Original Article

In-situ tracking of inclusion evolution in Ce-modified highstrength offshore steel: mechanisms governing mechanical performance

¹ School of Materials Science and Engineering, Inner Mongolia University of Technology, Hohhot 010051, PR China
² Engineering Research Center of Rare Earth Metal Materials, Inner Mongolia University of Technology, Hohhot 010051, PR China

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Received: 18 November 2025
Accepted: 30 January 2026

Abstract

This study investigates the in-situ evolution of inclusions in rare-earth cerium (Ce)-treated highstrength offshore platform steel using high-temperature confocal scanning laser microscopy (CSLM). Integrated characterization via scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), thermodynamic modeling, and first-principles calculations elucidates the underlying mechanism through which inclusion engineering enhances mechanical performance. Ce addition effectively converts irregular MnS and MnS-Al₂O₃ inclusions into spherical/ellipsoidal Ce–O–S composite particles. In situ observations indicate that Ce expands the austenite phase field and mitigates grain-boundary segregation. Thermodynamic analyses demonstrate improved stability of Ce-containing inclusions. First-principles calculations further reveal a significant reduction in the elastic modulus and hardness mismatch between these inclusions and the steel matrix, facilitating compatible plastic deformation and thereby elevating the low-temperature impact toughness. This conclusion is supported by complementary low-temperature impact tests and transmission electron microscopy examination of inclusions in fracture surfaces. Collectively, this work establishes a coherent mechanistic framework for Ce-driven performance enhancement in advanced offshore steels.