Steel-flux interaction during high aluminium steel continuous casting

More than 90% of the world steel is produced using the continuous casting process, where molten steel is delivered through a submerged entry nozzle into a water-cooled copper mould to form a continuous shell. In this process, mould flux plays an important role in ensuring heat insulation, avoiding oxidation of steel, absorbing inclusions from liquid steel, controlling heat transfer, and lubricating shell and mould. New grades of high-strength steel with high-Al contents are attractive materials for the automotive industry. However, in continuous casting, Al in the steel reacts with SiO2 in the mould flux, leading to a change in flux composition and properties. Therefore, conventional CaO-SiO2-based fluxes are not suitable for high-Al steel casting, therefore, CaO-Al2O3-based fluxes are developed. This project aims at studying the effects of different oxides in mould fluxes on flux-steel reaction at a high temperature which is very important for high aluminium steel flux development.In the researches on steel-flux reaction at 1773 K, the effects of initial Na2O content, CaO/Al2O3 ratio, B2O3 content, and SiO2 content were studied. The increase of initial Na2O concentration from 1.9 to 7.3 mass pct in CaO-Al2O3-based mould fluxes enhanced the reaction between flux and steel, leading to [Al] concentration decrease in liquid steel and [Si] concentration increase. The flux-steel interface after the reaction was perturbed with notable flux emulsions in the liquids steel. Increasing Na2O content reduced the emulsion because of an increased crystallization tendency and flux viscosity due to an enhanced flux-steel reaction, preventing flux droplet from necking and detachment. The increase of CaO/Al2O3 ratio enhanced the interfacial reaction. The accumulation of Al2O3 and the reduction of Na2O were accelerated by the increase of CaO/Al2O3 ratio. The increase of CaO/Al2O3 ratio sedated the emulsification phenomenon in the initial stage of the reaction. The increase of initial