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 MgAl₂O₄ (0.3–0.4 nm) < Al₂O₃ (0.4–0.6 nm), and the nucleation rate increases in the order of Al₂O₃ (1100 cm⁻³ s⁻¹) < MgAl₂O₄ (1200 cm⁻³s⁻¹), which is consistent with the experimental results. Moreover, the coarsening rate of MgAl₂O₄ inclusions was smaller than Al₂O₃ inclusions in both the value of k_d(cal.) from ostwald growth and the value of k_d(obs.) 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.

In order to study the effect of Ca and sulfur contents on the characteristics of inclusions, industrial experiments using 95CrMo steel were conducted. SEM-EDS detections and stereological analysis were used to probe the characteristics of inclusions, including their compositions, morphologies, size, number density, and distribution. The results indicate that there were mainly three types of inclusions in 95CrMo steel billets with 6–18 ppm Ca and 30–100 ppm S: inclusions with single-phased morphology mainly composed of oxides; isolated MnS/CaS-only inclusions; inclusions with multi-phased morphology. The three-dimensional inclusion size distribution suggests that there were more Type-1 inclusions with a small size in low S containing steels. The average diameter of all types of inclusions increased with increasing Ca or S content in 95CrMo steel, indicating that the formation of MnS and CaS coarsened their size. The density distribution of inclusions indicates that the more inclusions there are, the more easily they aggregate and collide. Moreover, it is presumably concluded that the formation of sulfide in the outer layer of oxide inclusions weaken the attraction between oxide inclusions. The equilibrated transformation and formation of inclusions during the cooling process of 95CrMo steel was discussed based on thermodynamic calculation. The equilibrated transformation trajectory of inclusions in 95CrMo steel during the cooling process was Ca₂SiO₄ + MgO → Ca₃MgSi₂O₈ → Spinel + CaS, which was corresponding to the detected results. The precipitation regular of sulfide was obtained. The formation mechanism for three types of inclusions was discussed.

In this study, solidified films of CaO-Al₂O₃-BaO-CaF₂-Li₂O-based mold fluxes with different contents of Al₂O₃ addition were acquired by immersing an improved water-cooled copper probe in bulk molten slags. This probe can obtain films with representative structures. Different slag temperatures and probe immersion times were employed to investigate the crystallization process. The crystals in the solidified films were identified using X-ray diffraction, the morphologies of the crystals were observed using optical microscopy and scanning electron microscopy, and the kinetic conditions, especially the activation energy of devitrified crystallization in glassy slags, were calculated and discussed based on the differential scanning calorimetry. The results indicated that after adding extra Al₂O₃, the growing speed and thickness of the solidified films increased, and more time was required for the film thickness to reach a steady state. In addition, fine spinel (MgAl₂O₄) precipitated in the films at the early stage of solidification after adding 10 wt% of extra Al₂O₃. Together with LiAlO₂, spinel (MgAl₂O₄) acted as nuclei for the precipitation of BaAl₂O₄. The apparent activation energy of initial devitrified crystallization decreased from 314.16 KJ/mol (original slag) to 297.32 KJ/mol (5 wt% Al₂O₃ added) and 269.46 KJ/mol (10 wt% Al₂O₃ added). The crystallization ratio of the films also increased after adding extra Al₂O₃.

It is difficult to observe the nucleation mechanism of inclusions in real-time. In this study, the nucleation process of zirconium oxide inclusions was systematically studied by classical nucleation theory and first principles. Zr deoxidized steel with 100 ppm Zr addition was processed into metallographic samples for scanning electron microscopy energy-dispersive spectroscopy observation. The electrolytic sample was analyzed by micro X-ray diffraction and transmission electron microscopy, and the zirconium oxide in the sample was determined to be ZrO₂. The nucleation rate and radius of the ZrO₂ inclusions were calculated by classical nucleation theory, and they were compared with the experimental values. There was a considerable difference between the experimental and theoretical values of the nucleation rate. The effect of the nucleation size was analyzed by first-principles calculation, and the thermodynamic properties of ZrO₂ clusters and nanoparticles were analyzed by constructing (ZrO₂)_n (n = 1–6) clusters. The thermodynamic properties of ZrO₂ calculated by first principles were consistent with the values in the literature. Based on two-step nucleation theory, the nucleation pathway of ZrO₂ is as follows: Zr_atom + O_atom → (ZrO₂)_n → (ZrO₂)₂ → core (ZrO₂ particle)–shell ((ZrO₂)₂ cluster) nanoparticle → (ZrO₂)_bulk.

In this study, novel slags with a high basicity index were used to refine silicon melts with carbon dioxide injection to effectively remove Ti from metallurgical-grade silicon. Different compositions of the initial slag were used, and silicon samples were obtained during the refining. The results indicate that the Ti-removal rate initially increased with an increase in the basicity index, and it decreased after the basicity index exceeded 1.4. During the refining, silicon emulsification was observed at the slag–silicon interface, which was restricted by the increased basicity index of slags. Impurities that were concentrated in silicon droplets near the slag–silicon interfaces were oxidized, wetted by slags, and transferred to the slag phase. After 15 min of refining, up to 59 wt% of Ti in silicon could be removed and the Ti-concentrating phase in the slag contained 2.05 wt% of Ti. The results of this study provide a reference for low-cost Ti removal from metallurgical-grade silicon using a refining method.

Scrap steel is a kind of resource that can be recycled indefinitely. However, the enrichment of arsenic in the recycling process will seriously affect the performance of the product, making the recycling process unsustainable. In this study, the removal of arsenic from molten steel using calcium alloys was investigated experimentally, and the underlying mechanism was explored based on thermodynamic principles. The results show that the addition of calcium alloy is an effective means of reducing the arsenic content in molten steel, with the highest removal percentage of 56.36% observed with calcium aluminum alloy. A thermodynamic analysis revealed that the critical calcium content required for arsenic removal reaction is 0.0037%. Moreover, ultra-low levels of oxygen and sulfur were found to be crucial in achieving a good arsenic removal effect. When the arsenic removal reaction occurs in molten steel, the oxygen and sulfur concentrations in equilibrium with calcium were $w_{\left[O\right]}=0.0012\%$ and $w_{\left[S\right]}=0.00548\%$, respectively. After successful arsenic removal, the arsenic removal product of the calcium alloy is Ca₃As₂, which usually does not appear alone. Instead, it is prone to combining with alumina, calcium oxide, and other inclusions to form composite inclusions, which is beneficial for the floating removal of inclusions and the purification of scrap steel in molten steel.