What is the magnetic permeability of materials? It refers to their ability to be attracted by a permanent magnet or to be influenced by a magnetic field.
What are ‘magnetic’ steels?
Which steels are classified as ‘magnetic’?
- Ferritic stainless steels
- Martensitic stainless steels
- Duplex steels
- Non austenitic steels.
Why are they identified in this way? These types of steels show a strong response (or pulling) to a magnetic field (such as a portable magnet).
Magnetism: material processing.
Austenitic stainless steels are classified as non-magnetic. The cold working process during the manufacture of fasteners can induce some residual magnetism, which, for example, can be lowered by a specific heat treatment process.
Low permeability applications: which steels to use?
For some applications it is necessary to use a stainless steel that has a very low permeability (the limit tends to 1.0 where the magnetic response of the material is the same as ‘free space’ or full vacuum). Austenitic stainless steels with a high austenitic stability are the most suitable for low permeability applications. This is precisely because they have low permeability:
- both in annealed conditions
- and cold conditions.
Any examples? Suitable for such applications are
- steels containing nitrogen (e.g. 1.4311/A2L and 1.4406/A4L)
- types with a high nickel content (e.g. 1.4845/AISI10S).
What if specific non-magnetic properties are required? It is necessary to seek the advice of a stainless steel materials expert before determining the specifications and the agreement between buyer and supplier established at the time of ordering.
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