In metallurgy, heat treatment is defined as the combination of heating and cooling operations carried out on a metal or alloy in the solid state. Heat treatment helps to achieve desired microstructure and properties. For steel, a wide range of mechanical properties can be accomplished by proper heat treatments. Heat treatment helps to improve mechanical properties such as tensile strength, impact resistance and ductility. It also improves magnetic and electrical properties. By heat treatment we can increase wear resistance, abrasion etc. Heat treatment also helps in improving machinability and refining grains. By suitable heat treatment, we can produce hard surfaces and soft interior portions. There are two types of heat treatment processes. They are full heat treatment and surface heat treatment. Recrystallization annealing, full annealing, partial annealing, process annealing, spheroidising annealing, normalizing, hardening, austempering and mastempering comes in the category of full heat treatment. Surface heat treatment includes pack carburizing, liquid carburizing, gas carburizing, cyaniding, nitriding, carbo-nitriding, flame hardening and induction hardening. Some advanced techniques of heat treatment are ion nitriding, plasma carburizing, electron beam hardening and laser hardening.
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