Mig Welding Stainless with mild steel wire

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To start, I am mostly familiar with stick welding, but I have an old airco mig I picked up for doing real thin stuff. I am not familiar with all the different types of Mig wire available. I belive I have ER70S-6 In the machine now, I bought it from a farmer that was retiring and it came with a roll of wire. I have the opportunity to get get some stainless scraps from work if I need to do something small, normally I would use some 309L if I am using stainless for something. I assume there is an equivalent for MIG. I'm not using the stainless for any other reason than It's available for no cost. So the million dollar question, Does using a wire that is designed for mild steed have any downside when used on stainless besides the ability for the weld to rust or is there going to be an issue with metal fusion? On a side note, is there a special shielding gas that should be used for stainless or is the normal Mig Mix OK for this? Should I be using straight argon? Thanks,Airco Auto-Pak 130Forney 235AC/DC
Reply:First, know that MIG welding stainless exposes you to high levels of toxic fumes: https://weldingweb.com/vbb/threads/7...ght=hexavalentSecond, using ER70S6 on stainless will sort of work, but stainless is prone to "sugaring" (oxidation on the back of the weld) and stainless reacts more to heat (warping) than mild steel, and in my mind you are making learning harder than it needs to be. If you were welding stainless with stainless wire, and looking to make the welds rust resistant, then in that case there is a special gas (its an argon/co2/helium blend). My advice is to ditch the stainless unless you specifically plan on welding stainless and need to learn how to do it correctly. In that case get stainless filler wire (308 or 309 wire should work for lots of stainless alloys), the tri-mix gas, and some solar flux for the back sides of the weld.Miller Multimatic 255
Reply:Typically tri mix is used for short circuit mig( argon ,CO2 and helium. 98-2 can be used for spray transfer ( argon , CO2). If you understand the rusting and realize the metal is somewhat compromised, I see no problem using the 70s6 wire. 308l stick electrodes may be a cost effective solution if you want to avoid rust.
Reply:QUOTE=Louie1961;8831312]First, know that MIG welding stainless exposes you to high levels of toxic fumes: https://weldingweb.com/vbb/threads/7...ght=hexavalentSecond, using ER70S6 on stainless will sort of work, but stainless is prone to "sugaring" (oxidation on the back of the weld) and stainless reacts more to heat (warping) than mild steel, and in my mind you are making learning harder than it needs to be. If you were welding stainless with stainless wire, and looking to make the welds rust resistant, then in that case there is a special gas (its an argon/co2/helium blend). My advice is to ditch the stainless unless you specifically plan on welding stainless and need to learn how to do it correctly. In that case get stainless filler wire (308 or 309 wire should work for lots of stainless alloys), the tri-mix gas, and some solar flux for the back sides of the weld.Yes, definitely wouldn't recommend stainless welding especially with mig, fcaw, or stick. You can get some nasty stuff like Cr+6 (Hexavalent Chromium) and some other nasty stuff. As well as that it may need preheating and shielding gas flow from the back as well. Definitely not beginner friendly or healthy to do with MIG. I'd pick up some cheap flat bar (mild steel/ low carbon steel) to avoid nasty fumes and complicated welds.
Reply:

Originally Posted by M J D

308l stick electrodes may be a cost effective solution if you want to avoid rust.
Reply:I still think these are the best deal if you are looking for coupons to learn on: https://www.jflf.org/ProductDetails....ductCode=METALA box of 10 "kits" gets you 60 1/8th inch coupons and 20 1/4 inch coupons, already cut and cleaned (cold rolled steel so no mill scale to deal with) for $45.Miller Multimatic 255
Reply:I am not using the stainless to try and learn Mig. I don't really have much issues welding mild steel with the MIG.I just have a convenient access to scrap stainless, so I am wondering if there welding stainless with Mild steel wire is going to cause fusion issues, vs using a wire designed for mild steel. I am not really concerned about rusting. Thanks for the replies.Airco Auto-Pak 130Forney 235AC/DC
Reply:I would agree, this reduces hazardous fumes, rids the need for shielding gas on the back and also allows c25 (a more versatile gas) to weld with. I can see where they're coming from not wanting to spend money on steel practice metal, but I would do it to save your lungs at the very least.
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Originally Posted by Roert42

I am not using the stainless to try and learn Mig. I don't really have much issues welding mild steel with the MIG.I just have a convenient access to scrap stainless, so I am wondering if there welding stainless with Mild steel wire is going to cause fusion issues, vs using a wire designed for mild steel. I am not really concerned about rusting. Thanks for the replies.
Reply:Thanks for the input guys. I mainly am using the machine to weld body panels at the moment, and swapping wire regularly seem a bit of a pain. It is what it is, I will probably pick up a small spool of 309L and use that when I am doing something with stainless as it is not expensive for a small roll. All that said, what's the downside of using C25 vs Trimix? Are we simply reducing the rust resistant properties of the stainless or reducing the weld quality?Airco Auto-Pak 130Forney 235AC/DC
Reply:I keep on hand a spool of 308 ss for few times I need to do stainless steel.  If have gas just try using what see works. I had argon for aluminum welding and used that gas. If is code or spec work I use the correct gas. Dave

Originally Posted by Roert42

To start, I am mostly familiar with stick welding, but I have an old airco mig I picked up for doing real thin stuff. I am not familiar with all the different types of Mig wire available. I belive I have ER70S-6 In the machine now, I bought it from a farmer that was retiring and it came with a roll of wire. I have the opportunity to get get some stainless scraps from work if I need to do something small, normally I would use some 309L if I am using stainless for something. I assume there is an equivalent for MIG. I'm not using the stainless for any other reason than It's available for no cost. So the million dollar question, Does using a wire that is designed for mild steed have any downside when used on stainless besides the ability for the weld to rust or is there going to be an issue with metal fusion? On a side note, is there a special shielding gas that should be used for stainless or is the normal Mig Mix OK for this? Should I be using straight argon? Thanks,