The use of RuO₂ coated titanium electrode as an insoluble anode for cathodic protection in sea water has been investigated. Electrodes were prepared by the thermal decomposition of RuCl₃ on titanium supports. The anodic polarization curves for RuO₂ electrodes were determined in NaCl, Na₂SO₄ solutions, and artificial sea water. Experiments by constant-current electrolysis and SEM observation were also conducted. A characteristic refractive point was observed on anodic polarization curves in Cl^- containing dilute solutions because oxygen over-voltage is much lower than that of Pt, etc. During constant-current electrolysis, RuO₂ electrode was corroded at high current density (ex. 40A/dm²). This phenomenon is assumed that RuO₂ coating layer became unstable due to the rise of electrode potential.

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The glycerin displacement method has been frequently used to measure the diffusible hydroger concentration in steel from a viewpoint of easiness in measurement. However, its accuracy is known not to be good enough. In this study, a comparison of this method with electrochemical one was made and the former was found to involve other questionable points. Based on such experiments, the glycerin displacement method is concluded not to be able to give the real content of hydrogen for mild steel in which the diffusivity is high although it can be applied to high strength steel having low diffusivity of hydrogen. However, the electrochemical method can be applicable to any steel regardless of the diffusivity of hydrogen.

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The effect of heating and cooling rate of test solutions on stress corrosion cracking of austenitic stainless steels in high temperature water was studied in static autoclave by using U-bended specimens. The results obtained are summerized as follows. (1) Slow heating to the test temperature of 250°C-300°C made stainless steels more liable to cause cracking during heating process than quick heating to the temperature. Increasing the susceptibility of alloys to cracking and/or concentration of chloride ion increased the critical rate of heating to cause cracking during heating process. (2) Cooling rate, on the other hand, showed no effect on cracking. (3) No crack was caused during heating to 230°C by not only quick heating (140°C/hr) but also slow heating (70°C/hr). However, the time to cracking at test temperature of 230°C was also affected by heating rate of the solution. The slower heating rate resulted the shorter time to cracking. (4) The cracking was caused by repeating heating and cooling down cycles even though the heating rate was quick enough not to cause crack during one cycle of heating and cooling. (5) The effect of heating rate on cracking was only observed at the temperature higher than 180°C. (6) Heating rate of the test solution must be precisely controlled to obtain accurate stress corrosion data.

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Carburization in austenitic alloys was reviewed by describing outline of carburization reaction, metallurgical factors influencing on carburization, its effect on physical and mechanical properties. Some examples of failures due to carburization attack in chemical plants were also given.

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Definitions and classifications of erosion-corrosion and of related terms are discussed through a historical review of studies on cavitation erosion. A review is made of unified theories on erosion of solids due to cavitation, impingement by liquid and solid particles, as well as of those on the mutual interaction of erosion and corrosion. This is followed by some thought on areas for future research.

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