Laboratory Study on Oxide Inclusions in High-Strength Low-Alloyed Steel Refined by Slag with Basicity 2–5

Abstract Non-metallic inclusions in high-strength low-alloyed steel refined by slag with basicity ( B ) 2–5 and Al ₂ O ₃ content 20%–30% (in mass percent) were investigated by slag–metal equilibrium experiments in laboratory and thermodynamic calculations. Most inclusions in equilibrium were quasi-spherical CaO-MgO-Al ₂ O ₃ -SiO ₂ system and the sizes were less than 5 µm. The average content ratio, CaO/Al ₂ O ₃ and CaO/SiO ₂ of the inclusions, increased with slag basicity increasing when Al ₂ O ₃ content in slag was around 25%, MgO/Al ₂ O ₃ and CaO/Al ₂ O ₃ increased with Al ₂ O ₃ content in slag decreasing when slag basicity was around 3.3. The MgO/Al ₂ O ₃ of the inclusions was influenced mainly by Al ₂ O ₃ content in slag and CaO/Al ₂ O ₃ was influenced mainly by slag basicity. To make the inclusions out of relative lower melting region (<1,773 K), the values of CaO/Al ₂ O ₃ , MgO/Al ₂ O ₃ and (CaO+MgO)/Al ₂ O ₃ of the inclusions should be enhanced by increasing basicity and decreasing Al ₂ O ₃ content in slag properly.