Effect of strain rate on the microstructural development through continuous dynamic recrystallization in a microalloyed steel

Continuous dynamic recrystallization (CDRX) is one of the possible mechanisms for the grain refinement in metals and alloys. In the present research, intercritical warm torsion testing under different strain rates was conducted on a low carbon microalloyed steel. The effect of deformation strain rate on the microstructural refinement during CDRX was investigated. Microstructural characteristics and deformation behavior of investigated steel were discussed by analyzing of warm flow curves, optical microscope and electron back-scattering diffraction (EBSD). The results show that the peak and steady-state stresses are influenced by increasing of strain rate. The effect of CDRX on grain refinement increases with increasing strain rate, so that the volume fraction of CDRXed grains increases and grain sizes decrease. It is also observed that at high strain rate subgrain sizes decrease significantly. In contrast, at lower strain rate the CDRXed grains become larger. It is realized that deformation under high strain rate allows little time for CDRX to occur. In addition, under high strain rate deformation the time for grain growth is diminished and the coalescence of CDRXed grains is inhibited.