Surface Fatigue Crack Growth Behavior of Low and High Carbon Steel Wires in Sea Water

概要

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The investigation of surface fatigue crack growth behavior in sea water was made for low carbon steel wire SWRM 22K, and also high carbon steel wires SWRH 32 and SWRH 42A in comparison with the previous test results of low carbon steel wire SWRM 10 at 0.33, 0.25, 0.17, 0.09 and 0.05Hz by the use of the measured crack growth rates and the examined fractured surface of specimens. The rates of crack growth for tested steels in air were nearly equal to each other in relatively low ΔK regime. At 0.33Hz, the rate of crack growth in sea water increased with increase of tensile strength (σB) of tested steels in order of SWRM 10, SWRM 22K, SWRH 32, and SWRH 42A. The environmental acceleration factor, (dl/dN)CF/(dl/dN)air was 1.6 for SWRN 10, 1.7 for SWRM 22K, 2.0 for SWRH 32, and 2.2 for SWRH 42A respectively at ΔK of 5.5MN/m3/2. When testing at lower frequencies, there appeared a critical frequency, at or below which the rate of crack growth in sea water slowed and finally stopped for each steel. This critical frequency decreased with increase of σB of each tested steel in order of 0.25Hz for SWRM 10, 0.17Hz for SWRM 22K, 0.09Hz for SWRH 32, and 0.05Hz for SWRH 42A. These observations can be explained reasonably by crack tip blunting caused by dissolution in sea water.
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