What is Annealing?
A metallurgical process of softening a metal by heating it and allowing it to cool slowly. This changes the physical and at times chemical properties of the metal which allows the metal malleable and easily minted into coins or bars.
Annealing takes place when the atoms that make up a material are scattered during the heating process.
For various alloys, the size of the crystal grain and phase composition which determines the properties of the particular material is controlled by the heating and cooling process that the alloy is subjected to. For certain ferrous metals, annealing is conducted by heating the metal to visibly high heat (until the metal is glowing a warm orange or red) and then allowed to cool down to room temperature. When subjecting brass, copper, and silver to the annealing process, the material is heated and then allowed to cool down slowly, either at room temperature or quickly by submerging in water. This process enables the forming, stamping, and shaping of these metals.
There are 3 critical steps in the annealing process. The steps are:
- Recovery.
- Recrystallization.
- Grain Growth.
In the recovery phase, malformed crystal grains reduce their stored energy by purging and reforming the defects in their structures. In the recrystallization phase, the malformed crystal grains are replaced by a new set of healthy grains that grow until they have consumed and replaced defected gains. In the grain growth phase, new crystal grains increase within the material and is the final stage of softening the metal. To keep the material from disintegrating entirely, the process is stopped by cooling and rehardening.
The high temperature involved in the process of annealing can lead to oxidation, resulting in scale. To avoid the development of scale, annealing must be carried out in special atmospheres.
What people ask…
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