Theoretical Bases and Technology of Steel Exhaustive Metal Desulfurization and Direct Microalloying with Boron Beneath Basic Boron-Containing Slags

Results of theoretical and experimental studies of the physicochemical properties of slags of the CaO–SiO 2 –B 2 O 3 system containing 15% Al 2 O 3 and 8% MgO lie at the basis for the development of technology for exhaustive desulfurization of metal beneath basic boron-containing slags formed in a steelpouring ladle in a ladle-furnace unit (LFU), and steel direct microalloying with boron. Methods of simplex lattice planning of an experiment, a software complex HSC 6.1 Chemistry (Outokumpu), and the method of electro-vibration viscosimetry are used. Results of thermodynamic modeling of the effect of slag basicity and B 2 O 3 content on sulfur and boron equilibrium distribution coefficient between slag of the oxide system under study and low-carbon metal are presented. The quantitative effect of basicity and B 2 O 3 content on slag viscosity containing 15% Al 2 O 3 and 8% MgO at a temperature of 1600°C and the influence of the slag chemical composition of the oxide system under study on the degree of wear of periclase-carbon refractory material are shown. Results of studying physicochemical properties of slags of the CaO–SiO 2 –B 2 O 3 system containing 15% Al 2 O 3 and 8% MgO are a basis for developing a ladle slag composition with low viscosity and providing exhaustive metal desulfurization, and direct microalloying of boron steel with low corrosive effect on periclase-carbon refractories. Development of this technology provides, depending on the steel grade, a boron content of 0.001–0.008%, low metal sulfur concentration at 0.004–0.014%, a reduction in manganese ferroalloy consumption from 0.5 kg/ton of steel 08KP to 1.4 kg/ton of steel 09G2S, exclusion of ferroboron and fluorspar additives in the ladle, and achievement of good finished metal product mechanical properties.