I have done something similar...................arc cut cast iron for the pot ,and made sure it was red hot before going in the furnace.....i thought of using the arc torch for heating the iron,but the intense heat soon overcomes any gloves or jacket ,and you have to retreat before you go up in smoke.....To arc cut,you hold the carbon near the tip........a custom made conductive holder would work,I think,but it might have to be water cooled ....As you know,the heat keeps you well away...................by the way,conductivity also changes with heat,resistance increases,....Anyway ,an oil fired furnace has plenty of heat,and burns up waste oil,the arc torch needs diesel at $1.50 per liter here,and arc carbons arent cheap either.