Is Stainless Steel Non-Magnetic?

It is commonly stated by many people that stainless steel is actually non-magnetic and this is not exactly true as in reality the situation is a bit more complicated and requires a lot more explanation.

Whether a material is classed as magnetic or not will depend on the degree of magnetic response or magnetic permeability of that particular material. This is then measured on a scale and thus a totally non-magnetic material will have a relative magnetic permeability of 1.

As you well known stainless steel is split into a number of types of stainless steel. Austenitic stainless steel because of its structure has a permeability of 1 because it is totally non-magnetic. In reality though the level of 1 is not achieved because within stainless steel there is always going to be ferrite present and therefore the values are never at a set 1 level. Rather you will see typically values such as 1.05-1.1 for austenitic stainless steel.

During stainless steel fabrication and stainless steel processing it can sometimes occur that the overall magnetic permeability of the austenitic steels will be changed and items such as welding will cause an increase in the total amount of ferrite.

Is stainless steel non-magnetic?

To answer this in practical terms, stainless steel which is austenitic are used for any applications where the material is required to be non-magnetic even though this is a lose term because they will still be ever so slightly magnetic. Sometimes when there is a requirement for non-magnetic stainless steel a decision must be reached by both parties of the customer and the supplier on what the maximum magnetic permeability will be.

If you do require a stainless steel which is magnetic then you need to ensure you get one of the following types of stainless steel:

  • Martensitic
  • Ferritic
  • Duplex
  • Precipitation Hardening

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