High-Temperature Deformation Characteristics and Constitutive Model of an Ultrahigh Strength Steel

The high-temperature deformation characteristics of an ultrahigh strength steel is studied by hot compression tests under the deformation temperatures of 920-1160 degrees C and strain rates of 0.01-10 s(-1). By employing the metalloscope and transmission electron microscope, the influences of deformation parameters (deformation temperature and strain rate) upon microstructure evolution are analyzed in detail. Results show that the hot deformation activation energy of the studied steel is estimated as 332.3 kJ/mol. The microstructure presents the typical dynamic recrystallization (DRX) features, and the DRX behaviors are mainly dominated by the discontinuous DRX mechanism under different deformation parameters. Under the low strain rate or the high deformation temperature, the continuous DRX behavior caused by the rotation of subgrains takes place. For forecasting the deformation stress of the studied steel, a physically-based constitutive model is constructed by combining dislocation density theory and DRX kinetics. The reproduced deformation stresses well close to the measured data indicates that the developed physically-based constitutive model enjoys a preferred prediction ability to forecast the high-temperature deformation behaviors for the studied steel.