Effect of Refining Conditions for Ultra Low Carbon Steel on Decarburization Reaction in RH Degasser.

Abstract

On the basis of a mixed-control mechanism involving the mass transfer of carbon and oxygen in the molten steel in the vacuum vessel and the transport of carbon and oxygen by the circulation flow, a new reaction model for RH decarburization has been developed to clarify the effect of oxygen concentration on the decarburization rate. The model can also predict the effect of the KTB method, in which oxygen gas is blown onto the molten steel in the vacuum vessel, on the decarburization rate.A significant dependence of the decarburization rate in the RH experiments on the oxygen concentration in the ladle, OL, has been found in the range of the carbon concentration in the ladle, CL, of more than 200 ppm. In the range CL200 ppm, the decarburization rate is apparently proportional to the carbon concentration, hence its dependence on OL is small. The model analysis predicts the dependence of the decarburization rate on OL, however, there is some difference between the calculated decarburization rate and the observed rate. This is presumed to be caused by an unidentified supply of oxygen to the molten steel in the vacuum vessel, which may result from the slag being drawn into the vacuum vessel and the leakage of atmospheric air.Volumentric coefficients of the mass transfer of carbon in the vacuum vessel of the RH, akC, was also investigated in the ultra low carbon range of less than 50 ppm using recent data, and was shown to have a strong dependence on the carbon concentration and the circulating flow rate, Q..