What is heat treatment and why is it done ?

it is a stress reliving process for metal for which undergo any mechanical process of manufacturing.

Heat treatment is the process of modifying physical and mechanical properties of metals. Metals are heated up to a specific temperature lower then the melting point and near about the re-crystallization temperature. After heating up its cooled down. There are different methods of heating and cooling. After the process the Physical and mechanical properties of metals are modified. There are many methods for heat treatment like Annealing, Normalizing, Quenching etc. Every method have different effect on the metallic properties.