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 ?
In addition to heat treat furnaces, Lindberg/ MPH designs and manufactures a full line of melting and holding furnaces for non-ferrous alloys.
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We have timed the product prebooking fulfillment date for fourth quarter 2002 to allow category managers ample time to work Heat Treat Foot Care insoles into their planograms prior to a full product launch in 2003," Saunders says.
Heat treat involves heating and cooling material to give it certain physical characteristics.
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The heat treat process results in an unavoidable size increase in tool steels due to the changes in microstructure.
Special care needed to heat treat today's new-generation materials.
The new furnace, model VTL-714 will be used to homogenize and heat treat refractory alloys, perform diffusion couple experiments as well as other proprietary heat treat work.
A new cost-effective technology to heat treat ferrous materials promises higher quality, reduced cycle times, and more applications than other comparable methods.
In addition to the company s full range of industrial gases, equipment, and technology solutions for the metals processing industry, Air Products will share some of its latest research, which can help metals processors increase production and improve product quality, at the Heat Treat 2013 Conference and Exposition in Indianapolis, Ind.
Marys, Ohio, is in the process of installing in-house heat treat capacity that it hopes to have online by mid-December.