Unravelling the mechanism of Ce microalloying on the mechanical properties of EH460 marine steel

Abstract

The effect of Ce microalloying on the mechanical properties of EH460 marine steel (EH460) was systematically investigated through experimental characterization and first-principles calculations. The results demonstrate that the addition of trace Ce significantly enhances the ductility of EH460 steel, increasing its elongation from 26.7 % to 31.5 %, while maintaining the ultimate tensile strength at 629.6 ± 2.3 MPa. Although the pearlite content in Ce-microalloyed EH460 steel exhibits only a slight increase from 20.9 % to 25.6 %, Ce induces a notable transformation in pearlite morphology. Specifically, the banded pearlite structure evolves into degenerate pearlite, characterized by the fragmentation of continuous cementite layers and the formation of a predominant fraction (91.1 %) of short rod-like cementite. Furthermore, the number density of Ce-modified inclusions (primarily Ce-O-S type) increases from 11.2 mm⁻² to 28.5 mm⁻², while their average size decreases significantly from 2.0 μm to 1.5 μm. First-principles calculations reveal that Ce segregation at grain boundaries (GBs) inhibits the segregation of C atoms to adjacent regions and elevates the diffusion energy barrier of C atoms near GBs from 1.25 eV to 2.39 eV. This indicates that Ce obstructs the long-range diffusion pathways of C atoms at GBs, thereby disrupting the formation of continuous cementite layers. The presence of short rod-like cementite and fine-sized inclusions reduces dislocation concentration, delays crack initiation, and enhances the uniform plastic deformation capability of EH460 steel. This gives EH460 steel superior resistance to the ratchet effect, providing a basis for designing offshore steel materials with higher safety margins.