Research on the reaction mechanism and control of aluminium enhancement for electroslag remelting high-quality turbine blade steel

Abstract

Based on laboratory experiments and thermodynamic analysis, this article reveals the reaction mechanism behind the increase in aluminium content during the electroslag remelting (ESR) process in a protective atmosphere. It investigates the effects of slag composition, steel composition, reaction temperature, and reaction atmosphere on the aluminium content in ingots to inhibit the increase of aluminium during the remelting process. The results indicate that the increase in aluminium content is accompanied by significant silicon loss in the steel and an increase in silicon dioxide in the slag. The aluminium content in the ingots is controlled by the thermodynamic reaction equilibrium between [Si] in the steel and (Al₂O₃) in the slag. The high-temperature conditions during the ESR process promote the occurrence of the aluminium addition reaction. In the ESR process without a protective atmosphere, the oxidation of the consumable electrode in air forms a ferrous oxide, leading to a decrease in silicon activity. Consequently, the trend of aluminium increase in ingots remelted in a nonprotective atmosphere is lower than that in ingots remelted in a protective atmosphere. Increasing the silicon dioxide content in the slag to 1.96%–7.62% is an effective approach to inhibit aluminium addition in the ingot. However, excessive addition of silicon dioxide can cause the burning loss of alloy elements and increase the content of silicate inclusions. Additionally, reducing the initial silicon content in the electrode from 0.55% to 0.40% further reduces the aluminium content in the ingot. Industrial experiments were conducted using the optimised S2 slag system (68.63% CaF₂–19.61% Al₂O₃–4.90% CaO–4.90% MgO–1.96% SiO₂). The results were consistent with laboratory experiments, and the aluminium content in the ingots met the standard requirements.