Ductility Loss in Ductile Cast Iron with Internal Hydrogen
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TRODUCTION
WITH a view to realize the so-called hydrogen society[1] in the near future, a great amount of efforts are being undertaken worldwide these days. For example, in the northern part of Kyushu Island in Japan, a number of field tests and substantiations are being actively conducted: (1) the supply of the by-product hydrogen gas from the steel-making plant using the hydrogen pipeline system, and (2) the utilization of the hydrogen gas in the fuel cells at houses, public and commercial facilities, and hydrogen stations for the fuel cell vehicles.[2] Similar efforts have been undertaken in the United States,[3] European countries,[4] South Korea,[5] etc. In the fuel cell system, a lot of metallic components, such as hydrogen pipes, valves, and tanks, are subjected to exposure to the high-pressure hydrogen environment. It is well known that hydrogen can easily diffuse into metals and thereby causes degradation of the mechanical properties, such as strength and ductility. Accordingly, to ensure the safer use of these systems, it is essential to understand the degradation process as well as to obtain reliable data about the degradation of various materials when they are exposed to hydrogen. HISAO MATSUNAGA, Associate Professor, is with the Department of Mechanical Engineering, Kyushu University, Fukuoka, Japan, also with the International Institute for Carbon-Neutral Energy Research (I2CNER), Kyushu University, Fukuoka, Japan, and also with the Research Center for Hydrogen Industrial Use and Storage (HYDROGENIUS), Kyushu University, Fukuoka, Japan, and also with the Institute of Materials Science and Technology, Fukuoka University, Fukuoka, Japan. Contact e-mail: [email protected] TERUKI USUDA, Graduate Student, is with the Graduate School of Engineering, Fukuoka University, Fukuoka, Japan. KEIJI YANASE, Associate Professor, and MASAHIRO ENDO, Professor, are with the Institute of Materials Science and Technology, Fukuoka University, and also with the Department of Mechanical Engineering, Fukuoka University, Fukuoka, Japan. Manuscript submitted April 19, 2013. Article published online November 14, 2013 METALLURGICAL AND MATERIALS TRANSACTIONS A
Ductile cast iron (DCI) is widely used for pipes in urban gas pipelines and is a prospective candidate material for hydrogen gas pipes. However, to the authors’ knowledge, there exist few studies about the effect of hydrogen on the strength properties of cast irons. On the other hand, with respect to the hydrogen-induced ductility loss in the ferritic or ferritic–pearlitic steels (e.g., carbon steels), a number of studies have examined the degradation process in the tensile properties.[6–13] These studies clarified that the ductility loss was mainly attributed to the hydrogeninduced acceleration of the fracture process (e.g., nucleation of voids or cracks and their subsequent growth). In addition to the ferritic–pearlitic matrix, DCI contains numerous spheroidal graphite materials, which can serve not only as stress-concentration sites but also as hydrogentrap s
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