Effect of Al<sub>2</sub>O<sub>3</sub> on Viscosity and Refining Ability of High Basicity Slag for Heat-resistant Austenitic Stainless Steel

Abstract

To optimize Al2O3 content in high basicity CaO-SiO2-Al2O3-8%MgO-8%CaF2 slag (%CaO/%SiO2=6) used for the refining of heat-resistant austenitic stainless steel, the effect of Al2O3 on the viscosity and refining ability of the slag was systematically investigated, and the relevant mechanism was clarified based on the analyses of solid phase precipitation behaviour and ionic unit structure transformation. The results demonstrated that the slag viscosity dramatically decreased and marginally varied in the Al2O3 ranges of 10%–20% and 20%–30%, respectively. At 1833–1873 K, both the slag viscosity and the activation energy reached the lowest values at 25% Al2O3. Al2O3 addition not only significantly inhibited the precipitation of CaO phase but also enhanced the polymerization degrees of aluminate and silicate networks. Furtherly, the inhibiting of Al2O3 on the solid phase precipitation dominated the viscosity reduction at 10%–25% Al2O3, while the enhancing of Al2O3 on the polymerization degree of networks led to the viscosity increase with further increasing Al2O3 to 30%. Finally, we optimized the reasonable high basicity slag containing 25% Al2O3 for Sanicro 25 steel due to the lowest viscosity and optimum refining ability of this slag.