Cementite

A compound of iron and carbon, known chemically as iron carbide and having the approximate chemical formula Fe3C. It is characterized by an orthorhombic crystal structure. When it occurs as a phase in steel, the chemical composition will be altered by the presence of manganese and other carbide-forming elements.

Cold Die Quenching

A quench utilizing cold, flat, or shaped dies to extract heat from a part. Cold die quenching is slow, expensive, and is limited to smaller parts with large surface areas.

Cold Treatment

Treatment carried out after quenching to transform retained austenite into martensite, involving cooling and holding at a temperature below ambient.

Columnar Structure

A coarse structure of parallel elongated grains formed by unidirectional growth, most often observed in castings, but sometimes in structures resulting from diffusional growth accompanied by a solid-state transformation.

Car Furnace

A batch-type furnace using a car on rails to enter and leave the furnace area. Car furnaces are used for lower stress relieving ranges.

Carbonitriding

A case hardening process in which a suitable ferrous material is heated above the lower transformation temperature in a gaseous atmosphere of such composition as to cause simultaneous absorption of carbon and nitrogen by the surface and, by diffusion, create a concentration gradient. The process is completed by cooling at a rate that produces the desired properties in the workpiece.

Carbonization

Conversion of an organic substance into elemental carbon. (Should not be confused with carburization.)

Carburizing

Absorption and diffusion of carbon into solid ferrous alloys by heating, to a temperature usually above Ac3, in contact with a suitable carbonaceous material. A form of case hardening that produces a carbon gradient extending inward from the surface, enabling the surface layer to be hardened either by quenching directly from the carburizing temperature or by cooling to room temperature, then reaustenitizing and quenching.

Carburizing Flame

A gas flame that will introduce carbon into some heated metals, as during a gas welding operation. A carburizing flame is a reducing flame , but a reducing flame is not necessarily a carburizing flame.

Carbide Precipitation

Occurs when austenitic stainless steel is heated within a temperature range of 800°–1600° F, 427°– 870° C for a critical period of time. Carbon moves from a solid solution to grain boundaries and combines with chromium. The metal adjacent to the grain boundaries is left with less chromium and is said to be sensitized. Corrosion resistance is therefore reduced in the grain boundary region.