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Frequently Asked Questions

These are some of the questions that we frequently get asked.

  1. What Is Stainless Steel?
  2. When was stainless steel discovered?
  3. What is stainless steel used for?
  4. Does stainless steel corrode?
  5. What forms of corrosion can occur in stainless steels?
  6. How many types of stainless steel are there?
  7. What are the correct standards for stainless steel?
  8. Is stainless steel non-magnetic?
  9. Can I use stainless steel at low temperatures?
  10. Can I use stainless steel at high temperatures?
  11. What surface finishes are available on stainless steels?
  12. How do I choose which stainless steel to use?
  13. What is 'multiple certification'?

Is stainless steel non-magnetic?

It is commonly stated that “stainless steel is non-magnetic”. This is not strictly true and the real situation is rather more complicated. The degree of magnetic response or magnetic permeability is derived from the microstructure of the steel. A totally non-magnetic material has a relative magnetic permeability of 1. Austenitic structures are totally non-magnetic and so a 100% austenitic stainless steel would have a permeability of 1. In practice this is not achieved. There is always a small amount of ferrite and/or martensite in the steel and so permeability values are always above 1. Typical values for standard austenitic stainless steels can be in the order of 1.05 – 1.1. See Composition effects on the magnetic permeability of austenitic stainless steels

It is possible for the magnetic permeability of austenitic steels to be changed during processing. For example, cold work and welding are liable to increase the amount of martensite and ferrite respectively in the steel. A familiar example is in a stainless steel sink where the flat drainer has little magnetic response whereas the pressed bowl has a higher response due to the formation of martensite particularly in the corners.

In practical terms, austenitic stainless steels are used for “non-magnetic” applications, for example magnetic resonance imaging (MRI). In these cases, it is often necessary to agree a maximum magnetic permeability between customer and supplier. It can be as low as 1.004.

Martensitic, ferritic, duplex and precipitation hardening steels are magnetic.

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