Abstract：The microstructure of Twinning Induced Plastic(TWIP)steel during tensile deformation was investigated with in-situ SEM observation.The results showed that the grains with twins started to deform and work harden,which lead to other grains formed favorable orientation in order to complete further deformation.This deformation mechanism of twinning induced plastic provided the specimens excellent elongation with no-necking phenomenon.In addition,microcracks generated at inclusions and grain boundaries,and merged to crack at the condition of stress concentration.A large amount of strain marks were observed in the tension specimens of the TWIP steel.The strain marks consist of slip lines and small mechanical twins.Because the kink bands and stepped structures appeared in grains for twinning induced plastic,the folding phenomenon of specimen surface occurred.
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