Abstract
Experimental and theoretical work were performed to estimate the effect of slag basicity and amount of reducing agents on the reduction of chromium oxide from the slag which interacted with molten steel at 1,600 °C. The slag system contained CaO, MgO, SiO 2 , CaF 2 and Cr 2 O 3 together with Fe-alloys (Fe-Si and Fe-Si-Mg). The CaF 2 and MgO contents in the slags were 10 mass % each; Cr 2 O 3 was 25%. The amount of the ferroalloys ranged from 12.5 to 50 g per 100 g of slag. The (CaO+MgO)/SiO 2 ratio was held at 1 and 2. The Cr yield was determined using both Fe-alloys as reducing agents. Some estimations were made to determine the theoretical effect of temperature, slag basicity, (CaO+MgO)/SiO 2 , and amount of reducing agents in the slag on the chromium recovery. The FACT (Facility for the Analysis of Chemical Thermodynamics) computational package is used to determine the equilibrium between the slag and molten steel.
Highlights
The slags in the stainless steelmaking process are subjected to both oxidizing conditions during carbon removal and reducing conditions in the final refining stage
The chromium oxide-containing systems are more complex than other transition metal oxide systems, such as the iron-containing systems, because chromium exists in three valencies, Cr^"*", Cr^"^ and Cr depending on the oxygen partial pressure, temperature and slag composition^
The software accesses a user-database of species in solution allowing to determine the equilibrium composition of a multiphase and multicomponent system at given temperature, pressure and initial composition. This program uses the method of minimization of free energy to determine the concentrations of each phase in equilibrium. This software uses the unified interaction parameter proposed by Bale and Pelton^^ for the molten steel and the quasichemical approximation"^ ^ for the slag
Summary
The slags in the stainless steelmaking process are subjected to both oxidizing conditions during carbon removal and reducing conditions in the final refining stage. The solubility of chromium oxide or the activity composition relation in the slag directly influences the metallurgical process as a high solubility increases the chromium losses to slag. The chromium oxide-containing systems are more complex than other transition metal oxide systems, such as the iron-containing systems, because chromium exists in three valencies, Cr^"*", Cr^"^ and Cr depending on the oxygen partial pressure, temperature and slag composition^. The results of this work show the effects of time of process, slag basicity and Fe-alloy additions in slag on the chromium content in steel
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