The corrosion resistivity was studied of TiN-coating steels (TiN/SS 41 and TiN/SUS 304) by anodic polarization in 1kmol/m³ HCl at 293K. The specimens were prepared by plasma assisted CVD. The results obtained are as follows: (1) The relationship between TiN film thickness (d) and anodic polarization current density (i), is log i=A+Bd, where A=3.1, B=-0.60 for TiN/SS 41 and A=2.0, B=-0.39 for TiN/SUS 304. (2) The sufficient film thickness for corrosion resistance is estimated to be 10μm for TiN/SS 41 and 12μm for TiN/SUS 304 judging from the point where the above equation intersects the current density of TiN-coating glass.

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Iron was oxidized in air at the temperature range from 873 to 1, 123K under cyclic heating and the weight increase was measured. The weight increase under cyclic heating was larger than that under continuous heating particularly at higher temperatures. The difference was larger than that obtained from the calculated value which was obtained by considering the weight increase during the heating or cooling period. Under the cyclic heating, the lowest temperature where the reaction temperature returned, and the heating rate (40K·min^-1 or more) didn't affect the weight increase. However, the weight increase depended on the holding time (the time of the reaction temperature of each cycle). The larger weight increase was observed at the shorter holding time. Under the cyclic heating, the step increase of weight was observed when the reaction was proceeded to 200-250g·m^-2 at 1, 073K. This might be caused by the large crack through the oxide scale which was formed during the heating or cooling process. The surface observation by SEM showed that the surface of specimen reacted under cyclic heating was covered by the oxide flakes. This flakes might be formed at each cyclic heating and also acceralated the oxidation reaction.

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Pitting corrosion and crevice corrosion sometimes occur on lead alloys in aqueous environments. The corrosivity of an aqueous solution environment was assessed. It varies with different solutes and their concentration in the solution. Impedance response measurements, anodic polarization curve measurements and crevice corrosion tests were carried out to assess the corrosivity. A 0.028% NaHCO₃ solution was used in the experiments to produce a passivation film on the lead alloy surface, and Cl^- ions were added to the solution to make it corrosive. The results obtained are summarized as follows: (1) A passivation film on a lead alloy surface was easily formed in a solution containing more than 20mg/l carbonic acid. It took 30 minutes before the film was functionaly passivated, and it needs more than 24 hours to get enough stability against corrosion. (2) Pitting corrosion and crevice corrosion occur in a solution that contains more than 60mg/l of Cl^- ions. The crevice corrosion current increased in proportion to the solution's conductivity. (3) It is possible to assess a solution's corrosivity by measuring the pitting current generated on a previously passivated lead alloy sample when it is anodically polarized at a fixed potential in the solution.

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Stress corrosion cracking (SCC) behaviors of type 304 stainless steel in a seashore atmospheric environment were investigated under three testing conditions; open air, transpalent plate covering, and steel plate covering. Wet and dry SCC tests, and half-immersion SCC tests were conducted experimentally to investigate the influence of temperature, humidity, pH, kind of salt and stress condition on SCC occurance. The following results were obtained: (1) SCC readily occurs more easily under the covering conditions than the open air condition, where rain rinses the surface of test pieces more often. The minimum value of the degree of sensitization, generating SCC susceptibility under the covering condition, was about 5% in terms of reactivation ration (JIS G 0580). (2) Temperature, humidity and hydroscopicity of salt, which influence the wet condition of steel surface, have an important effect upon SCC occurance. MgCl₂, being very hydroscopic, tends to make a wet condition under which SCC is promoted. Sea salt containing MgCl₂ also tends to make a wet condition. The critical temperature below which SCC dose not occur was estimated about 10°C.

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The mechanism of corrosion of stainless steels in highly concentrated sulfuric acid was studied by the electrochemical method and surface analysis as EPMA and Laser-Raman Spectroscopy. Cyclic potential changes occured in this system about between -0.2V (SCE) (active state) and 0.2V (SCE) (passive state). The anodic reaction was determined as the metal dissolution in both the active and the passive state. The cathodic reaction in the active state near -0.2V (SCE) was mainly dominated by the reduction of hydrogen ion which was clearly indicated by the evolution of hydrogen gas. On the other hand, catholic reaction at the passive state about 0.2V (SCE) was determined as the reduction of molecular sulfuric acid resulting in the formation of sulfur and water. By the analysis of EPMA, precipitated sulfur was found on the specimen surface polarized at 0.2V (SCE) potentiostatically. The in-situ observation of corroding surface by Laser-Raman spectroscopy indicated the formation of precipitated sulfur on the metal surface at the corrosion potential. Cyclic changes in corrosion potentials were considered due to the following mechanisms; dissolved metal ion at the active state formed metal sulfate films on the metal surface, leading the corrosion potential to the passive state. Inversely at the passive state, water as the product of the cathodic reaction accelerated the dissolution of the metal sulfate film to move the corrosion potential to the active state.

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The application of modulated UV-visible reflection spectroscopy to the in-situ analysis of passive films is reviewed. After a brief description of the principle and techniques of this method, following recent topics in the analysis of film composition are given: (1) qualitative analysis of passive films on Ni, (2) quantitative analysis of passive films on Fe-Cr and Ni-Cr alloys, (3) in-depth analysis of passive films on a Fe-Cr alloy, and (4) analysis of films on Fe at active-passive transition potentials.

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