order to maximize the case hardness and obtain the best possible mechanical properties.

This process is typically selected for case hardening plain carbon and low alloy steels that have poor hardenability and would not normally fully transform to martensite during quenching.

Carbonitriding Properties

•Increases surface hardness

•Improves wear resistance and fatigue strength

•The core of the material being hardened is tough and ductile

•Case depths are normally .058 to .762 mm deep depending on application and intended use

•Typically works best with plain carbon and low alloy steels (10xx, 11xx, 12xx, 13xx, 15xx, 40xx grades) that have a low carbon content of 0.05% to 0.30% C


•Parts which require increased surface wear resistance and fatigue strength

•Parts made from low carbon content and low hardenability steels