Characteristic Analysis of Solidified Crust for Basic Tundish Flux With Al-Killed Steel Casting

Abstract

The solidified crust was harmful to Al-killed steel casting using a basic tundish flux. After sampling from an actual tundish, XRD, SEM and EDX examinations were carried out to analyze the microstructure of solidified crusts. The conclusions were obtained as follows: main crystallization phases existing in tundish crust were Ca₁₂A₁₄O₃₃, Ca₂SiO₄ and a little spinel; spinel and Ca₂SiO₄ distributed between the grain boundaries of Ca₁₂Au₁₄O₃₃, which increased the connection strength of crystallization phases by pinning grain boundary, density or hardness of solidified crust maybe also significantly increases; when initial composition of tundish flux was located in spinel region of CaO-SiO₂-Al₂O₃-10%MgO phase diagram, it was easier to precipitate spinel from molten slag; three approaches of spinel formation in flux were summarized. When flux was saturated with magnesia on the metal/flux interface, MgO in flux was reduced by dissolved aluminum and then formed spinel. On the interface of steel/refractory, with feasible aluminum content, it was also easy to form spinel, and spinel inclusions will be floated and captured by tundish flux.