We investigated the correlation among deformation twin density, work hardening, and tensile ductility in an Fe-18Mn-1.2C twinning-induced-plasticity (TWIP steel, and discussed the correlation with the plastic instability condition. The deformation twin density was varied by changing the deformation temperature from 123 to 523 K. An important factor for the uniform elongation is the work hardening rate in a later deformation stage. The increase in the deformation twin density enhanced the work hardening rate significantly but not monotonically just before the fracture, since the deformation twin density is saturated against plastic strain. In addition, dynamic strain aging in a later deformation stage and ε-martensitic transformation were found to accelerate the fracture due to the localized deformation and the premature fracture, respectively. Accordingly, the relationship between uniform elongation and deformation twin density was not simple. The optimum conditions for the TWIP effect were concluded to be (1) considerable amount of deformation twinning in a later deformation stage, (2) suppression of dynamic strain aging in a later deformation stage, and (3) inhibition of ε-martensitic transformation.
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