What gas ?

Which of the 3 common shield gasses is best for MIG welding stainless steel ? I have on hand argon and CO2 , no C25 at this time but i can get
it if I need it .
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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 additions.
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.
Rich S
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On 25/06/2020 19:50, Richard Smith wrote:

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 https://www.boconline.co.uk/en/products-and-supply/industrial-gases/shielding-gases/argoshield/argoshield-light/argoshield-light . I didn't find the spec on the BOC site but here https://www.mig-welding.co.uk/welding-gas.htm 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 then.
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