Comparison of twinning evolution with work hardening ability in twinning-induced plasticity steel under different strain rates

For Fe-22Mn-0.6C (wt%) twinning-induced plasticity (TWIP) steel with grain sizes of 35 and 170 μm, both the ultimate tensile strength and uniform elongation decrease with increasing the tensile strain rates (from 10−4 to 100 s−1). The density of twin boundary (DTB) is presumed to be the major factor influencing mechanical properties. Accordingly, a parameter 2/(t+s) (t and s represent the thickness and spacing of deformation twins), also the inverse of the mean free path for dislocation slip, is proposed to characterize the planar-oriented twinned structure in infinite grain size (D»t≈s). It also evaluates the effect of DTB on the work hardening ability and ductility of the TWIP steel.