400 series stainless steel is magnetic, while the 300 series is usually nonmagnetic or has a weak magnetic attraction. Cold working stainless steel can induce/create magnetic attraction.
In general, the higher the nickel to chromium ratio the more stable is the austenitic structure and the less magnetic response that will be induced by cold work.
Old 304 stainless steel is usually nonmagnetic. New 304 is usually magnetic, as most producers have cut the passivated step as a cost saving measure.
Try the magnet test on any car that has a stainless steel exhaust.
John
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