The mechanistic implications of the high temperature, long time thermal stability of nanoscale Mn-Ni-Si precipitates in irradiated reactor pressure vessel steels

Post irradiation annealing (PIA) clarified the induced versus enhanced controversy regarding nanoscale Mn-Ni-Si precipitate (MNSP) formation in pressure vessel steels. Radiation induced MNSPs would dissolve under high temperature PIA, while radiation enhanced precipitates would be stable above a critical radius (rc). A Cu-free, high Ni steel was irradiated with 2.8MeV Fe2+ ions at two temperatures to generate MNSPs with average radii (r¯) above and below an estimated rc for PIA at 425°C up to 52 weeks. Atom probe tomography and energy dispersive x-ray spectroscopy showed MNSPs with r < rc dissolved, while those with r > rc slightly coarsened, consistent with thermodynamic predictions.