Unveiling the mechanism of yttrium significantly improving high-temperature oxidation resistance of super-austenitic stainless steel S32654

Aiming at serious catastrophic oxidation problem of super-austenitic stainless steel S32654, the influence of different rare earth elements on its oxidation behavior was comparatively investigated at 1200 °C. The mechanism of Y significantly improving high-temperature oxidation resistance of S32654 was unveiled. The results demonstrated that Y played much better beneficial roles than Ce and La in the initial formation of oxide layer: (1) Y promoted Cr segregation to steel surface to combine with O; (2) its preferential oxidation provided nucleation cores for Cr2O3. Both roles jointly promoted the selective oxidation of Cr and then the formation of protective Cr-rich oxide layer. This provided good prerequisites for inhibiting the formation and volatilization of MoO3. Additionally, Y cation segregation to oxide grain boundaries further promoted the selective oxidation of Cr and Si to form more protective oxide layer. These beneficial roles of Y essentially eliminated the synergistic effects of MoO3 volatilization and lamellar Cr2N precipitation on catastrophic oxidation. Accordingly, the oxidation resistance of Y-bearing S32654 was improved by 22%–45%.