Rare earth (RE) inclusions with high melting points as heterogeneous nucleation in liquid steel have stimulated many recent studies. Evaluating the potency of RE inclusions as heterogeneous nucleation sites of the primary phase is still a challenge. In this work, the edge-to-edge matching (E2EM) model was employed to calculate the atomic matching mismatch and predict the orientation relationship between La₂O₂S and γ-Fe from a crystallographic point of view. A rough orientation relationship (OR) was predicted with the minimum values of ${\mathrm{f}}_{\mathrm{r}}=9.43\%$ and ${\mathrm{f}}_{\mathrm{d}}=20.72\%$ as follows: ${\left[2\overline{1}\overline{1}0\right]}_{{\mathrm{La}}_2{\mathrm{O}}_2\mathrm{S}}$∥${\left[100\right]}_{\mathsf{\gamma }-\mathrm{Fe}}$ and ${\left(000\overline{3}\right)}_{{\mathrm{La}}_2{\mathrm{O}}_2\mathrm{S}}$∥${\left(00\overline{2}\right)}_{\mathsf{\gamma }-\mathrm{Fe}}$. The interface energy and bonding characteristics between La₂O₂S and γ-Fe were calculated on the atomic scale based on a crystallographic study using the first-principles calculation method. The calculations of the interface energy showed that the S-terminated and La(S)-terminated interface structures were more stable. The results of difference charge density, electron localization function (ELF), the Bader charges and the partial density of states (PDOS) study indicated that the La(S)-terminated interface possessed metallic bonds and ionic bonds, and the S-terminated interface exhibited metallic bond and covalent bond characteristics. This work addressed the stability and the characteristics of the La₂O₂S/γ-Fe interface structure from the standpoint of crystallography and energetics, which provides an effective theoretical support to the study the heterogeneous nucleation mechanism. As a result, La₂O₂S particles are not an effective heterogeneous nucleation site for the γ-Fe matrix from crystallography and energetics points of view.

This study compares high-grade non-oriented electrical steels without rare-earth addition and with a La-Ce combined rare-earth treatment. Optical microscopy, X-ray diffraction (XRD), and electron backscatter diffraction (EBSD) were used to characterize the hot-rolled microstructure, through-thickness texture, and local orientation heterogeneity. The investigated La-Ce specimen exhibited a smaller average as-cast grain size (1.2 mm versus 2.0 mm) and a smaller hot-rolled surface grain size (39.08 μm versus 57.39 μm), together with a smoother microstructural transition from fine surface grains to elongated center-layer deformation grains. XRD revealed pronounced through-thickness texture gradients in both specimens. After a non-negativity-constrained post-reconstruction correction of the exported harmonic ODFs, the maximum α-fiber orientation density was 2.830 and 2.573 at the surface, 4.223 and 4.521 at 1/4 thickness, and 36.995 and 16.636 at the center for the rare-earth-free and La-Ce specimens, respectively. The center-layer difference corresponds to an approximately 55.0% lower α-fiber maximum in the investigated La-Ce specimen. For the γ-fiber, peak and mean f(g) values increased modestly at the surface and more strongly at 1/4 thickness, whereas the sampled ideal center-layer γ-fiber in the La-Ce specimen reached the lower bound of the constrained ODF representation. EBSD-IPF, GOS, and KAM maps further revealed reduced long-range orientation continuity and finer spatial segmentation of deformation-related orientation heterogeneity in the La-Ce specimen. Overall, the results show that trace La-Ce treatment is associated with microstructural refinement and a pronounced redistribution of the hot-band deformation texture, particularly in the sheet center.