Abstract: The effect of Ca and S on inclusion removal during vacuum degassing refining process was investigated. The Ca content had a significant effect on inclusion removal. When the S mass fraction was in the range of 0.012 %－0.014 %, low Ca content was beneficial for inclusion removal. When the Ca mass fraction was 1×10^-6 in steel, the inclusion removal rate was 74.30 %. When the Ca mass fraction was 8×10^-6 in steel, however, the inclusion removal rate decreased drastically to 33.95 %. The reason was that the Ca element transferred the solid deoxidation product Al₂O₃-MgO inclusions to liquid calcium aluminate inclusions which were not easy to float and remove. When the Ca mass fraction was (7-8)×10^-6 in steel, high S content was beneficial for inclusion removal. When the S mass fraction was 135×10^-6 and 11×10^-6  in steel, the corresponding inclusion removal ratios were 33.95 % and 23.71 %, respectively. The reason was that high S content increased the CaS content in the inclusions, which made the melting point of inclusions increased. The sources of Ca and S elements were discussed, and measures were proposed to improve the inclusion removal ratio during vacuum degassing refining process.

Key words: vacuum degassing refining, inclusion, remove ratio, sulfur content, calcium content