Thermodynamic optimization of Fe-Sn-C system for the Future Application of Tramp Element Control in Ferrous Scrap

Abstract

The cost of the raw materials to produce pig iron is increasing and therefore, iron and steelmaking industries are increasing the usage of ferrous scrap. However, steel products produced from this scrap contain tramp elements including As, Cu, Pb, Sb, and Sn. It is well known through several studies in the past that these tramp elements are hardly removed once they are dissolved into the molten steel. But, there is insufficient research under what conditions the extraction and removal of these tramp elements are possible and systematic research requires on the extraction of the molten steel by the interaction between the components. Therefore, in the present study, thermodynamic modeling of Fe-Sn binary system and Fe-Sn-C ternary system were carried out. In order to treat strong positive interaction of Fe-Sn, modified quasichemical model was employed to the liquid phase. Solid solutions in the system were modeled using compound energy formalism. The liquid phase in the Fe-Sn system well elucidates the thermodynamic properties. However, it shows a deviation in the experimental results in the miscibility gap. It is seemed to have practical experimental problems in determining miscibility gap with ex-situ technique therefore in situ technique is required to determine the composition and consolute temperature of the miscibility gap. To determine the Fe-Sn-C ternary system, C solubility over Sn, distribution coefficient between Ag-Sn alloy and Fe-Sn-C alloy experiments were carried out. It showed that in the former experiment, C solubility was decreased as Sn was increased in liquid Fe-Sn-C. Moreover, after a certain amount of Sn charged into the liquid, no more dissolution of Sn was observed and shows the possibility of the miscibility gap. In the latter experiment, also appeared that C concentration in liquid Fe-Sn-C was increased, the Sn was decreased. These results were used in modeling the ternary Fe-Sn-C and showed fairly good agreement with the experimental results in the present study. However, the present study treats Sn-C as ideal solution, further study is required to verify the actual ternary system.