Clarifying the effect of irradiation and thermal treatment on the austenitic microstructure and austenitic hardening in austenitic stainless steel weld metal

The weld cladding on the inner surface of nuclear pressure vessels due to irradiation damage and thermal effect presents to a safety issue. Unfortunately, the effect of irradiation and long-term thermal treatment on the austenitic microstructure and austenitic hardening in austenitic stainless steel weld metals (ASSWMs) remains poorly understood. In this study, the effects of irradiation and thermal treatment on the austenitic microstructures and austenitic hardening of 308L ASSWMs were investigated using nanoindentation, atom probe tomography and transmission electron microscopy. The results suggested that irradiation resulted in the formation of Ni/Si-rich clusters, voids, and Frank loops in austenite, thereby inducing austenitic hardening. Subsequently, thermal treatment decreased the size and the number of Frank loops in irradiated austenite, which had a minor effect on austenitic hardening. However, thermal treatment promoted the growth of Ni/Si-rich clusters and void formation, which have a primary effect on austenitic hardening, thereby enhancing the hardening of irradiated austenite. Furthermore, thermal treatment has little effect on the microstructure and hardening of austenite. Then, irradiation promoted the formation of Ni/Si-rich clusters, voids, and Frank loops in thermally treated austenite, resulting in austenitic hardening. The interaction of irradiation and thermal treatment can promote the formation of voids. The austenitic hardening was mainly due to the contribution of Frank loops, voids, and Ni/Si-rich clusters, which acted as short-range barriers by pin-moving dislocations.