Volatile species were identified by means of mass spectrometry during the initial stages of oxidation of ferritic/martensitic steel FB2 (Fe-9Cr-1.5Mo-1.1Mn-0.05Si-0.1C-0.1Ni-1Co-0.2V-0.05Nb-0.008B) at 650°C and 800°C in a steam atmosphere of Ar + 40 %H2O for 180 and 150 h, respectively. The greater amount of Cr-containing volatile species detected, (i.e.) CrO3(g), CrO2(OH)(g) and CrO2(OH) 2(g), from the oxidized alloy at 800 C compared to 650 C showed that loss and breakdown of chromia (Cr2O3) are accelerated by increasing the temperature. For instance, the CrO2(OH) 2(g), which is responsible for the breakdown of chromia scales, was observed at 650°C for 150 h of oxidation, while the same species was detected at 800 C for 75 h. It was found that the hematite (Fe2O 3) that formed in the initial stage of oxidation was constantly evaporating during the test. Therefore, the sample gradually lost protection against oxidation, with chromia evaporating followed by volatilization of products that formed, such as the magnetite (Fe3O4) and wüstite (Fe1-x O). Eventually, oxidation breakaway of the sample was reached. Simultaneously, the oxidation kinetics of the samples was determined. The morphology/composition and structure of oxidized samples were also studied using the scanning electron microscopy-electron back-scatter diffraction/energy dispersive X-ray spectroscopy and X-ray diffraction techniques. © 2012 Springer Science+Business Media, LLC.