| In recent years, 7Al2O3·12CaO refining slag is being used to purify molten steel, desulfurize and remove inclusions in the processing of LF. Pre-molten refining slag is one of main research objects concerned by metallurgist currently, and the focused problem is how to choose proper refining slag in accordance to different steel grade. In order to understand the CaO-Al2O3 refining slag deeply, and establish theory base for application and production of the refining slag , the physicochemical properties such as melting temperature, viscosity and desulfurization capacity of the slag were studied in this paper.Literatures about the history and research situation of pre-molten CaO- Al2O3 slag have been reviewed, the thermodynamics and kinetics of desulfurization and removal Al2O3 inclusion in the condition of reducing atmosphere have been discussed. The CaO- Al2Os base slags containing MgO, CaF2, SrO as auxiliary components are designd by quadratic orthogonal regression method. Composition range of the designed slags is Al2O3/CaO=0.8~ 1.2, CaF2=3%~9%, MgO=4%~10%, SrO=0~10%.Effect of SrO on properties of refining slag was innovatively studied. Control devices of kinetics study was developed, and The solution of A12O3 in refining slag (1# and 8#) was experimentally studied. In accordance with the coexistence theory of slag structure, the model of mass action concentration for slag system of CaO-Al2O3-MgO-SrO-CaF2-SiO2 is established firstly. Calculated results had good consistency with experimental data. Based on the experimental results, mathematical models between composition and properties were established, and the effects of composition on molten properties and sulfur distribution were discussed. Optimized composition was obtained by orthogonal direct-visual method. Optical basicity was used to calculate sulfur capacity. Melting uniformity of pre-molten refining slags were observed through microscope, and melting temperatures of pre-molten slag and mixing slag were compared.The confirming test shown that the mathematical models was highly reliable. For desulfurization, while the value of Al2O3/CaO is bigger, the sulfur capacity is lesser, sulfur distribution is also lesser; viscosity of samples has a minimum value when MgO is reached 5%, while MgO has a little influence on molten temperature of samples. The effect of Al2O3/CaO on high temperature properties of refining slag behaved as thefeature of parabola; Viscosity of slag increases with the increasing of CaF2, but molten temperature changes slightly. There is a linear relationship between SrO and molten temperature; viscosity of slag has a minimum value when SrO is reached 6%. By comprehensive consideration of physicochemical properties of slag in the study, the optimized composition of refining slag ought to be 7%SiO2, 7%MgO, 5%SrO, 6%CaF2 and %Al2O3/%CaO=0.8.At the condition of the study, when %Al2O3/%CaO is between 0.7-0.9, the slag has high capacity of adsorbing Al2O3 inclusion, the original content of Al2O3 has little effect on property; when %Al2O3/%CaO is more than 0.9, that adsorption of Al2O3 in refining slag would be improved with decreasing of original Al2O3 content, enhancing of saturated concentration of Al2O3, decreasing of viscosity of slag and interface tension between slag and Al2O3 inclusion.
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