Effect of Slag Composition on Inclusions in Si-Deoxidized 18Cr-8Ni Stainless Steels

Abstract

Laboratory experiments and thermodynamic calculation for the Si-deoxidized 18Cr-8Ni stainless steel with CaO-Al₂O₃-SiO₂-CaF₂-MgO-MnO slag were performed to investigate the effect of slag composition on inclusions in Si-deoxidized 18Cr-8Ni stainless steels. A high-basicity slag improved the cleanness of stainless steel, while a low basicity slag lowered the Al₂O₃ content in inclusions, lowering the melting temperature of inclusions and improving the deformability of inclusions. Approximately, 15 pct content of MgO in the initial slag was beneficial to reduce the corrosion of refractory and would not influence the composition of inclusions. The Al₂O₃ in slag should be lowered to a minimum to reduce the Al₂O₃ content in inclusions in Si-deoxidized 18Cr-8Ni stainless steel. The $\log X_{{{\text{Al}}_{ 2} {\text{O}}_{ 3} }}^{i} + \log X_{\text{MgO}}^{i} - \log X_{MnO}^{i} - \log X_{{{\text{SiO}}_{2} }}^{i}$ of inclusions was expressed as a linear function of $\log a_{{{\text{Al}}_{ 2} {\text{O}}_{ 3} }}^{\text{s}} + \log a_{\text{CaO}}^{\text{s}} - \log a_{MnO}^{\text{s}} - \log a_{{{\text{SiO}}_{2} }}^{\text{s}}$ of the slag, which was used to predict the composition of inclusions based on the activity of Al₂O₃, CaO, SiO₂, and MnO in the slag. Moreover, the equilibrium curve of Al-O and the stability diagram of inclusions in Si-deoxidized 18Cr-8Ni stainless steel at 1873 K (1600 °C) were calculated.