Reconstitution techniques qualification and evaluation to study ageing phenomena of nuclear pressure vessel materials (RESQUE)

Study of Residual Stresses and Microstructural Changes in Charpy Test Specimens Reconstituted by Various Welding Techniques

Changes in the reactor pressure vessel (RPV) material properties due to neutron irradiation are monitored by means of surveillance specimen programs, which are used for realistic evaluation of the RPVs’ lifetime. Due to a limited number of surveillance specimens, the evaluation of reconstitution methods by various welding techniques after Charpy impact tests is of great importance. Time-of-flight (TOF) neutron diffraction method was used to determine the residual stress distributions and microstructural changes in Charpy specimens welded by arc stud, electron, and laser beam welding techniques. The lowest level of the residual stress in weld seams regions was found for the specimen welded by electron beam with optimal parameters as compared to other techniques. At the same time, this specimen exhibits the maximal level of microstrain, which points to high dislocation density in the material. The corresponding contributions to the yield strength due to various strengthening mechanisms were estimated.