Influence of process parameters, hot metal silicon content and slag properties on steel dephosphorization

Abstract

During the process of dephosphorization, the main solid phases formed in slag are dicalcium silicate (2CaO.SiO2), tricalcium silicate (3CaO.SiO2) and tricalcium phosphate (3CaO.P2O5). The last one is the main responsible for phosphorous removal. The present paper aims to study the influence of temperature, chemical composition, slag properties (viscosity, liquid amount, activities of CaO and FeO) and hot metal silicon (Si) content in the efficiency of steel dephosphorization. Different industrial heats with different slags, hot metal and steel compositions, were selected to be analyzed. The mentioned slag properties and phases were determined by computational thermodynamics using the software FactSage and the results of these analyzes was related to the dephosphorization efficiency from the slags respective heats. Based on these simulations, the parameter Dephosphorization Factor (FDeP = aCaO + aFeO + (Nliquid – Nsolid) ∗ KDeP) was used to measure the slags efficiency in hot metal dephosphorization and several analyzes were made by correlation observation. The results show that CaO activity is the most important parameter on the dephosphorization, whereas hot metal with higher Si content presents less efficiency in dephosphorization, due to the higher SiO2 formation, which increase the amount of solid phases, in addition to decrease in basicity and CaO activity. It was found that FDeP presents a high correlation (R2) with the dephosphorization efficiency and can be used to predict which slag will be the most efficient. The temperature, in the analyzed range, does not seem to be a directly relevant factor in the DeP efficiency.