In the acidic oxidizing solution containing chlorine 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, being in the passive state, does not corrode at all. When the surface of this high chromium stainless iron comes in contact with non-conductive substances, such as glass, cork or rubber, or noble metals like platinum or gold, a narrow crevice is formed, and the corrosion takes place, making pit or cavity at the point of contact. On 22% Cr, 22%Cr-3%Mo, 22%Cr-7%Mo, and 35% Cr stainless iron, two kinds of specimen, namely those annealed at 900° and those quenched in the water from 1000° or 1300°. 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 affectfd by the contact, the said effect is greatly reduced when it is alloyed with 3_??_7% molybdenum and quenched in the water, The author discusses briefly the method of prevention of the contact effects based upon the foregoing, experiments
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