Abstract
The influence of the austenite (gamma) phase fraction on the hydrogen embrittlement of duplex stainless steel is investigated. Heat treatments are performed to create two duplex stainless steel specimens, containing 50% and 44% of austenite, respectively. Mechanical testing with and without hydrogen charging reveals that significant embrittlement occurs regardless of the austenite fraction. A higher austenite fraction results in a reduced ductility loss under the presence of hydrogen. Samples with a higher ferrite fraction are embrittled more due to their higher hydrogen diffusivity. In-situ tensile tests, interrupted at the ultimate tensile strength, show hydrogen-assisted cracks on the specimen surface both in austenite and ferrite and across the alpha/gamma interface.
Highlights
Duplex stainless steels (DSS) are a family of stainless steel grades characterised by a mixed microstructure of austenite (γ, FCC crystal structure) and ferrite (α, BCC crystal structure)
The samples were free of intermetallic sigma phase, which may precipitate during heat treatment of DSS [24]
Magnetic measurements (Feritscope®) were considered to be more reliable since they analyze a relatively large volume of material compared to electron backscatter diffraction (EBSD), which is a local 2D technique and might not be representative for the entire sample
Summary
Duplex stainless steels (DSS) are a family of stainless steel grades characterised by a mixed microstructure of austenite (γ, FCC crystal structure) and ferrite (α, BCC crystal structure). They combine high mechanical strength with excellent corrosion resistance. DSS are attractive materials for application in a diverse range of industries, such as energy, marine, petrochemical, paper and oil & gas industry. Their use has largely increased during the last decade. Hydrogen can enter the DSS during production and processing, for example during welding, or during in-service conditions, such as for cathodically over-protected offshore structures or because of general corrosion that can be aggravated in environments where H2S is present [3,4,5]
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