The intergranular corrosion (IGC) susceptibility of ultrafine grains (~430 nm) and micrometer grains (~3.1–9.8 μm) 304 stainless steel obtained by cryogenic rolling and reversion annealing treatments were studied. Transmission electron microscopy (TEM) results showed that after sensitized treatment at 650 °C for 2h, the micrometer grains were sensitized with many M23C6 precipitates at the grain boundaries, while no precipitates in the ultrafine grains. The immersion corrosion tests in H2SO4-CuSO4 solution showed that ultrafine grains exhibited weaker IGC attacks than micrometer grains. The double-loop electrochemical potentiokinetic reactivation (DL-EPR) tests demonstrated the degree of sensitization (DOS) decreased from 26.61% to 1.52% with the grain ultra-refinement from micrometer to ultrafine. Corrosion studies indicated that the ultrafine grains exhibited lower IGC susceptibility compared with micrometer grains. According to the findings, the large number of grain boundaries generated by grain ultra-refinement inhibited M23C6 precipitates at the grain boundaries during the sensitized process, thereby reducing the susceptibility of ultrafine grains to IGC.

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