| Summary: | This study aimed to investigate the effect of Mg treatment on the nucleation and ostwald growth of inclusions. Deoxidized experiments with Al (0.05%Al) and Al-Mg (0.05%Al + 0.03%Mg) were carried out at 1873 K, and the composition, number, and size of inclusions were studied as a function of holding time. Homogeneous nucleation theory and ostwald ripening were utilized to calculate the nucleation rate, the critical size of nuclei, and coarsening rate of inclusions. The results show that small inclusions were more easily found in the steels with Al-Mg complex deoxidation, and the number of inclusions with Al-Mg complex deoxidation is larger at an early stage of deoxidation. The critical size of nuclei increases in the order of MgAl<sub>2</sub>O<sub>4</sub> (0.3–0.4 nm) < Al<sub>2</sub>O<sub>3</sub> (0.4–0.6 nm), and the nucleation rate increases in the order of Al<sub>2</sub>O<sub>3</sub> (1100 cm−3 s−1) < MgAl<sub>2</sub>O<sub>4</sub> (1200 cm−3s−1), which is consistent with the experimental results. Moreover, the coarsening rate of MgAl<sub>2</sub>O<sub>4 </sub>inclusions was smaller than Al<sub>2</sub>O<sub>3</sub> inclusions in both the value of <i>k<sub>d(cal.)</sub></i>from ostwald growth and the value of <i>k<sub>d(obs.)</sub></i>from inclusion size. The effect of Mg addition on coarsening of inclusion was analyzed and their mechanism was discussed based on ostwald ripening theory and Factsage calculation.
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