Effects of Long‐Term Ageing at High Temperatures on Oxide Scale Development and Evolution of Austenitic Steels Microstructure

This study is conducted to investigate the effects of long‐term air oxidation on the microstructural stability of HR3C, HR6W, and Sanicro 25 stainless steel. The materials are exposed to air atmosphere for 1000 and 10 000 h at 650, 700, and 750 °C respectively. The postexposed materials indicate some microstructural changes: the HR3C stainless steel develops Fe–Cr‐rich oxide scale, whereas HR6W steel forms a brittle, low adherent oxide scale consisting different concentrations of Cr, Mn, Fe, and Ni. Finally, Sanicro 25 stainless steel promotes the formation of a homogeneous‐rich Cr oxide scale at high temperatures. The analyses are performed using scanning electron microscopy (SEM)/energy‐dispersive X‐ray spectrometry (EDS) and X‐ray mappings. Long‐term exposure of high Cr steel is studied for 1000 and 10 000 h at 650–700 °C; microstructure changes are analyzed using scanning electron microscopy (SEM)/energy‐dispersive X‐ray spectrometry (EDS) and X‐ray facilities. Detailed analyses and theoretical consideration allow description of the mechanism that governs the degradation of high Cr austenitic steels at high temperatures.