The hydrogen content in a mild steel was measured in 0.1N H₂SO₄ solution containing different organic additives by using electrochemical technique. The hydrogen content in a mild steel is varied with electrode potential for a given system. That is, as the electrode potential was shifted to less noble direction, the hydrogen content in a mild steel increased and reached to maximum value. The inhibition action of many organic additives such as oleylpycolynium chloride upon decreasing the hydrogen content was found. The inhibition effect of such additives did not have straight correlation with the degree of corrosion inhibition. The hydrogen content in mild steel at the reversible potential of hydrogen electrode reaction was constant value of 3×10^-9 gr.atom/cm³ independent of organic additives.

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The characteristics of stress corrosion cracking (SCC) of pure Al and homogenized Al-Cu single crystals were investigated with reference to crack morphology and faceting dissolution at various potentials in 1mol/kg-NaCl solution, and then an electrochemical role of NaCl+H₂O₂ solution which has been used as a SCC testing solution was examined in connection with pitting potential. Fracture time in 1mol/kg-NaCl solution decreased exponentially with an increase of potential above the pitting potential (V_c′) determined without stressing. Cracks are classified into the following three types according to applied potentials: well-type cracks which appear near V_c′, similar cracks which issue from bottoms of pits with increase of potential and only pits which develope above -0.40V (vs. SCE). Cracks always grow due to (100) faceting dissolution. As growth rates of pits become larger than the rate of (100) faceting dissolution above -0.40V, ductile fracture occurs by reduction of area due to pitting. When potentiostated, pure Al also suffers from SCC similar to Al-Cu alloys at potentials near V_c′, but the susceptible potential range is narrow. The critical potential of SCC seems to correspond to the pitting potential under straining (V_cδ′). Spontaneous corrosion potential in 1mol/kg-NaCl+0.09mol/kg-H₂O₂ solution is higher than V_cδ′ for several minutes, and decreases slowly with time to a constant value below V_cδ′. This constant corrosion potential value is higher than the protection potential for Al-Cu alloys and lower than that for pure Al. Therefore, the cracks of Al-Cu alloys keep growing due to (100) faceting dissolution and those of pure Al stops growing due to pit repassivation.

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To evaluate corrosion resistence of stainless steels in hot water containing about 25-300ppm Cl^- at max. 80°C, anodic polarization measurements and corrosion tests have been carried out on the specimens having various types of crevice. Initiation of crevice corrosion was accelerated by existence of active sites such as oxide films with residue of vaporized tap water on the specimen surface. During corrosion test for max. 27 weeks in 100ppm Cl^- aq. solution crevice corrosion took place on some of the specimens having active sites, but the growth could not be observed at any specimens after removing into tap water containing about 25ppm Cl^-. On spot welded specimens, only pitting corrosion took place in ultra low carbon ferritic stainless steels, while intergranular corrosion and stress corrosion cracking (SCC) also took place in type 430 and type 304 steels respectively. Based on the change in couple current between crevice-containing and crevice-free specimens, pitting inside the crevice appeared to grow early in the test period and to become inactive thereafter. On the other hand intergranular corrosion and SCC appeared to continue through the test periods. Corrosion tests of stainless steel tubes, which were carried out using circulating water containing max. 300ppm Cl^- at 80°C for 47 weeks, showed almost the same results as described above. In type 304 tubes SCC was observed at the crevice parts under silicon rubber tube joints, while only pitting corrosion took place in ferritic stainless steel. It was estimated by analysis of corrosion potential-time curves that the crevice corrosion grew steadily in type 304 steels, but tended to become inactive gradually in ferritic stainless steels.

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This paper deals with the initiation and propagation of corrosion fatigue crack. Stress cycle frequency and stress wave form have much effects on the behaviors of corrosion fatigue. These effects are different with the sensitivity to stress corrosion cracking of materials. Metal subjected to corrosion fatigue deteriorates in its ductility.

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Current problems on the environmental effects on fatigue of metals have been reviewed. Contained items are as follows: atmospheric corrosion fatigue, exo-electron emission and corrosion fatigue, corrosion fatigue of a material sensitive to stress corrosion cracking, influence of stress cycle frequency, influence of stress wave forms, long life corrosion fatigue strength under service conditions and ΔK_TH, and electric protection against corrosion fatigue.

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