Microstructure evolution at the onset of discontinuous dynamic recrystallization: A physics-based model of subgrain critical size

• Evolution of subgrains to recrystallization nuclei is possible at very low strains.
• Dynamic recrystallization nuclei increases on a sigmoidal curve with strain.
• Nucleation rate increases up to a maximum and decreases to zero at peak strain.
• Growth of recrystallized nuclei diminishes to zero at or over the peak.
• Site saturation is the mechanism of dynamic recrystallization up to the peak.

A physical model based on the evolution of subgrains size is proposed to describe the nucleation and growth processes during discontinuous dynamic recrystallization. The evolution of subgrains to viable recrystallization nuclei was found possible at very low strains. Afterwards, the number of stable nuclei considerably increased on a sigmoidal trend with strain and reached a saturated state at about 0.6 times the peak strain. The dependence of nucleation rate on strain was modeled using an Avrami-type equation and the driving force for the growth of recrystallized nuclei was similarly modeled in terms of strain. It is also shown that “site saturation” is the governing mechanism for the initiation of the discontinues dynamic recrystallization at the grain boundaries. The flow stress of the material was calculated using the law of mixture of recrystallized and unrecrystallized regions with fractional softening as the stress-partitioning factor. Satisfactory agreement between predicted and experimental results was obtained, thereby confirming the validity of the proposed model.