Active element variation of G115 heat-resistant steel and its dependence on slag composition during electroslag remelting

Abstract

The steel-slag reactions and the changes of boron, aluminum, and silicon contents of G115 heat-resistant steel for ultra-supercritical power plants during protective argon gas atmosphere electroslag remelting (ESR) were investigated. The pickup of boron and aluminum was inhibited with the increase in SiO2 content of the slag during protective argon gas atmosphere ESR through inhibiting steel-slag reactions. The contents of silicon and aluminum in steel decrease, and the boron content increases with the increase in the B2O3 content of slag in protective argon gas atmosphere ESR. The change of aluminum and boron content of the steel during ESR is driven by chemical reactions [Si]-(Al2O3) and [Si]-(B2O3). A kinetic model for describing and predicting alloying element changes of G115 heat-resistant steel and their dependence on slag composition during ESR is developed. The kinetic model indicates that the proportions of aluminum pickup, silicon loss, and the pickup or loss of boron at the tip of electrode during protective argon gas atmosphere ESR are 57.62–68.69 mass%, 90.31–98.19 mass%, and 94.48–98.99 mass%, respectively. The boron content of the ingot increases from 0.0059 mass% to 0.0203 mass% as the B2O3 content of the slag increases from 0.2 mass% to 1.0 mass%. Alternative slag for electroslag remelting of G115 steel with the target of boron content (ranging from 0.0080 mass% to 0.0150 mass%) and aluminum content (lower than 0.0100 mass%) is composed of 47.34 mass% CaF2, 20.46 mass% CaO, 9.00 mass% SiO2, 0.50 mass% B2O3, 22.00 mass% Al2O3, and 0.50 mass% MgO.