It is a generalized term. It consists of metal`s heating at a particular temperature & then cooling it down at that particular rate that produces refined microstructure. Cooling rate is normally slow. This technique is often used for softening of metals for cold-working, for improving machinability and for enhancing properties like that of electrical conductivity. As this technique has various purposes, so its benefits are also according to the purposes it fulfills.
Among ferrous alloys, the technique of annealing is accomplished through heating metals at more than upper critical-temperature and then cooling it down very slowly. This results in peartile`s formation. Annealing is applied to remove hardness of cold workings in case of both pure-metals and alloys that cannot be done with heat treating. Metal is here heated at a temperature that causes re-crystallization, to repair defects resulting from plastic deformation. Cooling rate is thus found to have very little effect in case of these metals. Majority of non ferrous metals being heat treatable are also gone through annealing to relieve hardness caused due to cold working. These non ferrous alloys are cooled down slowly to allow the constituents` full precipitation and for producing refined microstructure. These ferrous alloys are normally process annealed or full annealed. Slower cooling rates are required for full annealing for forming coarse peartile whereas that of process annealing requires faster cooling rate, up to and comprising of normalizing. Process annealing`s main purpose is production of uniform microstructure. Mon ferrous alloys are normally subject to various annealing techniques, such as re-crystallization-annealing, partial-annealing, final-annealing and full annealing. Recrystallization is not a part of all techniques of annealing, such as stress-relieving.