Experimtents were carried out in 2x10(3) kg converter in order to quantitat
ively evaluate the contributions of condition of top and bottom blowing to
critical carbon content, Cp and (T.Fe) in slag. Cp decreased and (T.Fe) in
slag increased as increasing the bottom stirring power and ratio of cavity
depth to bath depth, L/Lo. Effect of L/Lo could not be explained by convent
ional indices such as ISCO, BOC and I because they did not take top blowing
condition into consideration precisely. Newly defined index For carbon oxi
dation, ICO. was introduced to attain good correlation between operational
conditions and (T.Fe) in slag. ICO=4.2x10(3) . (Q/W) . (L/Lo)(-0.4). epsilo
n(-0.33).[C](-1).