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Page 2 of 27 Liu et al. Microstructures 2023;3:2023020 https://dx.doi.org/10.20517/microstructures.2023.02

Keywords: Duplex stainless steel, passive film, pitting corrosion, stress corrosion cracking, hydrogen embrittlement

INTRODUCTION
Duplex stainless steel has gained wide acceptance in the papermaking, petroleum, food processing, and
marine industries as a material of choice for systems, structures, and components due to the combination of
high strength, good toughness and excellent corrosion resistance. This is attributed to the synergistic
collaboration between the ferrite and austenite phases. Duplex stainless steels are more resistant to
intergranular corrosion than austenitic stainless steels, because the combination of the austenite-ferrite
boundary and the ferrite phase enables the precipitation of chromium carbides without severely depleting
[1]
chromium at the phase boundaries . The high solubility and slow diffusion rate of hydrogen in the
austenite phase of duplex stainless steel make it more difficult for hydrogen to diffuse, distinguishing duplex
[2]
stainless steel from ferritic stainless steel .
However, as application fields have expanded, it has become clear that duplex stainless steel suffers from
corrosion problems. In acidic environments, duplex stainless steels suffer from severe selective corrosion of
the austenite phase . In the moist H S environment, duplex stainless steel faces the risk of sulfide stress
[3]
2
[4]
cracking . From 2000 to 2022, several failures have been documented in journals and conferences,
including CORROSION, Engineering Failure Analysis, and Journal of Failure Analysis and Prevention, as
illustrated in Figure 1 and presented in the supplemental material [Supplementary Table 1].
[3-8]
Environmentally-assisted cracking (EAC), which includes hydrogen-induced stress cracking (4.55%), sulfide
stress cracking (18.18%), and chloride-induced stress corrosion cracking (27.27%), accounted for 50% of the
failures. Pitting corrosion-induced failures accounted for 27.27% of the failures. Additionally, both
microbially-induced corrosion (MIC) and selective corrosion caused 9.09% of the failures. Crevice corrosion
was responsible for 4.55% of the failures. The majority of the failures were attributed to pitting corrosion
and EAC. To ensure the safety of duplex stainless steel in industrial practice, it is imperative to undertake
rigorous academic investigations into these issues.

Nevertheless, current review articles mainly emphasize the production processes, such as hot working,
machinability and weldments [9-14] . Only a few reviews have discussed the service processes of duplex
stainless steel. de Farias Azevedo et al. summarized some failures of duplex stainless steels, which focused
on the failures induced by improper heat treatment . However, the report is deficient in academic studies
[15]
concerning failures related to corrosion. Salthalaand highlighted failures in the oil and gas industry, which
focus on practical advice . Cassagne and Elhoud reviewed the hydrogen embrittlement of duplex stainless
[16]
steels [17,18] . Since their reviews were conducted ten years ago, new findings should be added, such as the
recent research on the distribution of hydrogen in the two phases and at phase boundaries. Pan performed a
mini-review summarizing research on passive films using synchrotron-based analyses . Han et al.
[19]
reviewed the function of the alloying elements in duplex stainless steel, which shed little on the corrosion
behavior . In response to the demands of industry and the paucity of comprehensive reviews dedicated to
[20]
corrosion related to practical applications, this review was undertaken to fill this knowledge gap.

This article aims to review the recent academic progress on the pitting corrosion and EAC of duplex
stainless steel, which are the most common causes of failures. Because the formation and degradation of the
passive film are the basis for understanding the corrosion of duplex stainless steel, this review first
introduces the research on passive films from the perspective of the formation process and degradation
process of the passive film. Subsequently, the progress on pitting corrosion research is reviewed and
summarized from the perspectives of alloying elements and microstructures. Various distinct pitting