Yes. After welding you will have a fair amount of residual delta ferrite in the welds. This is by design to suppress hot cracking. The ferrite is magnetic. It also has very poor corrosion resistance in acidic environments.
If you care about either of these issues then you will have to look at post weld annealing.
it could be also due to formation of martensite following cold work of SS.
"Cold working of austenitic stainless steels can partially transform austenite to martensite. As martensite is "ferromagnetic" this means that austenitic types which would be expected not attract a magnet can show a degree of "pull"."
this is taken from:"Magnetic Properties of Stainless Steel"
