Fig. 1. Microstructures of: (a) as-received material; (b) deformed sample (T = 950 ℃, ε = 0.69, $\dot{\varepsilon }\text{=0}\text{.1 }{{\text{s}}^{\text{-1}}}$).

Fig. 2. Detailed experimental process.

Fig. 3. TEM images inside the sample aged at 900 ℃ for 6 h: (a) the dislocation gathered around δ phase; (b) the inhibition of δ phase on grain. (c) crystal structure of δ phase and HRTEM graph of the phase interface between matrix and δ phase.

Fig. 4. SEM maps and EBSD kernel average misorientation maps (KAM) of deformed sample after AT at 900 ℃ for: (a, e) 3 h; (b, f) 6 h; (c, g) 9 h; (d, h) 12 h. (i) The scale label.

Fig. 5. Evolution indexes of microstructure: (a) area fraction of δ phase; (b) average KAM value.

Fig. 6. KAM maps and local misorientation distributions of deformed sample after heat treatments of: (a, d) 900 ℃ ×3 h + 980 ℃ ×60 min; (b, e) 900 ℃ ×6 h + 980 ℃ ×60 min; (c, f) 900 ℃ ×12 h + 980 ℃ ×480 min. (g) The reduction amount of area fraction of δ phase.

Fig. 7. Microstructure of deformed sample after heat treatment of 900 °C × 3 h + 980 °C × 30 min: (a) OM and (b) SEM images ( Uδ represents the area fraction of δ phase).

Fig. 8. KAM maps of deformed samples after heat treatments of: (a) 900 °C × 6 h + 990 °C × 10 min; (b) 900 °C × 6 h + 990 °C × 15 min; (c) 900 °C × 6 h + 990 °C × 20 min. Evolution indexes of grain microstructure: (d) average recrystallized grain size; (e) heterogeneous factor of recrystallized grain; (f) average KAM value; (g) area fraction of δ phase.

Fig. 9. EBSD images of samples after different heat treatments: (a, b) orientation image microscopy (OIM) images; (c, d) KAM maps; (e, f) SEM maps. (g) Grain size distribution of samples.

Fig. 10. Schematic illustration of microstructural evolution during RT in the deformed grain with: (a, b) high deformation energy; (c, d) low deformation energy.

Fig. 11. OIM maps of deformed samples after heat treatments of: (a) 900 ℃×9 h + 990℃×20 min; (b) 900 ℃×9 h + 990 ℃×30 min; (c) 900 ℃×9 h + 990 ℃×40 min. (d) 900 ℃×12 h + 990 ℃×20 min; (e) 900 ℃ ×12 h + 990 ℃×40 min;(f) 900 ℃×12 h + 990 ℃×60 min; (g) 900 ℃×12 h + 1000 ℃×10 min; (h) 900 ℃×12 h + 1000 ℃×15 min; (i) 900 ℃×12 h + 1000 ℃×20 min. Evolution indexes of grain microstructures: (j) average KAM value; (k) average grain size and heterogeneous factor; (m) area fraction ofδ phase.

Fig. 12. Microhardness of deformed samples after different improved annealing treatments.