Annealing Process: Understanding Its Benefits And Uses
The effect associated with cold working (for example, strain, hardening) can be reversed by simple heating of the metal. The process is called annealing.
- The more severe the cold working the more readily annealing occur.
- Annealing generally comprises of three stages.
- Recovery: In the recovery stage, the properties of the cold worked metal begin to disappear before any significant changes are observed under microscopic examination.
- Recrystallization: When a severely cold worked metal is annealed, recrystallization occurs after recovery. This involves a radial change in the microstructure.
- Grain growth: The average grain size of the recrystallized structure depends on the initial number of nuclei. The more severe the cold working, the greater the number of such nuclei, and the grain size for the recrystallized metal can range from fie to fairly coarse.
- This grain growth process is simply a bounded energy-minimizing process.
- The annealing is a relative process, the higher the melting point of the metal, the higher is the temperature needed for annealing.
Degassing:
It is also called desorption.
- It is preferred over annealing because at no stage there is not any recrystallization or stress relief intentional
- The primary purpose is to produce an atomically clean surface and render the material cohesive and workable.
- For non-cohesive gold, degassing is done to remove protective ammonia film which is placed on the surface by the manufacturer.
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