The Effect of Recrystallization and Pre-aging on the Oxidation Behavior of a 25Ni15Cr AFA Steel at 1123 K

To investigate the effect of recrystallization and pre-aging treatment on the oxidation resistance of alumina-forming austenitic (AFA) steels, the oxidation behavior and related mechanism of a 25Ni15Cr AFA steel under different microstructural conditions were systematically investigated at 1123 K in dry air. The results demonstrated that recrystallization treatment significantly enhanced the oxidation resistance of the AFA steel compared with that of the solid solution-treated sample, whereas subsequent pre-aging treatment failed to provide a further improvement. The recrystallized sample developed a uniform and dense oxide scale composed of fine oxide grains, primarily due to the accelerated diffusion of aluminum facilitated by grain refinement. In contrast, precipitates formed during pre-aging resulted in a negative impact on the oxidation resistance of AFA steel. The B2-NiAl phases caused uneven oxidation of aluminum, while the Laves phases hindered the short-circuit diffusion of aluminum along the grain boundaries of alloy matrix, thereby compromising the uniformity of the oxide scale. Based on the experimental findings, an oxidation model was developed to elucidate the influence of different microstructures on the oxidation mechanisms of the AFA steel.