Fig. 1. The schematic of the specimen after compression.

Fig. 2. Experimental and modified stress-strain curves at different temperatures: (a)700 °C, (b) 800 °C, (c) 900 °C, (d) 1000 °C.

Fig. 3. Relationship between the standard deviation of slopes of ln[sinh(ασ)]-lnε˙ curve at different temperatures and α values: (a) entire domain, (b) local domain.

Fig. 4. Relationship between fitted parameters and strain: (a) α, (b) n, (c) Q, (d) lnA. In literature [25], Samantaray et al. carried out the optimization of the selected α from 1000 numbers that were close to the suggested value from the ferrite steels [26,27]. Zhang et al. [16] viewed the parameter n as the slope of the linear regression lines, and found the proper α, which can minimize the standard deviation of n.

Fig. 5. Relationship between ln[sinh(ασ)] and lnε˙ at the strain: (a) 0.1, (b) 0.3, (c) 0.5, (d) 0.7.

Fig. 6. Relationship between ln[sinh(ασ)] and 1/T at the strain: (a) 0.1, (b) 0.3, (c) 0.5, (d) 0.7.

Fig. 7. Modified experimental stress and fitting results by two approaches: (a) 0.001 s-1, (b) 0.01 s-1, (c) 0.1 s-1, (d) 1 s-1.

Fig. 8. Result comparison between this two approaches.

Fig. 9. Schematic representation of G, J, and Jmax. For constitutive equation of a strain rate sensitive material, the flow stress is usually expressed in the form of Backoken’s relation:

Fig. 10. Power dissipator map of ATI425 alloy at strains of: (a) 0.1, (b) 0.3, (c) 0.5, (d) 0.7.

Fig. 11. The Prasad instability regions of ATI425 alloy at strains of: (a) 0.1, (b) 0.3, (c) 0.5, (d) 0.7.

Fig. 12. Original microstructure of ATI425 alloy.

Fig. 13. Microstructures after compression at 700 °C at different strain rates: (a) 0.001 s-1, (b) 0.01 s-1, (c) 0.1 s-1, (d) 1 s-1.

Fig. 14. Microstructures after compression at 800 °C at different strain rates: (a) 0.001 s-1, (b) 0.01 s-1, (c) 0.1 s-1, (d) 1 s-1.

Fig. 15. Microstructures after compression at 900 °C at different strain rates: (a) 0.001 s-1, (b) 0.01 s-1, (c) 0.1 s-1, (d) 1 s-1. Power dissipation factor takes up the half percentage of all the input energy, and transforms for the drive supply of microstructure evolution, so the higher the power dissipation factor, the higher the microstructure evolution, which is proven from the experimental results.

Fig. 16. Schematic of deformation mechanism for ATI425 alloy.

Fig. 17. Evolutional curves of recrystallization volume fraction and power dissipation factor with strain rate.