Direct microalloying of structural steels by boron from oxide system CaO–SiO<sub>2</sub>–B<sub>2</sub>O<sub>3</sub>–Al<sub>2</sub>O<sub>3</sub>–MgO

Abstract

The results of fundamental studies of the physicochemical properties of slags of the CaO–SiO2–B2O3–Al2O3–MgO system were used as the basis for the development of the technology for the formation of boron-containing slags in ladle-furnace units (LFU). The recommended composition of ladle slags (1–4% B2O3, 15% Al2O3 and 8% MgO) ensures the development of direct microalloying processes of steel with boron, low viscosity, not exceeding 0.32 Pa∙s, and preservation of sufficiently high refining properties. Colemanite (Turkey) was used as boron-containing raw material, having, %: 39–41 B2O3, 26–28 CaO, no more than 5% of SiO2 and 3% of MgO. The implementation of the developed technology of direct microalloying of structural steels of a wide grade composition by boron in the BOF shop of ArcelorMittal Temirtau JSC provided the boron content at the level of 0.001–0.008%, a decrease in the consumption of manganese-based ferroalloys from 0.3 kg/t of 08кп steel to 0.8 kg/t of steel 17Г1С-У, exclusion of additives into the ladle of ferroboron and fluorspar. The proposed mode of formation of slags of the recommended composition in the melt of LFU provided a sufficiently high degree of metal desulfurization in comparison with the existing production routes. For example, with pipe steel 17Г1С-У, despite a decrease in lime consumption by 500 kg per a heat and a decrease of the steel processing time at the LFU by 40 minutes, a high degree of desulfurization, reaching 66.7%, provided a sulfur content of 0.004% in the metal. Microalloying of structural steels by boron results in their high strength properties with invariance of plasticity apart from sufficiently high refining effect.