100kgf/mm^2 級高張力鋼の海水中における疲れき裂伝播速度への応力比の影響

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The effect of sea water on fatigue crack growth rate of three kinds of 100 kgf/mm^2 grade high yield strength steels has been investigated using a parameter γ_<0.167Hz>(≡(da/dN)_<cor>/(da/dN)_<air>), where (da/dN)_<cor> is a fatigue crack growth rate in sea water at the frequency of 0.167 Hz, and (da/dN)_<air> is fatigue crack growth rate in air. Stress ratios of 0.10, 0.50, 0.70, and 0.90 have been used. The results are as follows ; 1) In 104 steel, the relationship between the value of γ_<0.167Hz> and ⊿K are almost the same at the R-values of 0.10, 0.50, and 0.70. The same trend is also observed in 127 steel. The maximum values of γ_<0.167Hz> of two steels are about 2 and 4, which arise at the ⊿K-values of 70 and 48 kgf/mm^<3・2> respectively. regardless of R within 0.10 to 0.70. The fracture surface shows a transgranular fracture mode with corrosion pits. 2) The degree of the effect of sea water on da/dN, therefore, are controlled by ⊿K in 104 and 127 steels. 3) In 123 steel, the maximum value of γ_<0.167Hz> is 5.5 to 7.5 regardless of R. The value of ⊿K and K_<max> to the maximum value of γ_<0.167Hz> decreases and increases respectively with increase of R-value. The degree of the effect of sea water on da/dN is controlled by ⊿K and K_<max>. The fracture surface shows intergranular fracture mode due to hidrogen. 4) A lot of secondary cracks (branching) exists in 123 steel, which appear when the plastic deformation size at the crack tip is larger than the prior austenitic grain size. Branching of cracks gives no influences on the fatigue crack growth rates. 5) Dynamic K_<see> is controlled by ⊿K regardless of fracture mode.
1983-03-01

100kgf/mm^2 級高張力鋼の海水中における疲れき裂伝播速度への応力比の影響

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