Dynamic interaction of refractory and molten steel: Effect of alumina-magnesia castables on alloy steel cleanness

Abstract

High quality alloy steel is an important material needed for social and economic development. It is of great significance to major national projects and defence security. Refractories are used in the smelting process of steel; they are some of the main sources of impurities which have an important effect on the quality of steel. As alumina-magnesia refractories are the main lining materials used for steel refining, the influence of these refractories on the cleanliness of molten steel under dynamic smelting conditions has been studied. The size, quantity, composition, and structure evolution of inclusions in steel are analysed. The results show that after smelting, the content of alloy elements in the steel is stable, and that the total oxygen content and inclusions in the steel are increased by the corrosion of the alumina-magnesia castables. However, the maximum average particle size of the inclusions in the steel was limited to 20 µm, which did not cause large inclusions in the steel or seriously affect the quality of steel. During the dynamic melting process, because of the presence of Si and Mn in the alloy steel, the inclusions changed from homogeneous CaS wrapped Al2O3-MgO composite sphere to MnS wrapped egg-shaped structure. The alloy elements in steel were found to be beneficial, as they reduced the effect of alumina and magnesia inclusions on the quality of steel. The results indicate that it is feasible to smelt high quality alloy steel using alumina-magnesia carbon-free castable, and that it would be better to limit the refining time to 45 min during smelting.