The dynamic recrystallization (DRX) behavior of 5CrNiMoV steel was investigated through hot compression at temperatures of 830–1230°C and strain rates of 0.001–10 s−1. From the experimental results, most true stress-strain curves showed the typical nature of DRX that a single peak was reached at low strains followed by a decrease of stress and a steady state finally at relatively high strains. The constitutive behavior of 5CrNiMoV steel was analyzed to deduce the operative deformation mechanisms, and the correlation between flow stress, temperature, and strain rate was expressed as a sine hyperbolic type constitutive equation. Based on the study of characteristic stresses and strains on the true stress-strain curves, a DRX kinetics model was constructed to characterize the influence of true strain, temperature, and strain rate on DRX evolution, which revealed that higher temperatures and lower strain rates had a favorable influence on improving the DRX volume fraction at the same true strain. Microstructure observations indicated that DRX was the main mechanism and austenite grains could be greatly refined by reducing the temperature of hot deformation or increasing the strain rate when complete recrystallization occurred. Furthermore, a DRX grain size model of 5CrNiMoV was obtained to predict the average DRX grain size during hot forming.
Deformation behaviour of 5CrNiMoV steel was investigated at temperature 830-1230 °C and strain rate 0.001-10 s −1 . The flow curves were analyzed to illuminate the deformation characteristics. Comprehensive austenite microstructural investigation was carried out using optical microscope for deformed samples. It was found that discontinuous dynamic recrystallization mechanism played a leading part in the nucleation of dynamic recrystallization (DRX) nuclei and growth of DRX grains, and that the austenite grain size increased with deformation temperature, while a larger strain rate was conducive to grain refinement for the quickly generated strain storage-energy favorable for higher DRX nucleation rate. The parent austenite texture evolution and typical martensitic transformation texture for some deformed samples were characterized using electron backscattering diffraction technique and the software of the reconstruction of parent austenite. It was found that increasing temperature contributed to the increase of its maximum of random distribution (MRD) and the strength of rotated Cube texture component, which was probably for the behavior DRX and growth of DRX grains during the hot deformation. The rotated Cube was weakened with the strain rate rising, while the main texture component did not change significantly, which was due to the increase in number of active slip systems and grain fragmentation. Besides, the martensitic transformation texture was related to the parent texture for the variant selection.
Microstructure evolution during the hot forming shows a significant impact on material’s mechanical properties. To explore the deformation characteristics of 5CrNiMoV steel, numerical simulation and microscopic phase-field simulation of the multi-direction forgings were carried out. The strain distribution at each pass was investigated and the evolution of temperature, effective strain, effective strain rate, and grain size was acquired. The hot forging trials were carried out and three typical regions of forgings were taken to study the microstructure evolution. Detailed microstructure characterizations showed that the constructed parent austenite grain size of the forging in typical regions was slightly larger than the simulation results due to the grain coarsening during the air cooling. There were large amounts of high angle grain boundaries (HAGBs) for the occurrence of complete dynamic recrystallization and many bulging grain boundaries showed that discontinuous dynamic recrystallization (DDRX) could be the governing mechanism of nucleation and growth of dynamic recrystallization (DRX). Besides, the hot deformation texture changed significantly during the non-isothermal forging and the texture component differed remarkably at different regions of the forging. The main hot deformation texture components were Cube {001}<100> and Goss{011}<100>.
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