High-Temperature Fatigue Crack Growth Study of P91 Steel Using Acoustic Emission

The fatigue crack growth (FCG) behavior of ferritic steel P91 was studied at several temperatures ranging from 300 K to 823 K with simultaneous monitoring of acoustic emission (AE) signals. Compared with FCG, the AE count rate curve shows a peak in the transition regime due to intergranular cracking, and the peak position changes with test temperature. The count rate at different values of Δ K decreases with temperature followed by an increase with a minimum at 623–673 K corresponding to the maximum occurrence of dynamic strain aging. Comparison of Paris parameters and the parameters obtained from AE count rate versus ∆ K plots showed that the count rate slope values are higher than the Paris slope values in the temperature ranges corresponding to the maximum occurrence of dynamic strain aging.