Research progress on the control of reactive elements in remelted ingots during electroslag remelting process

Electroslag remelting (ESR) is an important secondary refining technique capable of removing impurity elements and non-metallic inclusions, improving the solidification structure of ingots, and enhancing the mechanical properties of the steel. When steel contains easily oxidizable alloying elements such as Al, Ti, Si, B, and rare earth elements, chemical reactions occur with unstable components in the CaF2-CaO-Al2O3-based ESR type slag system, leading to non-uniform distribution of alloying elements along the height of the ingot. To mitigate the oxidation loss of these elements during the ESR process, precise design of the slag composition in the CaF2-CaO-Al2O3-based ESR type slag system within the ESR temperature range enables accurate control of target elements in the steel. Apart from incorporating corresponding oxide additives into the ESR type slag system, the effects of common components like CaO and Al2O3, as well as temperature variations, on the content of different alloying elements in steel vary. The accuracy of mass transfer models during ESR depends on the precise estimation of thermodynamic activities of components in both slag and molten steel, temperatures at different reaction locations (electrode tip, metal droplet, interface between slag bath and metal pool), mass transfer coefficients, and geometric parameters. However, these parameters are significantly influenced by different ESR operations, slag compositions, and steel grades. Due to the difficulty in accurately estimating reaction temperatures and fluid flow effects on mass transfer coefficients at different reaction locations, kinetic studies of oxidation-prone elements remain relatively scarce compared to thermodynamic analyses. Physical parameters of the slag system also critically affect the surface and solidification quality of ingots. Current research on the physical parameters of remelting slag systems containing TiO2, SiO2, B2O3, and rare earth oxides mainly focuses on viscosity and crystallization ability, while laboratory studies on their activities are yet to be reported. The development of low-fluorine remelting slag systems is gaining attention, necessitating further research into the thermodynamic, kinetic, and slag physical parameters controlling oxidation-prone elements in such conditions.