Heat treating atmospheres from non-cryogenically generated nitrogen

摘要

A process for producing a nitrogen-based atmosphere inside a furnace for oxide annealing carbon steels comprises the steps of humidifying non-cryogenically produced nitrogen contg. up to 5% by volume residual oxygen, and then mixing it with less than four times the amt. of a hydrocarbon gas required to convert the residual oxygen to a mixt. of carbon dioxide and moisture. The mixt. of humidified nitrogen and hydrocarbon gas is fed into the heating zone of the furnace maintained at a temp. above 750 deg.C, so that the oxygen reacts with the hydrocarbon and is complete prior to the mixt. contacting the steel in the furnace, and is in a oxidising atmosphere. The pH2/pH2O and pCO/pCO2 ratios are controlled to effect oxide annealing.