<P> Various forms of casting exist in industry and academia . These include sand casting, investment casting (also called the lost wax process), die casting, and continuous casting . </P> <P> Metals can be heat - treated to alter the properties of strength, ductility, toughness, hardness and / or resistance to corrosion . Common heat treatment processes include annealing, precipitation strengthening, quenching, and tempering . The annealing process softens the metal by heating it and then allowing it to cool very slowly, which gets rid of stresses in the metal and makes the grain structure large and soft - edged so that when the metal is hit or stressed it dents or perhaps bends, rather than breaking; it is also easier to sand, grind, or cut annealed metal . Quenching is the process of cooling a high - carbon steel very quickly after heating, thus "freezing" the steel's molecules in the very hard martensite form, which makes the metal harder . There is a balance between hardness and toughness in any steel; the harder the steel, the less tough or impact - resistant it is, and the more impact - resistant it is, the less hard it is . Tempering relieves stresses in the metal that were caused by the hardening process; tempering makes the metal less hard while making it better able to sustain impacts without breaking . </P> <P> Often, mechanical and thermal treatments are combined in what are known as thermo - mechanical treatments for better properties and more efficient processing of materials . These processes are common to high - alloy special steels, superalloys and titanium alloys . </P> <P> Electroplating is a chemical surface - treatment technique . It involves bonding a thin layer of another metal such as gold, silver, chromium or zinc to the surface of the product . It is used to reduce corrosion as well as to improve the product's aesthetic appearance . </P>

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