Abstract
Fracture toughness, aqueous stress corrosion and environmental fatigue crack propagation tests have been carried out on specimens cut from a thick section forged bar of IMI 550. Fracture toughness varied from 50–70 MN/m3/2, while the KIscc in salt water was much lower, at 25–27 MN/m3/2. KIscc in distilled water was somewhat higher, above 35 MN/m3/2. Fatigue crack propagation rates in salt water were 2–5 times higher than those in air in the absence of stress corrosion cracking. Use of the KIc, KIscc and fatigue crack propagation data in a sample calculation of inspectable cyclic life for a component containing a corner flaw indicated the importance of variations in crack propagation resistance due to processing and changing the environment.
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