When molten iron or steel fully deoxidized with hydrogen or carbon contacts with such oxidizing gas as air, it is observed that an oxide layer or particles appear on the surface of molten metals before the oxygen content in the molten iron reaches the saturated value, [O] sat. We oxidized iron alloys with H20-Ar gas and studied the relations between oxidation conditions and oxygen content, [O] for carbon content, [C] f at the time, tf, when an oxide begins to form on the surface of molten metals, and time dependence of oxygen content.
Results obtained are as follows:
1) For carbon-free iron and its alloys, _??_is derived, where kf [O] sat/K, K is the equilibrium constant of reaction, H20=H2+O, Dm/δG and Do/δL are transport coefficient of H2O in gas and of O in liquid-side diffusion layer, respectively; M is atomic weight of oxygen and p is density of molten metal. Eq. 5 indicates that in accordance with an increase of Pi-120 and with a decrease of oxygen solubility in iron by the addition of alloying elements, [O] f decreases.
2) For carbon-containing iron and its alloys, [C] f is expressed by_??_where M'is atomic weight of carbon and Dc/l2 is transport coefficient of C in liquid-sidediffusion layer. From Eq. 12, it is considered that with an increase of PH2O in atmosphere, [C] f becomes higher and that when [O] sat decreases by the addition of other alloying elements [C] f becomes higher.
3) Accordingly, the time required for appearance of oxide on the surface, tf, is calculated approximately by Eqs. 15 or 16._??_where [O] o and [C] o are the initial contents at time t=0.
4) Present data were explained by the above equations qualitatively, but because of the lack of data on reaction kinetics, quantitative treatment could not be achieved.
Some data by other investigators on the oxidation of molten steels by air in teeming process were also explained by the application of present results.