New contributions to the understanding of rust layer formation in steels exposed to a total immersion test

Adherent (AR), differentiated as scraped and hit, and non-adherent (NAR) rusts formed on carbon and weathering steels exposed to chloride solutions in total immersion tests were examined by means of different techniques. The NAR for both steels is composed of lepidocrocite, the most abundant, akaganeite, and goethite, whereas the AR in both steels contains additionally a spinel phase (magnetite/maghemite), which is the most abundant. Differences in crystallographic, relative amount, physical and chemical properties of the compounds in the different rust layers on both steels are reported. For both steels around 21% of the corroded iron converts completely into adherent rust.