Corrosion fatigue crack initiation behavior has been investigated in a high-tensile strength steel HT80 weldment in synthetic sea water. The tests were conducted on plane bending specimens. Constant amplitude sinusoidal loads were applied at a frequency of 0.17Hz with a load ratio of -1.
In synthetic sea water, corrosion fatigue cracks were always initiated at corrosion pits. At high stress levels (σa≥147MPa), specimens were fractured at the softened area of heat affected zone, whereas final fracture at low stress levels (σa≤117MPa) occurred at the base metal. The fracture strength of HT80 weldments went down about 50% of that of HT80 plates in air or in synthetic sea water. The extreme value statistics were used to represent the growth of corrosion pits in the base metal, heat affected zone and weld metal at low stress levels. The pit growth rates in the base metal and heat affected zone were similar and were faster than that in the weld metal.
By assuming the corrosion pits as sharp cracks, ΔK values at the deepest points were calculated and the mean value of ΔK, ΔK*CF, was obtained at 1.1MPa·m1/2. The proportion of life spent in crack initiation was estimated at about 40% of the total life at σa≤117MPa.
Computer image processing technique was applied to corrosion pit analyses, and the 3-dimensional shapes of corrosion pits were obtained with a sufficient precision.
