Hot deformation behavior, dynamic recrystallization mechanism and processing maps of Ti–V microalloyed high strength steel

Abstract

The hot deformation behavior, dynamic recrystallization mechanism and processing maps of Ti–V complex microalloyed high strength steel under temperatures ranging from 840 to 1040 °C and strain rates varying from 0.01 to 10 s−1 were studied by using thermal-mechanical simulation (Gleeble-3800), optical microscopy (OM), and electron backscatter diffraction (EBSD). The true stress–strain curves of the investigated steel were obtained under the different deformation conditions, the thermal deformation activation energy was calculated, the thermal constitutive equations based on the true stress–strain curves were established, and the 3D power dissipation diagrams, the 3D plastic instability diagrams, and the thermal processing maps under different true strains were drawn. The results show that the flow stress curves are of dynamic recrystallization type at 960–1040 °C and strain rate of 0.01 s−1 and at 1040 °C and strain rate of 0.1 s−1, and the peak stress decreases gradually with the increase of the deformation temperature and the decrease of the strain rate. The hot deformation activation energy of Ti–V microalloyed steel was calculated to be 349.681 kJ/mol. The average grain size of austenite first decreases and then increases with increasing the strain rate under the deformation temperatures of 1000 °C and 1040 °C, and has the smallest value of 15.0 μm and 16.1 μm, respectively, after deformation at the strain rate of 1 s−1. With the true strain increasing from 0.2 to 0.6, the area occupied by the destabilized region increases and the machinable region area decreases. It reveals that the most available hot processing parameter ranges of Ti–V complex microalloyed steel are at the temperature range of 1000∼1040 °C with the strain rate of 0.01–1 s−1.