PSI - Issue 54

8

A.Fukunaga / Structural Integrity Procedia 00 (2023) 000 – 000

Akihiko Fukunaga et al. / Procedia Structural Integrity 54 (2024) 115–122

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4. Conclusions In this study, hydrogen embrittlement behavior of A286 was investigated through SSRT tests for specimens in high-pressure gaseous hydrogen. The following conclusions were drawn: 1. The RRA values of specimens in high-pressure gaseous hydrogen obtained from SSRT tests showed a strong strain rate dependence, and the fracture surfaces varied from dimple, quasi-cleavages, to intergranular fracture when the strain rate was decreasing. 2. The test environment was switched from gaseous hydrogen to air during the SSRT test to reveal the difference in hydrogen embrittlement behavior depending on the deformation degree. The RRA value decreased immediately in the initial elastic deformation region, recovered once beyond the yield point, and gradually decreased in the subsequent plastic deformation region. In addition, when stress cycles were applied in the initial elastic region, the RRA value decreased further and transgranular fracture with facets showing slip lines was observed, similar to the hydrogen charged specimens. 3. In the elastic deformation region, hydrogen diffuses uniformly due to the widening interstitial distance, while in the plastic deformation region, the hydrogen content at the crack tip increases due to the formation of defects and migration of dislocations. Therefore, for hydrogen compatibility of metallic materials under allowable stress, SSRT tests using hydrogen-charged specimens is appropriate, considering the hydrogen embrittlement behavior in the elastic region. Acknowledgements Part of this work was financially supported by ENEOS Co., part of this experimental was supported by Nippon Steel Technology Co. 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 2023 September 28] [2] NASA: Safety Standard for Hydrogen and Hydrogen Systems [Internet]. Available from https://ntrs.nasa.gov/api/citations/19970033338/downloads/19970033338.pdf [accessed 2023 September 28] [3] Tamura M, Shibata K: Evaluation of mechanical properties of metallic materials under 45 MPa high-pressure hydrogen gas. J. Jpn. Inst. Met., 2005;69:1039-1048. https://doi.org/10.2320/jinstmet.69.1039 [4] 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 [5] NAS STAINLESS STEEL STRIP MFG, CO., LTD. HP [Internet]. Available from http://www.nas-kotai.co.jp/leaflet/660.html [accessed 2023 September 28] [6] 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. [7] 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 [8] 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 [9] Kiuchi K, McLellan RB, The solubility and diffusivity of hydrogen in well-annealed and deformed iron. Acta Metall. 1983;31;961-984. https://doi.org/10.1016/0001-6160(83)90192-X. [10] Huang C. Nakajima A. Nishikata A. Tsuru T. Effect of mechanical deformation on permeation of hydrogen in iron. ISIJ Int. 2003;43:548-54. https://doi.org/10.2355/isijinternational.43.548 [11] Oriani RA, Josephic PH. Equilibrium aspects of hydrogen-induced cracking of steels. Acta Metall. 1974;22:1065 – 74. https://doi.org/10.1016/0001-6160(74)90061-3 [12] Birnbaum H. K. Sofronis P. Mater. Hydrogen-enhanced localized plasticity — a mechanism for hydrogen-related fracture. Sci, Eng. 1994;A176:191-202. https://doi.org/10.1016/0921-5093(94)90975-X [13] Nagumo M, Takai K, The predominant role of strain-induced vacancies in hydrogen embrittlement of steels: Overview. Acta materialia, 2019;165:722-733. https://doi.org/10.1016/j.actamat.2018.12.013