A Reaction Between High Mn-High Al Steel and CaO-SiO₂-Type Molten Mold Flux: Part I. Composition Evolution in Molten Mold Flux

In order to elucidate the reaction mechanism between high Mn-high Al steel such as twin-induced plasticity steel and molten mold flux composed mainly of CaO-SiO₂ during continuous casting process, a series of laboratory-scale experiments were carried out in the present study. Molten steel and molten flux were brought to react in a refractory crucible in a temperature range between 1713 K to 1823 K (1440 °C to 1550 °C) and composition evolution in the steel and the flux was analyzed using inductively coupled plasma atomic emission spectroscopy, X-ray fluorescence, and electron probe microanalysis. The amount of SiO₂ in the flux was significantly reduced by Al in the steel; thus, Al₂O₃ was accumulated in the flux as a result of a chemical reaction, 4[Al] + 3(SiO₂) = 3[Si] + 2(Al₂O₃). In order to find a major factor which governs the reaction, a number of factors ((pct CaO/pct SiO₂), (pct Al₂O₃), [pct Al], [pct Si], and temperature) were varied in the experiments. It was found that the above chemical reaction was mostly governed by [pct Al] in the molten steel. Temperature had a mild effect on the reaction. On the other hand, (pct CaO/pct SiO₂), (pct Al₂O₃), and [pct Si] did not show any noticeable effect on the reaction. Apart from the above reaction, the following reactions are also thought to happen simultaneously: 2[Mn] + (SiO₂) = [Si] + 2(MnO) and 2[Fe] + (SiO₂) = [Si] + 2(FeO). These oxide components were subsequently reduced by Al in the molten steel. Na₂O in the molten flux was gradually decreased and the decrease was accelerated by increasing [pct Al] and temperature. Possible reactions affecting the Al₂O₃ accumulation are summarized.