Mike...This depends which material the chair frames are made of. I doubt that they are chromoly but they COULD be. Any idea of the wall thickness?
I've actually welded thinwall chrome (covered) ms tubing with mig, .023 wire(S-6)/75/25 mix gas. Very carefully grind the chrome off before welding. Need about 1/8" on each side. This method will produce the least discoloration of the parent chrome.
Tig is the best for this but does discolor the chrome a bit more.
If you use ER80S-D2 or 70S-2 you'd still want to grind a bit of the chrome off(I use thin lil' cutoff wheels in an air powered cut off tool). This will give you the most ductile weld. You could also use ER70S-6 (like your mig wire) but it won't be quite as strong...although it'd prolly be acceptable.
SS filler? I'd only use 310 or 312 as most other SS fillers will be brittle.
You'd only need a few rods to do this. You''l find that tig fillers will break you. $200 to $300 for a tube of filler rods that may sit for years.
If you can back purge this you'll get the best welds...you almost have to when using SS fillers.
Russ (up before the chikkins )
I have tools I don't even know I own...