Effects of heat treatments on the stress corrosion cracking of alloy 600 in high temperature waters

Abstract

The effects of low temperature ageing treatments on the susceptibility of alloy 600 to stress corrosion cracking in simulated primary side nuclear reactor water have been studied by a variety of techniques. Chromium depletion at grain boundaries was assessed by Electrochemical Potentiokinetic Reactivation (EPR) and polythionic acid tests while cracking was investigated using U bend, constant strain tensile and slow strain rate tests. The susceptibility to cracking was increased by annealing at 925°C after a small amount of cold work and further enhanced by ageing for 60 h at 450°C. The activation energy for cracking is in the region of 190 kJ/mol, which indicates that marked cracking is only likely at relatively high temperatures in water.