This is more a question than an answer - Are cold laps/lack of fusion defects in short-arc welding more common if the steel is anything other than cleaned to bright metal before welding? Wondering about welding over steel that might have black scale, galvanize or paint on it? I am more familiar with...

A carbon steel bead on stainless will have, say, about 30% stainless (18% chromium 8% nickel) dissolved into that carbon steel. Turns the bead into a nice air hardening tool steel. An OK weld, just don't use that Widgit for anything practical, lest it snap. Sorry, guys, I am a metallurgist not a wel...