Influence of the direction of ferrite-austenite banding on hydrogen embrittlement of 2205 duplex stainless steel

Abstract

In this study, the fracture behavior of 2205 duplex stainless steel (DSS) under in-situ hydrogen charging is evaluated. For this purpose, fracture toughness tests are performed on single-edge notched bending specimens, in which hydrogen is introduced electrochemically in-situ, using an acid and a saline electrolyte at different current densities. The hydrogen content of both electrochemically and gaseous pre-charged specimens is measured to assess the influence of the aggressiveness of the environment. Three environments are evaluated: realistic, severe and highly severe. As the microstructure of DSS is characterized by the presence of ferrite and austenite bands, the influence of directionality on fracture toughness is also studied. For this purpose, specimens are machined in two directions, being crack growth parallel to the bands in one case, while crack growth is perpendicular to the bands in the other case. Fracture toughness was found to decrease with increasing current density and in a more aggressive environment, and to increase when crack growth was perpendicular to the bands. The fracture surface was also evaluated, revealing splits in the direction of the bands in all in-situ tests. The origin and propagation of these splits were studied using electron backscatter diffraction scans, concluding that splits propagated through the ferrite-austenite interface.