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 ?
In the second stage, heat treatment has been applied in the aimed three different temperatures (190, 200 and 210[degrees]C) for two hours to the samples dried up to approximately 0% humidity by rapidly increasing the oven temperature with the use of heat and steam in the first stage.
Furthermore, increasing the heat treatment temperature enhanced the chemical durability by reducing the chemical agent absorption.
a] values, only samples ground with a 600-grit diamond disc (corresponding to extra-fine diamond burs (10)) presented lower surface roughness, regardless of the heat treatment used.
The heat treatment duration also significantly affected the surface pitting.
They explained that heat treatment plays a vital role in industries of today as science and technology are in pursuit of designing materials of improved properties.
This shows that the difference in the refractive index of matrix and spherulites became very small by the heat treatment.
In addition, the ratings continue to draw comfort from the company's experience in providing heat treatment solutions mainly to the automotive sector, as well as the technology-focused nature of HTF's business, backed by its broad range of technical collaborations for speciality heat treatment processes, Fitch added.
Key words: numerical simulation, heat treatment, casting
This investment follows the success of the Heat Treatment Department, which already operates six furnaces, an existing Water Quench and a Polymer Quench.
The information obtained from the study is critical to the support of dielectric heat treatment as a universal alternative to conventional heat treatment and methyl bromide fumigation for wood movement worldwide," Mr.
The big move came after researchers said cancer patients whose tumors are targeted with heat treatment as well as chemotherapy are more likely to stay alive and cancer-free for longer than those who receive only chemotherapy.