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If I'm going to paint the stainless anyway, can I weld stainless with mild steel wire under CO2 shield???
I know to retain the stainless properties of the workpiece you need to use stainless wire and funky gas but is that the only advantage ie it is
isn't that you get cr@ppy birdpoo type welds or anything else....
You will be ok but the weld will rust in time
Cool! No problems. Going to get painted anyway!!!
good to know! i want a stainless exhaust, but i've got a mild steel flange (well, I haven't but the engine has )
That's exactly what my exhaust is.
Originally a stainless steel bike manifold, it was welded with mild wire and CO2.
Just take your time and watch the power settings if its thin stuff.
Today's project was 3mm mild onto 3mm mild, so I just whacked the power right all the way up 
Blowing holes in anything ain't a problem with my welder- it's only a 90A model!! Unless its 0.0001mm I'll be okay!!!
Wouldn't you have the same problem as with aluminium boats and stainless steel fittings, with the mild steel acting as a cathode and rotting away
much faster for being joined to the stainless?
I've no experience at all welding stainless to mild, but this is what I'd be worried about if I were doing it.
My fisher stainless exhaust looks like the head flange was welded to the downpipes with mild steel...
No galvanic corrosion between stainless and mild as stainless is still most iron anyway.
You can weld mild to stainless no problem in non critical applications. Similarly you can use mild wire to weld stainless no problems (other than the
weld will rust in time...)
Weld away
David
twin SU carbs/1
The manifold you can see is s/steel pipes welded to m/steel plate using m/steel wire in a mig
Jacko
Stainless steel is mostly iron with a couple of percent carbon and, at lest on some grades, 26% chromium, plus perhaps other alloying metals. Mild
steel can be mostly iron with a bit of carbon and some other stuff. MIG Welding wire is coated in copper.
When you weld, you melt both sides of the metal and the welding wire. What cools is an alloy of all 3 which sort of fades in concentration between
the two metals joined. Welding mild to stainless, you'll see rust on the mild part anyway, so why worry.
Welding stainless to stainless with mild wire, I'd expect the concentration of Chromium to be lower in the weld than the parent metal but it
still might resist rusting in a gentle environment, especially if the stainless was a good grade and the joint had almost no gap.
Ditto. When youve welded stainless with MS wire, you can oftern see the different metals in the weld, or certainly the pool.
Perfectly ok if painted, but i wouldnt use it structurally.
quote:
Originally posted by smart51
Stainless steel is mostly iron with a couple of percent carbon and, at lest on some grades, 26% chromium, plus perhaps other alloying metals. Mild steel can be mostly iron with a bit of carbon and some other stuff. MIG Welding wire is coated in copper.
When you weld, you melt both sides of the metal and the welding wire. What cools is an alloy of all 3 which sort of fades in concentration between the two metals joined. Welding mild to stainless, you'll see rust on the mild part anyway, so why worry.
Welding stainless to stainless with mild wire, I'd expect the concentration of Chromium to be lower in the weld than the parent metal but it still might resist rusting in a gentle environment, especially if the stainless was a good grade and the joint had almost no gap.
Stainless steel is anything with 10% chromium or greater, less than that and the passive oxide film doesn't regenerate so the protection
dissapears. So if the merged mild and stainless in the weld ends up less than 10% it will rust like mild.
I did a bit of digging - apparently the shipping industy uses mild steel as an anode to protect stainless against crevice corrosion, so there must be
some galvanic action there. No idea how much though, but I wouldn't be doing this with an exhaust with all its nasty corrosive gases, or with
anything structural.
Hi.
When welding stainless steel to mild steel the filler rod/wire to use is 309 stainless. (or 312)
Paul G