What is Annealing?
Annealing is a heat treatment which alters the physical and often chemical properties of a metal to see it increase in ductility and decrease in hardness. Annealing involves heating the metal to a certain point and then slowly cooling. It is often used to soften a metal for cold working, improve machinability, and increase electrical conductivity. Annealing is used for steel. Other materials such as brass, copper, and aluminium can undergo a different process called solution annealing.
It can help make a metal more ductile. When cold working on a metal, the metal can become so hard that it cracks under further work. By annealing the metal prior to cold working, the stress within the metal is released allowing for cold working to take place without the risk of cracking.
The steel is put in a large oven where there is enough room to allow air to circulate around the metal. The metal is heated to a specific temperature where ‘crystallisation’ occurs. During this stage, defects are repaired. The metal remains at this temperature for a period of time and is then cooled down very slowly to room temperature. The cooling process can be done by immersing the metal in a low heat conductivity substance i.e. sand, or by switching off the oven.
Glossary of Metal Terms Used
Crystallisation –A solid forms as a result of the atoms and molecules being highly organised into a structure (crystal)
Cold Working – Strengthening a metal by changing its shape without the use of heat
Machinability – Ease at which a metal can be cut by machinery