Annealing is a group of treating processes in which a material is softened to improve machinability, allow for cold work (bending, rolling, pressing), improve electrical conductivity, reduce residual stress, and increase dimensional stability.
Annealing works by heating the material above its recrystallization temperature (but below its melting point) and then cooling it after the material has been held at that temperature for a certain length of time. This causes a redistribution of the atoms that make up the material, changing its physical, and sometimes even chemical properties. Parts are heated and held at temperature depending on part geometry, material, and desired microstructure. Some forms of annealing will also include a controlled cooling rate.
Common Alloys that can go through Annealing
Most materials can be annealed, and there is very little out there that won’t benefit from this process. Remember, however, that annealing is a different process from Solution Annealing, a type of heat treatment that we also offer at TMT.
Thermal Modification Technology’s Annealing Capabilities
Annealing is a versatile process with several different subtypes and variations that we can offer our customers. For instance, we can anneal parts in a vacuum or an air atmosphere, depending on your needs. However, keep in mind that during high-temperature annealing, parts will become scaled if annealed in air.
We also have the capability to perform several types of annealing, such as:
- Sub-Critical Annealing: Also called “sub-annealing” and “process annealing,” this is a cost-effective method of annealing steel. Parts are heated to just below the critical point of steel and held there. This greatly reduces the residual stress and hardness of the material. And, because the parts don’t need a slow, controlled cool down from the annealing temperature, the cycle time is much reduced.
- Full Annealing: In this type of annealing, we heat steel above its critical point and then cool it slowly in a furnace. This is a more time-intensive process, but it’s especially beneficial for products that need a maximal removal of residual stress and hardness.
- Spherodize Annealing: This type of annealing is particularly beneficial for high-carbon steels. In spherodize annealing, parts are heated and cooled in a manner that forms a soft, ferritic matrix with spherical carbides. Spherodize annealing is often used for parts that will subsequently be subjected to large amounts of cold work.
- Induction Annealing/Normalizing: This selective heat-treating process limits the heat treating to certain areas of the part, rather than treating the whole part all at once. For more information, see Induction Heat Treating.
Applications of Annealing
Annealing is often used on materials that will later be machined, as this type of heat treating reduces hardness, making machining much easier. It also reduces stress from significant cold work, strengthening the part overall.
Specs/Standards associated with Annealing
- ASTM A668
- MIL 1684
What to consider when specifying your parts for annealing
- Furnace Atmosphere
- Spec (if required)