Synergistic optimization of strength and ductility in layered ferrite-martensite dual-phase steel

• A layered F-M structure steel was prepared through intercritical quenching and warm rolling. • The steel exhibited a high YS of 830 ± 10 MPa, and maintaining an elongation of 23.7 %. • The damage behavior of the F-M steel is governed by its strain localization mechanism. The development of ultrafine-grained (UFG) structural materials with high yield strength and superior ductility is crucial for the exploitation of marine energy. This study employed a synergistic regulation strategy involving intercritical quenching and large-strain warm rolling (WR) to prepare a UFG layered ferrite-martensite (F-M) structure steel. The test steel exhibited a high yield strength of 830 ± 10 MPa, while maintaining an elongation of 23.7 %. The excellent performance is attributed to the significant dislocation strengthening effect induced by WR. This effect effectively reduces the hardness difference between microstructures (ΔH V < 1.2 GPa), thereby promoting coordinated deformation. Simultaneously, under the mutual constraint of a layered heterostructure, the dispersed shear bands (SBs) are activated and dynamically propagated, promoting uniform strain distribution and thereby sustaining homogeneous plastic deformation. Additionally, compared with equiaxed grains, the layered heterostructure possesses a higher density of F-M grain boundaries and a more matched geometric necessary dislocations (GNDs) accumulation characteristic length ( l GND ), promoting the rapid accumulation of GNDs to achieve significant heterogeneous deformation induced (HDI) strengthening (>500 MPa). The superior strength-ductility balance achieved in F-M steel, attained through the optimization of grain size and microstructural distribution, offers a novel strategy for developing high-performance marine steels.