TheSamba.com :: View topic - Welding a Stainless Steel O2 Bung to a Mild Steel Exhaust

Fri Aug 21, 2015 10:45 am

Can a stainless steel O2 bung be welded to a mild steel exhaust?

Yes. I just did it using mild steel welding rod and an oxy/acetylene torch.

It may not be the most perfect metal junction, but just how long is the plain steel exhaust going to last anyway? It's not like you are going to put a huge load on the weld. It only needs to be strong enough to support the O2 sensor.

You'll still have the stainless steel at the O2 bung threads where you really want the corrosion resistance.

Scott Novak

Fri Aug 21, 2015 11:03 am

Not a problem

Fri Aug 21, 2015 11:06 am

I agree its no problem. The weld should be just as strong, not that it needs to be the ultimate strength. Good to see someone still using oxyacetylene. It makes very nice welds.

Fri Aug 21, 2015 11:18 am

i've got a mild steel bung and i'm planning on brazing it in with a all purpose rod, think its a silver alloy.
i only have a stick welder and this seems the better route! will seal really nice too

Fri Aug 21, 2015 11:32 am

andy198712 wrote: i've got a mild steel bung and i'm planning on brazing it in with a all purpose rod, think its a silver alloy.
i only have a stick welder and this seems the better route! will seal really nice too

Silver alloys typically melt and flow at a temperature at which mild steel glows a dull red. That part of your exhaust should never get that hot. More than one way to skin a cat.

Fri Aug 21, 2015 3:10 pm

Scott Novak wrote: Can a stainless steel O2 bung be welded to a mild steel exhaust?
Scott Novak

It will eventually crack, to do it properly you'll need 309 stainless welding rod. you can either tig weld it or arc weld.

Fri Aug 21, 2015 4:24 pm

Never cracks when I do it. You don't have a MIG do ya?

Braze should be ok too, but I'd tack weld it first to hold in place with the MIG.........why not just keep going!?? LOL

Fri Aug 21, 2015 4:35 pm

Kfeher2000 wrote: It will eventually crack

Sure it will. But I strongly suspect that the plain steel exhaust will rust out before the weld cracks.

Scott Novak

Sat Aug 22, 2015 9:30 am

I did the opposite and welded a mild steel bung to a stainless exhaust using stainless wire in a MIG welder. And a CO2/argon mix gas.

Sat Aug 22, 2015 9:48 am

I've mig and tig welded several stainless fittings to mild steel headers, and no failures yet. It's not a stressed joint that's subject to fatigue.

Sat Aug 22, 2015 2:57 pm

For the best results you should use 308 or 316L stainless rod/wire when welding stainless to stainless or stainless to steel. You do not get good if any penetration welding with oxy acetylene on stainless. For the best results you should Mig with stainless wire , tig with stainless rod, arc with a stainless rod or silver solder. I have had good results welding aluminum with aluminum arc rod and oxy acetylene. I also recommend a straight argon gas for that. There are some specialty mixes you can get but are more expensive. I use 75%co2 25% argon for mild steel.

Sat Aug 22, 2015 3:21 pm

I got rods for stainless steel at muggyweld.com. For use with a torch, they are a brazing rod with a pink flux on them. Your exhaust will never melt the braze and it allows working at a much lower temp. Downside is, they are $25 a stick and minimum is 4 sticks. Well worth it in my book, especially since I put it on the Corporate card! Bwahahahahaahahaha