Abstract
The corrosion fatigue (CF) crack growth rate of a 50 kgf/mm2 TMCP steel has been measured in ASTM synthetic sea water. The CF crack growth rate in synthetic sea water both at free corrosion and under a cathodic potential is smaller than that in air under a low ΔK level at R=0.1. The crack growth under a cathodic potential is proceeded by fatigue mechanism at a low ΔK level, while at a high ΔK level it is accelerated by hydrogen embrittlment. The CF crack growth characteristics under a cathodic potential can not be explained in terms of ΔKeff, since Ca and Mg deposits-induced wedge effect enlarges region II in load-strain hysteresis loops. A modified stress intensity factor range, ΔKcont, deduced from the load range shared by regions I and II is useful to explain the influence of cathodic potential on crack growth rate. When severe corrosive dissolution occurs at free corrosion potential, the crack growth characteristics can be uniquely explained in terms of effective crack growth rate considering the crack closure (da/dt)eff and ΔKcont.
