Hydrogen Embrittlement Mechanism in Fatigue of Austenitic Stainless Steels
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THE objective of this article is to elucidate the basic principles of hydrogen embrittlement (HE) in the fatigue of austenitic stainless steels. These steels are considered to be the most important candidate materials for infrastructure, from the standpoint of the safe future of the hydrogen society (or hydrogen economy), as well as for components of fuel cell vehicles (FCVs) and stationary fuel cell (SFC) systems. The materials used for the components of FCVs and SFCs and for the equipment for hydrogen stations, hydrogen pipelines, and transport systems are directly exposed to high-pressure hydrogen. Among these technologies, there has been a particularly difficult scientific problem termed ‘‘HE’’ in the presence of hydrogen. During the past 40 years, many articles have been published on HE. Although the term HE has been widely used to describe the phenomenon, no unifying theory has been established. The mechanism of HE is still a mystery. The decohesion model[1,2] is based on the theoretical calculation of the weakening of the lattice YUKITAKA MURAKAMI, Trustee, Kyushu University, is Director, Research Center for Hydrogen Industrial Use and Storage (HYDROGENIUS), National Institute of Advanced Industrial Science and Technology (AIST). Contact e-mail: ymura@mech. kyushu-u.ac.jp TOSHIHIKO KANEZAKI, Postdoctoral Researcher, is with the Research Center for Hydrogen Industrial Use and Storage (HYDROGENIUS), National Institute of Advanced Industrial Science and Technology (AIST). YOJI MINE, Assistant Professor, and SABURO MATSUOKA, Professor, The Research Center for Hydrogen Industrial Use and Storage (HYDROGENIUS), National Institute of Advanced Industrial Science and Technology (AIST), Fukuoka, 819-0395, Japan, are with the Department of Mechanical Engineering Science, Graduate School of Engineering, Kyushu University, Fukuoka, 819-0395, Japan. Manuscript submitted November 25, 2007. Article published online April 1, 2008 METALLURGICAL AND MATERIALS TRANSACTIONS A
strength by hydrogen, although no direct observation of lattice decohesion has been made. The hydrogen-enhanced localized plasticity (HELP) model is based on the in-situ observation by transmission electron microscopy (TEM)[3–5] of the dislocation movement enhanced by hydrogen. However, no direct observation of the fracture phenomenon caused by the HELP model has been made. Most research on HE over the past 40 years[1–31] has paid insufficient attention to two points that are crucially important in the elucidation of the true mechanism. One is that, in most studies, the hydrogen content of specimens was not identified. Only about ten references (for example, References 6, 7, 15, and 20) of the more than several hundred articles recently surveyed by the authors include data on the measurement of hydrogen content. The other point is that studies that have revealed the influence of hydrogen on fatigue crack growth behavior, based on microscopic observations, are very rare; most studies have examined the influence of hydrogen on tensile properties.[1–20] The p
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