Quasi-static and dynamic deformation mechanisms interpreted by microstructural evolution in TWinning Induced Plasticity (TWIP) steel

As automotive steels require high impact resistance for absorbing impact energy upon vehicle body collision, detailed investigation of dynamic deformation behavior of TWinning Induced Plasticity (TWIP) steels is essentially needed. Here we show a plausible explanation of improving dynamic tensile properties by investigating deformation mechanisms using transmission electron microscopy and electron back-scatter diffraction analyses of interrupted tensile specimens. According to microstructural evolution results, slip mechanisms change from wavy slip to (planar+wavy) slip with increasing strain rate. With respect to twinning, the transition occurs from stacking faults to primary twins with increasing strain under quasi-static loading, while twinning becomes more activated under dynamic loading. Due to favorable effects of increased planar slip and twinning on tensile properties, the TWIP steel shows higher strength and similar ductility under dynamic loading. Our results demonstrate desirable applications of the TWIP steel to automotive steel sheets demanding excellent safety requirement of vehicle body.