Fig. 1 a Phase diagram of 0.25C-4Mn-0.06Nb-0.5Mo steel calculated by JMATPRO; b C and c Mn concentration in each phase versus temperature

Fig. 2 Microstructures of samples held at different ART temperatures: a 630 °C; b 650 °C; c 670 °C; d 690 °C. e Volume fraction of retained austenite and its C concentration in the ART samples as measured by XRD; f RA distribution of sample annealed at 670 °C. α: ferrite; γ: austenite; θ: cementite; α′: martensite

Fig. 3 a Dilatometry curve of different ART samples during flash treatment; b comparison of critical phase transformation temperatures in a

Fig. 4 Microstructures of different ART samples after flash treatment: a 630 °C ART + flash; b 650 °C ART + flash; c 670 °C ART + flash; d 690 °C ART + flash; and e the volume fraction of retained austenite and its C concentration in the ART + flash samples as measured by XRD

Fig. 5 TEM microstructure of a 670 °C ART and c 670 °C ART + flash samples, with b and d corresponding Mn concentration distribution across RA

Fig. 6 a and d Engineering stress-strain curves of different ART and ART + flash samples; b and e comparison of uniform elongation, yield strength and tensile strength; c and f comparison of work hardening rate

Fig. 7 Evolution of transformed austenite with true strain of samples processed by different processes

Fig. 8 a Inverse pole figure (IPF) figure of BCC phase; b Schmidt factor distribution diagram of {111} < 110 > slip system of BCC phase; c phase distribution; and d-l strain distribution under different stresses of 670 °C ART sample. Note: the yield point was determined from a preliminary experiment with an extensometer; the local strain is calculated by directly dividing the displacement between the grips by the gauge length which is significantly deviated from the engineering strain in Fig. 6

Fig. 9 a IPF figure of BCC phase; b Schmidt factor distribution diagram of {111} < 110 > slip system of BCC phase; c phase distribution; and d-l strain distribution under different stresses of 670 °C ART + flash treatment sample. The yield point and the local strain are accessed in a similar way as shown in Fig. 8

Fig. 10 Dislocation distribution of 670 °C ART sample a before and b after deformation; and dislocation distribution of 670 °C ART + flash treated sample c before and d after deformation