Effect of properties of mold powder entrapped into molten steel in a continuous casting process

Abstract

Mold powder plays an important role in the continuous casting process for high quality steel production. Qualitatively, it is well known that mold powder entrapment causes surface defects in steel sheets, and high viscosity of the mold powder prevents the entrapment of the mold powder into the molten steel in ultra-low carbon steel. This paper deals quantitatively with the entrapment of mold powder caused by suction by Karman's vortex in a laboratory experiment. First, in a water model experiment using oil as a substitute for mold powder, the effects of the viscosity of the oil and the interfacial tension between the water and oil were investigated. Following this, hot model experiments were carried out with mold powder and molten steel. The amount of mold powder entrapment was affected by the viscosity of the molten mold powder and the interfacial tension between the molten steel and mold powder. As the result, the following equation for mold powder entrapment was obtained. m= 1.06 × 107η-0.225γm-s-2.18 where m: weight of entrapped mold powder (g/100 g-steel η;: viscosity of mold powder at 1573 K (Pa·s and γm-s: interfacial tension between molten steel and mold powder (mN/m). The amount of mold powder entrapment decreased when the viscosity and interfacial tension increased. However, the effect of viscosity on mold powder entrapment was larger than that of interfacial tension in the case of an industrial mold powder when viscosity was under 0.5Pa·s and interfacial tension was from 1200 to 1300 mN/m. © 2009 ISIJ.