1988 Volume 74 Issue 2 Pages 286-293
Conventional oxidation dephosphorising process has a shortcoming that when applies to chromium-containing molten steel it oxidizes the chromium as well. This study is aimed at developing a technique to produce low-phosphorus steel while preventing the chromium oxidation.
It has been found that the desired dephosphorization can be achieved while inhibiting the oxidation of chromium if the oxygen potential in the molten steel is controlled using chromium oxide, rather than iron oxide as an oxidizing source. The preferential oxidation of phosphorus depends on the equilibrium relation between chromium, phosphorus and oxygen. It has also been made clear that the slagging of flux is important from the viewpoint of kinetics.
Another study made on the mechanism of dephosphorization by the slag particles in molten steel has revealed that a film of chromium oxide is formed over the surface of slag particles to inhibit dephosphorization when iron oxide is used. Also, it has been confirmed that the addition of calcium fluoride and calcium chloride to dephosphorizing flux is conducive to the acceleration of the dephosphorizing reaction.
On applying the above finding to the dephosphorization of molten steel with an initial chromium concentration of 1 to 2 percent, as high a dephosphorization ratio as 80 percent was obtained while preventing the oxidation of chromium using a flux comprising 40% CaO, 20% CaF2, 20% CaCl2 and 20% Cr2O3.