What is annealing?
Working with metal can be a difficult task, and it is important to treat your materials appropriately to ensure they maintain the properties you require. There are a number of different treatments all with specific applications but today we are focusing on annealing, a type of heat treatment used to reduce hardness and brittleness and bring down the risk of failure or fracture, allowing a metal to stand up to further work or processing.
What Is annealing?
In metalwork, annealing is a common heat treatment process used to alter the physical and mechanical properties of certain metals to reduce hardness, increase ductility, and eliminate internal stresses. It is commonly used to reverse or reduce the effects of cold-working to allow for further processing. In some circumstances, annealing can also have an effect on a metal’s chemical and electrical properties.
Why Is annealing used?
The primary purpose of annealing is to alter the metal’s mechanical properties, making it softer and more workable. Annealing reduces the risk of material fracture, cracking and distortion. Hard, brittle metals are also more likely to cause excessive wear or damage to tools and machinery, and annealing reduces this impact. Annealing is often used after cold-working processes such as drawing, grinding, roll forming or bending to reduce its effects and allow the metal to be worked further. It is also commonly used to remove stresses that appear after welding. In some circumstances, annealing can be used to improve the electrical properties of a metal by making it more conductive.
How does annealing work?
Annealing works by heating the material above its recrystallisation temperature, holding it at that temperature for the desired length of time, then allowing it to cool at a specific pre-determined rate.
This broken down into three stages:
During the first stage, called the recovery stage, a furnace or alternative heat source is used to increase the temperature of the metal to a level which removes its internal stresses.
The structure of a metal is formed of crystalline structures known as grains. During this stage, the metal is further heated to above its recrystallisation temperature allowing new grains to form free from pre-existing stresses. It is important to calculate your desired temperature accurately to ensure it remains just below the metal’s melting point.
Grain growth stage
In this final stage, the new grains are allowed to develop under a controlled environment by cooling the materials at a pre-calculated rate. This rate determines the final composition of the metal. In some specific types of annealing, certain materials may be cooled quickly by quenching in water. The metal is then ready for any further processes such as shaping or forming.
What equipment is required for annealing?
Most importantly, annealing requires a heating device to bring the metal to its required temperature. This is commonly a furnace, a type of high-temperature oven that is capable of reaching temperatures between 700 °C and 900 °C, although some can reach 1000 °C or higher. It is best to use a furnace that is suitable for your needs, for example, if you have a high volume of parts to anneal, a conveyor-belt furnace may be able to speed up your process.
When working on smaller pieces such as copper wire or jewellery, it is possible to use a blow torch or other handheld device as a heat source.
Which metals can benefit from the annealing process?
Annealing is most commonly used in steels, but it is also possible to apply the process to aluminium, copper, brass and certain alloys. Different types of annealing apply to different metals.
Where are annealed metals most commonly used?
Annealed metals are useful in many situations, including where a metal may need to be worked on multiple times. Common applications include:
- Sheet metals that have been through a cold-rolling process and need further working such as bending or punching.
- Materials that have previously been exposed to high temperatures (such as those used in welding) causing residual stresses.
- Metal wire that has been through a drawing process to reduce its size.
- Copper tubing that requires bending or has previously had its structure compromised by other types of working.
Annealing is used across a wide variety of industries from construction and manufacturing, through to automobile and jewellery.
We stock a range of steel products that are supplied pre-annealed for your convenience. Browse our range of black annealed mild steel wire and bar here.