The anodic polarization curves of ferritic stainless steels, Type 405, 430, 446, and E-Brite 26-1, under various conditions of H2
concentration and temperature were obtained by means of the potential sweep method. The Flade potential, EF
, with potential scan to the noble direction is more noble than the potential with scan to the backward direction. The critical current density, iF
, at EF
is large compared to the current density, iF'
at the Flade potential, EF'
, with the backward scan. The Flade potential tends to noble with the solution temperature, and the critical current also increases. In a relatively dilute solution less than 30% H2
, the critical current density decreases with increase in Cr content of the alloy, whereas the current increases with the Cr content in 50% and/or 70% H2
. The critical current is also a function of the H2
concentration. That is, a maximum current was observed in 30% H2
. The critical current decreased in concentrated solutions such as 50% H2
, probably due to oxidation of steel surface by sulfuric acid. The passivation current density, iP
, is a function of the solution temperature and the set potential, but is almost independent of the H2
concentration. The Type 405 steel showed the largest current.