Effect of Direct Reduced Iron (DRI) on Dephosphorization of Molten Steel by Electric Arc Furnace Slag

Abstract

We investigated the effect of direct reduced iron (DRI) addition on dephosphorization of molten steel by electric arc furnace (EAF) slag at 1823 K (1550 °C). Various phenomena such as CO gas evolution and slagmaking by gangue oxides in DRI were experimentally observed at each reaction step. Thermodynamic behaviors of phosphorus, oxygen, and carbon were strongly dependent on DRI content. Basicity, which is the thermodynamic driving force of dephosphorization, decreased with the increasing DRI content because SiO2 concentration in the slag was proportional to DRI addition. The excess free energy of P2O5 increased with the increasing SiO2 content in slag. A higher DRI content made dephosphorization difficult by decreasing the basicity and stability of P2O5 in the slag. Therefore, when using DRI in EAF process, it is very important to control the basicity of slag.