Metal Annealing (Recrystallization Anneal)

This video discusses the recrystallization anneal process used with cold-worked metal to reduce its strength and increase its ductility.
Cold working is used during metal production to reduce sheet and plate thickness, reduce bar, rod, and wire diameter, and modify tube diameter and wall thickness. During cold working the number of dislocations in a metal increases, resulting in increased yield and tensile strength as the amount of cold working increases. At the same time, the metal’s ductility decreases. There comes a point when additional cold working will cause the metal to crack. At this point, the metal must be annealed if additional cold working is required.
During a recrystallization anneal, metallurgical changes occur that result in a reduction of the metal’s yield and tensile strength and an increase in its ductility, enabling further cold working. The metal must be heated above its recrystallization temperature for these changes to occur. The recrystallization temperature for a particular metal depends on its composition and amount of cold working.
During a recrystallization anneal of a cold-worked metal, new grains form from the cold-worked grains. These new grains have a greatly reduced number of dislocations compared to the cold-worked metal. This change returns the metal to its pre-cold-worked state, with lower strength and increased ductility.
Several factors influence the annealed grain size - initial grain size, amount of cold working, and annealing temperature and time. In turn, the grain size affects metal strength, hardness, and ease of forming.
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