Pit or Cavity-Corrosion of High Chromium Stainless Iron Caused by Contact with Non-Conductive Substances and its Prevention

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In the acidic oxidizing solution containing chlorite ion, for example, in aqueous solution of ferric chloride, the entire surface of 14% Cr stainless iron or steel corrodes, whereas that of 21%-35% Cr stainless iron, does not corrode at all, being in the passive state, When the surface of this high chromium stainless iron comes in contact with non-conductive substance such as glass, cork and rubber stopper, or with noble metals like platinum and gold, a narrow crevice acting as capillary is formed, and the corrosion takes place in pit or cavity at the point of contact. Of 22% Cr, 22% Cr + 3% Mo, 22% Cr + 7% Mo, and 35% Cr stainless iron, two kinds of specimens, namely those annealed at 900℃ and those quenched in water from 1, 090 or 1, 300℃, were tested in 5% ferric chloride aqueous solution to ascertain whether pit or cavity corrosion takes place by bringing them in contact with non-conductive substances. The mechanism which gives rise to the phenomenon is also discussed. It has been ascertained that while 22% Cr stainless iron is affected by the contact, the contact effect is greatly reduced when it is alloyed with 7% molybdenum and quenched in water. Whereas 35% Cr-stainless iron shows the contact effect to do reverse, i. e. the surface of annealed specimen is not subject to cavity corrosion, but it is by quenching. The author discusses briefly the method of prevention of the contact effects based upon the foregoing experiments.
東北大学の論文

著者

Endo Hikozo
The Research Institute For Iron Steel And Other Metals

Pit or Cavity-Corrosion of High Chromium Stainless Iron Caused by Contact with Non-Conductive Substances and its Prevention

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