Fig. 1. Dilatometric data of the heat-treatment condition for the 3h specimen. The specimen was heated to 950 ℃ at a rate of 5 ℃/s, held at 950 ℃ for 27 min, cooled rapidly to 300 ℃ at 100 ℃/s held at 300 ℃ for 3 h, then air-cooled to room temperature.

Fig. 2. EBSD inverse pole figure (IPF) and phase maps for the (a, b) 30m, (c, d) 3h, and (e, f) 24h specimens. The measured volume fractions of RA (Vγ) are 19.0%, 13.2%, and 9.8% in the 30m, 3h, and 24h specimens, respectively.

Fig. 3. XRD analysis data of the 30m, 3h, and 24h specimens.

Fig. 4. SEM images and EBSD image quality (IQ) + phase maps for the (a-c) 30m, (d-f) 3h, and (g-i) 24h specimens. (b, e, h) High-magnification SEM images of areas marked in (a, d, g), presenting overall features of bainitic microstructure. (c, f, i) EBSD IQ + phase maps for the identical areas to (b, e, h) in order to clearly identify the RA and island-type martensite (M).

Fig. 5. Overall V50 ballistic impact test data, presenting that the V50 values for the 30m, 3h, and 24h specimens are 440.3, 394.1, and 388.0 m/s, respectively.

Fig. 6. Photographs and optical micrographs of the half-sectional area of the complete penetrated specimens for the (a, b) 30m, (c, d) 3h, and (e, f) 24h specimens.

Fig. 7. (a) Quasi-static and (b) dynamic compressive stress-strain curves obtained from the quasi-static compressive and SHPB tests, respectively.

Fig. 8. (a) Schematic diagram showing an interrupted dynamic compressive test using a stopper ring. Optical micrographs of the half-sectioned area of the dynamically-compressed specimens at sequential strains of 32.5%-42.5% for the (b-d) 30m, (e-g) 3h, and (h,i) 24h specimens. (j) Schematic diagram of the strains for the maximum stress, the ASB formation, the cracking, the complete fracture during the dynamic compressive tests.

Fig. 9. TEM bright-field (BF) images and selected area diffraction (SAD) patterns of the (a, b) interior area of ASBs and (c, d) exterior area near the ASBs collected from red-boxed areas of Figs. 8(c) and 6(b), respectively, for the 30m specimen.

Fig. 10. (a) Volume fraction of martensite (VM) transformed from the RA as a function of dynamic compressive strain. (b) Hardness plot as a function of dynamic compressive strain. (c) Calculated C content in RA (Cγ) and measured Vγ for the 30m, 3h, and 24h specimens.

Fig. 11. EBSD GND density (ρGND) distribution maps of the (a) 30m, (b) 3h, and (c) 24h specimens.