Oxygen Potential in Basic Open-Hearth Furnaces

Fujii Takehiko

doi:10.2355/tetsutohagane1955.45.8_788

The rate of decarbonization in open hearth furnaces has been discussed mainly with carbon and excess oxygen contents, and ΔO in molten steel. But it is also necessary to consider the rate of movement of oxygen from slag to molten steel and the rate of running away of CO-bubbles. The author restricted this problem within the rate of movement of oxygen from slag to metal. Oxygen content, O'_equ in iron, which was in equilibrium with slag, was newly used for oxygen potential of slag, and oxygen content, O in molten steel was used for oxygen potential of metal as before. Then it was assumed that the difference of them, ΔO'=O'_equ -O gave not only the oxidation power of slag to metal quantitatively, but also the measure of moving speed of oxygen from slag to metal. In the open hearth furnace, the value of oxygen potential of metal, O was between O'_equ and O_equ (equilibrium value of O by the curve of Vacher & Hamilton), because carbon boil continuously occurred in molten steel. In this state, the potentiality of decarbonization was controlled by ΔO, and ΔO' made up for decrease of ΔO by the speed equal to the speed of decrease of ΔO. Then the speed of decarbonization was controlled by the speed of formation and growth of CO-bubble nucleus. Under this assumption, the change of O'_equ and ΔO' were examined in our 100t basic open hearth furnace (C; 0.08-0.80%), and moreover the change of O and ΔO in low carbon range were examined. The following results were obtained. (1) In the refining period in which carbon contents dropped from 0.80 to 0.08%, O and O'_equ was increased and moreover ΔO' was increased as the carbon was eliminated. (2) Accordingly excess oxygen, ΔO in steel was increased as the carbon was eliminated.

Oxygen Potential in Basic Open-Hearth Furnaces

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