heat treatment

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heat treatment

[′hēt ‚trēt·mənt]
(metallurgy)
Heating and cooling a metal or alloy to obtain desired properties or conditions.

Heat treatment (metallurgy)

A procedure of heating and cooling a material without melting. Plastic deformation may be included in the sequence of heating and cooling steps, thus defining a thermomechanical treatment. Typical objectives of heat treatments are hardening, strengthening, softening, improved formability, improved machinability, stress relief, and improved dimensional stability. Heat treatments are often categorized with special names, such as annealing, normalizing, stress relief anneals, process anneals, hardening, tempering, austempering, martempering, intercritical annealing, carburizing, nitriding, solution anneal, aging, precipitation hardening, and thermomechanical treatment.

All metals and alloys in common use are heat-treated at some stage during processing. Iron alloys, however, respond to heat treatments in a unique way because of the multitude of phase changes which can be induced, and it is thus convenient to discuss heat treatments for ferrous and nonferrous metals separately.

Ferrous metals

Annealing heat treatments are used to soften the steel, to improve the machinability, to relieve internal stresses, to impart dimensional stability, and to refine the grain size.

Hardening treatments are used to harden steels by heating to a temperature at which austenite is formed and then cooling with sufficient rapidity to make the transformation to pearlite or ferrite unfavorable.

Some heat treatments are used to alter the chemistry at the surface of a steel, usually to achieve preferential hardening of a surface layer. Carburizing consists of subjecting the steel to an atmosphere of partially combusted natural gas which has been enriched with respect to carbon. In the nitriding treatment, nitrogen diffusing to the surface of the steel forms nitrides. Chromizing involves the addition of chromium to the surface by diffusion from a chromium-rich material packed around the steel or dissolved in molten lead.

Nonferrous metals

Many nonferrous metals do not exhibit phase transformations, and it is not possible to harden them by means of simple heating and quenching treatments as in steel. Unlike steels, it is impossible to achieve grain refinement by heat treatment alone, but it is possible to reduce the grain size by a combination of cold-working and annealing treatments.

Some nonferrous alloys can be hardened, but the mechanism is one by which a fine precipitate is formed, and the reaction is fundamentally different from the martensitic hardening reaction in steel. There are also certain ferrous alloys that can be precipitation hardened. However this hardening technique is used much more widely in nonferrous than in ferrous alloys. In titanium alloys, the β phase can transform in a martensitic reaction on rapid cooling, and the hardening of these alloys is achieved by methods which are similar to those used for steels.

heat treatment

Heating and cooling a solid metal or alloy in order to produce changes in its physical and mechanical properties.
References in periodicals archive ?
The company said its facility will increase its OCTG heat-treat capacity by an additional 100,000 tons per year.
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Under these agreements, heat-treat customers will have access to a simplified market channel which integrates Praxair's gases, applications technologies and supply systems with process controllers and data acquisition software from Super Systems and precise furnace control panel systems from Atmosphere Engineering.
As Brian Sheehy, manager, heat-treat applications, Airco Industrial Gases Div, Murray Hill, NJ, explains, "Endothermic generators have been around since WWII, a very complicated piece of machinery, running at high temperature, with lots of moving parts such as pumps and valves with limited life.
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In addition, the agreement confirms Trentwood's position as a world-class provider of heat-treat aluminum products to the aerospace industry.
The melt, shakeout and heat-treat areas of the foundry are the only parts of the facility not air-conditioned.
Nasdaq: LIND), the largest commercial heat treater in the United States, today announced its has acquired Quality Heat-Treat, Inc.
Based on our strategic review of this project, and on Trentwood's improved performance over the last several months, we have concluded that we can build on our existing heat-treat capabilities in-house faster and more effectively than originally thought," said Raymond J.
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Lindberg estimates the aerospace industry will account for about one-third of 1998 heat-treat revenues.
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