The effects of preparative treatment on the composition of the passive film on duplex stainless steel

The effect of surface treatment on the characteristics of the resulting passive film on a super duplex stainless steel is addressed. Auger Electron Spectroscopy (AES) has been used to provide in-depth chemical profile analysis of the passivating film produced by various polarisation conditions. This study showed that the constitution of the film is largely dependent on the conditions under which it is produced or to which it is submitted. The passive films formed by polarisation in an alkaline solution (boric-borate solution) consist of two regions, an inner region rich in chromium and an outer region rich in iron, whilst the films produced in acid solution only present the chromium-rich region. The film thickness is also greatly affected by the polarisation conditions. It can vary from ca. 8 monolayers to about 20 monolayers, for cathodically and anodically polarised specimens, respectively.