The Influence of Sensitization Heat-treatment and Surface Finishing on the Properties of the SAF 2205 Duplex SS Passive Layer

In this study, the properties of the passive layer, formed on the surface of SAF 2205 duplex stainless steels in sulphuric acid solution, were investigated. The degree of sensitization of the samples sensitized for 1 h and 5 h were evaluated using double loop electrochemical potentiokinetic reactivation technique (DLEPR). The results were in good agreement with those of sodium hydroxide etch tests for classification of structures of duplex stainless steels. In addition, the potentiodynamic polarization test was performed to determine the passive potential range of the solution-annealed samples sensitized samples. Cyclic polarization in anodic branch revealed the beneficial effects of having less surface roughness on the protective properties of the passive layer. Mott-Schottky method was used to evaluate the density of point defects at the surface. The results showed that those samples with finer surface roughness, less degree of sensitization and more polarization cycles have less defects (up to 44%) in their passive layers. So, the more degree of sensitization and surface roughness lead to the formation of less intact passive layer due to the formation of sigma phase and less number of microcells at the surface.