GB1120817A - Partial decarburization of iron and steel - Google Patents

Abstract

Steel strip in the form of open coils is partially decarburised to a predetermined level by heating in a muffle furnace in a circulating non-oxidizing atmosphere to a temperature in the range 1100 DEG - 1600 DEG F., and, when the whole of the charge is at a uniform temperature, introducing water vapour into the furnace atmosphere so that the latter has a dew-point of 20 DEG F. to 120 DEG F. When the desired carbon level (which must be at least 0.005%) is reached, the introduction of water vapour is discontinued and the strip cooled in a non-oxidizing atmosphere. Determination of the end-point may be effected by monitoring of the carbon monoxide content of the affluent gases, introduction of water vapour being discontinued when the carbon monoxide reaches a specified value above 1%. The furnace atmosphere should initially be free of carbonaceous gases, and should contain sufficient hydrogen during the decarburising step to prevent oxidation of iron. Suitable atmospheres referred to are pure hydrogen, dissociated ammonia, 60% nitrogen, 40% hydrogen, or HNX gas formed by partial combustion of a fuel such as natural gas and subsequent removal of carbon oxides.