人工海水中における80キロ級高張力鋼溶接材の腐食疲労き裂発生挙動

概要

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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 0.17 Hz with a load ratio of -1. In synthetic sea water, corrosion fatigue cracks were always initiated at corrosion pits. At high stress levels (σ_a≧147 MPa), specimens were fractured at the softened area of heat affected zone, whereas final fracture at low stress levels (σ_a≦117 MPa) 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. 1 MPa・ml/2. The proportion of life spent in crack initiation was estimated at about 40% of the total life at σ_a≦117 MPa. Computer image processing technique was applied to corrosion pit analyses, and the 3-dimen-sional shapes of corrosion pits were obtained with a sufficient precision.
社団法人日本材料学会の論文
1987-02-15