heat treatment

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heat treatment

[′hēt ‚trēt·mənt]
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 ?
Meltham Mills Group is made up of Meltham Mills Engineering, which makes transmission parts for heavy, off-road vehicles, and Meltham Mills Heat Treatment, which provides heat treatment and surface engineering services to precision engineering companies.
This materials describes a range of nodular ductile iron which have been subjected to an isothermal heat treatment to produce an essentially bainitic structure in this material (Schissler et al.
A PEF treatment, combined with a moderate heat treatment, could improve the microbial stability of a yogurt-based product without causing a significant loss of the product's sensory and physical properties.
The court heard that the person responsible for overseeing the treatment in this instance was no longer employed by the company and that heat treatments were no longer offered to customers.
Heat treatment in France and Germany was also weak, it said, although its UK businesses were performing well.
0] is the sample length along the stretching direction before heat treatment, and L is the length of the heat treated membrane at 24 h after it was detached from the stainless steel plate.
The confused flour beetles, 50 per ring, were monitored at 60-minute intervals during the heat treatment.
This tendency did not change even if the samples were subject to an adhesion heat treatment whereby they were elongated by 4.
time curves for the surface and center of a heat treatment load undergoing an annealing heating cycle.
There are also two heat treatment plants,Controlled Heat Treatment which has been operating in Lye since 1946, and Express Heat Treatment in Cradley Heath.
Heat treatment is accepted for the phytosanitation of wood.
Whey proteins are very sensitive to any type of heat treatment that induces both structure unfolding and polymerization reactions.