Effect of phase transformation on the high-temperature tensile behaviors of SA508 Gr. 3 steel: A crystal plasticity finite element investigation

Abstract

The in-vessel retention (IVR) strategy, designed to maintain the structural integrity of reactor pressure vessels (RPVs) during severe nuclear accidents, will induce a huge temperature gradient across the RPV wall. This temperature gradient may lead to an austenitic phase transformation within RPV materials. Due to the dual-phase microstructure caused by this phase transformation, predicting high-temperature mechanical properties, e.g. tensile strength, becomes challenging, thereby impeding the implementation of IVR for RPVs. In this work, crystal plasticity finite element method (CPFEM) coupled with austenite transformation kinetics (ATK) was employed to model the tensile behaviors of SA508 Gr.3 steel, a typical RPV material, at three stages: 1) before phase transformation with ferrite phase (700–973 K), 2) during phase transformation with dual phases (973–1073 K) and 3) after phase transformation with austenite phase (1073–1273 K). The results demonstrate that stress concentrations primarily occur at a deflection of 140–150° between the normal direction of slip plane and loading direction in both ferrite and austenite grains, consistent with Schmid’s law. In materials undergoing phase transformation, the locations of stress-concentrated grains and their stress distributions are influenced by: 1) deflection angle, 2) grain type, and 3) misorientation angles between neighboring grains. The tensile behaviors during phase transformation with dual phases are predicted using this CPFEM-ATK method. These findings will provide comprehensive insights into the high-temperature tensile behaviors of RPV materials in IVR conditions.