Environment Enhanced Fatigue Crack Growth in High-Strength Steels
LEHIGH UNIV BETHLEHEM PA BETHLEHEM
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The current state of understanding of the phenomenology and mechanisms for corrosion fatigue of high-strength steels is reviewed. Particular attention is directed towards corrosion fatigue in hydrogen and in waterwater vapor environments. Since a comprehensive review of these topics was given during the 1971 International Conference on Corrosion Fatigue, this review will be restricted to a summary of the salient points and to work reported since 1971. Available experimental data indicate that fatigue crack growth in high-strength steels is influenced by loading variables, such as frequency, stress ratio and waveform in regions above and below KIscc. The influences of these variables are directly attributed to interactions with the external chemical environment. Corrosion fatigue behavior above KIscc may be correlated with stress corrosion cracking data. Below KIscc such correlation is not possible because of the synergistic interactions between environment and fatigue crack growth. Possible synergistic interactions and their relation to chemical reaction kinetics are indicated. Pertinent information on oxygen-metal and water-metal reactions is summarized. On the basis of the reviews, combined chemical and mechanical investigations that are needed for extending the resent understanding of corrosion fatigue are considered. Initial results from a coordinated program of study for determining the water-metal reaction kinetics and the kinetics of crack growth on a single high-strength steel are discussed.