Evaluating the Hydrogen Embrittlement Susceptibility of Aged 2205 Duplex Stainless Steel Containing Brittle Sigma Phase

Abstract

Duplex stainless steels (DSS) have a two‐phase microstructure of ferrite and austenite which results in a high strength combined with high ductility and good corrosion resistance. However, when DSS are heated to an inappropriate temperature range, e.g., during welding, the brittle sigma phase forms which deteriorates the mechanical properties. In the present work, a heat treatment is performed to intentionally create this deleterious phase. Hydrogen is introduced in this alloy to investigate the combined effect of embrittling phases (sigma phase) and hydrogen. Melt extraction analysis is performed to quantify the hydrogen uptake capacity in the steel. In‐situ mechanical tests are used to assess the hydrogen embrittlement susceptibility. The uncharged DSS shows a low ductility and almost no hydrogen embrittlement is observed via an in‐situ tensile test set‐up due to its intrinsic brittle nature under tensile mode. Complementary in‐situ bending tests which are more suitable for an intrinsically brittle material are done to further evaluate the role of hydrogen on the mechanical integrity. Hydrogen charging does indeed result in additional embrittlement in the in‐situ bending set‐up. The reason is thought to be the faster initiation, interconnection and propagation of cracks in the presence of hydrogen, as indicated by microstructural characterization.

Invasion/Permeation Hydrogen in Cathodic Charged SUS316 Columnar Crystals Evaluated with a Scanning Kelvin Probe Force Microscope

“…A higher surface potential in the σ phase than that of the surrounding austenite matrix has been detected in SKPFM measurements for aging stainless steels [27]. The hydrogen diffusion coefficient of the σ phase has been estimated as lower than that of the ferrite phases [28,29]. In the present multimodal measurements in spot 1 of area C on the exit surface (Figs.…”

“…8(b) and (c)] in the δ-ferrite phase adjacent to the precipitates strongly implies the effect of accumulating hydrogen on the precipitates. Although some studies have mentioned dissolution of hydrogen into the σ phases [28,29], the effect of accumulating hydrogen has been reported not at interfaces of σ phases but the intermediate χ phases [4]. Therefore, the intermediate χ phases evidently also included in precipitates in spot 1, and only some precipitates containing the χ phases would have the effect of accumulating hydrogen.…”