b'Nuclear Science User Facilities Technical ReportUnderstanding the Phase Transformation of Thermal Agedand Neutron Irradiated Duplex Stainless Steels Used in LWRsYong Yang University of Florida yongyang@ufl.edu T o understand the thermal- austenite phases upon thermal aging, aging and neutron-irradiationas the ferrite phase becomes hardened. effects on duplex stainlessTEM and APT characterizations show steels used in LWRs, in-situ testingthat neutron irradiation introduced a with wide-angle X-ray scatteringsimilar microstructural change in(WAXS) was used to quantify thethe ferrite phase, includingmechanical response of individualspinodal decomposition andphases under a tensile load. The X-rayG-phase precipitates. experiments were complementedIntroductionby microstructural characterizationsExtending the service lifetime of light-using transmission electronwater reactors (LWRs) beyond 60 years microscopy (TEM) and atom proberequires a good understanding of the tomography (APT). The aging effectsdegradation mechanisms of materials were quantified in terms of (1)and components in reactors. The macroscopic tensile property, (2)lifetime of reactor components made lattice-strain evolutions of both theof duplex stainless steels can be limited ferrite and austenite phases, and (3)by embrittlement from thermal aging, dislocation-density evolution duringneutron irradiation, or a synergistic plastic deformation. It was determinedeffect of both. Previous studies showed that thermal aging had a minimalthat the spinodal decomposition in the effect on the austenite phase; however,delta ferrite phase is a primary embrit-thermal aging dramatically increasedtlement mechanism of the duplex lattice strain and its yield strengthstructure stainless steels, while G-phase in the ferrite phase. The increase ofprecipitates were also identified [12]. strength saturated at or before 1000Most past studies focused on character-hours of thermal aging at 475C.izations of fine-scale precipitates and Pores that developed at the phasephase decomposition using TEM and boundary were only observed for theAPT [35]. The fundamental mecha-3000 hours aged specimen, with anism and kinetics of elemental segre-significantly decreased ductility. Thegations occurring in the ferrite has results also indicate that there is a loadnot been fully understood. The exact partition shift between ferrite and 46'