ANNEALING

Annealing, in metallurgy and material science, is a heat treatment wherein the microstructure of a material is altered, causing changes in its poperties such as strength and hardness. It is a process that produces equilibrium conditions by heating and maintaining at a suitable temperature and then cooling very slowly. It is used to induce softness, relieve internal stresses, refine the structure and improve the cold working properties. There are three stages in the annealing process, with the first being the recovery phase, which results in the softening of the metal through removal of crystal defects and the internal stresses which they cause. The second phase is recrystallization, where new grains nucleate and grow to replace those deformed by internal stresses. If annealing is allowed to continue once recrystallization has been completed, grain growth will occur, in which the microstructure starts to coarsen and may cause the metal to have less than satisfactory mechanical properties.