CHARACTERIZATION OF IASCC CRACK TIP IN HIGHLY IRRADIATED STAINLESS STEELS

摘要

Microstructure and microchemistry were examined for IASCC crack tips of cold-worked 316 stainless steels irradiated to 38 dpa. The cracks initiated within -100 hours at 750MPa under constant load testing in hydrogenated and oxygenated high temperature water at 320°C. The crack tips were located at 10 - 20 nm from the apparent open position with a width of less than 5 nm. No oxides were detected at the crack wall and tip whereas a small amount of O was detected at the crack wall and ahead of the crack tip. The Cr concentration became greater than the Ni concentration at and behind the crack tips whereas it was almost half the Ni concentration at grain boundaries far from the crack tip due to radiation induced segregation. These features were common to both crack tips in both hydrogenated and oxygenated water, and greatly different from the appearance of arrested subcracks in SSRT tests, in which the crack tip consisted of thin oxide layer together with oxide particles in the open crack. The results indicated that IASCC cracks in highly irradiated stainless steels propagated at a high rate without significant oxidation.