Metallurgy

Mechanical working of a metal is plastic deformation performed to change dimensions, properties, and/or surface conditions. Plastic deformation below the recrystallization temperature is called cold working. Plastic deformation above the recrystallization temperature, but below the melting or burning point, is called hot working.

Cold working produces a good surface finish, close dimensional tolerance, and does not result in weight loss during working. It produces considerable increase in strength and hardness, and reduces ductility. By repeatedly cycling a material through stages of annealing and cold working, a very strong material can be produced.

Hot working is actually a combination of working and annealing that involves deforming the metal above the recrystallization temperature. Ductility is restored during recrystallization, and grain growth during or immediately following recrystallization.

Effects of hot working a metal piece may include: densifying the metal; refining the grain structure; introducing homogeneity into the metal; introducing a preferential orientation into the metal.