Carbonitriding is a process in which carbon and alloy steel gears are held at a temperature above the transformation range in a gaseous atmosphere of such composition that the steel absorbs carbon and nitrogen simultaneously. The gears are then cooled at a specific rate to room temperature that produces the desired properties. Carbonitriding is generally regarded as a modified gas carburizing process, rather than a form of nitriding. This chapter briefly describes the case depth that can be achieved with carbonitriding, how case depth is measured, and the materials and applications that are suitable for carbonitriding.

Carbonitriding is a modified form of gas carburizing. It is performed in a closed furnace chamber with an atmosphere enriched with a gaseous compound of carbon and nitrogen. This chapter provides information on the carbonitriding of steels, the applications of carbonitriding, the typical case depths, and the hardenability of carbonitrided parts. In addition, the chapter also discusses the processes involved in quenching, tempering, and distortion of carbonitrided steels.

This chapter provides information on various contributors to failure of carburized and carbonitrided components, with the primary focus on carburized components. The most common contributors covered include component design, selection of proper hardenability, increased residual stress, dimensional stability, and generation of quenching and grinding cracks. They also include insufficient case hardness and improper core hardness, influence of surface carbon content and grain size, internal oxidation, structure of carbides, and inclusion of noncarbide. Details on micropitting, macropitting, case crushing, pitting corrosion, and partial melting are also provided.