In order to examine the mechanism of the generation of MgO in CaO–MgO–Al₂O₃ inclusion during Ca addition, the variations of inclusion composition and molten steel composition were measured during and after FeMg and CaSi addition to 2 kg heats of Al killed molten steel at 1873K. From experimental studies, the equilibrium reaction was discussed by the relationship between Ca concentration in molten steel and MgO concentration in inclusion and apparent equilibrium constant of magnesium deoxidation was obtained.
The results obtained are summarized as follows;
(1) The addition pattern of calcium and magnesium affected composition variation path, although it had no effects on final composition of inclusion.
(2) The boundary condition of formation and disappearance of MgO in Ca–Al–O inclusion was given by Ca concentration and Mg concentration in molten steel.
(3) The reaction of MgO formation in Ca–Al–O inclusion was expressed as follows.
CaO·Al₂O₃ in inclusion+Mg=MgO·Al₂O₃ in inclusion+Ca
(4) The apparent equilibrium constant log K′_Mg was estimated to be −7.2 by thermodynamic calculation.
log K′_Mg=a_Mg·a_O=−7.2