The kinetics of dynamic recrystallization and construction of constitutive modeling of RAFM steel in the hot deformation process

The dynamic recrystallization (DRX) behavior of austenite in reduced activation ferritic/martensitic steel was investigated by isothermal compression tests and constitutive modelling. The flow stress decreases with deformation temperature increasing and strain rate decreasing. The constitutive equations were constructed based on the analysis by Arrhenius equations. Based on the dynamic material model, the hot processing map was constructed. In the stability region, the power dissipation efficiency (eta) increases with increasing strain, and the softening is dominated by DRX when eta grows to a specific value. However, eta decreases as strain increases further after the complete evolution of DRX, indicating coarsening of DRXed grains. As the strain increases, the processing stability region shifts to the low temperature and high strain rate region. A novel recrystallization kinetics model was developed by considering the characteristics of the recrystallization velocity with strain increasing. It can reflect the slow-rapid-slow growth trend of recrystallization volume fraction (X-DRX). The relationship between X-DRX and (D) over bar (average grain size of austenite) was constructed, which indicates that (D) over bar decreases with strain increasing after the onset of DRX. When X-DRX is greater than 50%, the decrease rate of (D) over bar slows down until the steady-state is reached. Although strain increase further, the grain size remains constant. This suggests that the expected (D) over bar can be obtained by controlling X-DRX during hot deformation. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study investigates the DRX behavior of austenite in reduced activation ferritic/martensitic steel through isothermal compression tests and constitutive modelling. Flow stress and softening behavior are found to be influenced by deformation temperature and strain rate. A new recrystallization kinetics model is developed to understand the relationship between recrystallization volume fraction and grain size during hot deformation, providing insights for controlling grain size in industrial processes.