GB946964A - Dephosphorization of melts of ferrous metals - Google Patents

Abstract

A phosphorus bearing pig iron, cast iron or steel melt is dephosphorized without loss of carbon by a method comprising forming on the melt a molten basic slag layer containing at least one constituent known to dephosphorize iron such as lime and iron oxide together with fluxing agents, the temperature of the melt being not more than 200 DEG C. above its solidification temperature, continuously supplying oxygen and feeding a solid oxidizing, basic slag-forming mixture containing the reactive constituent to the melt, either to the surface or below the surface thereof, and simultaneously withdrawing slag from the layer. Preferably the slag-forming mixture, which may be granular, powdered or compacted into rods, is fed to the same area of the layer to which the oxygen is supplied and wherein the temperature is higher. For example, at least a portion of this mixture may be powdered and blown with the oxygen on to or below the slag surface. The oxygen is preferably supplied at a constant rate through a forked lance (see Division F4) and only the rate of feeding of the mixture varied. Slag from the later stages of treatment may be cooled, comminuted and recycled by admixing to the slag-forming mixture. The melt may be contained within a basic, neutral or an acid lined container such as a ladle which is tilted for the continuous removal of slag. An example of a slag-forming mixture is: 33% rolling scale, 27% burnt lime, 24% blast furnace flue dust, 13% soda ash and/or glass waste, and 3% fluorspar.