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To investigate the evolution of inclusions in high‐Al steel with addition of La, a series of laboratory experiments and thermodynamic calculations are performed, considering the reaction time and amount of La added. The main inclusions in the high‐Al steel without the addition of La are Al2O3, MnS, and Al2O3–MnS. The La treatment can efficiently modify Al2O3 to La–Al–O or La–O–S inclusions. For La additions less than 0.0041 wt%, the evolution route for the inclusion in high‐Al steel is Al2O3 → LaAl11O18 → LaAlO3 with an increase in reaction time. For high La additions, the evolution route for the Al2O3 inclusion is Al2O3 → LaAl11O18 → LaAlO3 → La2O2S → La2S3. The experimental results correlate with those of the thermodynamic analysis. Notably, excess La in high‐Al molten steel may consume O and S to form La oxysulfide and sulfide, respectively, which prevents the precipitation of MnS inclusion and promotes the formation of AlN inclusion during solidification.

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Synthetic slag samples of the CaO-SiO2-MgO-Al2O3-Cr2O3 system were obtained to clarify the effect of FeO on the formation of spinel phases and Cr distribution. X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS), as well as the thermodynamic software FactSage 6.2, were used for sample characterization. The results show that the addition of FeO can decrease the viscosity of molten slag and the precipitation temperatures of melilite and merwinite. The solidus temperature significantly decreases from 1400 to 1250• C with the increase of FeO content from 0wt% to 6wt%. The addition of FeO could enhance the content of Cr in spinel phases and reduce the content of Cr in soluble minerals, such as merwinite, melilite, and dicalcium silicate. Hence, the addition of FeO is conducive to decreasing Cr leaching.

The composition, morphology, number, area, size and average distance of inclusions in Fe-23Mn-xAl-0.7C steels were evaluated through an inclusion automatic analysis system (INCA Feature). According to their composition and morphology, six types of inclusions are classified in the present steels: MnS(Se), AlN, Al 2 O 3 , AlN-MnS(Se), Al 2 O 3 -MnS(Se), and other inclusions (i.e. Al 2 O 3 -AlN and MgO-Al 2 O 3 ). Thermodynamic calculation results show that AlN inclusions are formed in molten steel with Al contents of 3.28 and 6.76 wt-%. Irregularly shaped MnS(Se) inclusions precipitate during the solidification processe. AlN and Al 2 O 3 generally serve as sites for the heterogeneous nucleation of MnS(Se). Sometimes, AlN particles can precipitate on the surfaces of Al 2 O 3 and MnS(Se) inclusions in the solidification process. As the Al content increases to 6.76 wt-%, a large number of agglomerated AlN and AlN-MnS(Se) inclusions are observed. Agglomerated AlN inclusions normally form in the smelting process due to the combined effects of the cavity bridge force and viscous resistance.