Phenomenological model for the effect of strain rate on recrystallization and grain growth kinetics in the 617B alloy

Highlights: • Major DRX nucleation mechanism of alloy 617B is DDRX with some characterization of CDRX. • A segmented DRX model of strain rate and grain growth model are established for alloy 617B. • The accuracy of the model is validated by comparison between FEM results and actual microstructure. The recrystallization behavior of alloy 617B is investigated by isothermal hot compression tests in a temperature range of 1120–1210 °C with a strain rate scope of 0.01–20 s⁻¹. The effect of deformation parameters on DRX behavior is studied by optical microscopy and electron backscatter diffraction (EBSD) technique. The major dynamic recrystallization (DRX) mechanism of alloy 617B is confirmed to be discontinuous dynamic recrystallization (DDRX), accompanied by some characteristics of continuous dynamic recrystallization (CDRX). The DRX process is apparently influenced by strain rate and is accelerated in high strain rate condition, which is different from traditional awareness that high strain rate can inhibit DRX. As a result, a segmented model of strain rate is proposed to describe the DRX kinetics of alloy 617B. Furthermore, a grain growth model is also developed for the simulation of actual manufacture process. DEFORM-2D software is adopted for hot extrusion simulation and FORTRAN language is used for secondary development to invoke the developed model effectively. The simulated microstructure agrees well with the actual manufactured pipe of alloy 617B, demonstrating that the models and simulation method proposed in present study can be used for microstructure prediction and optimization for alloy 617B during hot deformation.