Investigation of micro-electrochemical activities of oxide inclusions and microphases in duplex stainless steel and the implication on pitting corrosion

In this study, the oxide inclusions contained in the 2205 duplex stainless steel were characterized, and the pitting corrosion initiated at the inclusions was statistically analyzed. The micro-electrochemical behavior was measured by a home-designed capillary microelectrode technique. Results show that three types of oxide inclusions are contained in the steel, namely, Al–Mg–O (inclusion A), Al–Si–Ca–O (inclusion B), and Al–Mg–Si–Ca–O (inclusion C) inclusions. Inclusion A possesses higher electrochemical stability than the steel substrate, and there is no corrosion pit initiated on the inclusion. Inclusions B and C are more electrochemically active than the steel, and pitting corrosion occurs on both inclusions. The α phase has higher electrochemical activity and lower corrosion resistance than the γ phase. Pitting corrosion is more likely to occur at the inclusion/α phase interface, rather than the inclusion/γ phase interface. When the inclusion is located at the α/γ interface, the pit initiation is dominated by the α phase on the coexisting dual phases.