陸上鉄骨構造物防食研究会では全国7ヵ所で大気暴露試験を行なっているが,その後低合金鋼類3種類と, 比較材3種類の追加試験を行なった。また暴露開始の時期を6ヵ月遅らぜた場合について試験を行なった。
この1ヵ年の平均侵食度はNi-Cr 鋼#2は0.037mm, Cr-Mo 鋼#4は0.050mm, Ni-Cr-Mo鋼#8は0.039mmで, 比較材のキルド鋼は0.056mm, 含銅転炉鋼は0.049mm, 耐候性高張力鋼は0.041mmであった。
わが国のように四季の気候に差のあるところでは, 暴露開始の時期を春から始めて1ヵ年経過したものと, 秋から始めて1ヵ年経過したものを比較すると, 初期の6ヵ月間は著しく腐食量に差が認められる (輪島, 帯広は例外) が, 1ヵ年間を経過するとほとんど同じ程度になることが明らかとなった。従って暴露期間は1ヵ年を単位とした暴露試験を行なう必要がある。

抄録全体を表示

Hot dipped tin plate is lustrous and very corrosion-resistive, and therefore, widely used for food cans which need corrosion resistance. But, when the plate is used for such a purpose, it is often observed that the cans become discolored purple or black in time. This phenomenon causes not only poor look of the cans but also spoiling of their contents, and seems to be one of serious problems in can manufacturing industry and in can packing industry. To prevent it, the plate is usually coated with special lacquers or is electrochemically treated.
Extent of the discoloration depends largely on the state of the microstructure of the tin plate surface, which is divided into two different types: one is susceptible to discoloration and the other is not.
Many investigations have been reported on the mechanism of the tin plate corrosion. But, we can't obtain any knowledge on the microstructure of tin plate surface from the majority of them, which can only provide electrochemical data. The present investigation was carried in order to clarify the relation between metallographical factors and corrosion, by measuring corrosion rate in acid solution, oxidation rate in the atmosphere and observation of surface microstructure by means of an optical microscope.
It was concluded that the surface which is susceptible to discoloration corresponds to rapid dissolution rate, rapid oxidation rate and large density of dislocations.

抄録全体を表示