Annealing is a special heat treatment aimed at making metals easier to work with. By changing the properties of a metal, annealing makes it less hard and more ductile (softer and simpler to manipulate). Although annealing usually happens on a large scale using machinery, there are other examples. When a farrier or blacksmith heats and shapes horseshoes, for example, this is an example of annealing. Read on to find out more about the process.
What Happens During Annealing?
During annealing, metal is heated until it reaches the molten stage. It is then kept at a high temperature for a specified amount of time. Finally, the metal is carefully reheated to room temperature (and its solid form). Metal can be left to cool to room temperature gradually, but sometimes the process is sped-up with water or sand. The method used for cooling depends on the material being annealed and the desired finished results.
How Does Annealing Work?
When a material is heated over its recrystallisation temperature, changes take place in its microstructure. You might not be able to see the differences between metal that has been annealed and that which hasn’t, but those structural changes make a big difference to performance. By altering the structure (and mechanical properties) of a material, you can transform its hardness, malleability and more.
What Are the Three Stages of Annealing?
There are three main stages to the annealing process. They are:
- Recovery – The metal is heated, usually in a furnace, to a temperature at which internal stresses are relieved.
- Recrystallisation – The material is further heated, to a temperature below its melting point, but above crystallisation.
- Grain Growth – The material is carefully cooled at a controlled rate, resulting in the development of more grains (crystallites) in the metal’s structure. It is this growth in grains that makes the treated metal softer than it was before the process began.
Why Does Metal Get Annealed?
Annealing makes metals softer and therefore easier to work with. Metal that has been annealed can be easily stamped and shaped. The process also increases machinability; sometimes when materials are too hard, they can damage tools or machinery. This issue is reduced by annealing. Some metals’ magnetic and electrical-conducting properties are increased by being annealed. What’s more, annealing also reduces the metals’ internal stress, making it less brittle.
What Are the Disadvantages to Annealing?
Although annealing makes metals easier to work with, it can also weaken them, so this must be taken into consideration. Another disadvantage is that annealing can be time consuming and expensive, and that it uses a lot of energy.
What Materials Can Be Annealed?
Can I Anneal Metal at Home?
It is possible to perform annealing at home, but you would need to have a heat treatment oven. As these are expensive, most annealing tends to take place in a specialist manufacturing setting.