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Towards understanding hydrogen embrittlement of duplex atainless steel using operando high-energy X-ray diffraction and digital image correlation technique
* 1 , 2, 3 , 1 , 4 , 5 , 6 , 2 , 2 , 1 , 2 , 7 , 6
1  Istanbul Technical University
2  DESY Deutsches Elektronen-Synchrotron
3  Anton Paar GmbH
4  AB Sandvik Materials Technology
5  University of Sussex
6  KTH Royal Institute of Technology
7  Lund University


Despite the over 140 years of research with over 38,000 peer-reviewed publications, hydrogen embrittlement has remained little understood. That is because hydrogen is not trivial to detect, and it operates over various time and space scales. The detection of hydrogen, i.e., its position in the material, and its instantaneous effect on the microstructure, which creates precursor events for the evolution of cracks, are needed to be investigated under operando (and ideally non-destructive) conditions for understanding hydrogen-induced material degradation.

In this talk, recently obtained results from operando synchrotron high-energy x-ray diffraction measurements on a commercial 25Cr-7Ni super duplex stainless steel during electrochemical hydrogen charging will be presented. Miniature-sized tensile specimens were subjected to uniaxial mechanical loading and hydrogen absorption while simultaneously mapping local diffraction patterns with a local resolution of 20 µm across the entire sample thickness. The infusion of hydrogen resulted in the evolution of tensile lattice strains in austenite grains at the surface region parallel to the loading axis, more extensive than those developed in the ferrite, which increased gradually with charging time. Most strains were developed perpendicular to the loading direction and the surface, with the strain evolution in the austenite being more pronounced than the ferrite. The strain evolution in the bulk interior had an alternating character between compensating compressive and tensile strains, with their magnitude increasing to levels beyond the yield point. The same experiment was repeated under an optical microscope, and a set of micrographs from the surface were recorded in time-lapse. Processing these images using Digital Image Correlation revealed numerous strain hot-spots developing in the austenite and interphase boundaries corroborating the synchrotron diffraction data. This talk will introduce a new way of testing hydrogen-microstructure interactions. It will showcase the need to test under operando conditions to better understand hydrogen embrittlement.

Keywords: Hydrogen embrittlement; duplex stainless steel; high-energy x-ray diffraction; digital image correlation; strain; hydrogen absorption; microstructure; ferrite; austenite; operando; in-situ; tensile testing; electrochemical hydrogen charging