The composition of the furnace atmosphere created by an endothermic generator is as follows: CO ~ 20%, CO2 ~ 1.0%, Hydrogen ~ 40%, Nitrogen ~ 35% and 4% methane. This will produce an atmosphere with a carbon potential of approximately 0.35%. This atmosphere is not neutral to the 0.5% carbon in the steel part. The result is decarburization. In order to prevent surface decarburization of this part, enrichment gas – methane or propane – must be added at the furnace.