Austenitic stainless steels work-harden when they are deformed, fabricated or drawn. This gives a significant increase in yield strength and an associated drop in elongation.
Why deformed areas can become magnetic
Cold work converts a small part of the austenitic microstructure to martensite, which is magnetic. Parts of an austenitic component can therefore appear magnetic, particularly at corners and edges where deformation is highest.
A good example is a stainless steel sink: the flat drainer has little magnetic response, whereas the pressed bowl has a higher response because of the martensite formed in its corners.
When non-magnetic behaviour matters
Austenitic stainless steels are sometimes chosen specifically for their non-magnetic properties. More unusual examples are in medical and sensing equipment, such as magnetic resonance imaging (MRI) units, which require metals with a maximum magnetic permeability as low as 1.004.