Dynamic Recrystallization and Metadynamic Recrystallization Behavior and Its Dynamic Model of 18CrNiMo7-6 Gear Steel

The dynamic recrystallization (DRX) and metadynamic recrystallization (MDRX) behaviors of 18CrNiMo7-6 gear steel were studied by single-pass and double-pass thermal compression tests under different deformation conditions (deformation temperature at 1 000–1 150 ℃, strain rate of 0.01–5 s⁻¹, pass interval time of 5–30 s). The dynamic models of DRX and MDRX were established to predict DRX and MDRX volume fractions of the steel under different thermal deformation conditions, and the prediction accuracy was analyzed. The results show that during thermal deformation, the DRX volume fraction increased with the increase of deformation temperature and the decrease of strain rate, and the MDRX volume fraction increased with the increase of deformation temperature, strain rate and pass interval time. The prediction accuracy of DRX and MDRX dynamic models was high. The determination coefficient of the DRX volume fraction curves predicated by the former and the results obtained by the flow curves was greater than 0.9; the average relative error between the MDRX volume fraction by the latter and the results obtained by the 2% stress compensation method was 6.619%. The activation energies of DRX and MDRX obtained by Zener-Hollomon parametric equation for this steel were 47.381, 291.802 kJ · mol⁻¹ · K⁻¹, respectively.