Oxide interface-mediated plasticity and irradiation hardening behavior in Ni-free high-Mn ODS austenitic steel

Structural materials for magnetic confinement fusion reactors must simultaneously withstand neutron irradiation, maintain mechanical integrity across operating temperatures, and remain non-magnetic. Current candidates fail to meet all requirements: ODS ferritic steels are ferromagnetic and may suffer from low-temperature embrittlement, while conventional ODS austenitic steels contain Ni that severely activates under irradiation. Here, interface engineering in Ni-free Fe-30Mn-6Al-1Si ODS austenitic steel is demonstrated to simultaneously achieve room-temperature strength–plasticity (9 ± 1 % uniform elongation at 1267 ± 12 MPa yield strength), high-temperature performance (783 ± 10 MPa at 500 °C), and suppressed irradiation hardening at 0.1–0.2 dpa (one-fifth of non-ODS austenitic steel). A multimodal oxide distribution underpins this performance: fine particles (∼6 nm) provide Orowan strengthening and defect sink capacity, while large incoherent particles (>10 nm, ∼10 % lattice mismatch) generate stress concentrations triggering sequential 9R → stacking fault → deformation twin transformations in the high-SFE (∼64.4mJ/m 2 ) matrix. This interface-mediated mechanism activates deformation twinning independently of bulk composition or grain structure, while achieving defect sink strength comparable to ODS ferritic steels. These results demonstrate that engineering oxide size distribution—rather than oxide density alone—offers a design principle for reconciling defect-sink capacity with plastic deformability in extreme-environment structural materials.