Influence of irradiation temperature on microstructure of EU batch of ODS Eurofer97 steel irradiated with neutrons

A TEM investigation of an EU batch of oxide dispersed strengthened (ODS) Eurofer97 steel specimens, irradiated to 1 and 3 dpa at 300, 450 and 550 degrees C in high flux reactor at Petten, has been performed to understand the influence of irradiation temperature on the characteristics of irradiation defects and, eventually, on the resulting mechanical properties of this material. Specimens irradiated at 300 degrees C revealed the presence of a high density of black dot damage and small self-interstitial atom (SIA) dislocation loops causing substantial hardening and embrittlement. In contrast, negligible black dot damage, low density of large SIA loops and networks of dislocations are observed in specimens irradiated at 450 and 550 degrees C. The lath martensitic structure and ODS particles remain unaffected after irradiation in all specimens. These results are discussed in view of possible activation of defect annihilation mechanisms to explain the observed recovery of mechanical properties at high irradiation temperatures.