Is it ok to weld stainless steel exhaust tubing with carbon steel mig wire?
Its definitely not a good idea. We have proof right here.
Stainless exhaust is sometimes made from 304 stainless, but there are also quite a few exhaust components that use 400 series stainless like 409.
Either way, to get the best service and longest life out of a stainless steel exhaust system, its important to weld stainless steel exhaust with a matching or at least similar filler metal....not cheap carbon steel mig wire.
This Stainless header is off a Honda car and the collector was welded using a mig gun and plain carbon steel wire.
Who knows why? Maybe it had a big gap.
Before I decided how to weld the header, I used a magnet on the weld as well as flanges and bung to learn that The flanges and bung seemed to be carbon steel but those welds were holding up fine since they were tig welded with stainless wire.
The magnet stuck to the mig weld strongly letting me know for sure that the weld was carbon steel.
By the way, its a good idea to have keep a magnet handy for jobs where you are not really sure of the metal type.
so here are the high points of this stainless exhaust weld repair...
• cleaned the inside using a wire brush and a straight grinder....and cleaned the outside using a rolled abrasive. aka tootsie roll.
• purged the inside making sure to put the vent holes at the top to let the whole thing fill with argon.
• used about 15 cfh of argon and only let it purge for a couple minutes before welding.
• 1/16" 2% lanthanated electrode sharpened very much
• set amperage to about 75 but using 50 pps 50% peak on time, 40% background yielded about 50 amps output.