Inclusion Characteristic in Tinplate Steel in RH Refining and Kinetics Limitation of Calcium Transfer by Refining Slag

Abstract

The characteristics of inclusions including composition, morphology, number, and size in tinplate steel were studied by industrial experiments and thermodynamic calculations during the RH refining process. The results indicated that two types of Al₂O₃ inclusions including cluster and single-particle are generated at first after Al addition. With the slag-metal and refractory-metal reactions, Al₂O₃ inclusions, CaO·Al₂O₃ inclusions, MgO·Al₂O₃ spinel inclusions, and CaO–MgO–Al₂O₃ ternary system inclusions are found in the middle of RH refining. Only single-particle Al₂O₃, CaO·Al₂O₃ inclusions with high melting point, and CaO–MgO–Al₂O₃ ternary system inclusions are found at the end of RH refining. From Al addition to the end of RH refining, the total number of inclusions showed a decreasing trend and the proportion of the number density decreased by 70%. About 62% of inclusions are smaller than 10 µm at the end of RH refining, which are difficult to be removed from the liquid steel. The mass transfer of Ca from the refining slag to the liquid steel has a significant effect on the content of [Ca] in liquid steel. Al₂O₃ inclusions generated in liquid steel can only be modified to CaO·Al₂O₃ inclusions in the present RH refining time. Aiming to generate 12CaO·7Al₂O₃ inclusions quickly, moderate calcium treatment as a supplementary measure for refining slag is recommended to modify inclusions during the RH refining process.