The Magnetic properties of materials are affected by their composition, metallic structure, processing methods and physical condition. Ferromagnetic materials are strongly attracted to a permanent magnet. Magnetic permeability is the property of a material to carry magnetism, indicated by the strength of the attraction to the magnet. All stainless steel, with the exception of wrought, austenitic groups are strongly attracted to magnet.
Wrought, austenitic stainless steels, such as 304 and 316, are generally regarded as non-magnetic in the annealed condition, i.e. they are not attracted significantly by a magnet. However, if they are cold worked by wire drawing, rolling or even center-less grinding, shot blasting or heavy polishing. After substantial cold working, Grade 304 may exhibit quite strong response to a magnet. Grades 310 and 316 will in most instances still be almost totally non-responsive. The change occurs because the cold work deformation induces a transformation of the microstructure from austenite to martensite. Once martensite is formed, it may also become magnetised sufficiently to pick-up light objects such as paper clips. It is possible to remove the magnetic effects by solution annealing and water quenching but, this will also reduce the tensile properties and may give rise to distortion.