MECHANISTIC STUDIES OF STRESS CORROSION CRACKING OF NICKEL-BASE ALLOYS IN HIGH TEMPERATURE HIGH PRESSURE PWR ENVIRONMENT

摘要

This study investigates the effect of the strain path on the stress corrosion cracking (SCC) behaviour of two Ni base alloy materials. Specimens with different strain paths have been produced from two plant components (forged CDRM nozzle and rolled divider plate) and tested in high temperature (360 °C) high pressure primary water environment under constant load for 5000 hours or until failure. Results show the susceptibility to stress corrosion cracking of the forged material and the high resistance to initiation of the rolled material (even cold worked at 21 %). The SCC susceptibility results were consistent with the carbide distribution, intergranular for the rolled material and intragranular for the forged material. The effect of the strain path on SCC of the CDRM nozzle was significant as the maximum crack depth increased by a factor three between the axial (0°) and 45° orientation for the same applied stress. Nevertheless, the stress does not appear to be the pertinent parameter to compare the different orientations and the stress to yield strength ratio seems to be more relevant.