Fig. 1 Morphological characteristics of ausformed Co sample with 8% reduction by ECC technology under different magnifications: a the coexistence of acicular laths and blocky laths; b and c irregular morphologies in blocky laths; d slender and rectangular morphologies in the acicular laths; e slender laths, f rectangular laths within the white rectangles in d

Fig. 2 Morphological characteristics of ausformed Co sample with 40% reduction by ECC technology under different magnifications: a acicular laths in each grain in different flow directions; b high density of laths inside one prior austenite grain; c two flow directions (marked by blue arrows) for the slender laths; d different flow directions inside the different prior austenite grain; e, f nano-sized rectangular substructures in acicular laths

Fig. 3 EBSD maps for the ausformed Co samples. IPF maps for the 8% reduction sample a 1 and the 40% reduction sample b 1 ; phase maps in a 2 , b 2 showing a dual-phase microstructure, including γ phase (blue color) and ε phase (red color); grain boundary (GB) maps in a 3 , b 3 showing the GBs characteristics, including low grain boundaries (LABs, marked by gray lines), high grain boundaries (HAB, marked by black lines), annealing twinning boundaries (∑3 boundaries, marked by blue lines) in γ phase and special boundaries with 70.5°/<11$\bar{2}$0> misorientation (SB, marked by red lines) in ε phase

Fig. 4 GB misorientation angle statistics of γ phase and ε phase, in which the misorientation distributions in ε and γ phases for 8% and 40% reduction samples are shown in a, b

Fig. 5 Magnified high-resolution EBSD maps for ausformed Co with 40% reduction sample showing blocky and slender laths in a 1 , b 1 , c 1 , d 1 . Phase maps in a 2 , b 2 , c 2 , d 2 showing a dual-phase microstructure, including γ phase (blue color) and ε phase (red color). Grain boundary maps in a 3 , b 3 , c 3 , d 3 showing low grain boundaries (LABs, marked by gray lines), high grain boundaries (HAB, marked by black lines), annealing twinning boundaries (marked by blue lines) in γ phase and special boundaries with 70.5°/<11$\bar{2}$0> misorientation (SB, marked by red lines) in ε phase

Fig. 6 Microstructural characteristics of ausformed Co sample with 40% reduction under different annealing treatment: a 200 °C—1 h; b 360 °C—10 min; c 360 °C—1 h

Fig. 7 EBSD images (IPF, phase and GB maps) showing ausformed Co samples after annealing treatment: a 200 °C—1 h; b 360 °C—10 min; c 360 °C—1 h

Fig. 8 Schematic illustrations of microstructural evolution for ausformed Co sample. a Recrystallated grains for received state, b deformation behaviours in cell blocks during hot-rolling process, c acicular and blocky laths in ausformed Co sample