It is one of the effective ways to obtain excellent comprehensive performance of 2205 duplex stainless steel (DSS) to adjust the volume ratio and grain size of α and γ phases. In the present paper, 2205 DSSs with micro-nano structures were successfully prepared by aluminothermic reaction under appropriate Fe2O3 excess conditions, and the formation mechanism of micro/nano structures was studied from the aspects of the preparation process, element equivalent, and residual Al content. Here, the Creq/Nieq ratio of the 2205 DSS is 2.09, indicating that the solidification mode belongs to mode F, that is, L → L + α→α→α + γ. The residual Al content and the volume percentages of α and γ phases and their grain sizes can be controlled by reasonably adjusting the excess percentage of Fe2O3. When the excess percentage of Fe2O3 is 5.0%, the volume percentages of α and γ phases reach the minimum and maximum values, respectively. However, when there is a large amount of unreacted Al in the alloy or an inappropriate excess percentage of Fe2O3 for preparation, only the α phase is contained in alloys.
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