Influence of the Solution-Treatment Temperature and Short Aging Times on The Electrochemical Corrosion Behaviour of Uns S32520 Super Duplex Stainless Steel

Abstract

Sigma phase leads to deterioration of corrosion resistance of super duplex stainless steels (SDSS) and its volume fraction increases as the time which the materials is exposed in determined temperature increases. In the present study, the effect of the short aging time on the formation of the sigma phase and on the corrosion behavior of UNS S32520 SDSS at 3.5% sodium chloride solution was evaluated using microstructural characterization, linear potentiodynamic polarization curve and electrochemical impedance spectroscopy. The results indicated that the SDSS sample solution-treated at 1150ºC and aged at 850ºC for 5 min may improve the corrosion resistance in comparison with the as-received and solution-treated conditions, due to the better partition of the elements Cr, Mo and dissolution of certain amount of sigma phase in the microstructure. However, results also showed that when SDSS solution-treated at 1150ºC is aged at 850ºC with the aging time slightly superior (10 min), the precipitation of sigma phase increases leading to a rapid deterioration of the corrosion resistance of the material.