The 10 to 13 wt% Cr-containing ferritic and ferrito-martensitic stainless steels are seen as promising reactor core structural materials for fast breeder reactors and first wall materials for fusion reactors.
The studies involved diffraction electron microscopy and X-ray microanalysis on the 10 to 13 wt% Cr-containing steels and alloys to examine their structural phase variations after irradiation with 3-MeV Cr+3 ions across a wide range of irradiation doses and temperatures (1 to 150 dpa, 270 to 630°C).
We found that the phase composition of these steels and alloys under irradiation depends upon the concentration of solutes. The undoped Fe-12Cr alloy displays the development of α′-phase. The ferrito-martensitic steels doped with Mo, Nb, and V show the radiation-induced M2X, MX, and x-phases. The ferritic steel containing 6% Mo, which was dispersion-hardened with the Laves phase particles, showed the formation of x and MX phases. We also determined the influence of impurity elements (C + N) on the nucleation and evolution of the α′-phase and the dislocation structure in the test alloys Fe-12%Cr. It was found that the impurity elements predominantly affect the nucleation and to a lesser degree the evolution of the dislocation structure.
We have determined the temperature region of the existing α′-phase and the temperature relationships of the dislocation structure parameters for the irradiated ferrito-martensitic steel.
The dislocation structure components were identified as being dislocation loops and a dislocation network. Although voids were observed in these steels, the void swelling values were very low. This can be attributed to low void growth rates.
Studies were also made on behavioral characteristics of a dispersion-hardened ferritic steel in the temperature range from 400 to 600°C irradiated to the dose 150 dpa.
As found, the irradiation temperature increase causes the radiation-induced M2X-phase to appear, which may entail a considerable embrittlement of the material.
We conclude that doping is an effective tool for suppressing the α′-phase precipitate formation, consequently diminishing the proneness of ferritic steels to embrittlement, which can be done by getting the materials to intensively nucleate secondary phases under irradiation that precludes embrittlement.