A Study of Physical and Chemical Properties and Dynamic Control of Slag for the Low Carbon Al-killed Steel Refining Slag

In order to improve the castability of low carbon Al-killed steel, based on the thermodynamic calculation of low carbon Al-killed steel refining slag, the effects of typical components CaO/Al₂O₃ (C/A), SiO₂ and FeO on the liquidus temperature, 1 650 ℃ viscosity and surface tension of the refining slag were studied. Combining the test results of the physical and chemical properties (melting temperature and viscosity–temperature curve) of the refining slag, a dynamic control model for the argon-blowing top-up refining slag was established and implemented in production practice. The results show that as C/A increases, the melting point of the refining slag increases when SiO₂ mass fraction is 5%, while it first decreases and then increases when SiO₂ mass fraction is 10%. Meanwhile, with the increase of C/A, the viscosity of refined slag and the inflection temperature on the viscosity temperature curve increase. When the composition range of refined slag is C/A 0.75−1.50, SiO₂ mass fraction of 0−10%, and FeO mass fraction of 2%−6%, lower liquidus temperature, higher viscosity, and higher surface tension can be obtained. The production application of the established model enables the dynamic addition of slag-former materials, and the stability of physical and chemical properties of refining slag is significantly improved.The standard deviations of the calcium aluminum ratio (C/A) and total iron (TFe) mass fraction of refined slag are significantly reduced, and the average values of its liquidus temperature, viscosity at 1 650 ℃, and surface tension is reduced by 6.9 ℃, increased by 0.020 6 Pa•s, and 0.010 9 N/m, respectively. In practice, the average mass fraction of oxygen content (TO) decreases from 2.78×10⁻³% to 2.25×10⁻³%, an improvement of 19.1%, and the castability of molten steel is significantly improved.