| Abstract: | The effect of martensite on the corrosion properties of 18 Cr-10 Ni steel The corrosion properties of the martensitic phases formed in an austenitic matrix by (i) cooling to low temperature (-196 and ?269°C resp. ?320 and ?452°F) and (ii) cold working at room temperature was investigated for two chromium-nickel stainless steels of the 18 Cr10 Ni type. Austenite and martensite have the same chemical composition but different lattice structures. In sulfuric acid, both martensitic phases formed at low temperature and by cold working arc preferentially attacked in the active range of corrosion. The effect of potential on the corrosion attack was elucidated by potentiostatically controlled experiments with subsequent light-optical and SEM-investigation of the specimens. Selective corrosion attack of the martensitic phase was found down to a potential being 0.8 V more negative than the cathodic limiting potential of the active corrosion range of a fully austenitic steel, irrespective of the way of the martensite transformation. The preferential attack of martensite may be explained by the supposition that the deposition of cathodically protecting layers possibly consisting of nickel is rendered more difficult at the martensitic surface areas. In sulfuric acid, no differences in the corrosion properties between austenite and martensite were found in the passive and transpassive range. In chloride containing aqueous solutions, the resistance to pitting is not effected by martensite formed at low temperature. From this it is concluded that also martensite formed by cold working does not effect the pitting resistance. |
