Method of heating, holding or heat treatment of metal material

Abstract

In an indirectly heated, gas-fired furnace (10) for the heat treatment of metal material in an atmosphere of processing gas consisting predominantly of nitrogen, the processing gas is produced using the heating exhaust gases as the principal raw material. The exhaust gases are cooled, filtered and freed of carbon monoxide and water vapor, whereupon a small amount of air is added to impart a predetermined value to the oxygen content and a controlled amount of liquefied petroleum gas or other hydrocarbon gas is added. A processing gas consisting predominantly of nitrogen, hydrogen and carbon monoxide is produced by thermal cracking of the liquefied petroleum gas in a catalytic reactor (25) and fed to the furnace (10). If a processing gas free of carbon and consisting predominantly of nitrogen and hydrogen is required, the reactor (25) may be replaced by a deoxo reactor into which the exhaust gases, after their oxygen content has been adjusted, are fed together with a controlled amount of hydrogen gas.

Dependencies are inferred from the claim text.