Influence of refining slag on the inclusions in SUS444 ferrite stainless steel

The equilibrium experiment between VOD refining slag and SUS444 ferrite stainless steel was carried out in the MgO crucibles at 1 873 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,xMgO/xAl2O3,increased with increasing the activity ratio of MgO to Al2O3 in the refining slag,a(MgO)/a(Al2O3).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.