THE EFFECT OF TEMPERATURE AND CYCLIC FREQUENCY UPON FATIGUE-CRACK GROWTH-BEHAVIOR OF SEVERAL STEELS IN AN ELEVATED-TEMPERATURE AQUEOUS ENVIRONMENT

The fatigue crack propagation (FCP) behavior of several ASTM A302-B an d A508-2 steels was characterized in deaerated elevated temperature aq ueous environment. FCP behavior was determined over the range 121-degr ees-C to 343-degrees-C at a constant value of DELTAK, stress ratio, an d load rise time. A complex response of FCP rates as a function of tem perature was observed, and this is discussed in the light of similar r esults developed by others within the nuclear industry. Corrosion pote ntials (referenced to the standard hydrogen electrode) were measured f or each of the steels over the above temperature range and comparisons are made to the observed FCP behavior. Cyclic frequency effects were studied at two temperatures, 149-degrees-C and 243-degrees-C, and thes e are analyzed within the ''time domain'' format first suggested by Sh oji et al. The results, when expressed in the time domain format, clea rly show regions where environmentally assisted cracking (EAC) occurs, and regions where EAC does not occur. A ''threshold'' for EAC was not ed at 149-degrees-C, and the possibility of an EAC threshold was obser ved at 243-degrees-C.