Welding dissimilar metals

By john biundo Date 04-21-2002 08:43

Hi - I'm hoping I can get some advice on the topic of welding stainless and mild steel.

I'm a novice, but have managed to produce decent welds on mild stock. In my first attempts to weld SS and mild steel, I've been much less successful.

I'm using a 110V home MIG welder, and have tried using SS wire and tri-mix gas. The welds appear porous, generally don't look nearly as good as my other mild steel welds, and don't stand up as well to my tests (trying to break the weld in a vice). I'm pretty sure I'm getting good gas flow, and I'm welding indoors with no significant air currents.

Given my relative confidence with mild steel (using both gas and self-shielded techniques), I think I may be better off using one of these techniques with on the SS and mild. I'm not worried about rust on the weld, so with that given, is it OK to use mild steel wire (self-shielded) for this application? Would doing so result in a substantially weaker joint than using 309 wire and tri-mix gas?

Thanks in advance for any suggestions.

john

By Niekie3 (***)

Date 04-22-2002 18:09

The problem with using a C/Steel filler is that you are liable to end up with a brittle weld. This is so because in lower concentrations, Cr and Ni makes steel very hardenable. (Can be seen on a Schaefler diagram.) You need a filler that has higher concentrations of Cr and Ni to take the composition out of the hardenable range. Such a filler is typically type 309.

You mention that you are using a tri-mix gas. Which mix exactly? In general, it is suitable to use a 98%Ar 2%O2 mix for most S/Steel welding. Rarely do tri-mixes add much benefit. Especially not in a home shop type set-up.

Hope this helps

Regards
Niekie Jooste

By Brad_J

Date 04-27-2002 16:37

I agree strongly with Niekie.
I have seen it successfully welded with ER70 GMAW & C25 Argon mix gas. The transport trailers this was done on have proven they were sufficiently welded. I would never try this without testing the strength of your weld and being sure it is suitably strong for your application. (The welds were painted so I assume road salt stayed out of the weld for a few years) Corrosion may be a concern you want to check.