Kinetics of CO Gas Dissolution into Stirred Liquid Fe at 1823 K and Its Impact on Nozzle Clogging during Continuous Casting

Abstract

CO gas generated by a carbothermic reaction in Submerged Entry Nozzle (SEN) can reoxidize an Ultra Low C (ULC) steel during continuous casting. When Ti presents in the ULC steel, the CO gas oxidizes the liquid steel and Fe_tO–Al₂O₃–TiO_x liquid oxide mixed with solid alumina forms at the interface between the steel and the nozzle. The reoxidation is partly responsible for the nozzle clogging. In the present study, the kinetics of CO gas dissolution into liquid Fe at 1823 K was investigated in order to understand how fast the reoxidation occurs, which is responsible for the liquid oxide formation and the nozzle clogging. A series of gas-liquid reaction experiments were carried out under various conditions (gas flow rate, stirring speed, the partial pressure of CO). Dissolved C and O contents in the liquid Fe were analyzed in order to find possible rate controlling step. It was found that a gas phase mass transfer is a possible rate controlling step at low rate of CO gas supply if the flow rate (Q) is lower than 0.75 L min⁻¹, which is thought to be higher than the actual CO gas supply rate in a typical SEN (~0.15 L min⁻¹, volume corrected at room temperature). Therefore, the reoxidation is limited by the supply of CO gas to liquid steel. Decreasing CO gas generation from the nozzle is recommended to suppress the nozzle clogging.