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 ?
Seventy-nine indicated that they would simply comply with the new requirements, 14 indicated they would buy heat-treating equipment, 13 indicated they would raise prices, 12 reported they would possibly quit the business, 6 said they would do nothing, 3 stated they would buy heat-treated lumber, and one would out-source phytosanitary treatment.
And Dana has signed an agreement with ALD Vacuum Technologies (Hanau, Germany) to develop the AtmoPlas technology for heat-treating and carburizing.
This procedure follows heat-treating and is used to stabilize the material to increase the life of the dies.
Polymer quenchants, such as PAG (poly alkylene glycol)based fluids, have been used for many years to provide improved distortion control and cracking in various heat-treating operations.
When austenitizing, care must be taken to avoid carburization or decarburization by carefully monitoring the heat-treating atmosphere.
About the same proportion (61%) certify each heat-treating job, although fewer than half (47%) certify each plating or other surface-coating job.
This arrangement with Praxair will help us to build on our global presence while providing our customers with the best solutions to meet their heat-treating requirements," said Eric Jossart, vice president of sales for Atmosphere Engineering.
As he sees it, the key trend today is using more robotics to automate heat-treating systems and make them flexible enough to process different types of parts.
The European Union has adopted new regulations requiring all non-manufactured wood packing materials to meet heat-treating standards.
There are many synergistic opportunities to combine the expertise and experience in our heat-treating and processed steel business with SCM to build and strengthen our combined businesses," said Mr.
With this in mind, Farrar devised a 10-year plan, in which the company would expand with the construction of a new foundry, machine shop and heat-treating facility.
B&W also provides a comprehensive range of other heat-treating processes and services, including controlled atmosphere processing, salt bath processing, continuous mesh belt processing, and low-frequency induction.