In order to evaluate the effects of relative humidity (RH) at room temperature and kinds of chlorides on atmospheric stress corrosion cracking (SCC) of SUS 304 and 316 L stainless steels in contact with chlorides, SCC tests were carried out in RH controlled environments by using U-bend specimens deposit of 0.5 N chloride solutions (NaCl, MgCl2, CaCl2, ZnCl2, LiCl) or synthetic sea water. The maximum SCC susceptibility of steels was observed at the inherent relative humidity (RHmax) for each chloride. The SCC susceptibility in contact with synthetic sea water was governed by MgCl2 which is a minor solute component of sea water. Even with a long time test period of 24 months, atmospheric SCC was observed in a very limited RH range around RHmax. From measurements of the maximum crack length (Lmean) at RHmax of the different chloride solutions, it was concluded that a higher saturated concentration of chloride gave a higher SCC susceptibility. However, the acidic chloride, ZnCl2, gave a smaller Lmean than that overall tendency obtained without ZnCl2.

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Theoretical rotating ring and disk electrodes voltammograms are discussed for a process consisting of two consecutive charge transfer steps under steady-state conditions. The relationship between total disk current, id, and ring current, --Jr, is examined. Plots of -id/ir vs. the reciprocal of the square root of the rotation rate, 1/V~, are classified into three cases depending on the reversibility of the second charge transfer step. Although the voltammograms of the disk electrode may be those of a single wave, a distorted s-shape, or a well-separated two step, the ratio -id/ir is not affected by the kinetic parameters of the first charge transfer step, except for the number of electrons.

Uniaxial constant load SCC experiments have been performed on sensitized SUS 304 stainless steel in high temperature water. Experimental variables included temperature, dissolved oxygen concentration, pH, anion species, crevice and their combinations. The former three factors give their individual dependencies of IGSCC susceptibility and their threshold values, below which the IGSCC could hardly occur. Combinations of more than two environmental factors increase the severity of the IGSCC and change the threshold values. The specific IGSCC behavior with variations of the combined environmental factors was interpreted in connection with the stability of passive films in a corrosive environment under stressed or strained condition.

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