STUDY OF THE PASSIVITY OF UNS S32003 LEAN DUPLEX STAINLESS STEEL IN NaCl SOLUTION BELOW CRITICAL PITTING TEMPERATURE

摘要

In this work we carry out the characterization of two alloys: the lean duplex UNS S32003 and the stainless steel UNS S31603 in NaCl solution at different temperatures; both materials have been used in different applications that require corrosion resistance under chloride environment. The lean duplex alloy favors the mechanical properties while maintaining corrosion resistance and it can be a cost effective alternative to UNS S31603 and UNS S32205 for various applications such as offshore topside structural components and subsea flow-lines. Stainless steels above their specific critical pitting temperature can form different interfacial processes that allow susceptibility to this type of localized corrosion. In this study, the electrochemical performance for UNS S32003 lean duplex steel and UNS S31603 steel is investigated by DC and AC basis techniques. Potentiodynamic polarization tests resolve the active-passive interfacial states at temperatures close to CPT when exposed to higher concentrations of NaCl [1M] is revealing the passive region. Electrochemical impedance spectroscopy (EIS) is used to quantify different mechanisms due to the association of interfacial processes with passive electrical elements. The surface morphologies following DC basis are examined by using stereomicroscopy, and 3D optical microscopy.