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利用热力学计算软件FactSage确定了精炼渣中MgO质量分数合理范围为4％～8％，以6％最佳。由工业取样结果结合FactSage分析了1873K时SiO2-CaO-Al2O3-6％MgO准三元系液相区及CaO饱和的固液两相区渣一钢平衡。结果表明：高碱度高w（CaO）／w（A12O3）（C／A）精炼渣有利于钢液的低氧低硫和低硅控制，但并非造得越“白”越好，相反过高的CaO对脱氧和硅含量控制不利。通过钢渣平衡分析得到了酒钢SPCC精炼渣优化成分范围（质量分数）为：CaO为50％～55％，Al2O3为30％～36％，SiO2为1％～6％，MgO为4％～8％，6％为最佳，碱度为9．0～14．0，w（CaO）／w（A12O3）为1．5～1．8，实验室渣-钢平衡试验和工业生产结果均验证了优化的渣系较原渣藁藉慎析渠百们衍械．能镌同时缢低钢审鸶茸磕和硅含暑．也能有效控制钢中夹杂物的成分。

The reasonable content of MgO in refining slag calculated by the thermodynamic calculation software Fact Sage ranges from 4% to 8%, in which 6% is the best. In addition, slag-steel equilibrium at 1873K between SiO2 CaO-Al2O3-6 % MgO quasi ternary slag and liquid steel were analyzed on the basis of results of industrial sampling combined that calculated by FactSage both in liquid region and solid-liquid coexisting region with CaO saturation. It indicates that the refining slag with high basicity and high w(CaO)/w(Al2O3) (C/A) is favorable for control of low oxygen, low sulfur and low silicon. However, slag with too much CaO is disadvantageous of deoxidation and desili conization that suggests refining slag is not the whiter the better as the supersaturated CaO do not take part in the slag-steel reaction and even worsen its kinetic conditions. Furthermore, the optimized compositions of refining slag in LF for SPCC in Jiuquan Iron and Steel Corporation (JISCO) are: CaO 50%-55%, Al2Oa3 30%-36%, SiO2 1%- 6%, MgO 4%-8 % and 6 % is best, basicity 9.0-14.0 and w(CaO)/w(Al2 03 ) is 1.5-1.8. Finally, both slag-steel equilibrium experiments in laboratory scale and industrial trials in plant scale verified that optimized slag has a better ability for deoxidation, desulfurization and control of silicon content, and could better control inclusion composition as well as its removal.