Fig. 1 Initial microstructure of the cold-rolled MMS a and illustrations of the two thermal schedules: the normal 1S-ART processing route b and the 2S-ART processing route c

Fig. 2 SEM images a, b and TEM bright-field micrographs c, d showing the microstructures of the 1S-ART a, c and 2S-ART c, d samples. (αG: granular-shaped ferrite, γG: granular-shaped retained austenite, αL: lath-shaped ferrite, γL: lath-shaped retained austenite)

Fig. 3 XRD patterns of samples annealed after the 1S-ART, Pre-ART and 2S-ART heat treatments

Fig. 4 EBSD image quality maps superimposed with phase distribution a, d, inverse pole figures (IPF) b, e, and kernel average misorientation (KAM) maps c, f of the Pre-ART sample a, b, c and the 2S-ART sample d, e, f. Green colors indicate retained austenite, and red colors indicate ferrite or martensite phases. Regarding the color of the phase map in a and d, the black lines indicate grain boundary misorientations greater than 15°, the gray lines indicate that between 2° and 15°

Fig. 5 Microstructures and Mn distribution detected by STEM of the Pre-ART a-d and 2S-ART e-h samples. a and e STEM micrographs showing the microstructures of the Pre-ART a and 2S-ART e samples. b, c are HAADF images with EDXS analysis showing the fine microstructure and Mn distribution map in the Pre-ART sample. f, g are that of the 2S-ART sample. d and h Mn concentration profiles along the green lines indicated in a and e, respectively. (αM: fresh martensite)

Fig. 6 Engineering stress-strain curves a and corresponding strain hardening rate curves b of the 1S-ART and 2S-ART samples