Comprehensive Understanding of Ductility Loss Mechanisms in Various Steels with External and Internal Hydrogen
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INTRODUCTION
THE objective of the present study is to comprehensively interpret tensile-fracture mechanisms of various materials with external and internal hydrogen obtained via slow-strain-rate tensile (SSRT) tests in consideration of the hydrogen distribution in a specimen. ‘‘External
OSAMU TAKAKUWA and SABURO MATSUOKA are with the Research Center for Hydrogen Industrial Use and Storage (HYDROGENIUS), Kyushu University, 744 Moto-oka, Nishi-ku, Fukuoka, 8190395, Japan. Contact e-mail: [email protected] JUNICHIRO YAMABE is with the Research Center for Hydrogen Industrial Use and Storage (HYDROGENIUS), Kyushu University and with the International Center for Hydrogen Energy, Kyushu University, Fukuoka, Japan and also with the International Institute for Carbon Neutral Energy Research (I2CNER), Kyushu University, Fukuoka, Japan. HISAO MATSUNAGA is with the Research Center for Hydrogen Industrial Use and Storage (HYDROGENIUS), Kyushu University and with the International Institute for Carbon Neutral Energy Research (I2CNER), Kyushu University and also with the Department of Mechanical Engineering, Kyushu University, Fukuoka, Japan. YOSHIYUKI FURUYA is with the National Institute for Materials Science (NIMS), Tsukuba, Japan. Manuscript submitted June 23, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
hydrogen’’ was realized through non-charged specimens tested in a high-pressure hydrogen gas environment, while ‘‘internal hydrogen’’ was realized through hydrogen-charged specimens tested in air or inert gas (materials with external and internal hydrogen are referred to here by the use of ‘‘External-H’’ and ‘‘Internal-H,’’ respectively). Hydrogen charging was performed by exposing the non-charged specimens to high-pressure hydrogen gas, and the specimen obtained an equilibrium state of hydrogen concentration. The tensile properties and related fracture morphologies for External-H and Internal-H materials are not necessarily the same because of a significant difference in the hydrogen distribution in a specimen. Hydrogen has the potential to be an alternative energy carrier as it is clean, movable, and abundant. Fuel cell vehicles have just been commercialized in Japan, and construction of hydrogen fueling stations has also been promoted. To safely use such systems, it is necessary to properly control the strength degradation of the mechanical components used in the hydrogen environment and to perform strength design of the components in consideration of the detrimental effect of hydrogen[1,2] as well as develop innovative technique to
prevent these detrimental effects.[3,4] In selecting materials for the metallic components used in a high-pressure hydrogen gas environment, the relative reduction in area (RRA) has often been employed as a criterion for characterizing the hydrogen compatibility of materials.[5] The RRA is obtained by SSRT testing, which defines the ratio of a reduction in area (RA) in hydrogen gas, /H, to a RA in inert gas, /, i.e., RRA = /H//. Conventional gas pipelines and pressure ves
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