Abstract
The refining characteristics of stainless steel in top and bottom blown converter was studied by using a 45 ton LD converter in LD-VAC process where the bottom was equipped with two tuyeres blowing Ar and N2 gases. The results obtained are as follows:
1) The perfect mixing time (τs) shown in eq. (2) is effectively available to evaluate agitating and mixing characteristics of the top and bottom blown converter even in the refining of stainless steel through the consideration on the relations between [C] and (Cr2O3) at blow end and the carburization rate. The index of BOG is also available to use even if the oxide mainly formed is not FeO but Cr2O3.
2) The refining characteristics are improved by the top and bottom blowing when the rate of bottom blowing gas increase up to 0.06 Nm3/t·min at which τs is corresponding to 60 sec. The apparent partial pressure PCO becomes 0.9 to 1.0 and the C-O reaction seems to be equilibrium. On the other side, the apparent PCO in the conventional top blowing converter is more than unity and the reaction as a whole melt seems not to be equilibrium.
3) Nitrogen can sufficiently be used as a agitating gas, although the amount of ten to twenty percent of blowing nitrogen is absorbed into melt.
