Generally speaking, stainless steel is not magnetic in terms of austenite. But martensite and ferrite will have magnetic properties, but austenite is also possible to have magnetic properties. The reasons for this are twofold.  
When solidification, because some of the reasons for smelting will remain part of the magnetic, 304 for example, will remain 3-8% is normal, so austenite should belong to non-magnetic or weak magnetic.
Austenitic stainless steel is not magnetic, but its cold processing hardening, γ phase will be part of the generation of martensite phase change will produce magnetic. Available heat treatment methods to eliminate this martensitic organization and restore its non-magnetic.