PSI - Issue 68

Akihiko Fukunaga et al. / Procedia Structural Integrity 68 (2025) 1059–1065 Akihiko Fukunaga / Structural Integrity Procedia 00 (2025) 000–000

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charged specimen shows slip surface separation due to hydrogen directly reducing the deformation ability in the grain (HEDE mechanism), resulting in facet within each grain. Then facet combines to cause transgranular fracture (Fig 5 (b)).

4. Conclusions SSRT tests were conducted for A286 in 70 MPa gaseous hydrogen and 56 ppm hydrogen charged A286. For A286 specimen in 70 MPa gaseous hydrogen 1) Fracture morphology and RRA values were strongly affected by strain rate. 2) Fracture was influenced by surface cracking, and hydrogen-induced strain localization near the fracture surface occurred (e.g. HELP, and HESIV), proved by KAM map of EBSD. For 56 ppm hydrogen charged A286 specimen 3) Fracture morphology and RRA values were less affected by the strain rate than those in 70 MPa gaseous hydrogen. 4) No surface cracks and no localization of deformation near the fracture surface were observed. Internal hydrogen directly reduced the strength within the grains, causing transgranular fracture (e.g. HEDE), proved by KAM values. From the above results, it can be clarified that the hydrogen embrittlement behaviors differ depending on hydrogen environments Acknowledgements The author thanks T. Mino for operating EBSD measurement in Kagami memorial research institute for materials science and technology of Waseda University. References [1] Fukunaga A: Technology to reduce the cost of next-generation hydrogen stations. JXTG Technical Review 2019;61:25-33 [Internet]. Available from https://www.eneos.co.jp/company/rd/technical_review/pdf/vol61_no01_07.pdf [accessed 2024 October 8] [2] Frisk R, Andersson NA, Rogberg B, Cast structure in alloy A286, an Iron-nickel based superalloy. Metals, 2019; 9:711. https://doi.org/10.3390/met9060711-29 [3] NASA: Safety Standard for Hydrogen and Hydrogen Systems [Internet]. Available from https://ntrs.nasa.gov/api/citations/19970033338/downloads/19970033338.pdf [accessed 2024 October 8] [4] R.A. Oriani, P.H. Josephic, Equilibrium aspects of hydrogen-induced cracking of steels, Acta Metall. 22 (1974) 1065–1074, https://doi.org/10.1016/0001-6160(74)90061-3. [5] Beachem C.D., A new model for hydrogen-assisted cracking (hydrogen “embrittlement”), Metall. Trans. 3 (2) (1972) 441–455, https://doi.org/10.1007/ BF02642048. [6] Nagumo M, Takai K,, The predominant role of strain-induced vacancies in hydrogen embrittlement of steels, overview, Acta Mater. 165 (2019) 722–733, https://doi.org/10.1016/j.actamat.2018.12.013. [7] M.B. Djukic, V.S. Zeravcic, G. Bakic, A. Sedmak, B. Rajicic, Hydrogen damage of steels, a case study and hydrogen embrittlement model, Eng. Fail. Anal. 58 (2015) 485–498, https://doi.org/10.1016/j.engfailanal.2015.05.017. [8] Fukunaga A, Effect of high-pressure hydrogen environment in elastic and plastic deformation regions on slow strain rate tensile tests for iron based superalloy A286. Int. J. Hydro. Energy, 2023;48;18116-18128. https://doi.org/10.1016/j.ijhydene.2023.01.266. [9] Fukunaga A. Hydrogen embrittlement behaviors during SSRT tests in gaseous hydrogen for cold-worked type 316 austentic stainless steel and iron-based superalloy A286 used in hydrogen reueling station. Engineering Failure Analysis, 2024;164;108158-108172. https://doi.org/10.1016/j.engfailanal.2024.108158. [10] Fukunaga A, Differences between internal and external hydrogen effects on slow strain rate tensile test of iron-based superalloy A286. Int. J. Hydro. Energy, 2022;47:2723-2734. https://doi.org/10.1016/j.ijhydene.2021.10.178. [11] Fukunaga A, Slow strain rate tensile test properties of iron-based superalloy SUH660 in hydrogen gas. ISIJ Int. 2019;59:359-367. https://doi.org/10.2355/isijinternational.ISIJINT-2018-539.