A couple questions on gas for mig welding stainless

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I know this has been touched on many times but I am still unclear as to what will be the result of using 75/25 over 100% C02 on stainless steel.I have a mig welder and would like to weld a couple stainless projects with it. I currently have 75/25 Argon/C02 mix and was needing to know if I can get by with this for occasional welding of stainless or would I be causing myself more trouble than it is worth. I could buy another bottle with 100% C02 but I doubt I will be welding enough stainless steel to justify buying another bottle of a different gas. If 75/25 mix will work for occasional welding of stainless steel what kinds of things am I going to run into by using it instead of 100% C02.Also do they make any fluxcore stainless wire that does not need gas or would work better using the 75/25.
Reply:Plain CO2 on stainless = rusted weldsC25 aka 75/25 argon-CO2 on stainless = rusted welds but not as bad as pure CO2The rusted welds could happen as fast as overnight in the damp!The 'right' gas for GMAW (aka MIG) on most stainless alloys and using most stainless fillers is usually 98-2 argon-O2 (that is usually 'the' gas for spray transfer as well) or a low CO2 mix with argon (low as in C2 up to C5) or tri-mix (helium + argon + a little CO2).ESAB lists several FCAW fillers for stainless.  www.esabna.com and go to the products page.  308L and 309L and 316L all in FCAW.  Also several FCAW-G and gas-shielded metal-core wires.There are lots of SMAW (aka 'stick') for stainless too.
Reply:You cannot let oxygen contaminate your weld pool.CO2 is 1 carbon and 2 oxygens.Wire feed for stainless  would work best with tri-mix gas.just ask your welding supply store.If you try to weld stainless with a 110V wire feed the results are not very good.i spent the money and i tried it with a Lincoln SP125. With 16 ga, it looked like tooth paste out of a tube. it was hard to control. Not much penetration.Last edited by Donald Branscom; 06-13-2008 at 03:19 AM.
Reply:On most things I don't see a difference. I use 75/25 occasionally for quick fixes on stainless if I'm in a hurry. The set up for back purging is still the same though. TIG will look nicer.Dean
Reply:Thanks for the education guys. So what you are saying is even with the stainless wire I will have corrosion issues without the proper gas.Could I possibly get by with buying a bottle of 98/2 argon/O2 for my stainless projects and using it for small occasional aluminum also or is the 2 percent O2 enough to cause problems with the aluminum.Dang I hate to buy 3 bottles of different gases but it looks like that is what I may have to do.
Reply:No O2 or CO2 in the mix when doing aluminum!Pure argon, or argon-helium mix, for use on aluminum.