Heterogeneous plastic deformation and HDI strengthening of the heterostructured dual-phase steels investigated by in-situ SEM-DIC

Heterostructured dual -phase (DP) steels comprising different martensite volume fractions (HS740 steel, VM:41 %; HS780 steel, VM: 54 %) were produced by cold rolling and intercritical annealing. HS780 steel produces a nearideal heterostructure where the grains are mostly isolated by the F/M interfaces, resulting in a superior combination of strength -ductility (ultimate tensile strength, UTS: 1064 MPa; uniform elongation, UE: 9.8 %). The excellent mechanical properties is primarily attributed to the stronger hetero-deformation induced (HDI) strengthening and hardening of HS780 steel. The relationships between HDI hardening and the heterogeneous plastic deformation of the heterostructured DP steels were elucidated based on the in -situ tensile tests and digital image correlation analysis. The insights from these results will improve our understanding of the deformation behavior of heterostructured materials and guide the design of low -carbon steels with outstanding mechanical properties.