TGA‐MS study of steam oxidation resistance of HCM12A steel at 750 and 800 °C

Initial oxidation stages of the ferritic/martensitic HCM12A steel at 750 and 800 °C in Ar + 40%H2O for 190 h were studied in a closed steam loop by means of mass spectrometry (MS) and thermogravimetric analysis (TGA). TGA measures verified that mass gained by the HCM12A oxidized steel at 750 °C was up to two times lower than for HCM12A oxidized steel at 800 °C. Thermo-Calc program under same oxidation conditions of experiments was used for study of some theoretical oxidation simulations. The MS measurements at 750 °C of the HCM12A steel for 190 h indicated the presence of low intensity (in order of ppm) volatile species Mn(OH)3(g), Mn(OH)7(g), and CrOOH(g). While the HCM12A oxidized steel in steam at 800 °C and under same oxidation conditions emitted only a volatile CrOOH(g) species of double intensity. Therefore, it confirmed that the loss and rupture of the chromium scale of the steel can accelerate when the oxidation temperature increases. The morphology, composition, and structure of samples by scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD), X-ray energy dispersive spectrometry (EDAX), and X-ray diffraction (XRD) are described.