Influence of microstructure on the corrosion resistance of the duplex stainless steel UNS S31803

Duplex stainless steels (DSS) are high strength corrosion resistant materials used in the chemical and petrochemical industries. When compared to conventional austenitic grades (AISI 304L, 316L, 317L), DSS are more expensive, but present higher strength levels and are more resistant to Cl− environments. In the present work it was investigated how microstructural variations can affect the corrosion resistance of a DSS UNS S31803 in artificial sea water media. Pitting corrosion resistance in 3.5%NaCl solution was evaluated by cyclic polarization tests at room temperature and 60 °C. The double loop electrochemical potentiodynamic reactivation test (DL-EPR) was also used to evaluate the degree of sensitization due to tertiary phases, such as σ and Cr2N. Structures containing sigma phase were found to be the most susceptible to pitting and localized corrosion. Cr2N, present in the as-melted sample, decreases the pitting potential but does not cause sensitization.