Physicochemical characteristics, production and application of boron-bearing complex ferroalloys

The expediency of producing and using complex ferroalloys in steelmaking is analyzed in terms the manufacturing technology, the raw materials employed, and the interactions of the ferroalloys with the molten steel. The need to produce complex ferroalloys with boron is established. The fundamental principles for determining the best composition of such alloys are presented. The basic compositions of complex ferroalloys with boron (ferrosilicomanganese with boron, ferrosilicon with boron, ferrosilicomanganese with boron and chromium) are established by studying the physicochemical properties of alloys and their interactions with the steel melt. If the characteristics (melting point, density, melting time of the ferroalloy in liquid steel, etc.) of complex ferroalloys with boron are compared with those of ferroboron, which is widely used, the complex alloys have clear benefits. The composition of the complex ferroalloys with boron includes active elements (Si, Al, Ti) facilitating the binding of oxygen and nitrogen from the steel melt in strong compounds and hence preventing their reaction with boron. The recommended boron content in the ferroalloy is 0.7–2%. That permits increase in the quantity of complex ferroalloys with boron in the steel and hence increase in the reliability and stability of boron assimilation. At elevated temperatures (1430–1570°C), the oxidation of ferrosilicoboron is 4–7 times less than that of ferroboron. Data are presented regarding the industrial production and use of ferrosilicoboron in the steel-smelting shop. The boron assimilation from complex alloys in microalloying of the steel is studied. The use of ferrosilicoboron does not require significant changes in the existing system for reduction by ferrosilicon; the boron assimilation is 77.8–96.3% (mean 86.6%). With a boron concentration of 0.0021–0.0027% in the steel during ladle treatment, its content in the cast metal will be no less than 0.0020%. If boron is introduced in steel by means of ferrosilicomanganese with boron, the boron assimilation is increased by a factor of 1.6 (from 48 to 77%, on average) in comparison with the use of ferroboron.