Fig. 1 Schematic diagram of heat treatments for conventional a and I-Q&P b samples. OQ oil-quenching, RT room temperature

Fig. 2 Microstructure of tested steel before Q&P process (PAGB: prior austenite grain boundary): a conventional sample; b I-Q&P sample

Fig. 3 SEM micrographs of conventional a and I-Q&P b samples (PAGB, TM, UM, AM, RA, ARA, and F refer to prior austenite grain boundary, tempered martensite, untempered martensite, acicular martensite, retained austenite, acicular-retained austenite, and ferrite, respectively)

Fig. 4 EBSD images of conventional a and I-Q&P b samples with the color region representing retained austenite

Fig. 5 Volume fraction of retained austenitic as a function of tensile deformation for tested steels

Fig. 6 Variations of k values as a function of true strain in tested steels

Fig. 7 Dilatometry curves for conventional a and I-Q&P b samples after different heat treatments

Fig. 8 Heat flow of tested steels as a function of temperature at heating rates of 5 K/min a, 10 K/min b, 15 K/min c, 20 K/min d

Fig. 9 Kissinger analysis (ln (T 2 /Θ) vs. 1/T) for determination of activation energy of retained austenite decomposition

Fig. 10 Engineering stress-strain curves of tested steels

Fig. 11 Cupping force-travel curves and photos of conventional a and I-Q&P b samples after Erichsen testing

Fig. 12 Instantaneous work-hardening exponent n for conventional and I-Q&P samples as a function of true strain

Fig. 13 SEM micrographs of fracture surfaces of conventional a and I-Q&P b samples