Fig. 1. EBSD maps of the initial specimens: (a) band contrast (BC) map with twin boundaries (green lines); (b) inverse pole figure (IPF-Z); (c) phase map; (d) grain size distribution of austenite and ferrite.

Fig. 2. (a) Retained austenite and (b) annealing twin in the initial undeformed specimen.

Fig. 3. (a) Engineering stress and strain curve and (b) Multi-stage strain hardening rate with true stress curves of tensile specimens. The red arrows refer to the strain for microstructure analysis.

Fig. 4. Microstructures at different engineering strains: (a) 5%, (b) 10 %, and (c) 20 %.

Fig. 5. EBSD analysis results of the specimens at different engineering strains: (a) IPF-Z, (b) phase map and (c) grain boundary misorientation.

Fig. 6. TEM micrographs of microstructures in the tensile specimen at strain 10 %: (a) austenite twinning and (b) SAED pattern; (c) deformation-induced martensite and SAED patterns of (d) martensite and (e) its parent RA; (f, g) dislocation structure of δ-ferrite.

Fig. 7. TEM micrographs of microstructures in the tensile specimen at strain 20 %: (a) Martensite; (b) austenite twin; (c) dislocation structure; (d) retained austenite.

Fig. 8. The volume fraction and transformation rate of retained austenite at different engineering strains.

Fig. 9. PF and IPF maps of austenite phase at different engineering strains: (a) 0 %; (b) 20 %.

Fig. 10. ODF sections of austenite on φ2 = 0°, 35°, 45°and 65° at different engineering strains: (a) 0%, (b) 5%, (c) 10 %, and (d) 20 %.

Fig. 11. Schematic of typical texture components and fibres in austenite on φ2 = 0°, 45°and 65° ODF sections.

Fig. 12. Orientation density f(g) along the (a) α-fibre, (b) β-fibre, (c) γ-fibre and (d) τ-fibre of austenite at different strains.

Fig. 13. Schmid factor maps of austenitic slip system {111}<110> group at strains of (a) 0%, (b)10 %, (c) 20 %, and (d) their statistical distribution.

Fig. 14. Austenite grain size distribution at different strains.

Fig. 15. Statistical distribution of grain boundary misorientation angle between austenite grains and its adjacent grains at different strains: (a) 10 %; (b) 20 %; (c) 40 %.

Fig. 16. Schematic of deformation behavior between austenite and adjacent grains, showing the coordinated deformation in austenite grains.

Fig. 17. Misorientation distribution in (a) the local region and in the corresponding (b) ferrite and (c) austenite phases of the specimen at the strain of 10 %.

Fig. 18. Schematic of strain hardening mechanism. (a) The contribution of martensite transformation to the strain hardening rate (red bars represent the strain hardening rate of martensite, while gray bars represent the total strain hardening rate). (b) Illustration of the dominant mechanisms evolution in the strain hardening stages.