Study on Recrystallization Initiation Model and Microstructure Evolution Mechanism of 18CrNimo7-6 Steel During Hot Deformation

Abstract

The hot deformation behavior of 18CrNiMo7-6 steel at temperatures of 900 ~ 1150 °C and strain rate of 0.01 ~ 5 s⁻¹ was studied by isothermal single-pass compression experiment. The critical recrystallization model was used to determine the relationship between the critical stress and the peak stress as $\sigma_{{\text{c}}} /\sigma_{{\text{p}}} = 0.89$. Meanwhile, the dynamic recrystallization mechanism of the samples at different deformation stages was analyzed by electron backscatter diffraction (EBSD) and metallographic microscope. The microstructure evolution shows the following: when the strain is 0.05, the work hardening is the main mechanism, and the lattice distortion near the grain boundary leads to the accumulation of dislocations, which provides the impetus for the recrystallization nucleation at the grain boundary; when the strain is 0.2, the dynamic recrystallization mechanism crystal has just started, and the small-sized recrystallized grains are formed at the grain boundary; in the meantime, dislocation rearrangement occurs in the coarse grain. When the strain is 0.5, the dynamic recrystallization consumes a large number of low-angle grain boundaries into high-angle grain boundaries by means of subgrain rotation and finally forms fine recrystallized grains in the coarse grains. This process will continue until the end of recrystallization, and the dislocations in the material matrix will tend to homogenize.