STRESS CORROSION CRACKING BEHAVIOR OF DISSIMILAR METAL WELD A508/52M/316L IN HIGH TEMPERATURE WATER ENVIRONMENT

The stress corrosion cracking(SCC) behavior of advanced dissimilar metal weld A508/52M/316L in simulated primary water environments of pressurized water reactor(PWR) at 290℃was investigated by means of slow strain rate testing(SSRT).The tests were performed at various applied electrode potentials which correspond to the electrochemical conditions of the weld in various water environments,from low potentials with ideal water chemistry to high potentials with oxygen -contaminated water chemistry.The weld exhibits complicated microstructure and chemical composition distributions,especially,significant changes appear around the A508/52M interface and the 52M/316L interface.For tensile specimens in SSRT,sharp notches were machined at important and typical places,i.e.,at the two interfaces and in the bulk parts of the low alloy steel,Ni base weld metal and stainless steel of the weld.Results showed that the specimens always failed in bulk zone of the Ni base weld metal with ductile appearances when tested in the potential range from -780 mV to—300 mV(vs SHE).When electrode potential was raised into the range from -200 mV to +200 mV which corresponds to oxygen-contaminated water chemistry,the weld exhibits significant SCC. The area around the A508/52M interface is the weakest place,transgranular stress corrosion cracking (TGSCC) happened both along the interface and in A508 heat affected zone(HAZ),intergranular stress corrosion cracking(IGSCC) occurred in the Ni base weld metal close to the interface.The cracking mechanism and the engineering practical significance were discussed.