Effects of preautoclaved Fe₃O₄ film, dissolved oxygen and water velocity on corrosion and rest potential of carbon steel were examined in high purity water at room temperature. Although the preautoclaved carbon steel with defective film suffered slight pitting in static water saturated with air, corrosion of carbon steel with the preautoclaved Fe₃O₄ film was prevented in any high purity water. Rest potential of the preautoclaved carbon steel was similar to that of sintered Fe₃O₄ electrode. Release rate of iron corrosion product from Fe₃O₄ powder was less than that from Fe powder. In the case of a polished carbon steel, the corrosion rate and the rest potential were strongly controlled by water quality conditions. In static water, the corrosion rate increased with increasing dissolved oxygen levels, and also the rest potential slightly shifted towards noble value but never exceeded -0.5V (vs. SCE). In flowing water, however, the corrosion rate decreased by the addition of oxygen, and then the rest potential remarkably shifted towards noble value near 0V (vs. SCE). Carbon steel can be passivated in flowing water saturated with air at velocity higher than 0.1cm/sec. Pitting in the preautoclaved carbon steel with defective film was prevented with this passivation.

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This work was carried out to obtain some information about relationship between intergranular stress corrosion cracking (IGSCC) of Ni-base Alloy 600 in aerated acidic high temperature solutions and acid intergranular corrosion (IGC). Specimens were solution treated at 900-1150°C and post heat treated at 550-750°C for 5-50 hours. The application of electrochemical potentiokinetic reactivation method (EPR) to Ni-base Alloy 600 was developed. The IGC susceptibility was sensitively detected by a potentio sweep from -400mV to +600mV (vs. SCE) in 0.25M H₂SO₄+10^-3M KSCN solutions, and after 10 minutes rest at +600mV a back scan was performed to -400mV. The most severe intergranular attack was observed when specimens were solution treated at 1100-1150°C and post heat treated at 650-700°C for 5-20hours. IGSCC susceptibility in aerated acidic high temperature solution showed good agreement with IGC sus- ceptibility detected by EPR. Disappearance of Cr-depleted zone by re-diffusion of chromium resulted in low susceptibility to IGC and IGSCC. These results show that cracking mechanism of Ni-base Alloy 600 in aerated high temperature water is dissolution of Cr-depleted zone.

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A study has been made of corrosion fatigue crack growth for 7075 aluminum alloy in 3.5% NaCl solutions under both open circuit and cathodic charging, a pure water, an air and a dry argon at ambient temperature. The effect of aging treatment at 150°C on the corrosion fatigue crack growth rate (da/dN) as a function of ΔK was examined and the fracture surfaces were observed. The crack propagation curves (da/dN vs. ΔK) for 7075 alloy solution-treated underaged, peakaged, overaged and as-received were obtained in above different environments. The value of da/dN for solution-treated, underaged and overaged alloys was arranged in the following order of the environments: open circuit>catholic charging>pure water>air>dry argon. In peakaged 7075 alloy, the crack growth rate under cathodic charging was greater than that in open circuit, and this acceleration of crack growth was explained by the influence of hydrogen embrittlement. The relative contribution of the corrosive environment to the fatigue crack propagation was well evaluated by comparison of (da/dN)_{c. f.} in each environment with (da/dN)_ref. in a reference dry argon environment at a certain ΔK. The additional effect of stress corrosion cracking (SCC) to corrosion fatigue crack propagation was discussed on the basis of the value of K_ISCC and from both sides of the active path corrosion and the hydrogen embrittlement types for SCC mechanism in 7000 series aluminum alloys -3.5% NaCl solution system.

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Stress corrosion cracking (SCC) behaviors of Al-4.5 Zn-1.5 Mg alloy were investigated in 3% NaCl solution at 30°C and 70°C, using a slow strain rate technique (SSRT). The effects of crosshead speed (CS), specimen thickness and temperature on the SCC behaviors were studied in this method. The susceptibility to SCC increased with decreasing CS and was independent of specimen thickness at both temperatures. Crack propagation rate showed constant value for the changes of CS or specimen thickness. It has become clear that SSRT method is available for SCC test method of this alloy-corrosive system. The results of tesnile test in laboratory air after exposure to the corrosive at 70°C without stress indicated that the loss in ductility of specimens is the results of intergranular hydrogen embrittlement. It has been found by a high voltage electron microscope observation (JEM 1000) of specimens pre-exposed to the corrosive that the strain field contrast revealed hydrogen bubbles was formed in association with the grain boundary precipitates.
The results of ion micro analysis for the specimen after SCC test in 3% NaCl deuterium solution at 70°C has shown that the peak of secondary ion intensity corresponding to deuterium (m/e=2) is observed at the oxide-metal interface. From above results SCC of the specimen has been explained by a hydrogen embrittlement mechanism.

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The transpassive dissolution and the oxygen evolution of SUS 304 and SUS 316 steels were investigated as a function of potential in a 1kmol·m^-3 H₂SO₄ solution by means of electrochemical technique and Inductively Coupled Plasma Emission Spectrometry (ICP). It was found in the anodic polarization and metal ion dissolution curves on both steels that the maxima and minima of the current density and the amount of dissolved ions were clearly present around 1.6V and 1.8V, respectively. On the basis of the result for the compositions of metal ions dissolved, it was concluded that the preferential dissolution of Fe took place together with the small enrichment of Cr and Ni on SUS 316 surface, but no its dissolution occurred in Fe, Cr and Ni on SUS 304. Because of the preferential dissolution of Mo, the transpassive dissolution on both steels was suggested to be equal to the dissolution of a film, not to that of a substrate caused by film destruction. From the comparison between the amounts of total anodic charge and electric charge estimated from dissolution, Fe or/and Cr on both steels were found to dissolve in the form of metal ion with the ionic valencies, Z_Fe=2 or/and Z_Cr=3. Furthermore it was found that the ratios, Q_d/Q_t, for both steels kept constant with a value of 0.6-0.8 below 1.8V and decreased to a value less than 0.4 above 1.8V. It was deduced from the results obtained that below 1.8V, the reaction combined metal ditsolution with oxygen evolution occurred, and above 1.8V, the reaction subjected to oxygen evolution mainly took place, as follows;

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