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Home  >  Journal list  >  Journal of the Society of Materials Science, Japan  >  Vol.57  No.11 (2008)  >  pp.1077-1083

Journal of the Society of Materials Science, Japan
<<Previous article Vol.57  No.11 (2008)   pp.1077 - 1083 Next article>>

Influence of Irreversible Hydrogen on the Fatigue Crack Initiation Life in Cold Drawn High Strength Steel

Masanori NAKATANI1), Takashi KATO1), Masayuki SAKIHARA2) and Kohji MINOSHIMA2)
1) Osaka Univ.
2) Dept. of Mech. Eng., Graduate School of Eng., Osaka Univ.


This paper discusses the influence of irreversible hydrogen on the fatigue crack initiation life in cold drawn eutectoid steel. Fatigue tests were conducted for the sample having an artificial small notch fabricated by focused ion beam (FIB) system. Samples were cathodically hydrogen charged, and internal hydrogen states were changed as follows : (a) virgin sample and (b) the one that contained only irreversible hydrogen. In the notched sample, the fatigue strength was lower than that of smooth sample. The slope of the S-N curves became steeper and the influence of irreversible hydrogen was not observed. This is because the fatigue life was almost dominated by fatigue crack propagation life, resulted from a crack being easily initiated at a notch root owing to high stress concentration. The surface fatigue crack propagation rate, obtained by using fatigue life data for notched sample, was not affected by irreversible hydrogen. Using the obtained fatigue crack propagation rate and the rate in high vacuum corresponding to the propagation in a fish-eye region, the crack initiation life from an internal inclusion for smooth sample was estimated, and it shows that the irreversible hydrogen reduced the fatigue crack initiation life, compared with those of a virgin sample. This is a reason why the fatigue strength of a smooth sample was decreased by irreversible hydrogen.


Keyword:
Fatigue, Hydrogen embrittlement, Crack initiation, Crack propagation, Irreversible hydrogen, Small notch, Inclusion, Focused ion beam (FIB)

Received: March 12, 2008
Published online: November 20, 2008
Copyright (c) 2008 by The Society of Materials Science, Japan

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