31 Corrosion Fatigue Cracking in High-Strength Steels: Effects of Cycle Frequency, Waveform, and Potential

Corrosion-fatigue crack-growth rates (da/dN) in high-strength steels in aqueous NaCl have been measured for a range of cathodic potentials and cycle frequencies (with varying rise-time and fall-time) at a constant ΔK of 30 MPa√m. Observations include: (i) increasing da/dN with increasing rise-time/fall-time (with a sigmoidal dependency), (ii) increasing da/dN with increasing cathodic protection, but with only small increases beyond -1050 mV(SCE), (iii) a small shift in the sigmoidal curves along the rise-time/fall-time axes of da/dN-time plots for specimens with coated sides compared with bare specimens, and (iv) cleavage-like fractures. The data can best be explained in terms of the adsorption-induced dislocation-emission (AIDE) mechanism of hydrogen-assisted cracking, with da/dN determined by rates of crack-tip surface-reactions and hydrogen-transport to nano-voids ahead of cracks.