Influence of neutron irradiation on hardening and embrittlement phenomena in reactor pressure vessel cladding material

SA508 cl.3 reactor pressure vessel steel plates were overlay cladded with type ER309L welding consumables by submerged arc welding. The microstructure of the clad was composed of fcc austenite, a few percent of bcc delta-ferrite and brittle a phase. The irradiation-induced hardening and its related mechanical property changes of the clad were investigated using tensile, small punch (SP) and electrical resistivity measurements. Neutron fluences of irradiated specimens at 290 C were ranged from similar to5 x 10(18) to similar to5 x 10(19) n/cm(2) (>1MeV). Not only yield stress but electrical resistivity were increased with irradiation and the delta-ferrite showed an approximately 1.5 times higher hardening than the austenite matrix. The general hardening may come from the irradiation-produced fine size defect clusters in the austenite matrix. The SP ductile/brittle transition temperature (SP-DBTT) moved to higher temperature with irradiation, and the SP-DBTT was substantially influenced by the amount of brittle a phase.