[en] K41X (AISI 441) stainless steel evidenced a high electrical conductivity after 3000 h ageing in H_2/H_2O side when used as interconnect for solid oxide electrolyser cells (SOEC) working at 800 C. Perovskite (La_1_-_xSr_xMnO_3_-_δ) and spinel (Co_3O_4) oxides coatings were applied on the surface of the ferritic steel for ageing at 800 C for 3000 h. Both coatings improved the behaviour of the steel and give interesting opportunities to use the K41X steel as interconnect for hydrogen production via high temperature steam electrolysis. Co_3O_4 reduced into Co leading to a very good Area Specific Resistance (ASR) parameter, 0.038 Ωcm"2. Despite a good ASR (0.06 Ωcm"2), La_1_-_xSr_xMnO_3_-_δ was less promising because it partially decomposed into MnO and La_2O_3 during ageing in H_2/H_2O atmosphere. (authors)

[en] Highlights: • Study of surface finishing effect on the corrosion behaviour of a stainless steel. • Mirror polished samples were compared to as-rolled material. • Two oxidation mechanisms were identified depending on the surface finishing. • Before oxidation, native chemical phases are identical for both samples. • Subsurface dislocations generated by the polishing process promote Cr_2O_3 formation. - Abstract: The corrosion behaviour and the oxidation mechanism of a ferritic stainless steel, K41X (AISI 441), were evaluated at 800 °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)_3O_4/Cr_2O_3 scale formed on the polished samples whereas external Fe_3O_4 and (Cr,Fe)_2O_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.