Role of multicomponent nanoprecipitates on strength and low-temperature toughness of simulated heat-affected zone (HAZ) in high-strength low-carbon steel

• Ni(Al,Mn) and Cu multicomponent nanoparticle co-precipitation critically governs the strength and low-temperature toughness of heat-affected zones in high-strength low-carbon steels. • At 30 kJ·cm−1 heat input, the intercritical HAZ shows dense Ni(Al,Mn) reprecipitation and Cu coarsening, retaining high strength but reducing impact toughness to 142 J. • The fine-grained HAZ achieves superior impact toughness (196 J) through a refined ferritic–bainite matrix and fine precipitates, while the coarse-grained HAZ reaches 186 J via re-precipitated nanoparticles mitigating grain coarsening. • Toughening arises from the synergistic actions of the matrix, precipitates, and deformation twins, providing a mechanistic framework to optimize welding parameters for tailored applications.