We have derived equilibrium formulas for oxygen gas, FeO-Fe
2O
3-CaO-SiO
2 molten slag and Fe-Si-O molten iron by the statistical thermodynamic method, made their approximation to evaluate the concentration of Fe
2O
3 in the molten slag and the oxygen pressure Po
2 equilibrating with the system, and evaluated the concentration of silicin and oxygen dissolved in the molten iron by the electronic computer. Details can be summarized as follows.
(1) The Fe
2O
3 quantity in the total FeO is a negligible quantity in the numerical calculation, when no Fe
2O
3 is added to the molten slag, FeO-Fe
2O
3-CaO-SiO
2. If Fe
2O
3 is forcibly added, however, the oxygen pressure is greatly increased.
(2) With a decrease in FeO, the oxygen pressure Po
2 equilibrating with the composition of the T.FeO-CaO-SiO
2 molten slag and the molten iron decrease. Where FeO is low, the minimum value shifts to the CaO side.
(3) In relation to the steel-making reaction of the basic open hearth, the temperature is low, and the silicon reduction is little. In the welding exposed to high temperature, however, the reduced silicon greatly increases in relation to the composition of the slag of much SiO
2 content, so discloses the calculation, too.
(4) According to the conventional equilibrium study of chemical metallurgy of the Fe-Si-O system, if silicon increases, O decreases; but O increases, if silicon decreases. The statistical thermodynamic analysis has, however, disclosed that O also increases, if silicon increases beyond a certain extent. It seems to be attributable to the fact that silicon and O of some bond force are dissolved in the molten iron.
(5) The oxygen quantity in the welded metal is far more than that in the steel-making reaction, because the welding is a high temperature reaction, and still the molten slag composition is rich in SiO
2. In the reaction at high temperature, therefore, it is necessary to make such choice of the slag composition that the oxygen quantity may be minimum.
View full abstract