| Effects of Pco/Pco₂ on the contents of chromium, manganese, cobalt and nickel in molten binary alloy steels are investigated at 1650℃ under basic slag, and equilibria for oxidation of chromium and manganese in molten steel by CO₂ gas are discussed. When Pco/Pco₂ is more than 1.5, the activity of chromium in liquid steel is proportional to Pco/Pco₂, for chromium contents within the range 9∼12 wt.% and stags saturated with chromium oxides. α_(cr)=5.35×10^(-2)Pco/Pco₂ or Cr wt.%≒5.8×Pco/Pco₂ Close agreement between these experimental results and equilibrium data calculated leads to predictions that chromium oxide is present in the divalent form, CrO, in slag, under CO gas atmosphere, which could not be confirmed on the investigations of Cr-O system. There is a miscibility gap below Pco/Pco₂=1.5 and Cr=9 wt.% that activity of chromium dully decreases, as Pco/Pco₂ decreases, Activity of manganese of liquid steel in equilibrium with CO-CO₂ gas mixture is agreed with the value calculated from the standard free energy changes at Mn=9 wt.%, but above this, the experimental data is less than the value owing to difficulty of saturation of slag with MnO. Nickel and cobalt oxides were reduced by iron during melting. According to oxidation loss of iron by CO₂ gas in Fe-Ni and Fe-Co binary alloy, the contents of nickel and cobalt increase below Pco/Pco₂=1.5. Carbon contents slowly reduce as chromium and manganese contents decrease in equilibrium with CO·CO₂ gas mixture, but drop suddenly as partial pressure of CO₂ gas increases. Equilibrium problems in Fe-Cr-C-O and Fe-Mn-C-O system are more complicated owing to oxidation of iron by CO₂ gas and oxides in slag with increasing partial pressure of CO₂ gas. |
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