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.


Introducing nitrogen into a solid ferrous alloy by holding at a suitable temperature (below Ac1 for ferritic steels) in contact with a nitrogenous material, usually ammonia.


Heating a ferrous alloy to a suitable temperature above the transformation range and then cooling in air to a temperature substantially below the transformation range.


Annealing is a heat treating process that is performed to produce a "soft" structure, consisting generally of small carbides which are evenly distributed in ferrite. This structure provides for lower tensile strength, lower hardness, and high ductility in the material processed. The processing temperature and the rate of cooling depends upon the material being annealed and the purpose of the heat treatment. Annealing can then be basically described as heating metal to, and holding at a suitable temperature, and then cooled at a suitable rate.


Increasing hardness by suitable treatment, usually involving heating and cooling. When applicable, the following more specific terms should be used: age hardening, flame hardening, induction hardening, laser hardening, precipitation hardening, and quench hardening.


Heating an alloy to a suitable temperature, holding at that temperature long enough to cause one or more constituents to enter into solid solution, and then cooling rapidly enough to hold these constituents in solution.


A change in the properties of certain metals and alloys that occurs at ambient or moderately elevated temperatures after hot working or a heat treatment (quench aging in ferrous alloys, natural or artificial aging in ferrous or non-ferrous alloys) or after a cold working operation. The change in properties is often, but not always, due to a phase change (precipitation), but never involves a change in chemical composition of the metal or alloy.


A group of welding processes that join solid materials together by heating them to a suitable temperature and using a filler metal having a liquidus above 450°C (840°F) but below the solidus of the base materials. The filler metal is distributed between the closely fitted surfaces of the joint by capillary action.


The bonding of adjacent surfaces in a mass of particles by molecular or atomic attraction on heating at high temperatures below the melting temperature of any constituent in the material. Sintering strengthens a powder mass and normally produces densification and, in powdered metals, recrystallization.


Spheroidizing is an annealing process that produces a round or globular form of carbide in a matrix of ferrite. The cementite (iron carbide) layers of the material are caused by time and temperature to collapse into spheroids, or globules of cementite which is normally required for cold forming processes.

Stress Relieving

Heating to a suitable temperature, holding long enough reduce residual stress, and then cooling slowly enough to minimize the development of new residual stresses.

Vacuum Carburizing

A high temperature gas carburizing process using furnace pressures between 13 and 67 kPa (0.1 to 0.5 torr) during the carburizing portion of the cycle. Steels undergoing this treatment are austenitized in a rough vacuum, carburized in a partial pressure of hydrocarbon gas, diffused in a rough vacuum, and then quenched in either oil or gas. Both batch and continuous furnaces are used.


In heat treatment, reheating hardened steel or hardened cast iron to some temperature below the eutectoid temperature for the purpose of decreasing hardness and increasing toughness. The process also is sometimes applied to normalized steel.

Ferritic Nitrocarburizing (FNC)

Ferritic Nitrocarburizing is a range of case hardening processes that diffuse nitrogen and carbon into ferrous metals at sub-critical temperatures.


A case hardening process in which a suitable ferrous material is heated above the lower transformation temperature in a gaseous atmosphere f 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.

Other process types:


Automated Press Quenching

Black Oxide


Bright Annealing


Carbon Baking

Carbon Restoration





Gas Carburizing

Gas Nitriding

Heat Flattening

High Temperature Tempering



Ion (Plasma) Nitriding

Ion Carburizing

Low Pressure Carburizing




Post Oxidation



Press Quenching


Pyrolysis Resource Recovery




Reheating for Press Quench

Scale Free Heating


Solution Treatments

T6 Heat Treatment

Thermal Destruction



Vacuum Heat Treating


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