为探究近服役温度时效行为对ODS钢微观组织和力学性能的影响，通过SEM、TEM和拉伸性能测试等方法，研究了9Cr ODS钢在700℃时效不同时间后的碳化物(M₂₃C₆)、纳米氧化物演变和力学性能变化。结果表明：在时效初期(≤ 200 h)，M₂₃C₆在晶界处呈条带状快速析出并聚集长大，纳米氧化物无明显变化；在时效中期(200和1000 h)，M₂₃C₆和纳米氧化物稳定长大；在时效后期(2000和3000 h)，M₂₃C₆达到亚微米级，纳米氧化物的平均尺寸和数密度趋于稳定，与初始态相比，其平均尺寸的增长率为19.7%，数密度的下降率为27.1%。因纳米氧化物对不断增殖位错的钉扎，在部分晶粒内出现了位错胞和回复亚晶。9Cr ODS钢的拉伸强度在时效初期快速下降。在时效中后期，虽然纳米氧化物平均尺寸增加、数密度降低，但其钉扎作用仍然显著，以及基体中不断增殖的位错使得材料的拉伸强度维持稳定，延伸率在时效1000和2000 h期间处于低谷。

Compared to second- and third-generation nuclear power systems, the Generation IV fission and future fusion reactors have higher service temperatures and irradiation doses, as well as harsher corrosive conditions and complex alternating loads. The structural materials for advanced reactors need to be researched and developed further. The oxide dispersion strengthened (ODS) steel has excellent high-temperature performance and irradiation resistance and is considered a promising structural material for advanced nuclear power systems. To reveal the effect of aging on microstructure and mechanical properties of ODS steel at near-service temperatures, the evolution of carbide M₂₃C₆ and nano-oxide particles (NPs) as well as the changes in the mechanical properties of 9Cr ODS steel after aging at 700^oC for varying durations were studied using SEM, TEM, and tensile testing. M₂₃C₆ rapidly precipitated along grain boundaries, gradually aggregated, and grew during early aging (≤ 200 h). While the NPs showed no noticeable change. During the midstages of aging (200 and 1000 h), NPs and carbides grew stably. In the later stages of aging (2000 and 3000 h), carbide particles grew to the micron scale. The average size and number density of the NPs tended to be stable. Compared to the initial 9Cr ODS steel, the growth rate of the average size was 19.7%, and the reduction rate of the number density was 27.1%. Dislocation cells and recovered subgrains appeared within some grains because of the pinning effect of NPs on continuous proliferation dislocations. The tensile strength rapidly decreased at the initial stages of aging. In the intermediate and later stages of aging, although the average size of the NPs increased and the number density decreased, its pinning effect was still prominent. Continuous proliferation dislocations were observed in the matrix, so the tensile strength remained stable. Furthermore, the tensile elongation was low during aging time of 1000 and 2000 h.