subject: Get To Know More About Some Heat Treatment Processes [print this page] The process of heat treatment involves controlled heating and cooling of the metals for altering their mechanical and physical properties without having any change in their shapes. This process is sometimes conducted inadvertently because of the manufacturing method, which either cool or heat up the metal like forming or welding. Here are some heat treat methods to enhance your knowledge.
Annealing is the method of heating steel and holding the material to a certain temperature followed by cooling down at a suitable rate. This in fact improves the machinability, softness and cold working features of the steel and even helps in removing the stresses of the material thereby managing to get the desired structure. In full annealing the material gets heated up to a temperature where carbide is partly or wholly taken into solution and the steel is then cooled down slowly in the furnace. Sub critical annealing takes place at a temperature below the temperature at which the carbide starts to be taken into the solution.
Ageing is a process that causes structural changes, which usually occurs in definite alloys and metals at atmospheric temperature or at high temperatures. Due to ageing, hardness values, proof stress and maximum stress are increased with reduction in the ductility. There are certain conditions, where ageing is done by heating at an elevated temperature. This is usually referred to as artificial ageing and this process results in precipitation hardening.
Carburising is just an introduction of the carbon into steel's surface layer that has low content of carbon. It might get effected by heating in a liquid, solid or gaseous carbon-containing medium. This at higher temperatures gives a supply of the carbon to be absorbed by the carburised material. The carbon concentration and its depth in steel surface varies by controlling the time span and temperature needed for the heat treatment.
Hardening is the process that increases the hardness of the material by the heat treat. This normally implies heating up to a temperature just above the critical range by maintaining the temperature where diffusion gets completed and by quenching in oil, water or air.
Induction hardening is the process used for hardening steel by heat treat. It is generally done by alternating magnetic field to a temperature above or within the transformation range followed by quenching. Induction hardening is applied to both full hardening and surface hardening.
Normalising is a heat treat method which requires heating to and when necessary even holding the same at a temperature followed by cooling down in still air so that cooling occurs rapidly at a moderate level. Its main object is to relieve the internal stress, give the structure a more uniform shape, refine grain size and improve all its mechanical properties. The process is usually used for castings and large forgings which cannot be tempered and quenched.
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by: John Samual
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