Effects of Combined La–Ce Rare-Earth Treatment on the Hot-Rolled Microstructure and Texture of High-Grade Non-Oriented Electrical Steel

Abstract

Abstract

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.