Fig. 1 Schematic illustrations of the two thermal schedules: a conventional ART, and b PA-ART

Fig. 2 SEM micrographs a, b, c and TEM bright-field images d, e, f showing the microstructures of the ART0.5 h a, d, ART1h b, e, and ART6h c, f samples. (θ: cementite, γ: retained austenite, αF: ferrite)

Fig. 3 a X-ray diffraction patterns and b volume fraction of retained austenite of the steel treated by the conventional ART

Fig. 4 SEM micrographs a-c and TEM bright-field images d-f of the samples pre-annealed with different temperatures: a, d 680 °C, b, e 700 °C, and c, f 720 °C. (θ: cementite, αF: ferrite, αM: fresh martensite)

Fig. 5 SEM micrographs a-c, TEM bright-field images d-f and TEM dark-field images g-i showing the microstructures of the PA-ART680 (left images), PA-ART700 (middle images) and PA-ART720 (right images) samples. (θ: cementite, γ: retained austenite)

Fig. 6 X-ray diffraction patterns a and the volume fraction of retained austenite b of the steel subjected to PA-ART processing with different pre-annealing temperatures

Fig. 7 Tensile properties of the conventional ART samples with different annealing time: a engineering stress-strain curves, b changes in the YS, UTS, and TEL

Fig. 8 Tensile properties of the PA-ART treated samples with different pre-annealing temperatures: a engineering stress-strain curves, b changes in the YS, UTS and TEL

Fig. 9 TEM micrographs showing the microstructure evolution during the ART process at 700 °C with different annealing time: a 5 s, b 60 s, c 600 s, d 1800s. (θ: cementite, αF: ferrite, αM: fresh martensite)

Fig. 10 EBSD images of band contrast overlapped by phase distribution a, d, inverse pole figure (IPF) b, e and KAM maps c, f of the sample after pre-annealing at 700 °C a, b, c and PA-ART700 sample d, e, f. In the phase map, retained austenite is shown in green, and ferrite or martensite (αM) is red. The blue and black lines in a and d denote boundaries with misorientation of 2° < θ < 5° and θ > 15°, respectively

Fig. 11 TEM micrographs showing microstructures a, c and Mn line profiles b, d of the sample pre-annealed at 700 °C for 0.5 h a, b and the PA-ART700 sample c, d. (αF: ferrite, αM: fresh martensite, γ: retained austenite.)