Effect of Titanium and Calcium Addition Sequence on Inclusions in Ti‐Stabilized Ferritic Stainless Steels

Solid oxide inclusions in Ti‐stabilized ferritic stainless steels may cause nozzle clogging during continuous casting. It was necessary to increase the liquid fraction of inclusions at the steelmaking temperature. In this study, industrial trials and thermodynamic calculations were conducted to explore the effect of titanium and calcium addition sequence on inclusions in Ti‐stabilized ferritic stainless steels. During the ladle furnace (LF) refining process, for the heat in which calcium was added after titanium, the liquid fraction of inclusions was 93.05%, which exhibited higher CaO content, smaller size, and number than the reverse sequence. Thermodynamic calculations revealed that when calcium treatment followed titanium addition, the liquid fraction of inclusions at both the end of LF refining and in the tundish was significantly higher. Under the experimental conditions, the evolution sequence of inclusions with increasing calcium content was: Ti 3 O 5 (s)+MgO·Al 2 O 3 (s) → liquid inclusions → Ca 2 SiO 4 (s)+Mg 2 SiO 4 (s). As titanium content in steel increased, the 100% liquid window gradually narrowed, making calcium modification more difficult. It was found that lower titanium content combined with higher aluminum content could widen the liquid window. Specifically, when the titanium content was between 0.1% and 0.35%, the liquid fraction of inclusions first increased and then decreased as calcium content rose from 0 to 50 ppm. When titanium exceeded 0.35%, the liquid fraction remained low and was barely affected by calcium content. Finally, thermodynamic calculations were employed to establish the relationship between calcium/titanium concentrations and the liquid fraction of inclusions.