Corrosion-Fatigue Crack Propagation Below K sub Iscc in Four High-Yield-Strength Steels

The useful life of steel structures that contain crack-like defects and that are subjected to cyclic loads in an aggressive environment is determined primarily by the time required for the defects to grow from subcritical dimensions to the critical size at which unstable fracture occurs. For these structures, subcritical crack growth is caused either by fatigue or by corrosion fatigue. Thus, as part of a long-range program to establish the necessary relations for predicting the corrosion-fatigue behavior of structural steels, the corrosion-fatigue crack-growth rates in four high-yield-strength steels (140 to 184 ksi) were investigated under sinusoidal loading at 6 cycles per minute in a 3 percent solution of sodium chloride. The results were analyzed by using linear-elastic fracture-mechanics concepts and were compared with fatigue-crack-propagation data obtained in a room-temperature air environment.