Modeling Study on the Evolution of Slag-Entrained Inclusions Containing La₂O₃ in a Calcium-Treated Aluminum-Killed Steel

In the current study, tracer industrial trials using La₂O₃ were conducted to determinate the origin of inclusions. A kinetic model was developed to predict the variation in composition of slag-entrained inclusions. Large-size inclusions in the steel were found to be composed of CaO–Al₂O₃–SiO₂–MgO–CaS. The morphology of these inclusions indicated a high likelihood of entrainment from the slag, but a notable difference in composition was observed compared to the slag, particularly for CaO and Al₂O₃ content. Specifically, the content of CaO in inclusions was significantly lower, while the Al₂O₃ content was higher. Results from calculations using the kinetic model demonstrated that the initial La₂O₃ content in the slag had minimal impact on the final composition of slag-entrained inclusions but did significantly affect the transformation process. After reacting for 10,000 seconds, with initial La₂O₃ content of 1, 5, 20, and 50 pct, the Al₂O₃ contents in the slag-entrained inclusions were simulated to be 66.13, 66.73, 66.79, and 65.46 pct, respectively. A set of criteria for judging slag-entrained inclusions was proposed based on kinetic results, wherein the CaO index ranged from 0.52 to 1, the Al₂O₃ index ranged from 0.56 to 2.37, the MgO index ranged from 0.15 to 1, the La₂O₃ index ranged from 0.29 to 1. When the composition of an inclusion in Al-deoxidized steels satisfied all four of these criteria, it could be concluded to be a slag-entrained inclusion.