Investigation of dynamic and static recrystallization behavior during thermomechanical processing in a API-X70 microalloyed steel

Recovery and recrystallization phenomena and effects of microalloying elements on these phenomena are of great importance in designing thermomechanical processes of microalloyed steels. Control of these phenomena can lead to manufacturing of products with suitable structures and desirable properties. The aim of this study was to investigate the microstructural evolution occurring during thermomechanical processing through hot compression testing. The niobium carbonitride approximate solution temperature was initially determined to guess the optimum reheating temperature. Then continuous and interrupted compression tests were utilized to physically model the dynamic and static recrystallization (SRX) behavior of the steel during thermomechanical processing. The parameters of the flow stress model and the activation energy of dynamic recrystallization (DRX) were calculated and the effects of deformation conditions on peak strain of DRX were evaluated. In addition, a kinetic study of the static softening of austenite indicated that the plateau occurred in recrystallization fraction-time curves below 1025 °C. This was considered in determining the Static Recrystallization Critical Temperature (SRCT) and construction of the Recrystallization Retardation-Temperature Time (RRTT) diagram for this steel.