It has been reported by K.M. Rahman et al. 16 that deformation twinning of TWIP steels is strongly dependent on grain size. K.M. Rahman et al. 16 have shown that with decreasing grain size of Fe-15Mn-2Al-2Si-0.7C TWIP steel from 84 to 0.7 µm, the yield strength increased from 350 to 720 MPa without substantially change in the ductility. G. Dini et al. 17 have obtained a yield strength of 572 MPa in an Fe–31Mn–3Al–3Si TWIP steel with a mean grain size of 2.1 µm. Y.Z. Tian et al. 18 have obtained fully recrystallized ultrafine grained Fe-22-Mn-0.6 C (wt .%) TWIP steel (with grain size of 550 nm) through a repeating cold rolling and annealing process with good strength-ductility balance (the yield strength of 793 MPa, tensile strength of 1247 MPa, and uniform elongation of 47%). Similarly, R. Ueji et al. 19 have shown that the grain refinement of Fe-31Mn–3Al–3Si (wt. %) TWIP steel down to 1.8 µm provides high yeild strength (525 Mpa) with large ductility (uniform elongation of 48%). S. Kang et al. 20 have investigate the effect of grain refinement (with grain sizes of 2, 10, and 50?m) on yield strength, strain hardening, and deformation twinning in Fe–18Mn–0.6C–1.5Al TWIP steel during tensile deformation and have concluded that samples with grain size of 2 ?m exhibited higher yield strength of 500 MPa in comparison to coarse grained specimens.