Abstract

The aim of this study was the microstructural characterization of UNS S31803 duplex stainless steel samples thermally treated at 650 °C for 2, 3, 4, 6 and 8 h in order to promote the precipitation of intermetallic phases. The study was carried out using optical microscopy, scanning electron microscopy and energy dispersed X-ray spectroscopy. To reveal the microstructure of the material, a combined electrolytic attack was designed considering two steps: the first with 10% oxalic acid and the second, 20% NaOH. The monitoring of the microstructural evolution revealed the increase in the fraction of austenitic phase, which suggested the formation of secondary austenite and also the presence of precipitates after 2 h of treatment. According to their location and morphology these could be nitrides and carbides of chromium, whose fraction increased with treatment time, presenting more notable agglomerations after 6 hours. Additionally, the results of the elemental analysis reported the enrichment in chromium of the regions where the different precipitates were concentrated, which coincide with the presumed presence of the Cr2N and M23C6 phases. Likewise, the analyses using scanning electron microscopy suggested the possibility of formation of the sigma phase at longer treatment times.