Fig. 1 Initial microstructure of the experimental material

Fig. 2 Experimental procedure for in situ observations

Fig. 3 Experimental procedure for hot compression experiments

Fig. 4 Microstructures at soaking temperature of a 1173 K, b 1273 K, c 1373 K, and d 1473 K and soaking time of 600 s

Fig. 5 Microstructures at the soaking time of a 0 s, b 180 s, c 300 s, d 480 s and the soaking temperature of 1473 K

Fig. 6 Average austenite grain size at different soaking processes

Fig. 7 Microstructures at the deformation temperature of 1273 K, strain rate of 0.01 s-1, austenitizing temperature and strain of a 1173 K and 1.2, b 1473 K and 1.2, c 1473 K and 0.1, d 1473 K and 0.35

Fig. 8 Average grain size at a different austenitizing temperatures; b different strains

Fig. 9 Microstructures at the austenitizing temperature of 1473 K, strain of 1.2 and deformation temperature and strain rate of a 1273 K and 0.1 s-1, b 1273 K and 10 s-1, c 1173 K and 0.01 s-1, d 1473 K and 0.01 s-1

Fig. 10 Average grain size at a different strain rates and b different deformation temperatures

Fig. 11 Comparison between the experimental and calculated values of average austenite grain size

Fig. 12 Comparison between the experimental and calculated values of average DRX grain size

Fig. 13 Relationship between the hardening rate and flow stress

Fig. 14 Typical stress-strain curves obtained by hot compression experiments

Fig. 15 Variation of critical strain and peak strain at different deformation conditions

Fig. 16 Comparison between the experimental and calculated strain: a $\mathrm{ln}{\varepsilon }_{\mathrm{c}}$, b $\mathrm{ln}{\varepsilon }_{\mathrm{p}}$

Fig. 17 DRX kinetic curves at a strain rate of 0.01 s-1, and b deformation temperature of 1273 K

Fig. 18 Comparison between the experimental and predicted average DRX grain size at the austenitizing temperature of 1473 K, strain rate of 0.01 s-1, deformation temperature of 1273 K, and strain of 0.1-1.2

Fig. 19 DRX map at the strain of 1.2

Fig. 20 Average DRX grain size at a strain of 1.2