[QUOTE=DaveO;18514]
Quote Originally Posted by zoama585 View Post
You need a larger cup and higher argon flow for stainless.
QUOTE]

I was wondering if this might be a shielding gas problem. Doesn the black appear on the top surface by the weld, and does it scrape or brush off? I recall a while back there was a discussion of back-ourging stainless steel tubing to prevent black oxidation on the underside of the weld, but this is different.
Just about any metal will soot up without sufficiant shielding gas. For stainless to remain "stainless" in needs good shielding. You can checkout some stainless welding videos at weldingtipsandtricks.comr on youtube.