Strength and strain-hardening enhancement by generating hard delta-ferrite in twinning-induced plasticity steel

A dual-phase (12 vol.% delta-ferrite + 78 vol.% austenite) high manganese twinning-induced plasticity (TWIP) steel was produced by hot rolled and annealing treatment. In comparison with the fully austenitic TWIP steel, both the yield and ultimate tensile strength of the dual-phase TWIP steel reinforced by hard delta-ferrite are significantly increased. It was found that the delta-ferrite in dual-phase steel exhibits a high hardness owing to the formed DO3 structured intermetallic phase within ferrite. The presence of delta-ferrite dramatically improves the strain-hardening ability of TWIP steel. This is principally attributed to the effects of strain partitioning between hard delta-ferrite and softer austenite on the kinetics of deformation twinning and/or additional geometrical necessary dislocation (GND) during the deformation process.