When a piece of metal is hot forged it must be heated significantly. During hot forging, the temperature reaches above the recrystallization point of the metal. This kind of extreme heat is necessary in avoiding strain hardening of the metal during deformation. It helps with the production of discrete and complicated parts which would be difficult to produce from simple bar stock machining. It also has an advantage over casting as cast parts can develop pin holes which is avoided by hot forging.
Materials : Brass, Bronze, Aluminum etc.