Heat Treating vs Annealing
In the magnetic shielding business, we often times receive requests for us to “hydrogen anneal for maximum magnetic permeability”. While we understand what our customer is looking for, we try to educate them about the difference between “annealing” and “heat-treating.”
The definition of annealing is: “heat metal and allow it to cool slowly, in order to remove internal stresses and toughen or soften it.” While we need to anneal mumetal and other magnetic shielding alloys during the magnetic shield fabrication process, we do not anneal for maximum magnetic permeability. As noted in the definition, the annealing step is done to relieve stress within the material that was introduced as a part was being formed or bent.
When we are heat-treating our mumetal and Alloy 49 magnetic shielding materials, we are actually changing the physical properties by enlarging the grain structure, allowing for more magnetic flux to be absorbed by the magnetic shield.
In conclusion, both annealing and heat-treating are necessary during the magnetic shield fabrication process, but both serve a very different purpose. If you need to relieve stress in material, soften or toughen it, you want to anneal it. If you are trying to achieve maximum permeability, you want to heat treat the material.
It should also be noted that material in our kits have been annealed for forming, but is not heat-treated for maximum magnetic permeability.