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.

IntroductionAustenitic stainless steels are generally non-magnetic with magnetic permeabilities of around 1.0. Permeabilities above 1.0 are associated with the amount of either ferrite or martensite phases present in the 'austenitic' steel and so depend on:chemical composition cold work and heat tr