Heat treatment involves controlled heating and cooling of metals to alter their properties and is used to improve machining, reduce forming forces, and restore ductility. Key heat treatments include annealing to reduce hardness and residual stresses, normalizing to obtain a uniform structure, and precipitation hardening using a solution treatment, quench, and aging steps. Heat treatment processes are aided by phase diagrams which show temperature effects. Proper design and material selection are important to avoid issues from nonuniform sections or residual stresses during heat treatment.