Radiation response of a Fe–20Cr–25Ni austenitic stainless steel under Fe²⁺ irradiation at 500 °C

The radiation response of a Fe–20Cr–25Ni austenitic stainless steel under self-ion irradiation at 500 °C was systematically investigated. The steel was irradiated at 500 °C by 3.5 MeV Fe²⁺ ions to 10, 50, and 150 peak dpa, respectively. In the 200–400 nm depth region, radiation-induced Frank loops were relatively stable in both size and number density from 10 to 150 peak dpa. Anisotropic distribution of Frank loops was observed in the 50 and 150 peak dpa specimens, possibly due to interaction of Frank loops and network dislocations with preferred orientations. Coarse voids were found only in the 50 and 150 peak dpa specimens in depths less than 750 nm, suggesting that injected interstitials at deeper regions suppressed the void nucleation. The peak swelling was very low (~0.4%) for both 50 and 150 peak dpa irradiation. Radiation also led to the formation of intragranular plate-like Cr-rich carbides. Radiation-induced segregation of Ni and Si was found at various sinks: dislocation loops, void surfaces, and carbide-matrix interfaces. Finally, irradiation hardening was measured by nanoindentation and the results are consistent with microstructure-based calculations using the dispersed barrier hardening model. The major contributor to irradiation hardening changed from Frank loops at the lowest dose to network dislocations at the highest dose.