heat treatment

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heat treatment

[′hēt ‚trēt·mənt]
Heating and cooling a metal or alloy to obtain desired properties or conditions.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

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.

McGraw-Hill Concise Encyclopedia of Engineering. © 2002 by The McGraw-Hill Companies, Inc.

heat treatment

Heating and cooling a solid metal or alloy in order to produce changes in its physical and mechanical properties.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.
References in periodicals archive ?
Therefore, the microstructure of the WS heat-treated at 700[degrees]C was consisted of untempered martensite and tempered martensite.
When compared to control samples, L* value has decreased up to respectively 46%, 54% and 62% at 190, 200 and 210 [degrees]C in heat-treated scotch pine samples; and it has decreased up to respectively 48%, 58% and 64% in Eastern beech samples.
Representative color changes after the accelerated UV weathering test are shown in Figure 3 for both heat-treated and untreated samples.
They applied various techniques, including 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) radical-scavenging activity, to investigate the antioxidant activities of the heat-treated samples.
The same official estimated that China's annual exports of heat-treated poultry products to the EU could reach 100,000 tons worth $1 billion.
When unprocessed and processed juices were compared, samples exposed to the alternative hurdle approach displayed fewer color differences and greater ascorbic acid retention than did the heat-treated samples.
The enhanced hydrophobic character of heat-treated wood is well known.
Because it hasn't been heat-treated, unpasteurised milk can contain bacteria that could cause food poisoning.
Features include top-removable gearing for easier maintenance, double reeved, heat-treated sheaves for true vertical lift, and Ace Toshiba flux vector controls.
"The additional capacity is designed to position Ipsco for further growth in value-added energy tubular product markets by taking advantage of the growing demand for high-grade heat-treated products," said Joseph Russo, Ipsco's senior vice president and chief technology officer.
* Dual heat-treated steel ripper shanks can be quickly lowered to a depth of 7 inches to loosen hard packed areas.
If you order from DLA, write in the remarks box of the requisition: heat-treated lumber only.