Effect of Slag on Titanium, Silicon, and Aluminum Contents in Superalloy During Electroslag Remelting

Abstract

Many factors influence the chemical composition in electroslag remelting (ESR) steel, including atmosphere in crucible, melting rate, slag composition, deoxidation, and so on. Fluoride-based slag, which is exposed to liquid metal directly, influences the chemical composition of ESR ingots to a large extent. The present paper focuses on the effect of slag on the titanium, silicon, and aluminum contents in ingots based on the interaction of the slag and metal. In present work, superalloy of GH8825 and several slags containing different CaO contents have been employed for investigating the effect of slag on titanium, silicon, and aluminum contents in an electrical resistance furnace under argon atmosphere. Results indicate that the higher CaO content in slag has better capacity for avoiding loss of titanium caused by the reaction of titanium with silica in slag, especially in case of remelting superalloy with high titanium and low silicon content. The CaO has a great effect on the activities of TiO₂, SiO₂, and Al₂O₃. Thermodynamic analysis is applied to investigate the CaO behavior. Based on the ion and molecule coexistence theory of slag, activity model is established to calculate the activities of components containing titanium, silicon, and aluminum elements in a six-component slag consisting of CaO-CaF₂-Al₂O₃-SiO₂-TiO₂-MgO. The components containing titanium, silicon, and aluminum in slag are mainly CaO·TiO₂, 2CaO·SiO₂, CaO·SiO₂, CaO·Al₂O₃, and MgO·Al₂O₃. With the increase of CaO mass fraction in slag, the activity coefficient of SiO₂ decreases significantly, whereas slightly change happens for Al₂O₃. As a result, the $\lg ({{\gamma_{{{\text{SiO}}_{2} }} } \mathord{\left/ {\vphantom {{\gamma_{{{\text{SiO}}_{2} }} } {\gamma_{{{\text{TiO}}_{2} }} }}} \right. \kern-0pt} {\gamma_{{{\text{TiO}}_{2} }} }})$ decreases with increasing CaO content, which is better for preventing loss of titanium caused by the reaction of titanium with silica in slag. The slag with high CaO and appropriate TiO₂ content is suitable for electroslag remelting of GH8825.