Abstract: The physical and chemical properties of RH top slag for non-oriented electrical steel were studied by FactSage 7.2 thermodynamics software. The top slag optimization plan were proposed in combination with industrial production. Studies have shown that FeO and SiO₂ in RH top slag would cause secondary oxidation of steel. Combined with thermodynamic analysis, calculation of the absorption capacity of the top slag for Al₂O₃ and industrial tests, the ideal RH refining process top slag composition range is w(CaO)=50 %～60 %，w(SiO₂)≤5.01 %，w(CaO)/w(Al₂O₃)=1.5～2.0. At the end of refining, the slag system is close to the low melting point,w(CaO)/w(Al₂O₃)≈1.25. Industrial experiments showed that after the top slag compositions were optimized, T.O mass fraction of steel reached 14×10^-6 at the end of refining, the surface flaw rate of cold-rolled products decreased from 4.6 % to 0.3 %， and the smelting effect of RH top slag was excellent.

Key words: non-oriented electrical steel, RH refining, slag optimization, w(CaO)/w(Al₂O₃), surface flaw