<p>The solidification kinetics and grain refinement mechanisms in Fe–Al-based ferritic steels with varying Al and Ce concentrations were investigated. <i>In situ</i> observations using high-temperature confocal laser scanning microscopy (HT-CLSM) were conducted on three steel compositions cooled at 5&#xa0;°C/min. The individual and combined effects of Al and Ce on the solidification evolution were elucidated through inclusion characterization, thermodynamic analysis, and quantitative analysis of pinning effect and constitutional undercooling. Results indicate that elevating Al content from 4 to 6 pct significantly coarsens the solidified macrostructure. This coarsening is attributed to the higher Al content, which makes AlN tend to precipitate and float on the melt surface before solidification, thereby depleting the effective pinning sites at the grain boundaries and accelerating grain growth. The addition of 0.04 pct Ce induces a potent grain-refining effect. In the nucleation stage, the formation of Ce₂O₂S and CeS in the molten steel provides effective heterogeneous nucleation sites for ferrite, increasing the nucleation density and the initial solidification undercooling. In the grain growth stage, dispersive Ce inclusions exert a robust pinning force, effectively suppressing grain boundary migration. While calculations identify Carbon as the primary solute contributing to constitutional undercooling, the refinement in steel with higher Ce content is mainly controlled by the synergy of heterogeneous nucleation and the pinning effect. This study clarifies the competitive roles of Al and Ce grain refinement and provides a theoretical framework for the micro-alloying design of Fe–Al-based Ferritic Steel.</p>