Structure of Rust Layer Formed on Atmospheric Corrosion Resistant Steel

Abstract

SynopsisThe distribution oj elements in rust la)'eI" Jormed on IowaI/o)' steels (lfter several l)eriods oj exposures up to seven )'ears in industrial and rural atmospheres was investigated by means oj microscopic examination and electron probe microanalysis. The rust layer in large Pits contains coPI)er. I)hosphorus, and chromium with their locali:::ed distribution. Chromium and phosphorus concentrate around defects in th e rust such as voids and cracks. Th e local concentration oj col)l)er seems to diminish as the exposure I)eriod becomes longer. The rust la)ler nn tilefla t swface surrounding large I)its and also the surface layer above large I)its have shown no evidence qf localized concentration oj col)l)er and j)/lOsj)hol'lls and are characterized by the Jact that little chromium content is Jound in the rust. Silicon, main constituent qf dusts. has been Jound in these parts oj the rust, but none in the Pits. It is supposed that chromium. j)/lOsphorus. and copper transferred by corrosion reaction intn the solution I)resumably Jorm Jar less soluble compounds than Jerrous ion which diffuses out Jrom the pits and I)recipitates on outer surface.