Near atomic-scale comparison of passive film on a 17 wt% Cr-added 18 wt% Mn steel with those on typical austenitic stainless steels

The passive films on typical stainless steels (SS) and on a newly developed high-Cr (17 wt%)-added 18 wt%-Mn steel (HCr-HMnS) were compared by Cs-corrected scanning transmission electron microscopy and atom probe tomography. Although the passive films of all samples having similar Cr contents had the same thickness, unprecedented hexagonal wurtzite MnO inside the passive film of HCr-HMnS specimen was susceptible to corrosion cracking; this was not observed in the SS samples. This MnO caused crack formation during potentiodynamic polarization test, suggesting that reducing the harmful MnO by adding Mo and Ni facilitates the development of high-Mn base SS materials . Furthermore, higher MoO 2 composition of the passive films on 316 type austenitic SS than 304 type series might would result in primarily the improved pitting resistance. (c) 2021 The Author(s). Published by Elsevier Ltd on behalf of Acta Materialia Inc. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )

Automated summary

This study compared the passive films on typical stainless steels and a newly developed high-Cr-high-Mn steel, finding that MnO in the high-Mn steel was prone to corrosion cracking while this was not observed in stainless steels. Adding Mo and Ni can reduce harmful MnO, facilitating the development of high-Mn base stainless steel materials. Higher MoO2 composition in the passive films on austenitic stainless steels may lead to improved pitting resistance, particularly in 316 series compared to 304 series.