Low Magnetic Permeability Applications: Which Type of Steels to Use?

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magnetic permeability

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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