Creation of alloy design concept for anti air-born salinity weathering steel

摘要

Alloy designing methods, such as Ca or enhanced Niaddition together with elimination of Cr, for anti air-born salinityweathering steel were established, utilizing various findings interms of colloidal function of rusts. Addition of Ca to steel is ameasure aiming at increasing pH at corroding interfaces, resultingin stabilization of iron oxy-hydroxides, alteration of ionexchanging properties of the colloidal corrosion products, andmaintaining passive state of locally bare steel surfaces at defects ofrust layers. Enhanced nickel prescription decreases activedissolution rates of the steel, to reduce acidification of thecorrosion interface caused by hydrolysis of metallic ions. Soformed rust may contain Ni(II) ions to stabilize Fe(II,III) oxides,which may be beneficial to alter its ion-exchanging properties toeven facilitate alkalization at steel/ rust interfaces. Elimination ofchromium is essential to improve corrosion resistance of low alloysteels applied to the coastal atmospheres because of its acidifyingproperties. Practicality of the established concept was confirmedthrough 9 year exposure tests of so-prescribed steels to the severecoastal environment, resulting in the first commercialization ofanti air-born salinity weathering steel. This paper mainly describesauthors' seed investigating activities carried out from 1984 to1989 together with the recently obtained penetration curves.