Superior strength-ductility synergy achieved by synergistic strengthening and strain delocalization in a gradient-structured high-manganese steel

Here the combination of synergistic strengthening and strain delocalization effects is realized in high-manganese steel by gradient microstructure designing, which results in an excellent strength-ductility synergy. Specifically, the gradient structure consists of two gradient surface layers sandwiching a coarse-grained center. Hardness and microstructure examinations reveal that the synergistic strengthening is originated from the enhanced twinning behavior and extra work hardening in gradient layers. The formation of dispersed strain concentration bands is found in the nanostructured surface layer, which evolves steadily and undertakes large applied strain, thereby leading to delocalized straining response. The formation and stabilization mechanisms of strain concentration bands are analyzed in depth with respect to the microstructure gradient. These findings shed light on the deformation fundamentals of gradient structure, especially on the hetero-deformation induced effects.