I don't know the answer offhand, never have needed die steels (air, oil and water hardening) to be charcoal blued after welding- I would check with Doug Turnbull in NY-- Coat hanger wire is a mild steel, but as wire coat hangers need ductility (to be bent and wrapped for the hanging loop) it should flow under the arc of a TIG - surface condition of any filler rod used in TIG is critical- any contaminants can cause weld porosity and possibly undercut at the edge(s) of the weld bead-- IMO, as 90% of a good quality weld, no matter the process, depends of proper preparation of the weld joint and knowledge of the parent metal to be welded,I would never "skimp" on filler rod and only use those rods certified by AWS from a reputable welding products distributor--just my approach, others may see it differently--
