Characterizing accelerated precipitation in proton irradiated steel

•Proton irradiation reproduces precipitation leading to embrittlement of reactor steel.•Small-angle neutron scattering probes precipitate fractions, sizes and magnetism.•Power-law scaling accounts for radiation dose rate effects on precipitate fraction.•Carbon plays key role in precipitate growth together with radiation dose rate.•Useful irradiation-characterization route demonstrated with protons and scattering. [Display omitted] Ion irradiation provides a promising substitute to neutron tests for investigating the effects of radiation on materials for fission and fusion reactor plants. Here we show proton irradiation can quantitatively reproduce precipitation that leads to embrittlement in reactor pressure vessel steels, at dose rates 104 times greater than experienced in fission reactor operation. Small-angle neutron scattering (SANS) is used to characterize precipitate size distributions in copper-containing steels irradiated to average doses of ≃7 mdpa with 5 MeV protons. Comparing our results with the literature on reactor pressure vessel steels containing ≥1 at.% nickel, we find a power-law scaling of dose with exponent 0.25–0.30 accounts for the effects of dose rate on precipitate volume fraction over 6 orders of magnitude in dose rate. In conjunction with dose rate, carbon is identified as performing a leading role in determining precipitate sizes, adding to the known effects of nickel, manganese and irradiation temperature. We discuss the composition of precipitates inferred from SANS, taking previous atom probe tomography studies into consideration.