Breakdown of the passive films on iron and stainless steel has been investigated by intermittent galvanostatic and quasi-potentiostatic polarization methods in aqueous solutions containing hydrogen sulphide and chloride ions.
Considering the changes in the characteristics observed on galvanostatic potential vs. time diagrams and on the potentiostatic polarization curves when varying the experimental conditions, conclusions are drawn concerning the possible mechanism of passive film breakdown.

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Fluctuations of the corrosion potential have been analyzed for aluminum immersed in 0.05M NaCl solutions with and without 20mg/l Cu²⁺. The potential fluctuations were sampled at 10-millisecond intervals, and they were separated into several types of signals by digital filters. The autocorrelation functions of the signals were calculated in order to extract the periodic signals related to catholic gas evolution. Further, the power of the signals was determined in the time domain, and the correlations between the power and the corrosion rate were investigated in several frequency ranges. It was found that the periodic signals having their fequencies at 1-2Hz existed in the potential fluctuations. The amplitude of the potential fluctuations decreased as the frequency increased. This decrease was more pronounced in the solution without Cu²⁺ addition than in the solution with Cu²⁺ addition. The power of the signals filtered by the highpass and lowpass filters having their cut-off frequency at 1Hz and 5Hz, respectively, was found to be closely proportional to the rate of growth for the deepest pits.

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In order to study the role of deformation structure in crack propagation process of Type 304 stainless steel, the relationship between the crack propagation rate and dissolution rate of α′-martensite was examined.
The measurement of crack propagation rate suggested that the stress corrosion cracking was accelerated by the deformation structure formed during the prestraining process or under the applied stress. On the other hand, the crack propagation rate was measured to be between the dissolution rate of α′-martensite without stress and the mean dissolution rate during repassivation process at slip steps of the specimen which had the same dislocation density with α′-martensite.
It is thought that the crack propagation of Type 304 stainless steel in H₂SO₄-NaCl solution depends on the preferential dissolution of the strain induced martensite or the region of high dislocation density.

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In order to investigate the effects of environmental factors on the atmospheric corrosion of carbon steel in Kubiki village, Niigata prefecture, the rate of corrosion and the concentrations of chemical pollutants in atmosphere were determined at 30 sites and the data of some meteorological elements were obtained for three years from November 1974 to October 1977. The summary of the results are as follows: 1) Corrosion rate was high in autumn-winter season because a lot of chloride was carried from sea by northwestern monsoon. This fact was very similar pattern to the results in the previous papers of Niigata and Toyosaka. 2) The ratio of the corrosion rates of the rural, coast and industrial area was 1.0:2.0:3.0, respectively. By the results, the pollutants from an industrial area were not neglected for the increasing of corrosion rate in the industrial area. 3) According to the results of the single correlation coefficients of atmospheric pollutants (chloride, sulfate, sulphur oxides and nitrogen oxides) and meteorological elements (precipitation, relative humidity, air temperature, solar radiation and wind velocity) for corrosion rate, chloride, sulfate and wind velocity showed the positive correlation of 1% level of significance, air temperature and solar radiation showed the negative correlation of 5% level of significance and sulphur oxides showed the positive correlation of 5% level of significance. The increasing of corrosion rate in autumn-winter season is understandable because a lot of sea salt particles are carried by wind in the season of low air temperature and poor solar radiation. Sulfate and sulphur oxides are also increased by discharged gases of combustion in this season. This tendency was very similar to the results in Niigate and Toyosaka presented in the previous paper. 4) The multiple regression equations of (3) and (4) which were obtained from only two variables of chloride and sulfate in Niigata were applicable to the estimation of the corrosion rates for industrial and coast areas, but were not applicable to clean air of the rural area in Kubiki village.

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Three kinds of erosion testing apparatus (rotating method, jet-in-slit method and abrasive paper method) were built to study the influence of velocity, pH and powders characteristics of slurry on erosion-corrosion phenomenon, and to evaluate the erosion-corrosion resistivity of various kinds of materials. The following conclusions were obtained. (1) Erosion attack increases with increase of the slurry velocity, particle size and particle hardness. (2) Erosion-corrosion damage increases remarkabley with the decrease of pH, though the influence of pH on corrosion damage is negligibly small in case of static slurry solution. (3) The influence of slurry velocity on the erosion-corrosion damage is evaluated to be small in a acidic solution, but large in a neutral or basic solution. (4) The magnitude of erosion attack increases in the order of the rotating method, the jet-in-slit method and the abrasive paper method. (5) Corrosion resistant alloys such as stainless steels and Ni base alloys show a good erosion-corrosion resistance in low velocity and acid slurry. Hard materials such as hard facing alloys show a good erosion-corrosion resistance in a high velocity and basic slurry.

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