For practically all alumina formers like the FeCrAl alloys for automotive catalyst Support foils a critical temperature interval exists, in which metastable phases like theta-Al2O3 are formed, that on further exposure to temperature transform into the stable alpha-Al2O3. Ail initially enhanced alumina scale growth and a faster Al Consumption are the consequence. High temperature X-ray diffraction was applied to investigate the isothermal oxide scale formation of OC404 in air at 900degreesC in situ. Low amounts of theta-Al2O3 were detected, but the accelerated formation of alpha-Al2O3 in the initial state and the micrographs indicate the presence of theta-Al2O3, which transforms very quickly to alpha-Al2O3. In in situ experiments it has been observed that on heating recrystallisation processes occur besides oxidation. For a better Understanding samples exposed to 900degreesC in air for different times were analysed by X-ray diffraction with a general area detector yielding meso-structure information like grain size and texture. The results show a grain coarsening at 900degreesC with mostly reproducible texture obviously linked with the rolling direction.