High Temperature Deformation Behavior of 4340 Steel: Activation Energy Calculation and Modeling of Flow Response

The 4340 steel is extensively utilized in several industries including automotive and aerospace for manufacturing a large number of structural components. Due to the importance of thermo-mechanical processing in the production of steels, the dynamic recrystallization (DRX) characteristics of 4340 steel were investigated. Namely, hot compression tests on 4340 steel have been performed in a temperature range of 900–1200 °C and a strain rate range of 0. 01–1 s−1 and the strain of up to 0. 9. The resulting flow stress curves show the occurrence of dynamic recrystallization. The flow stress values decrease with the increase of deformation temperature and the decrease of strain rate. The microstructure of 4340 steel after deformation has been studied and it is suggested that the evolution of DRX grain structures can be accompanied by considerable migration of grain boundaries. The constitutive equations were developed to model the hot deformation behavior. Finally based on the classical stress-dislocation relations and the kinematics of the dynamic recrystallization; the flow stress constitutive equations for the dynamic recovery period and dynamic recrystallization period were derived for 4340 steel, respectively. The validity of the model was demonstrated by demonstrating the experimental data with the numerical results with reasonable agreement.