This analysis evaluates pitting corrosion in duplex stainless steels with varying manganese levels, revealing significant impacts on microstructural features.
The effects of Mn on pitting corrosion resistance for Fe-22Cr-9Ni-3Mo-(0, 2, 4)Mn (wt%) duplex stainless steels (DSSs) were investigated, by considering the microstructural change and the Mn content in the solid solution state. By fabricating the ingots under carefully controlled conditions and performing hot rolling and solution treatments, three DSSs were prepared to have similar microstructural features in terms of phase fraction, grain size, and volume fraction of nonmetallic inclusions (NMIs). The NMIs in the DSS without Mn were found to be Cr₂O₃, and those in the DSSs containing Mn were (Cr,Mn)₂O₃. Accordingly, the Mn content in the solid solution state and the type of NMI were considered as the primary factors affecting pitting resistance. Potentiodynamic polarization tests in neutral NaCl solution showed that the pitting resistance decreased as the Mn content increased. After the polarization tests, it was found that the (Cr,Mn)₂O₃ in the DSSs containing Mn acted as pitting initiation sites, whereas Cr₂O₃ in the DSS without Mn remained uncorroded. In addition, the critical dissolution rate of the DSSs measured in strongly acidic HCl solution increased with increasing Mn content, suggesting that the pit propagation rate was accelerated by Mn addition. In conclusion, the Mn addition to DSSs reduced pitting resistance by providing more pit initiation sites and also increasing the pit propagation rate.
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Lee et al. (2025) studied this question.
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