Fatigue crack propagation was studied in HY-130 steel base plate, as-deposited shielded metal-arc weld metal, and gas metal-arc weld metal using compact specimens. The effects of seawater, cathodic protection, frequency and hold time were investigated. The results indicated that saltwater increased crack-growth rates in HY-130 base plate at stress intensity factors below 60 ksi $in$. No significant effects of cyclic load-wave pattern or of frequency (0.10 to 10 cycles per min.) were evident. Cathodic potentials from zinc (−1.05 V) and magnesium couples (−1.40 V) increased fatigue crack-growth rates in seawater. Fatigue crack growth in the weld metals showed different characteristics than in wrought materials in that higher stress intensities were required to initiate crack growth, and growth rates increased over a narrow range of stress intensity. Results of the environmental effects of weld metals indicated that, even under the most severe conditions of cathodic potential in seawater, fatigue crack-growth rates in weld metal were lower than those observed with base plate in air.

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