In the cases of steel, copper, brass and silver, this process is typically performed by heating the material for a while and then slowly allowing the material to cool to its room temperature in still air. Silver, copper and brass can all be cooled slowly in air or quickly by means of quenching the material in water, unlike the ferrous metals like steel which has to be cooled slowly first in order to be annealed. In this way, the metal will be softened and is prepared to do further work like stamping, shaping and forming.
Annealing happens with the diffusion of atoms inside a solid material so that the material will progress towards its static state. The heat will increase the rate of diffusion by providing the right amount of energy which is needed to break bonds. The movement of atoms also has the effect of eradicating and redistributing the dislocations in metals as well as in ceramics. This alteration of the existing dislocations enables the metal object to become deformed more easily thereby increasing its ductility.
Furthermore, the amount of process initiating free energy in a deformed metal is typically reduced by the use of the annealing process. In industry and in practice, the reduction of the free energy is referred to as the stress relief. The relief in the internal stresses is a spontaneous process in thermodynamics. However, when operated at room temperature, the process is thought of to be very slow. The high temperatures at which annealing occur serve to accelerate this particular process. The reaction which also facilitates the return of the cold- worked metal to its stress-free state has a lot of reaction pathways which mostly involves the elimination of lattice vacancy gradients inside the body of the metal. To add, the creation of the lattice vacancies is being governed by the Arrhenius equation and the diffusion or migration of lattice vacancies are governed by the so-called Arrhenius equation and the diffusion or migration of lattice vacancies are governed with the Fick law on diffusion.
When it comes to steel, there is a decarbonation mechanism which is described as three distinctive events: the reaction at the steel surface, the interstitial diffusion of the carbon atoms and finally the dissolution of the carbides within the steel.
There are typically three stages in the process of annealing which proceed as the temperature of the material is increased and are as follows:
- Grain growth