Control of Non-metallic Inclusion Plasticity and Steel Cleanliness for Ultrathin 18 Pct Cr-8 Pct Ni Stainless Steel Strip

Laboratory-scale slag-steel equilibrium experiments as well as thermodynamic analyses and industrial tests were performed for 18 pct Cr-8 pct Ni stainless steel to study the effect of slag composition on non-metallic inclusion plasticity and steel cleanliness. First, the results showed that saturated MgO should be added in refining top slag, in particular for low-basicity slag, to avoid heavy corrosion of the refractory lining. Further, the content of MgO + Al₂O₃ increased and MnO content decreased in inclusions with an increase in the slag basicity; thus, the plasticity of inclusions decreased correspondingly. Conversely, higher-basicity slag was favorable for reducing the total oxygen (T.O.), while the content of dissolved aluminum (Als) in steel increased. On the basis of experimental results and thermodynamic analyses, it was concluded that comprehensive favorable inclusion plasticity and relatively high steel cleanliness could be achieved for slag basicity (CaO/SiO₂) in the range of 1.4 to 1.8 and Als lower than 10 ppm. This was verified by industrial test results.