Dynamic recrystallization behavior and microstructure evolution of high-strength low-alloy steel during hot deformation

Abstract

The dynamic recrystallization (DRX) behavior and microstructure evolution of the high-strength low-alloy (HSLA) steel were studied by isothermal compression experiments at temperatures ranging from 850 to 1150 °C and strain rates ranging from 0.01 to 10 s−1 with a true strain of 0.8. The true stress-strain curves show that the flow stress increases with increasing strain rate and decreasing deformation temperature. The constitutive equation of the HSLA steel was established based on the peak stress, and the deformation activation energy was calculated to be 414.263 kJ/mol. Processing maps corresponding to different true strains were constructed based on the dynamic material model. High strain rates and low deformation temperatures are more likely to lead to flow instability. The microstructure deformed at low temperatures and high strain rates mainly consists of elongated initial grains. The DRX nucleation mechanism of the HSLA steel was explained. Many fine grains nucleate at the initial grain boundaries, forming a necklace structure. The serrated or bulged grain boundaries are the beginning of DRX. In addition, the DRX volume fraction model was established, and the DRX grain size was analyzed. High temperatures and low strain rates promote the nucleation and growth of the DRX.