The tensile properties and microstructure evolution of cold-rolled Fe–Mn–C TWIP steels with different carbon contents

Fe–18Mn-1.0C and Fe–18Mn-0.6C twinning-induced plasticity steels are cold rolled at various rolling reductions, and their tensile properties, evolution of dislocation density, and twinning behavior during tensile deformation were systemically investigated. With increasing the cold rolling reduction, the yield strength and tensile strength of both steels increase obviously, especially for Fe–18Mn-1.0C steel; concurrently, the elongation to fracture decreases largely while this decrease is not as significant for Fe–18Mn-1.0C steel as for Fe–18Mn-0.6C steel. Furthermore, dislocation density and the amount of deformation twins increase with increasing rolling reduction and tensile strain. Such increase is more obvious for Fe–18Mn-1.0C steel than for Fe–18Mn-0.6C steel. A maximum (or saturation) dislocation density and a maximum (or saturation) amount of deformation twins are observed in specimens when they are deformed to fracture. Compared with Fe–18Mn-0.6C steel, the saturation values of dislocation density and amount of deformation twins are obviously larger in Fe–18Mn-1.0C steel, regardless of cold rolling reductions. The contributions of lattice friction stress, dislocations, twins and dynamic strain ageing (DSA) to flow stress were quantitatively analyzed using a parametric model. Dislocation strengthening and twin boundaries strengthening are found to play a dominant role in increasing the flow stress during tensile deformation, and the contribution from DSA is negligibly small.