gas welding carbon steel to stainless

[Shield Arc]

I've never done much O/A welding, and far less soldering. Years ago I did a lot of stainless welding with SMAW. At one time I was certified in Stainless to mild steel with SMAW process, used 309.

I have read where people have used 7018 to weld stainless to stainless, with OK results.

 

[Gary Fowler]

You asked about using OA torch only. I dont think you will be able to OA weld SS to CS using any type of carbon steel or stainless steel filler. The CS filler is going to crack at the junction and SS would oxidize and not flow at all between the boundary layers. You will be limited to silver solder for the joint and it isnt going to be super strong. Since you didnt specify the grade of stainless, we can only guess. You can stick rod it with E-309 for just about any combo grade of SS. For most home jobs, I would say that you would be able to make it stay together with just about any grade of SS stick electrode or TIG wire. There may be a high tensile strength brazing rod that you could use, but I am not familiar with using OA on stainless. TIG would be my preference, but stick would work well if the piece is thick enough to support a stick weld. If you want a good weld and dont have Stick or TIG capability, I would suggest you take the part to a welding shop to have it TIG welded.

 

[yomax4]

If none of the above works for you, You can always Silver Solder the joint. It would be pretty strong. 45% content or more.

 

[Raspy]

If brazing won't hold, then it will have to be welded. The best I've found, and I've done a lot of it with mild or hardened steel to stainless, is to use 309/316 rod and arc or tig or mig it. Don't consider those metals to be dissimilar unless they are used under water on a boat.

I know you said it would have to be done with gas welding, but I don't know if you can gas weld stainless very well.

I don't think sil-floss will help you because it's not stronger than brazing as far as i know and might be harder to get to alloy in compared to 45% silver solder. Silver solder might be a better choice. Sil-floss works wonders on copper.

 

[handirifle]

Thanks, I have tons of experience with sil fos on copper, but didn't know how well it would solder the steels. I have used silver to solder steel to copper, but no experience with soldering steel to steel. Maybe welding isn't what I should do, on this part either. A replacement part might just have to be ordered.

 

[Gary Fowler]

Regarding SMAW/TIG welding dissimilar metals: Yes you can weld stainless with carbon steel E7018 or ER70S-2 wire but it has a severe tendency to crack. IF you can get it welded together with the carbon steel electrode without it cracking then it will likley be as strong as welding with E309. I do recall a weld on a boiler steam drum that was made with TIG and ER70S-2 wire to a 316 SS pipe and our engineers let it stay. The joint was supposed to be CS to CS but the manufacturer of the steam drum put a SS insert in it. The joint was xrayed, passed and allowed to stay since at some point in a dissimilar weld there is a boundary layer that is all carbon steel. The only reason to use the high grade material for welding is that it flows better to the high grade alloy and is more resistant to cracking at the boundary layer which is what usually happens when you weld two different metals together. E 7018 rod is pretty amazing stuff for mild steel as it will adhere to cast steel, stainless steel and even cast iron when properly applied and hold together pretty well but to do a job right, go with the higher alloy that more nearly matches the composition of the highest grade material that you are working with. INCOLOY rods are pretty much compatible with all high alloy materials, except the exotic stuff like titanium and zirconium, and can be used to weld just about any dissimilar metal.
By the way a dissimilar metal is dissimilar regardless of where it is used.