Mössbauer spectroscopy was used for the identification of the components in iron rusts formed on steel plates, nails and bolts exposed to air for long periods. The Mössbauer absorption spectra of the rusts were measured at both room and liquid nitrogen temperatures as a function of the calcination temperature, and compared with the spectra obtained for uncalcined and calcined α-, β-, γ -and superparamagnetic α-FeOOH. The main components of the rusts were identified as γ-FeOOH, α-Fe₂O₃, superparamagnetic α-FeOOH and superparamagnetic α-Fe₂O₃. β-FeOOH was found only in the sample exposed to a marine environment. The spectrum for magnetite, Fe₃O₄, was not obtained for any of the rusts, because sampling was made by avoiding the vicinity of the metal phase.

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The effect of tarnish films on corrosion fatigue crack growth behavior of hard drawn, tough pitch copper in dilute ammoniacal solutions of various concentrations (0.02M-0.07M) at 55°C was investigated by measuring the rate of fatigue crack growth by the use of a cantilever type fatigue tester. The threshhold stress intensity factor range ΔK_th, below which no detectable air-fatigue crack growth is observed was estimated at 7.4kg·mm^-3/2 from crack growth curves in air. Scanning electron microscopy was employed to study the fractography of corrosion fatigue crack surface of specimens tested in ammoniacal solutions. The crack surface was all covered with tarnish films as thick and black as those on the surface of the specimen. The rate of crack growth in ammoniacal solutions is found to be nearly equal to that in air at the early time of crack growth, but from a certain crack depth it becomes smaller than in air. This critical depth is strongly dependent on the growth rate of tarnish films in cracks. As a result of decrease of this depth in accordance with increase of the tarnish film growth rate in cracks, the decrease of crack growth rate occurs at the earlier time of crack growth. These phenomena can be explained from the wedge action of tarnish films formed in fatigue cracks. From the above results, it is considered that the plastic insulated cable of hard drawn copper can be used in tarnishing environments on the basis of fatigue crack growth characteristics in air.

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Effect of cold work on intergranular stress corrosion cracking (IGSCC) of SUS 304 and SUS 304L was investigated in high temperature pure water, and the results were compared with intergranular corrosion behaviors by H₂SO₄-CuSO₄ test. The results obtained are as follows: 1) Sensitization temperature-time region of SUS 304 where IGSCC occurs is greatest around 5 to 10% cold work, and this region becomes smallerr again at the higher cold work level. The susceptibility to IGSCC of SUS 304 which is cold worked and subsequently sensitized for a short time is much higher than that without cold work. 2) Cold work of 5 to 10% reduction accelerates chromium carbide precipitation along grain boundaries, but at the higher cold work level the carbides precipitate at slip bands as well as grain boundaries. The effect of cold work on IGSCC can be satisfactorily explained on the basis of these carbide precipitation behaviors. 3) Deformation induced martensite in SUS 304 increases the resistance to cracking, which is considered to be due to the metallurgical and electrochemical effects. 4) SUS 304L is much resistant to cracking compared with SUS 304. 5) The susceptibility to IGSCC in high temperature pure water does not necessarily agree with that to intergranular corrosion by H₂SO₄-CuSO₄ test.

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The localized corrosion of type 304 stainless steel was investigated using the a-c automatic corrosion monitor deviced recently in our laboratory, with special interest to detect the initiation of localized corrosion. The a-c corrosion monitor permits to record the time-course of the net corrosion rate of specimen. The corrosion rate of the stainless steel in NaCl solution was relatively low at initial periodes but, after certain incubation time, it increased rapidly by more than forty times indicating a pit propergation. It was also noticed that higher the corrosion rate during the incubation time, shorter the incubation time. A similar incubation time was also observed on crevice corrosion of the specimen with an artificial crevice. The rate of crevice corrosion of type 316 stainless steel was less than that of type 304 and 304-L, while the rates also depended on the ratio of anode/cathode area.
Since the net corrosion rates measured by the a-c corrosion monitor were well consistent with those estimated from the weight loss of the specimen, it is found that the corrosion monitor can be used to monitor not only general corrosion but also localized corrosion.

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Corrosion of a motor car is an electrochemical process caused by retained moisture and trapped water. De-icing salts spread on high ways accelerate the corrosion during winter. Flying stones and gravel from the roads damage the paint. Galvanized-, galvannealed and zinc primer coated steels are used successfully in main corroded parts, e. g. doors, front fenders, rocker panels. The coating itself gives the protection and when these steels are painted, the protective effect is more striking. The current change from anodic to cathodic electrophoretically deposited primer is also expected to bring about more resistance.

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