Abstract
Ferritic–martensitic steel EK-181 was irradiated with 0.5 MeV ⁵⁶Fe⁺ ions to a fluence of 5 × 10¹⁷ cm⁻² at 350 °C to simulate near-surface radiation damage. Surface morphology and composition were examined by SEM-EDS, while depth-dependent mechanical properties were evaluated using instrumented nanoindentation (Oliver–Pharr method). The irradiation produced a distinct two-zone structure. In the near-surface layer (~250 nm), Fe depletion with Cr, C, and Al enrichment was observed, consistent with selective sputtering, resulting in modest hardening and a reduced Young’s modulus. At greater depths (~250–500 nm), where the composition approaches the pre-irradiation state, pronounced hardening and an increased modulus occurred. These deeper changes may be associated with the accumulation and migration of irradiation-induced defects beyond the primary damage zone predicted by SRIM. The results demonstrate how selective sputtering and radiation-induced segregation together produce a two-zone mechanical response in EK-181, providing insights for optimizing ferritic–martensitic steels in nuclear applications.