The stacking-fault energy, dislocation slip, mechanical twinning, strain hardening and yield and tensile strengths were systemically investigated in Fe-18Mn-0.6C-1.5Si twinning-induced plasticity steel. The results were compared with those for Fe-18Mn-0.6C and Fe-18Mn-0.6C-1.5Al TWIP steels. The stacking-fault energy decreased at the rate of 4mJ/m2wt%Si. The addition of Si increased both the yield strength (due mainly to solid-solution hardening) and the tensile strength; owing to the high strain-hardening that occurred while maintaining a large elongation of over 60%. The volume fractions of the primary and secondary mechanical twins were quantitatively evaluated by combining the merits of electron back-scattering diffractometry and transmission electron microscopy. The volume fractions of both primary and secondary twins were highest in Fe-18Mn-0.6C-1.5Si TWIP steel, which had the lowest stacking-fault energy of the three TWIP steels. The volume fraction of the secondary mechanical twins increased rapidly with the addition of Si. The contributions of dislocation storage, mechanical twinning and dynamic strain aging to strain-hardening were quantitatively evaluated for the three TWIP steels. The Si-added steel exhibited the highest strain hardening; due mainly to the active primary and secondary twinning, and experienced negligible dislocation slip.

The Effects of Si on the Mechanical Twinning and Strain Hardening of Fe-18Mn-0.6C Twinning-Induced Plasticity Steel. K.Jeong, J.E.Jin, Y.S.Jung, S.Kang, Y.K.Lee: Acta Materialia, 2013, 61[9], 3399-410