The corrosion-fatigue crack growth properties of several types of HY-100 steel weldments were studied, primarily in an environment of seawater with cathodic protection by zinc anode. Shielded metal-arc (SMAW), gas metal-arc (GMAW) of both pulsed and spray are processes, and submerged-arc (SAW) weldments were included. The fatigue crack growth tests were conducted on compact specimens removed from the weldments to confine the path of the growing crack in all-weld metal. Constant-amplitude sinusoidal loads were applied at a frequency of 0.17 Hz with a load ratio (minimum-to-maximum) of 0.10. In general, fatigue crack growth in weldments was considerably slower than that in HY-100 plate under the same conditions of load and environment, where the applied potential accelerated crack growth rate. The results showed minor differences among the weldments. It was suggested that the residual stress state along the weld centerline, the inhomogeneity of the weld metal with respect to the crack path, defects, and minor porosity all act to retard crack growth, especially at lower stress intensity levels. These factors tend to mask the environmental effects. However, weldments prepared with high heat input showed greater resistance to fatigue crack propagation than weldments prepared at low heat input. The corrosion fatigue crack growth exhibited by the HY-100 weldments was similar to that of HY-80 and HY-130 weldments where weld process, environment, and loading conditions were similar.

Fatigue crack-growth rate tests of cast NAB and NAB weld metal specimens were conducted to determine the threshold for fatigue crack growth (ΔKth). The tests were conducted in accordance with ASTM E 647, Standard Test Method for Measurement of Fatigue Crack Growth Rates, in artificial seawater at a cyclic frequency of 2 Hz at R-ratios of +0.05, +0.40, and +0.60. The specimens were machined from both poor and good quality, as-cast NAB. Production NAB weldments were used for NAB weld metal specimens. The fatigue crack growth-rate curves for duplicate tests at each R-ratio of cast NAB in seawater were analyzed in the near-threshold regime to determine ΔKth. With increasing stress intensity ratio (R), ΔKth decreased. Compared to the values for cast NAB, higher ΔKth and higher crack closure levels in NAB weld metal tests were noted, due to the residual stress in the weldment. The same fatigue crack growth-rate curve sets were corrected for crack closure, and the near-threshold stress intensity decreased significantly when the closure loads were deducted. The closure-corrected, near-threshold stress intensity, based on ΔKeff, ranged from 4.4 to 6.1 MPa-√m for cast NAB versus 4.4 to 7.4 MPa-√m for NAB weld metal.

The effects of mechanical notches and saltwater corrosion on the flexural fatigue behavior of seven high-strength structural alloys were investigated over a broad life range of 1,000 to 100 million cycles. The seven alloys (three ferrous, three titanium, and one aluminum) had approximately the same ratio of yield strength to density. Results showed that notches were most damaging in the high-cycle life range, and that only titanium alloys exhibit a fatigue limit when subjected to corrosion fatigue. When compared on the basis of fatigue strength in air, the high-strength steels are superior over the entire life range. If, however, comparisons are made on the basis of ratio of fatigue strength to density, all seven alloys are approximately equal. The comparison of fatigue strength and ratio of fatigue strength to density over the broad life range for corrosion fatigue shows the titanium alloys to be superior at intermediate and long lives.