Online ISSN : 1883-2954
Print ISSN : 0021-1575
ISSN-L : 0021-1575
Effect of Stress Ratio on Fatigue Crack Growth Rate of 100kgf/mm2 Grade High Yield Strength Steels in Sea Water
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1983 Volume 69 Issue 3 Pages 420-427


The effect of sea water on fatigue crack growth rate of three kinds of 100 kgf/mm2 grade high yield strength steels has been investigated using a parameter γ0.167Hz(≡(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 γ0.167Hz and ΔK 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 γ0.167Hz of two steels are about 2 and 4, which arise at the ΔK-values of 70 and 48 kgf/mm3/2 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 ΔK in 104 and 127 steels.
3) In 123 steel, the maximum value of γ0.167Hz is 5.5 to 7.5 regardless of R. The value of ΔK and Kmax to the maximum value of γ0.167Hz decreases and increases respectively with increase of R-value. The degree of the effect of sea water on da/dN is controlled by ΔK and Kmax. 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 Kscc is controlled by ΔK regardless of fracture mode.

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