Suppressed deformation instability in the twinning-induced plasticity steel-cored three-layer steel sheet

Deformation instabilities (i.e., yield point phenomenon (YPP) and serrated flow) were investigated for twinning-induced plasticity (TWIP) steel-core with low-carbon (LC) steel outer layer sheets. During tensile tests, both the YPP and serrated flow were suppressed as the volume fraction of the TWIP steel-core decreased. Electron backscattering diffraction analysis indicated that a strain gradient was induced, and that geometrically necessary dislocations (GNDs) accumulated at the TWIP-LC steel interface. With increase in the dislocation density by plastic deformation, the deformation instabilities in the TWIP-cored layer steel sheets were suppressed due to the reduced probability of interaction of dislocation with carbon-solutes. This result indicates that the strain gradient at the interface of the layered sheets not only enhances the mechanical property, but also suppresses deformation instability.