Microstructure and Oxidation Behavior of C‐HRA‐5 Austenitic Heat‐Resistant Steel in Air at the Temperature Range of 650–750 °C

This study investigates the oxidation behavior and microstructure characterization of C‐HRA‐5 (i.e., a new austenitic heat‐resistant steel) in the air at temperatures ranging from 650 to 750 °C over a 1000‐hour duration. The oxidation behavior and mechanism are analyzed using gravimetric evaluation, thermodynamic analysis, microscopic morphology, and microstructure characterization. The results indicate that the oxidation behavior follows a parabolic law at each temperature. With increasing temperature, the oxide film gradually grows and transforms from small lump particles to strips and needles, eventually covering the entire substrate surface over time. Moreover, long‐term oxidation exposure promotes the formation of various phases, including M 23 C 6 , σ, MX, Z, nanosized Cu‐rich, and Laves phases, within the metallic substrate. Considering potential applications in new‐generation power plants, this study provides a solid foundation to disclose the possible oxidation of C‐HRA‐5 austenitic heat‐resistant steel at high temperatures.