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 ?
Results from the subjects' responses data showed that both raw and heat-treated ginger lowered muscle pain intensity after eccentric exercise by 25 and 23 percent, respectively.
The obvious choices are to engage the services of a custom heat treater, reduce overall production to meet current heat-treating capacity, or purchase heat-treated lumber and fabricate WPM without the need of on-site treatment capability.
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.
Delphi is one of the largest producers of heat-treated products in the world, so it was of great interest to us to develop the nickel alloy further in partnership with D.
We are the only company I know of that pours ductile iron castings from 1-65 lb, has its own in-house pattern shop, foundry and machine shop, get its parts heat-treated and assembles them," said Farrar, who has seen his company's total sales steadily increase from $3.
Japan now bans imports of beef and meat-based cattle feeds that are not heat-treated from countries hit by the brain-wasting illness.
After heat-treated coagulants were approved by the government in 1985, the Green Cross executives approved the sale of the tainted and untreated agents to avoid losing money from lost inventory, continuing to do so even after Green Cross began selling heat-treated products in early 1986.
Thus, the precise end-point temperature of heat-treated chicken can be obtained by measuring the residual catalatic activity.
The government has admitted that, in 1983, it knew about the risks of conventional blood products but chose to wait until 1985 to approve new heat-treated versions.
If one assumes that there are no significant surface activity variations among the four heat-treated carbon blacks in table 2, then the modulus levels for the vulcanizates containing these samples should be dependent on [V.
I see a trend toward maintaining the fine metallurgy that vacuum has given us for years and producing big increases in productivity of the final heat-treated product.
com/reports/c43390) has announced the addition of Acrylamide and Other Hazardous Compounds in Heat-Treated Foods to their offering.