Annealing plays a key role in the production of high-quality steels and precision alloys and is one of the important stages in the heat treatment of metal workpieces. This process involves heating the parts to a predetermined temperature, holding them under such temperature conditions, and then slowly cooling them down. The purpose of annealing is to eliminate residual stresses, to ensure a uniform and stable structure of precision alloys and high-quality steels, and to give them the necessary plasticity.
There are several types of annealing that differ in their effect on the internal structure of the material.
Full annealing
Used for pre-eutectoid steels, such as 08KP, 08PS, 20, 70containing less than 0.8% carbon. It is aimed at forming small austenitic grains, which, when cooled, form a uniform ferrite-pearlite structure, which significantly improves the characteristics of steel. The heating temperature and holding time directly depend on the size of the workpieces, their placement in the furnace, chemical composition and other production factors. To protect semi-finished products and finished products from oxidation and decarburization, heat treatment is carried out in protective atmospheres.
Isothermal annealing
It is aimed at improving the machinability of alloys, such as 12X18N9 et 12X18H10T, and obtaining a more homogeneous ferritic-pearlite structure. It reduces the time of recrystallization, which is especially important for alloy steels, since after full annealing, they take quite a long time to cool down to reduce hardness.
Incomplete (spheroidizing) annealing
Recommended for carbon and alloy steels, such as 60S2A, 65G, 70S2HA, U8A, Y10A. They are widely used for eutectoid (containing from 0.8% to 2.14% carbon) materials, and to a limited extent for pre-eutectoid materials. This type of annealing leads to the formation and growth of new crystalline grains (almost complete recrystallization) and the formation of a spheroidal form of perlite instead of the usual lamellar one. As a result of heat treatment, alloys and steels are better cut and also acquire improved properties for cold rolling, stamping and drawing.
Homogenization annealing
It is used to eliminate chemical heterogeneity in alloyed steels and alloys that occurs during the crystallization of metal. It involves heating the workpiece to high temperatures, followed by prolonged exposure and slow cooling. The result is a material with coarse grain, which, if necessary, can be reduced by pressure or additional heat treatment. Used for alloys 50N, 50NP, 79NM, 49K2FA, 27KHto ensure high magnetic properties.
Annealing to relieve internal stresses
It is aimed at reducing the residual stresses that occur in the metal during various technological operations, such as forging, welding, and cold rolling. The purpose of this heat treatment is to reduce or completely relieve the stress that has arisen as a result of external mechanical stress.
Recrystallization annealing
It involves heating cold-deformed steel to a temperature higher than the onset of recrystallization, holding it at a predetermined temperature and further slow cooling. It is carried out in order to increase the plasticity of the metal before cold pressure treatment, remove the rivet between technological operations and impart the necessary physical and mechanical properties.
Normalization
It is often used as an intermediate operation to soften steel or alloy before pressure treatment or cutting, as well as to eliminate defects and improve the structure of the material. During the normalization process, the steel is heated to a high temperature and then left to cool slowly in the air. Compared to annealing, it makes it possible to obtain a more durable material.
In some cases, normalization is preferable to annealing if both processing methods produce comparable results. This is due to the fact that normalization is more economical in terms of cost and time.
The annealing of steels and precision alloys is an important process aimed at improving the mechanical and physical properties, as well as the structure of the material. This type of heat treatment can significantly improve the manufacturability of an alloy or steel, improve their structure, eliminate defects and reduce internal stresses.
In addition, annealing improves machinability, which facilitates operations such as milling and drilling. This process also increases the weldability of the material, which is critical for the reliability and durability of welded structures in the oil and gas and energy industries.
