On here I see welding stainless steel to carbon (mild) steel discussed often, and people seem to think you shouldn't do it.

Technically, there is nothing wrong with it at all. The only difference between stainless and carbon steel is that stainless steel is an alloy of carbon steel. It is not like they are completely different materials.

Stainless is a steel that has had chrome and nickel added during the steel making process, and is in fact remains about 70 percent carbon steel. So stainless can be welded to carbon using ordinary welding processes, using stainless or carbon consumables.

The only bit you do have to watch, is the required corrosion resistance for the application.

Also, some people seem to think that the only finish you can leave stainless steel in, is raw, brushed or polished (this is a whole other subject though, involving proper housekeeping, nitric acid pickling and passivation etc.)

Stainless can be prepared and painted in exactly the same way as carbon steel, and then you have the benefits of the decorative coating, and also the corrosion resistance of the stainless, if the paint should chip or wear away.

Okay, rant over.

Cheers

Fred WB

I didn't know that - I'd always assumed they wouldn't weld together very well

I totally agree with Fred and have never found any real issues in lots of different applications.
It always looks better if you use stainless wire though .
I must admit to (at home ) using standard argoshield to weld stainless in low stress applications only. ie welding stainless exhausts and coolant pipes etc.
In my work applications we use stainless to join hardened steel wear strips to mild steel fabrications,therefore finding it ideal to give a good strength to the joining of different grades and types of steels.

I`ve welded them together too no probs but I do notice there are rods specified particularly for "dissimilar" metals. Maybe for use on critical applications. If you use stainless rods on mild steel they flow beautifully and are easy to strike. It is however expensive and theoretically not as strong as standard rod.
Alex

I've welded them together frequently; especially when combining exhaust components. The only noticible difference is that the stainless likes more heat/amperage.

I find this jolly interesting, I have been pondering how to make custom exhaust manifolds.. I was thinking of making out of stainless and tacking up with my mig using mild steel wire and argoshield, then getting someone to tig it fully. this conversation suggests to me that it wasn't a bad idea.

that will work fine but you may get some corrosion of the welds near to your tacks. If you can live with that (think I could!) then that would be fine.

Otherwise get a diddy hobby roll of stainless mig wire and a disposable argon bottle from machine mart and tack it with that.

Hi All


Firstly, my only concern is that on reading this thread, somebody will weld a
s/s item to their mild steel chassis, using mild steel filler wire / rods.

I accept that if a weld cracks on an exhaust, it's not the end of the world.

Also, sorry if this gets a bit technical but I can't think of a simple way to explain it.




If you use a mild steel filler rod, the carbon from the m/steel combines with the chromium
in the s/s to form chrome carbides, (ugh, nasty) which is known as "weld decay".
This is within the metal, not just a surface thing.

To make acceptable strength welds, m/s to s/s, I would suggest using 316 s/s filler wire / rods.
These form molybdenum carbides which are o k.

The correct method is to use a rod / wire with a higher alloy content than both parent metals
to be joined, in this case, a 25/20/3 (Cr/Ni/Mo), i.e. 309 s/s.
This results in a weld equal in strength, or greater than both parent metals,
and is what I would use in my "day job".

I hope I havn't offended anyone by posting this; it's just that
sometimes a little knowedge is a dangerous thing.

ATB

Paul G

Bu66er! I had better find the bloke who bought my Discovery with stainless inner wings welded to the m/steel bulk head!!