Uniaxial Tension Andserrated Plastic Flow Behavior Of High Manganese Austenitic TWIP Steel

TWIP?Twinning-induced plasticity?steels have been received extensive attentions as a promising candidate for the next generation of automotive steel,which possesses high strength and excellent ductility.Excellent mechanical properties of TWIP steels have been attributed to the high rates of work hardening during deformation.A large number of studies showed that the high work hardening rate is primarily due to deformation twins and DSA.However,current research on TWIP steel is still in its infancy.In this paper,comparing the tensile behavior of two C content TWIP steels?Fe-18Mn-1.0C and Fe-18Mn-0.6C?and the results showed that the yield strength and tensile strength of TWIP increased with the increasing of C content,as compared with the medium-carbon TWIP steel.At low strains,deformation twins were suppressed in the high-carbon TWIP steel due to its higher SFE with the increased C content;however,the dynamic strain aging was enhanced and the formation of thinner twins was more rapidly and persistently at high strains in the high-carbon TWIP steelthan that in the medium-carbon TWIP steel.The unique twinning behavior and the enhanced dynamic strain aging sustain the high strain-hardening rate of high-carbon TWIP steel up to higher strains are the main reasons for its superior tensile properties.At room temperature,the tensile test of Fe-18Mn-0.6C steel at a strain rate of 3×10^-3s^-1 and 3×10^-5s^-11 was carried out.The characteristics of the serration on the tensile curve are analyzed by calculating the strain period and drop amplitude of serrations.The results indicated that the test about the strain rate about 3×10^-5s^-1 has smaller strain period and larger drop amplitude.Type A serrations is nucleated from the lower end and propagating towards the upper end of the parallel section of the specimen,Which were analyzed by digital image correlation?DIC?technique.However,the last band propagates so slowly and finally becomes almost immovable,leading to severe localized deformation,the onset of necking and final fracture at the front of the stagnated deformation band,after a certain distance.Hardness test demonstrated that the hardness of PLC area is higher than Non-PLC area,but the hardness are almost same when fractured,which indicated that PLC bandinfluenced the localized deformation and mechanical properties of TWIP steels.