Electroshock-driven differentiated evolution of martensite/bainite heterostructure enables a breakthrough in strength-toughness synergy of ultra-high strength steel

Constructing a heterogeneous structure with an appropriate martensite/lower bainite (M/LB) ratio is key to resolving the strength-toughness trade-off in ultra-high strength steels. However, significant phase volume differences cause severe stress concentration at heterogeneous interfaces, inducing microcracks and limiting toughening potential. To address this, this study proposes a novel millisecond-scale ultrafast electroshock treatment, which leverages differential electrical pulse energy absorption by M/LB phases to achieve localized energy deposition at weak interfaces, realizing “precise strengthening of weak zones while preserving strong ones.” The treated material exhibits a yield strength of 1752 MPa and impact energy of 36.8 J, representing a simultaneous enhancement of over 28% and 120% compared to conventional fully martensitic microstructures. Multiscale characterization shows that electrical pulse energy preferentially deposits at high-stress M/LB heterointerfaces, inducing ordered interfacial atom rearrangement, reducing interfacial disorder width and lattice distortion, and suppressing microcrack initiation. Post-treatment, enhanced M/LB interface dislocation storage and expanded heterozone boundary-affected regions improve stress transfer efficiency of lower bainite (increasing hetero-deformation induced stress by ∼65 MPa). Shearable ultra-nano ε-carbides at heterointerfaces reduce mobile dislocation mean free path, contributing ∼251 MPa to precipitation strengthening. Reduced M/LB hardness difference promotes uniform geometrically necessary dislocations and back stress fields, enhancing strain compatibility and suppressing interfacial crack initiation, thus fully exerting the heterogeneous structure's strength-toughness potential.