The phenomena induced in austenitic stainless steels by cathodic charge of hydrogen were phase transformation, hydride and numerous surface cracks formation as previously reported. In this study, the hydrogen induced phases were compared with those of quench or stress induced, and the hydrides were compared with those induced in high nickel alloys. The hydrogen induced phases were found identical with those of stress or quench induced but different morphology. The hydrides formation depends on nickel contents and these hydrides themselves were unstable. The habit plane of surface cracks was determined by X-ray and optical microscope.

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A new electrochemical method using a relatively simple apparatus has been developed to determine the hydrogen content and diffusion coefficient in various metals. In this method, called the “two-sided extraction method”, hydrogen is dissolved into the metal until the hydrogen concentration is uniform, and then the dissolved hydrogen is extracted electrochemically at constant potential with anodic hydrogen ionization current which changes with time. The relationship between the anodic current and the time of hydrogen ionization can be used to estimate the hydrogen content and diffusion coefficient with the aid of theoretical hydrogen extraction kinetics. The thin coating of gold was necessary for this technique to apply the case of steel in order to prevent the passivation and to promote the hydrogen ionization reaction. The optimum thickness of coated gold that was required for steels was determined experimentally to be 300-600Å.

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The nature of corroding titanium surfaces and the meaning of polarization resistance were discussed based on the dual barrier model, and electrochemical measurements of titanium corrosion in sulfuric acids were carried out. It was confirmed from the experimental results that titanium dissolved in acid solution as trivalent ion. The corrosion potential of titanium was in a potential region which, although belonging to the active dissolution region, was close to the passive region, indicating a strong resistivity of the metal to corrosion. Analyses were made for the corrosion rate of titanium using various electrochemical methods. Among them, the polarization resistance measurement gave a fairly good estimation of the corrosion rate. A polarization resistance method was also proposed, which enabled small potential jumps produced by small current steps to be measured in a very short time interval without causing any significant changes of the surface conditions of titanium.

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