Abstract
Local strain development in the microstructure of a commercial 25Cr-7Ni super duplex stainless steel was mapped using high-energy x-ray diffraction during cathodic hydrogen charging under constant uniaxial load. The infusion of hydrogen resulted in tensile strains in austenite grains, one order of magnitude larger than those in the ferrite. Most strain evolution occurred at the near-surface, with compensating compressive forces developed in underlying regions, with up to two-times more compression occurring in the ferrite than the austenite. The strains along the loading axis were more pronounced than in the transverse direction, in which mostly compressive strains developed in the ferrite.
Highlights
Hydrogen in metals is well-known to degrade both mechanical and corrosion properties, a phenomenon known as hydrogen embrittlement [1,2,3]
The atomic hydrogen can be absorbed ultra-fast into the material and lead to strain localization, which often results in local plastic deformation and void formation and coalescence, with the latter often transiting to the formation of micro-cracks [5,6]
The data obtained via these delicate techniques, may not necessarily represent the entire microstructure as, for example, the effect of the austenite spacing of duplex stainless steel, which has been known to be a life-determining factor for hydrogen embrittlement, requires analysis of far larger volumes to be captured, which is beyond the possibility of current technology
Summary
Hydrogen in metals is well-known to degrade both mechanical and corrosion properties, a phenomenon known as hydrogen embrittlement [1,2,3]. The interaction of hydrogen with the microstructure at both atomic/ local scale and mesoscopic/macroscopic lengths has remained poorly understood due to the difficulty in detecting the hydrogen, in real-time, and its effects on various length scales [1,4,5]. The data obtained via these delicate techniques, may not necessarily represent the entire microstructure as, for example, the effect of the austenite spacing (a mesoscopic parameter) of duplex stainless steel, which has been known to be a life-determining factor for hydrogen embrittlement, requires analysis of far larger volumes to be captured, which is beyond the possibility of current technology. In-situ studies under operando conditions using non-destructive techniques are needed to provide local information at both microscopic and macroscopic scales in real-time. There are far more experimental data of hydrogen-microstructure interactions needed to improve our understanding of hydrogen embrittlement of duplex stainless steel. The work reported in this paper improved understanding of the earliest stages of hydrogen-induced material degradation in duplex stainless steel
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