What is Annealing Process

 

Annealing

Annealing involves heating steel to a specified temperature and then cooling at a very slow and controlled rate.

Annealing is commonly used to:

• Soften a metal for cold working
• Improve machinability
• Enhance electrical conductivity

Annealing also restores ductility. During cold working, the metal can become hardened to the extent that any more work will result in cracking. By annealing the metal beforehand, cold working can take place without any risk of cracking, as annealing releases mechanical stresses produced during machining or grinding.

Annealing is used for steel, however, other metals including copper, aluminum and brass can be subject to a process called solution annealed.

Large ovens are used for annealing steel. The inside of the oven must be large enough to allow air to circulate around the metal. For large pieces, gas fired conveyor furnaces are used while car-bottom furnaces are more practical for smaller pieces of metal.

During the annealing process, the metal is heated to a specific temperature where recrystallization can occur. At this stage, any defects caused by deformation of the metal are repaired. The metal is held at that temperature for a fixed period, then cooled down to room temperature.

The cooling process must be done very slowly to produce a refined microstructure, thus maximizing softness. This is often done by immersing the hot steel in sand, ashes or other substances with low heat conductivity, or by switching off the oven and allowing the steel to cool with the furnace.