When we admit endothermic gas into our continuous furnace and we are heat treating AISI 1050 steel we produce a decarburized surface on the steel, yet it appears to be clean after quenching. What is causing the decarburization?

Answer The endothermic gas is causing the decarburization. You need to enrich the endo gas at the furnace with a hydrocarbon gas such as methane. The endo gas will have a carbon potential of approximatly 0.35% carbon. Therefore you do not have equilibrium in the atmosphere to the carbon content of your steel. Thus, the result is decarburization.