Several cases of tarnishing and discoloration on copper wire surface were studied with electron microscope and diffraction. The tarnishing was caused by thin films of corrosion products formed on copper surfaces during drawing process, brightannealing, storage, and transportation. Cu₂S, CuO, and Cu₂O were detected in those thin films which were produced during bright-annealing. This type of tarnishing can be reduced by preventing the bright-annealing atmosphere from sulphur contamination. The tarnishing which occurred during storage and transportation was much affected by the atmospheric factors, e. g., relative humidity, temperature, or gas contamination, and the thin films consisted of Cu₂O. A particular case of discoloration caused by fretting corrosion occurred on the surface of special shaped wire which was transported for about 500km by land. This type of discoloration was associated with a number of pits which were filled with powdery corrosion products containing Cu₂O and Cu. The discoloration was easily prevented by avoiding contact and relative movement at the interface.

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This paper deals with the result of high temperature oxidation tests on the heat resisting cast steels for use in cement clinker at high temperatures. The samples used in this study were 28% Cr-20% Ni-Si-Al steel and commercial 25% Cr- 12% Ni steel. These steels were oxidized continually in cement clinker at 1, 100°C for 100, 250 and 500 hours; and at 700°C also for 100, 250, 500 hours and further for 1, 000 hours. At 1, 100°C the weight loss of 28% Cr-20% Ni-Si-Al steel was much lower than that of 25% Cr-12% Ni steel, while at 700°C the difference between the weight losses of the two steels was rather slight. The effect of heat treatment on the oxidation resistance of these two steels was also investigated and it was confirmed that the water cooling from 1, 150°C for 28% Cr-20% Ni-Si-Al steel caused increase of the weight loss at 1, 100°C. However, for 25% Cr-12% Ni steel, the same heat treatment reversely caused decrease of the weight loss at 1, 100°C. The effects of heat treatment on each steel were discussed in the relation with the microscopic changes.
Furthermore, the effect of addition of silicon and aluminum on the oxidation resistance of 28% Cr-20% Ni-Si-Al steel was examined. In this experiment the steels of various silicon and aluminum contents, ranging from 1 to 3% for silicon and from 0.35 to 1.05% for aluminum, were used. Under the condition that the silicon content of the steels. does not exceed 2%, the weight loss at 1, 100°C slightly decreased as aluminum content increased. It was considered that the most suitable content of aluminum plus silicon for decrease in weight loss was between 3 and 4%.
We concluded that 28% Cr-20% Ni-Si-Al steel had excellent oxidation resistance in cement clinker at 1, 100°C, but for practical use it had a serious weakness, that is, the formation of sigma phase at about 700°C.

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