Controlled Atmosphere Carburizing

That's not a common welding technique, sounds like a made-up process. In welding, you generally don't want carburization; it makes the steel hard and brittle. If you're talking about case hardening, that's done via carburizing or pack hardening, but that's a separate heat treatment step, not part of the welding process. Forget about carbon in the shielding gas, that'll only get you trouble with porosity and cracking.