Corrosion behavior in simulated PWR primary water and microstructural changes of stainless steel welds after thermal aging and ion-irradiation

Abstract

Austenitic stainless steel weld 316L and 308L specimens embrittled by temperature-accelerated thermal aging at 400 ºC for 10,000 h were irradiated with 6.4 MeV iron ions at 300 ºC to 5 dpa and exposed to simulated pressurized water reactor (PWR) primary water at 320 ºC for 1,020 h to study synergetic effects of irradiation and thermal aging on corrosion behavior of the weld metals. The microstructural changes in austenite phase, ferrite phase and austenite/ferrite boundary were examined by an atom probe tomography (APT) observation. Surface oxidation was examined by a scanning electron microscope (SEM) observation. Thermal aging and irradiation do not change the duplex oxide film formation mechanism on the weld metals. An austenite phase was mainly oxidized and oxidation of ferrite phases was limited. Thermal aging had no significant enhancement of oxidation. Irradiation enhanced the surface oxidation of austenitic phase, and synergist of thermal aging enhanced the oxidation of austenite/ferrite boundary. Radiation induced segregation of Cr and Si at austenite/ferrite boundary accelerated by thermal aging promoted the oxidation of austenite/ferrite boundary.