采用静态高压釜腐蚀实验研究了添加不同含量的Nb (0.5%、1.0%、2.0%，质量分数) 对Fe22Cr5Al3Mo合金在500 ℃、10.3 MPa过热蒸汽中耐腐蚀性能的影响；采用EBSD、TEM、EDS、SEM等手段研究了合金的显微组织及腐蚀不同时间后的氧化膜显微组织。结果表明，添加Nb的合金中析出了Nb(C, N)、Fe₂(Nb, Mo)和Cr₂(Nb, Mo)第二相，细化了合金晶粒；当Nb≥1.0%时，随着Nb含量的增加，合金的耐腐蚀性能得到进一步改善。合金氧化膜从外向内依次是Fe、Cr、Al的氧化物；含1.0%Nb的合金不同氧化物的界面比不含Nb合金的更清晰，由不同成分氧化物引起的分层现象更明显；含1.0%Nb合金的氧化膜厚度比不含Nb合金的更均匀；在金属和氧化膜界面处，不含Nb合金中的Al氧化膜呈不连续分布，在基体和Cr氧化层中都发现了Al氧化物颗粒，说明不含Nb合金发生了Al的内氧化现象；而1.0%Nb合金中的Al氧化膜呈连续均匀分布，说明添加Nb能够抑制Al的内氧化，促进均匀且致密的Al氧化膜的形成，从而降低合金的氧化速率。

Fe-Cr-Al alloy is a promising candidate accident tolerant fuel (ATF) cladding material. It is helpful to developing Fe-Cr-Al alloy with excellent corrosion resistance by investigating the effect of chemical composition on its corrosion behavior under the normal condition of simulated nuclear reactor operation. In this work, the effect of Nb content (0.5%, 1.0%, 2.0%, mass fraction) on the corrosion resistance of Fe22Cr5Al3Mo alloys in 500 ℃ and 10.3 MPa superheated steam was investigated by static autoclave tests. The microstructures of the alloys and oxide films formed on the alloys after different exposure time were observed and analyzed by EBSD, TEM, EDS and SEM. The results showed that the second phase particles (SPPs) of Nb(C, N), Fe₂(Nb, Mo) and Cr₂(Nb, Mo) were precipitated and the grains were finer in the Nb-containing alloys. The corrosion resistance of the alloys was further improved with the increase of Nb content (in the case of Nb≥1.0%). The oxides of Fe, Cr and Al were formed separately in the oxide layer from outside to inside. Compared with the Nb-free alloy, the interfaces of different oxides were clearer and had a more obvious stratification resulting from the oxides with different composition appeared in the oxide film on the alloy with 1.0%Nb. The thickness of oxide film on the alloy with 1.0%Nb was more uniform than that on the alloy without Nb. At the oxide film and metal matrix interface, the alumina layer on the Nb-free alloy was dispersive, and the alumina particles were detected in both the matrix and chromium oxide scale, which illustrated the internal oxidation of aluminum occurred. While the alumina layer on the alloy with 1.0%Nb was more uniform and continuous. This indicated that the addition of Nb inhibited the internal oxidation of aluminum, and promoted the formation of uniform and continuous alumina layer, therefore reduced the oxidation rate of the alloy.