Magnetic Properties of Austenitic Stainless Steel
Austenitic stainless steel are usually described as 'non-magnetic' since their response to a hand-held magnet is negligible. However, ferritic, martensitic, duplex and most precipitation hardening stainless steel are usually classified as magnetic since they exhibit a strong response (or pull) to a hand-held magnet.
For some applications, it is necessary to use a stainless steel which has very low or negligible response to electromagnetic fields. The lowest relative magnetic permeability of any material is 1.0, i.e. the magnetic response of the material is the same as 'free space' or a complete vacuum.
The permeability of austenitic stainless steel is quite different from ferritic, martensitic and duplex stainless steel. Austenitic steel can be classed as 'paramagnetic' with relative permeabilities of 1.0 (generally in the range of 1.003 to 1.05 in the fully annealed condition). These low permeabilities enable austenitic steel to be used where 'non-magnetic' material are required. Include casing for medical equipment such as body scanner, and concrete reinforcing bars for radar installation.
Permeabilities above 1.0 are associated with the amount of either ferrite or martensite phases present in the 'austenitic' steel and so are dependent on: chemical composition and Cold work and heat treatment conditions.
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