**5. Conclusions**

A Fe-Cr-Zr alloy with a dispersed Fe2Zr phase in the α-Fe matrix was produced, and the oxidation behaviors of the Fe-Cr-Zr alloy were investigated in stagnant air and in oxygen-saturated stagnant liquid Pb-Bi eutectic, respectively.

Delayed oxidation of Fe2Zr phase with respect to the α-Fe matrix is found during oxidation in air and in liquid Pb-Bi eutectic at 823 K and 923 K based on the experimental results and the thermodynamic calculations.

After oxidation in air at 923 K, a duplex structure including an outer Fe2O3 layer and an inner (Fe,Cr,Zr)2O3 layer was developed due to the inadequate supply of Cr. The incorporated Fe2Zr phase with delayed oxidation in the scale would obstruct the diffusion of solute/oxygen across the scale, resulting in the nonuniform oxidation behavior. The greater oxidation rate of Fe-Cr-Zr alloy than that of ferritic/martensitic steels is directly correlated with their microstructural differences.

After oxidation in oxygen-saturated stagnant liquid Pb-Bi eutectic at 823 K, a threelayered structure consisting of an outer magnetite layer, inner Fe-Cr spinel layer, and internal oxidation zone is formed. The incorporated Fe2Zr phase in the inner Fe-Cr spinel would obstruct the diffusion of Fe across the Fe-Cr spinel, which is a limiting step for the scale growth. A reduction in the Fe supply to the magnetite/Fe-Cr spinel interface is present adjacent to the Fe2Zr phase, leading to the creation of cavities in the outer magnetite layer with prolonged oxidation time. Comparable growth rates of oxide scale thickness between Fe-Cr-Zr alloy and ferritic/martensitic steels are due to that the differences in the microstructural features have little effect on the limiting step of scale growth.

**Author Contributions:** Conceptualization, S.C. and L.R.; methodology, S.C.; validation, S.C. and L.R.; formal analysis, S.C.; investigation, S.C.; resources, L.R.; data curation, S.C.; writing—original draft preparation, S.C.; writing—review and editing, S.C.; visualization, S.C.; supervision, L.R.; project administration, L.R.; funding acquisition, L.R. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work is financially supported by the National Natural Science Foundation of China (No. 51871218), Youth Innovation Promotion Association, CAS (No. 2018227), and Natural Science Foundation of Liaoning Province (No. 2020-MS-010).

**Data Availability Statement:** Not applicable.

**Acknowledgments:** The authors are grateful to Xiaojie Jin for help with oxidation tests in oxygensaturated stagnant liquid Pb-Bi eutectic.

**Conflicts of Interest:** The authors declare no conflict of interest.
