Studies of Evaluation of Hydrogen Embrittlement Property of High-Strength Steels with Consideration of the Effect of Atm
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INTRODUCTION
INTENSIVE efforts have been invested toward our understanding of hydrogen embrittlement phenomena. Recent rising demand to increase the strength level of high-strength steels draws our attention still more to hydrogen embrittlement because, in general, the susceptibility of high-strength steels increases with their strength level.[1] Development of evaluation method for hydrogen embrittlement property is also important subject for safety and reliability of the use of highstrength steels. Since it is acknowledged that hydrogen embrittlement is induced by hydrogen diffusible at room temperature, parameters characterizing hydrogen embrittlement of steel such as stress ratio, time to failure, and KISCC have been evaluated as functions of factors representing hydrogen concentration such as baking time after hydrogen charging,[2] H2 gas partial pressure,[3,4] potential,[5] and current density of cathodic hydrogen charging.[6] EIJI AKIYAMA and YUUJI KIMURA, Principal Researchers, SONGJIE LI, Postdoctoral Researcher, and KANEAKI TSUZAKI, Managing Director, are with the National Institute for Materials Science, Tsukuba 305-0047, Japan. Contact e-mail: akiyama.eiji@ nims.go.jp MAOQIU WANG, Professor, formerly with the National Institute for Materials Science, is now with the Central Iron and Steel Research Institute, Beijing 100081, P.R. China. ZUOGUI ZHANG, Researcher, formerly with the National Institute for Materials Science, is now with China First Heavy Industries, Tianjin 300457, P.R. China. NOBUYOSHI UNO, Executive Managing Director, is with Nippon Steel & Sumikin Metal Products Co., Ltd., Tokyo 135-0042, Japan. Manuscript submitted January 6, 2012. Article published online September 29, 2012 1290—VOLUME 44A, MARCH 2013
There are various hypotheses proposed so far for the mechanism of hydrogen embrittlement.[7–11] Some of the representative models are, for example, pressure model,[12] adsorption model,[13] decohesion model,[14–17] dislocation interaction model,[18] hydrogen-enhanced localized plasticity model,[19] and hydrogen-enhanced strain-induced vacancy model.[20,21] Recent computational science applied to the studies of hydrogen embrittlement mechanism[16,17,22] and hydrogen diffusion, etc.[23–27] makes us expect further progress of our understanding. Although the mechanism of hydrogen embrittlement phenomena is still controversial, the common understanding is that mechanical loads, hydrogen uptake, and diffusion of mobile hydrogen[23–26] are involved. Because of the advancement of the quantitative analysis of hydrogen content in metals using thermal desorption analysis (TDA),[28] critical hydrogen concentration, HC, for initiation of hydrogen embrittlement fracture has been proposed as a parameter for hydrogen embrittlement property.[29,30] Suzuki proposed an evaluation method according to HC obtained by constant load tensile tests of circumferentially notched bar specimens.[29] Kushida et al.[31] and Enos and Scully[32] undertook a slow strain rate test (SSRT) for a hydrogenprecharged smooth bar spec
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