The corrosion behaviour and the oxidation mechanism of a ferritic stainless steel, K41X (AISI 441), were evaluated at 800 degrees C in water vapour hydrogen enriched atmosphere. Mirror polished samples were compared to as-rolled K41X material. Two different oxidation behaviours were observed depending on the surface finishing: a protective double (Cr,Mn)(3)O-4/Cr2O3 scale formed on the polished samples whereas external Fe3O4 and (Cr,Fe)(2)O-3 oxides grew on the raw steel. Moreover, isotopic marker experiments combined with SIMS analyses revealed different growth mechanisms. The influence of surface finishing on the corrosion products and growth mechanisms was apprehended by means of X-ray photoelectron spectroscopy (XPS) and residual stress analyses using XRD at the sample surfaces before ageing. (C) 2017 Elsevier B.V. All rights reserved.