13th International Conference on Fracture June 16–21, 2013, Beijing, China -9- graphite and graphite/matrix interface zone. In the early stage of the fracture process in the hydrogen-charged specimen, the interspace generated by interfacial debonding between graphite and matrix is filled with hydrogen gas, which hinders the formation of ductile dimple by facilitating the cracking. Even in the subsequent fracture process, hydrogen is incessantly emitted from graphites. Such a local hydrogen gas atmosphere coupled with a stress-induced hydrogen diffusion inside the material attracts hydrogen to the crack tip. Accordingly, the delayed hydrogen supply causes the time-dependent degradation. To evaluate the hydrogen-induced degradation in DCI, the pivotal role of graphite as a local hydrogen supplier should be taken into consideration. Acknowledgements The authors gratefully acknowledge Mr. Kenshin Matsuno of ShinMaywa Industries, Ltd. and Mr. Kazuhisa Hatakeyama of National Institute of Advanced Industrial Science and Technology (AIST) for their support in the experimental work. This research has been supported in part by: (1) The International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), sponsored by the Japanese Ministry of Education, Culture, Sport, Science and Technology. (2) The NEDO, Fundamental Research Project on Advanced Hydrogen Science (2006 to 2012). References [1] R. Garber, I.M. Bernsteln, A.W. Thompson, Effect of hydrogen on ductile fracture of spheroidized steel. Scripta Metallurgica, 10 (1976) 341-345. [2] H. Cialone, R.J. Asaro, The role of hydrogen in the ductile fracture of plain carbon steels. Metallurgical and Materials Transactions A, 10 (1979) 367-375. [3] H. Cialone, R.J. Asaro, Hydrogen assisted fracture of spheroidized plain carbon steels. Metallurgical and Materials Transactions A, 12 (1981) 1373-1387. [4] S.P. Lynch, Environmentally assisted cracking: Overview of evidence for an adsorption- induced localised-slip process. Acta Metallurgica, 36 (1988) 2639-2661. [5] H. Nishiguchi, Y. Fukushima, S. Matsuoka S, Y. Murakami, Effects of hydrogen and pre-strain on tensile properties of carbon steel STPG 370 (0.19C-0.21Si-0.56Mn, mass%) for 1 MPa hydrogen gas pipelines. Transactions of the Japan Society of Mechanical Engineers A, 74 (2008) 1016-1025. [6] H. Nishiguchi, Y. Fukushima, S. Matsuoka, Y. Murakami, Effects of hydrogen on tensile properties of ferritic-pearlitic carbon steels. Transactions of the Japan Society of Mechanical Engineers A, 76 (2010) 1459-1468. [7] T. Matsuo, N. Homma, S. Matsuoka, Y. Murakami, Effect of hydrogen and prestrain on tensile properties of carbon steel SGP (0.078C-0.012Si-0.35Mn, mass%) for 0.1MPa hydrogen pipelines. Transactions of the Japan Society of Mechanical Engineers A, 74 (2008) 1164-1173. [8] K. Yokogawa, S. Fukuyama, K. Kudo, Tensile fracture surfaces of carbon steels in high pressure hydrogen in room temperature. Journal of the Japan Institute of Metals, 44 (1980) 870-875. [9] K. Ogi, H. Hagi, A. Tahara, A. Sawamoto, H. Ikeda, Y. Hayashi, Behavior of hydrogen in ferritic spheroidal graphite cast iron with heavy section. Journal of Japan Foundry Engineering Society, 64 (1992) 186-191. [10] A. Sawamoto, Y. Hayashi, N. Ohtani, Journal of the Japan Institute of Metals, 43 (1979) 513-519.
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