I was welding some 3/16" stainless steel and the weld was turning black on me. I cleaned the welded area and it looks like it was contaminated. I was welding the end of two pieces together and I'm thinking that I needed to back flow Argon gas on the inside of the box. Any input would be great.

 

you can just use solar type b flux its for use with stainless. Also are you moving to slow with to much heat? That how one of the guys welds are at work almost black and I showed him turn down the heat a bit and move a little faster. Itmigght work for you.