Abstract:  The equilibrium experiment between VOD refining slag and SUS444 ferrite stainless steel was carried out in the MgO crucibles at 1873 K. The influence of refining slag on the total oxygen content in stainless steel and the composition, quantity and size distribution of inclusions were investigated. It is concluded that the mass fraction of T. O in the deoxidized steel sample ranged from 0.006 3 %- 0.007 4 %. The T. O content in the steel decreased with the increasing of refining slag basicity and the decreasing of Al₂O₃ activity in the slag. With the increasing of basicity of refining slag, the number of inclusions per unit area as well as the average area fraction of inclusions in the steel sample decreased during the refining process. The mean particle size of inclusions reduced with the decreasing of Al₂O₃ content in the slag. After adding the deoxidizing alloy, the inclusions in the sample were Al₂O₃ and MgO×Al₂O₃ and complex oxides containing a small amount of SiO₂ and MnO. After calcium treatment, the main inclusions in steel were spherical MgO·Al₂O₃-CaO. The mole ratio of MgO to Al₂O₃ in the MgO×Al₂O₃ inclusions, ， increased with increasing the activity ratio of MgO to Al₂O₃ in the refining slag, . By present experiments, the refining slag, which the composition was R=3.5, w(Al₂O₃)=10 %, w(MgO)= 10 %, w(CaF₂)= 5 %, had a good refining effect.

Key words: VOD refining slag, ferrite stainless steel, deoxidation, inclusions