Synergistic Inclusion Modification in Steel Using Calcium, Magnesium, Rare Earths, and Hybrid Treatments: A Review

High‐performance steels with superior mechanical properties, fatigue resistance, weldability, and corrosion resistance need advanced strategies for inclusion modification. Nonmetallic inclusions, detrimental as stress concentrators and crack initiators, are a critical determinant of steel quality. Conventional deoxidation practices, particularly those involving aluminum, result in hard, angular alumina inclusions that impair mechanical integrity and operational efficiency. To address these challenges, secondary metallurgy has evolved to include targeted modification of inclusions using calcium, magnesium, and rare earth elements. Calcium treatment transforms solid alumina into liquid calcium aluminates, thereby improving castability and reducing nozzle clogging. Magnesium modification yields thermally stable spinel inclusions, whereas rare earth elements form stable spherical oxysulfides, both of which contribute to enhanced mechanical and surface properties. Despite their individual merits, these treatments face limitations such as incomplete modification, process instability, and high costs. Hybrid strategies that combine calcium, magnesium, and rare earth elements have emerged as promising solutions that leverage synergistic effects for optimized inclusion control. Advances in computational thermodynamics and machine learning have further improved the predictability of inclusion engineering. This review synthesizes the mechanisms and industrial applications in inclusion modification, highlighting the pivotal role of advanced metallurgy in the production of ultraclean steels for demanding automotive, aerospace, and infrastructure applications.