Dissolution behavior of Al2O3 into tundish slag for high-al steel

Abstract

Tundish slag composition is of vital importance to the control of steel cleanliness. In the present study, computation of phase diagram, accompanied with steel–slag reaction, was performed to preliminarily determine the tundish slag composition for high-Al steel 38CrMoAl, and the rotating cylinder method was, then, applied to further clarify the influence of slag composition on Al2O3 dissolution into tundish slag. Thermodynamic analysis suggested that SiO2-minimized CaO–Al2O3 (wt%CaO/wt%Al2O3 = 1.0–1.4) slag with MgO<6 wt% was suitable for tundish operation of 38CrMoAl steel. The results of rotating experiment indicated that the mass transfer in the liquid slag was the rate-limiting element of Al2O3 dissolution into the CaO–Al2O3 based slag and hence the dissolution rate was strongly related to the slag viscosity. The Al2O3 dissolution rate was found to be improved by increasing the wt%CaO/wt%Al2O3 ratio as well as adding small amounts of CaF2 and Na2O. The optimal slag composition for Al2O3 dissolution was put forward: wt%CaO/wt%Al2O3 = 1.1, MgO = 5 wt%, CaF2 = 6 wt%, Na2O = 5 wt%, and SiO2 content should be minimized. Results from plant trials demonstrated the benefit of inclusion removal for present tundish slag.