Abstract
In order to reduce the amount of fluorite during the steelmaking process for environmental protection, it is essential to investigate the fluorine-free slag system. Thus, high-basicity CaO–SiO2–FeOx–MgO slag with B2O3 content from 0% to 15% was designed, and its melting characteristics and viscosity were investigated. The influence of B2O3 content on the phase diagram of the slag system was calculated using FactSage 7.3, and the break temperature was determined from the curves of temperature-dependent viscosity. The results show that, with the increase in B2O3 content, the melting characteristics of the CaO–SiO2–FeOx–MgO/B2O3 slag system, including liquidus temperature, flow temperature, softening temperature, and hemispheric temperature, all decreased; the main phase of the slag system transformed from Ca2SiO4 into borosilicate, and finally into borate; the viscous flow activation energy reduced from 690 kJ to 130 kJ; the break temperature reduced from 1590 °C to 1160 °C. Furthermore, the melting characteristics and the break temperature of the slag system with 5% and 8% B2O3 content were found to be the closest to the values of fluorine-containing steel slag.
Highlights
World crude steel production was 1816.61 million tons in 2018, 70.64% of which was produced using an oxygen converter [1]
Dimensional (2D) triangular [BO3] units occur in the slag system, gradually becoming the dominant structure associated with B–O arrangements, favoring slag flowability and resulting in an apparent reduction in activation energy [17]
With the B2 O3 content increasing, two-dimensional (2D) triangular [BO3 ] units occur in the slag system, gradually becoming the dominant structure associated with B–O arrangements, favoring slag flowability and resulting in an apparent reduction in activation energy [17]
Summary
World crude steel production was 1816.61 million tons in 2018, 70.64% of which was produced using an oxygen converter [1]. As an important physical property of slag, melting characteristics and viscosity have great influence on element diffusion, the reaction between slag and steel, gas escape, heat transfer, metal loss, and lining life. Fluorite is often added as a slag melting agent in order to reduce the melting characteristics and viscosity of slag in the process of converter steelmaking. If the fluorite usage is 2–3 kg/t in general, it can consume metallurgical grade fluorite of 1.64–2.46 million tons, based on the crude steel capacity of 820.20 million tons produced via converter in China in 2018 [2]. China no longer issues new “fluorite mining licenses” as of 2003 in order to protect fluorite resources
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