PSI - Issue 2_A

Junichiro Yamabe et al. / Procedia Structural Integrity 2 (2016) 525–532 J Yamabe et al/ Structural Integrity Procedia 00 (2016) 000–000

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by Eq. (12) and the peculiar dependence of FCG rate on hydrogen pressure, test frequency and test temperature could be unified by using a novel parameter representing the gradient of hydrogen concentration near crack tip. 4. Conclusions This paper presented the effects of hydrogen pressure, test frequency and test temperature on the fatigue crack growth (FCG) properties of low-carbon steel, JIS-SM490B. To estimate hydrogen-diffusion properties at crack tip, having severe plastic deformation, hydrogen diffusivity was also determined with cold-rolled JIS-SM490B. The hydrogen diffusivity was lower with an increase in the rolling ratio; however, became constant at rolling ratios higher than 20 %. The hydrogen-assisted FCG acceleration always accompanied a localization of plastic deformation near crack tip and it was inferred that a steep gradient of hydrogen concentration caused the slip localization at crack tip. The peculiar dependence of FCG rate on hydrogen pressure, test frequency and test temperature could be unified by using a novel parameter representing the gradient of hydrogen concentration near crack tip, in consideration of the ratio of the penetration depth of hydrogen per cycle to the ordinary plastic zone in air. This work was supported by the New Energy and Industrial Technology Development Organization (NEDO), Fundamental Research Project on Advanced Hydrogen Science (2006 to 2012) and Hydrogen Utilization Technology (2013 to 2018). The authors gratefully acknowledge the support of the International Institute for Carbon-Neutral Energy Research (I2CNER), established by the World Premier International (WPI) Research Center Initiative funded by the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), Japan. References Asano, S., Hara, K., Nakai Y., Ohtani, N., 1974. The trapping effect of dislocations on hydrogen diffusion in mild steel. 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