A Reaction between High Mn-High AI Steel and CaO-SiO2-Type Molten Mold Flux: Reaction Mechanism Change by High Al Content ([pct AI]0=5.2) in the Steel and Accumulation of Reaction Product at the Reaction Interface

A series of laboratory-scale experiments were carried out in order to elucidate the reaction mechanism between high Mn-high Al steel and CaO-SiO2-type molten mold flux at 1 450 degrees C, which represents the reaction taking place during continuous casting of the steel. Compared to the previous study [Kim etas., Metall. Mater. Trans. 44B (2013) 299-308], high Al content in the liquid steel ([pct AI](0) = 5.2) and high MgO content in the liquid flux ((pct MgO)(0) = 5 to 15) were employed, in order to confirm change of rate-controlling step from mass transport of Al in liquid steel to more complicated steps including mass transport in liquid flux. It was found that Al2O3 was rapidly accumulated near the interface of the flux, and SiO2 and Na2O were reduced simultaneously, regardless of (pct MgO)(0). At the early stage of the reaction (1 min), MgAl2O4 particles were observed in the flux near the interface, then the particles were spreading out into the bulk flux as the reaction time passed. Other solid phases (CaAl4O7, Al2O3) were also observed due to local depletion of MgO in the flux. The MgAl2O4 formation mechanism and its effect on mass transfer in the molten flux were discussed. A series of simple kinetic analyses showed that the mass transport of Al in liquid steel is no more controlling the reaction rate. It was concluded that there were possibilities of mass transport in the flux phase contributing reaction rate controlling step.