Features of the restructuring of ods steels with different nanostructures under irradiation

Nanoscale mechanisms of radiation hardening of oxide dispersion-strengthened (ODS) steels steels with different nanostructures, differing in the type of inclusions, their sizes and number density, were compared. Model ODS steels (ODS Eurofer, ODS 10Cr and ODS KP3) are more finely dispersed, have an order of magnitude greater number of oxide particles (~ (4 – 13)·1022  m–3) and nanoclusters (~ 2·1023 m–3), unlike industrial EP450 ODS and EP823 ODS steels with oxide cluster number density ~ (2 – 3)·1021  m–3. Ultramicroscopic study of the effect of Fe ion irradiation up to a dose of 30 dpa at a temperature of 350 °C was carried out. Dislocation loops were formed in all steels, however, this mechanism of radiation degradation, typical for conventional ferritic-martensitic steels, was suppressed in model ODS steels with higher oxide dispersion. They revealed an order of magnitude fewer dislocation loops (~ 1021 m–3) than in industrial ODS steels. In addition, the formation of a large number (~ 1023 m–3) of radiation-induced Ni-Mn-Si clusters typical for irradiated ferritic-martensitic steels was observed in EP823 ODS steel after irradiation. In the remaining ODS steels, signs of the nanostructure re-arrangement under the irradiation were observed, as well as changes in the quantitative characteristics of oxide particles and clusters. According to the calculations of the ultimate strength using the DBH model, industrial ODS steels were strengthened by 25 %, and model ODS steel were softened (ODS 10Cr and ODS KP3) by 20 % under the irradiation. ODS Eurofer steel was the most stable under irradiation up to 30 dpa at 350 °C.