Solid wire stainless MIG - definitely not CO2, no Ar/CO2.
The gas needs to be inert. OK - s'less MIG often uses Ar with
1%oxygen to make the arc more fierce and make the weld-pool more
fluid. Just 1%O2 so don't lose significant amounts of alloying
Problem with pure Ar and MIG is it's so not penetrative. It's easy to
put a bottle of TIG gas (100%Ar) onto a MIG machine with stainless
wire and find out how not penetrating it is. It's an experience.
Only stainless MIG I've ever done was with an Ar/He/something-else
gas, and it worked well.
Shocked them with neat little "spray" (transfer) fillet beads.
Look for more advice, hopefully appearing on this thread.
I've used Argoshield light for MIG welding stainless 304 and it worked
well although I can't compare as the only other gas I have is argon and
BOC list Argoshield light as OK for stainless in non critical
applications so went with that
. I didn't find the spec on the BOC site but here
mentions it's 93% Argon,
5% CO2 and 2% oxygen. I was welding 6mm 304 with 1mm wire and 160A and
got good results. I did once try straight argon MIG on steel as BOC was
out of stock of Argoshield and the guy thought argon would be OK, not
good really poor penetration so called it in and they agreed to take
back the bottle and exchange it for Argoshield which they had back in by