高張力鋼の海洋波浪応力下の腐食疲労き裂進展特性

抄録

The corrosion fatigue (CF) crack growth behavior of 3.5 % Ni-Cr-Mo-V steel for offshore structures, which was heat-treated to two strength levels (846 MPa, I 150 MPa), was investigated under simulated sea-wave loadings and sinusoidal waves of constant amplitude. The sea-wave loadings were obtained from field tests in a seawater environment. The tests were performed at a free corrosion and a cathodic potential of - I 050 mV vs. Ag/AgCl in synthetic seawater. The CF crack growth rates of the higher-strength-level steel were highly accelerated compared to those of the lower-strength steel under simulated sea-wave loadings as well as under constant amplitude sinusoidal waves. At the free corrosion potential, the CF crack growth rates under the simulated sea-wave loadings were lower than those of the constant amplitude waves. At the cathodic potential, the crack growth rates of both tests were almost the same. The difference in crack growth rate between the simulated sea-wave and the constant amplitude waves was explained in terms of their fractographic features. The growth rates of the simulated sea-wave were nearly equal to the rates of the field tests : the CF behavior in the seawater field environment could be analyzed from the data obtained through simulated sea-wave loading tests in the laboratory.