Effect of Li 2 O on the crystallisation behavior of continuous casting protective slag under magnetic field

Abstract

With the acceleration of slab continuous casting, achieving a balance between the thermal resistance and lubrication of mould flux has become increasingly challenging. This study proposes a composite regulation strategy involving a 40 mT static magnetic field and 0% to 1% Li₂O addition. The effects of magnetic fields and Li₂O on crystallisation behaviour were investigated using isothermal crystallisation and micro-structural analysis. Results show that the magnetic field effect is temperature-dependent: it significantly shortens nucleation time (>70%) at 1300 °C and 1250 °C, has minimal impact at 1200 °C, and promotes nucleation but delays overall crystallisation at 1150 °C due to insufficient nuclei. Li₂O addition modifies this effect, turning crystallisation promotion into suppression at 1300 °C and weakening the magnetic field's influence between 1250 °C and 1200 °C. At 1150 °C, Li₂O enhances crystal growth suppression. At temperatures ≥1200 °C, Li₂O synergises with the magnetic field to accelerate crystallisation and alters the crystal growth mode from unidirectional to multidirectional, inducing secondary nucleation and forming a bimodal structure. These findings provide theoretical guidance for the design of mould flux under high-speed casting conditions.