CORROSION FATIGUE CRACK-GROWTH OF STEELS IN AQUEOUS-SOLUTIONS .1. EXPERIMENTAL RESULTS AND MODELING THE EFFECTS OF FREQUENCY AND TEMPERATURE

The objective was to develop a model for the effects of stress intensity factor range DELTAK, cyclic loading frequency f, and temperature T on the enhancement of the crack growth rate (ECGR) for medium to high strength steels in aqueous environments. An experimental study was performed to determine the crack growth (CG) response of a HY- 1 30 steel in de-aerated 3.5% NaCl solution, as a function of DELTAK, f, and T. The results show that the crack growth rate (CGR) exhibited an exponential-like dependence on 1/f, with saturation occurring as the frequency decreased. Increases in temperature shifted the CG response curve to higher frequencies, with an apparent activation energy of almost-equal-to 30 kJ mol-1, while increases in DELTAK increased the saturation CGR and shifted the data to lower frequencies. A heuristic model was developed to link the chemical and mechanical processes occurring at the crack tip. ECGR was assumed to result from hydrogen embrittlement and was controlled by the rate of the electrochemical surface reactions. The CG response was related to the charge transferred during the transient reactions, which explained the frequency and temperature dependence in terms of reaction kinetics and time.