Microstructural and mechanical responses of 316H and weld metal under Helium irradiation at 550 °C

Abstract

The irradiation microstructure and nanoindentation of 316H base metal and weld metal after He ions irradiation were systematically studied at 550 °C. The evolution of He bubbles and Frank loops were quantitatively characterized. Rate theory calculation demonstrated that the bias for interstitial atoms induced by high density of dislocation in 316H weld metal resulted in the low number density of Frank loops and larger sized He bubbles. Segregation of He bubbles in the γ/δ interface of 316H weld metal was also observed. The irradiation hardening in 316H weld metal was lower than that in the 316H base metal. Microstructure based calculation showed that the Frank loops dominated the irradiation hardening in 316H base metal. Whereas, in the 316H weld metal, Frank loops dominated the irradiation hardening under the low irradiation fluence, and He bubbles dominated the irradiation hardening under the high irradiation fluence. The irradiation hardening induced by Frank loops in 316H weld metal was obviously alleviated compared with that in 316H base metal. The insights into the microstructure evolution and irradiation hardening mechanism in irradiated 316H base metal and 316H weld metal can benefit the structural integrity assessment and optimization of austenitic steel in Gen-IV nuclear energy system.