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 ?
After 35 d of storage, followed by four days of shelf life, the heat treatment at 40 [degrees]C provided a lower ethylene production in relation to the other treatments, with exception of the application of ethanol vapor at 1500 [mucro]L [L.sup.-1], followed by 1-MCP (1,0 [mucro]L [L.sup.-1]) and the heat treatment at 37 [degrees]C.
Although differences in survival after vapor heat treatment among the 3 B.
The heat treatment in the samples, by not having a significant result, shows that, to achieve positive results for hygroscopic and residual swelling, it must increase the treatment temperature and time to degradation occurrence of its more hydrophilic constituent, the hemicellulose, and thus, has a possible increase in the dimensional stability.
The samples have been rested under atmospheric conditions for 2-3 weeks after the heat treatment. Following that; the samples have been cut in the dimensions 80 x 80 x 10 mm (longitudinal direction x tangent direction x radial direction) and in a way that it will have six repetitions (n=6) for each variable (Figure /Sekil 3).
Lactulose, a molecule not present in raw milk, is formed by epimerization of lactose due to heat treatment. The isomerization process is closely linked to the pH, time, and temperature of the thermal treatment; therefore the lactulose determination is intended to evaluate the severity of the heat treatment of milk.
The absolute magnitude of effects of all process input variables are close to each other and have the same trend, that is, increasing the ash content, heat treatment temperature, or pressing pressure tends to barely decrease the chemical absorption.
X-ray diffraction data (Figure 2) show that grinding promoted a higher m-phase content than the control group, and that heat treatment induced the reverse transformation of the monoclinic phase, achieving a m-phase content similar to that of the control group.
Compared with heat treatment with a thermal medium, few studies have addressed changes in chemical composition and crystallinity during vacuum heat treatment.
The effectiveness of heat treatment, however, may vary from species to specie and different fruit require different temperatures and treatment duration for desired benefits (Barki-Golan and Phillips, 1991).
Furukawa Electric's new distortion resistant CuNb reinforced Nb3Sn superconducting cable can be wound after heat treatment for Nb3Sn generation, and Furukawa delivered mass produced products with a gross length of 7.8 kilometers to Toshiba in March of this year.
Firefighters at Coventry Heat Treatment on the Bayton Road Industrial Estate in Exhall
If some of the castings do not reach the desired temperature or are not at it for the full 12 hours, inadequate heat treatment would occur.