First-principles study on the effect of Ce on segregation behavior of bcc-Fe grain boundaries in low-carbon low-alloy steel

Herein, we investigated the effect of Ce on the segregation behavior of bcc-Fe grain boundaries (GBs) in low-carbon low-alloy (LCLA) steel through experimental techniques and the first-principles calculations. The experimental results showed that the addition of 66 ppm Ce refined the grain size from 17 μm to 10 μm. Electron probe microanalyzer (EPMA) analysis showed that Ce segregated at GBs, but the distribution of Ce at GBs was uneven. The first-principles calculations were implemented to systematically study the segregation energy, GB energy (γ GB ), strengthening energy (E s ) and differential charge density of Ce at symmetrically tilted grain boundaries (STGBs) (Σ3/Σ5/Σ7/Σ9/Σ11) in bcc-Fe. The deep coupling of experimental results and theoretical analysis showed that Ce selectively tended to segregate at high Σ-value GBs (e.g., Σ9 and Σ11), which can reduce γ GB and inhibit grain coarsening. And the redistribution of electrons further demonstrated that Ce segregation enhanced GB cohesion, ultimately achieving the synergistic effect of grain refinement and GB strengthening. By establishing a quantitative correlation between Ce segregation behavior and GB structural characteristics, an atomic-scale theoretical basis is provided for rare earth (RE) microalloying design. Based on the concept of segregation engineering, it is proposed to regulate the targeted distribution of Ce at specific GBs through alloy design and mechanical processing, which provides an innovative idea for the development of the new generation of RE steel with high strength and toughness.