Polarization and weight loss tests on iron-chromium alloys were conducted in saturated monocarboxylic acid solutions. The results obtained were as follows:
(1) The critical current density and passive current density decreased as increasing the chromium content in alloys.
(2) Alloys of high chromium content began to dissolve in the hexavalent condition of chromium at a potential of about E_h=1.2V in the same manner as in inorganic acid solutions.
(3) The corrosion rate of alloys containing up to 18% Cr was greater than that of pure iron in formic and acetic acid solutions. But, in propionic and butyric acid solutions, the corrosion rate decreased gradually as chromium content increased.
(4) The corrosion rate decreased as increasing the carbon content in saturated monocarboxylic acids.

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A study has been made of the effect of the passivation treatment upon the stability of passive stainless steel against pit formation. The specimens used were SUS 27 stainless steel which were passivated at definite potential between +0.2- +0.7V (vs. SCE) in 5wt% H₂SO₄ solution.
The stability against pit formation was evaluated by measuring the time elapsed until the steady rise of the passive current (say induction time τ) after addition of definite quantity of chloride ion into the solution.
The experimental results were as follows;
(1) Induction time τ for pit formation was found to become larger, the more basic the passivation potential, particularly at E_crit=+0.4V and above this critical potential τ showed very small and nearly constant value.
(2) The irregular change of the passive current before the steady increase in current was very characteristic for the passive steel kept in lower passive region than +0.4V, while few fluctuation was observed above +0.4V.
(3) τ became remarkably smaller, when the passivated specimens were heated under vacuum at 300°C, and the irregular change of the current was found to decrease.
From these experimental facts, the function of the film for the pitting resistance of the stainless steel was discussed, referring to the bound water and the chemical composition of the passive film.

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[in Japanese]

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