Tetsu-to-Hagane
Online ISSN : 1883-2954
Print ISSN : 0021-1575
ISSN-L : 0021-1575
Acceleration of Superlong Fatigue Failure by Hydrogen Trapped by Inclusions and Elimination of Conventional Fatigue Limit
Yukitaka MURAKAMIHiroshi KONISHIKen-ichi TAKAIYasuo MURAKAMI
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2000 Volume 86 Issue 11 Pages 777-783

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Abstract

The mechanism for fatigue failure in extremely high cycle fatigue in the regime of N>107 is discussed. A special attention was paid to a newly found particular fracture morphology in the vicinity of fracture origin (subsurface nonmetallic inclusions) of a heat treated Cr-Moalloy steels (Specimen QT). The particular morphology looks a dark area inside fish-eye mark by optical microscopic observation. Specimens with short fatigue life of the order of Nf=105 do not have such dark area, ODA (optically dark area), in fish-eye. To investigate the influence of the hydrogen trapped nonmetallic inclusions on fatigue properties, specimens quenched in a vacuum (Specimen VQ) were prepared. Specimens VQ contained 0.01 ppm hydrogen and on the other hand QT 0.7-0.9 ppm hydrogen. Specimens VQ had much smaller ODA than Specimens QT. Hydrogen was detected by Secondary Ion Mass Spectrometry at the inclusion at fracture origin of Specimens QT but not at the inclusion of VQ. Thus, it can be concluded that the formation of ODA is closely related to hydrogen trapped by nonmetallic inclusions. The predictions of fatigue limit by the √area parameter model are approximately 10% unconservative for fatigue limit defined for 107 cycles. However, if we consider the area of ODA into the fatigue limit estimation, the √area parameter model can successfully predict the fatigue limit very accurately.

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© The Iron and Steel Institute of Japan
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