Abstract
The effect of neutron irradiation on the microstructure of VVER-440 type reactor pressure vessel steels was studied by small-angle neutron scattering (SANS). The SANS spectra were fitted by a model of non-ferromagnetic particles in saturated ferromagnetic matrix, which permitted us to evaluate apparent volume fractions (weighted by scattering contrast), size distributions and mean ratio of magnetic to total scattering cross-sections for small ( R<3 nm) irradiation-induced precipitates. Close correlation between the apparent volume fraction of the damaged domains and ductility transition temperature was observed. Differences in the volume fractions obtained from magnetic and nuclear scattering indicated that chemical composition varied with increasing fluence and could be explained by increasing concentrations of solute atoms in the damaged domains. This coarsening effect is also manifested on the size distributions by slight growth of mean domain radius.
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