On the Oxide Films Formed on Hydrogen-absorbed Stainless Steels in High-Temperature Water

Abstract

Effects of absorbed hydrogen and surface polishing conditions on the structures of the initial oxide films formed on hydrogenated 18Cr, 18-8 and 18-18 stainless steels in high-temperature water at 300°C for 1 hr were investigated by means of electron microscopy, transmission electron diffraction and characteristic X-ray microanalysis.
Main results obtained are as follows:
(1) The corundum type oxide containing Fe and Cr was produced on the mechanically polished surface of 18-8 stainless steel; however, on the hydrogenated surface of this steel after mechanical polishing the spinel type oxide having Fe and Cr was formed.
(2) The oxide film formed on hydrogenated 18-18 stainless steel was identical with the spinel type oxide consisting of Ni besides Fe and Cr.
(3) The spinel type oxide containing Fe and Cr was produced on the hydrogenated surface of 18Cr stainless steel; on the other hand, the corundum type oxide was formed on the non-hydrogenated surface of this steel.
(4) No effects of surface polishing conditions on structures of oxide films were noticed for the present steels.
(5) From the above, surfaces of 18-18 and chemically polished 18-8 stainless steels showed the fcc phase and those of 18Cr and mechanically polished 18-8 stainless steels presented the bcc one; the latter was especially sensitive to the cathodic treatment, resulting in the formation of Fe⁺⁺ ion which was necessary for forming of the spinel type oxides.