Austenitic plate is welded with matching or over-alloyed filler: 308L for 304L, 316L for 316L, 347 for 321, 2209 for 2205 duplex. Keep heat input controlled and interpass temperature low to avoid sensitisation and distortion.
Duplex needs controlled heat input and a nitrogen-bearing filler to keep the ferrite-austenite balance; too fast cooling gives excess ferrite, too slow gives intermetallics. Follow the mill's welding guidance.
After welding, remove heat tint by pickling paste, electropolishing or mechanical cleaning; heat tint left on the surface corrodes first. Never use carbon steel brushes or tools on stainless.