wrong your doing it.
Its all in the type of filler wire and heat. Stainless resists rust based on the composition, the amount of chromium. Too much heat and chromium will burn off during welding it and it will loose its rust resistance. that’s the first thing that will cause stainless to rust… by itself.
introduce other filler metal to a molten stainless and its a different issue. If you use standard copper coated steel wire, it wont have the chromium content to keep it from rusting. Fail.
The MIG I did with the stainless wire was 309L wire, which is supposed to be good for joining dissimilar stainless metals, while preserving the rust resistance for the weld.
Same goes for tigging if you burn it or use the wrong filler, it will rust still.
The thing about MIG welding it, even with the right filler wire is the lack of post flow gas coverage to shield the red hot weld while it cools from oxides that can make it sugar or turn porous. But do the old tack and wack, weld method: tack, tack, tack, tries to keep the heat down and should reduce (not remove)the need for post weld shielding gas. It really doesn’t matter what mixture you run, as long as it cools the weld and pushes away the oxygen it’s doing its job.
Corey, is your shit rusting?!?! you can be dead honest, if it is (I doubt and hope it isnt) i wont take offense just let us know.