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. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.