Microstructure evolution and constitutive analysis of nuclear grade AISI-316H austenitic stainless steel during thermal deformation

Abstract

Compression experiments were performed on AISI-316H austenitic stainless steel using Gleeble-3800 at temperatures ranging from 900°C and 1200°C and strain rates ranging from 0.01 and 10 s-1, up to the actual strain of 0.69. The tests aimed to examine the material's microstructure evolution and flow stress behavior. Based on OM and EBSD studies, it was found that thermal deformation mostly induces discontinuous dynamic recrystallization (DDRX). The proportion of recrystallization nucleation increases steadily with increasing deformation temperature, while the impact of strain rate on recrystallization is complex. At the same deformation temperature, the recrystallization volume fraction initially declines and rises as the strain rate rises. In low strain rate regime, the longer (deformation) time available for grain boundary migration, the higher recrystallization volume fraction. In high strain rate regime, the higher stored energy (and thus the increased boundary velocity) raises the probability of nucleation events, stimulating twin formation. As a result, the twin promotes a dynamic recrystallization (DRX) process. An abundance of Σ3 twins was notably observed in uniformly refined recrystallized grains at a true strain of 0.69, at a temperature of 1200°C, and a strain rate of 10 s-1. As a result, it was discovered that DRX occurs at higher strain rates and deformation temperatures. In addition, the flow stress curves were modified to account for adiabatic heating at strain rates exceeding 1 s-1. The findings demonstrated that adiabatic heating increased when strain level and strain rate increased and deformationm temperature decreased. The strain compensation Arrhenius model is developed following the given stress-strain curve while considering strain. The model exhibits high accuracy, with a correlation value of 0.986. According to a kinetic study, the average activation energy for hot deformation of the tested steel was 444.994 kJ/mol. These findings provide fundamental insights into the microstructure control technology and the outstanding mechanical properties of the austenitic stainless steel AISI-316H.