Grain cooperative deformation of heterogeneous low-carbon steel: Strengthening achieved through low deformation and rapid low-temperature annealing

A heterostructure engineering strategy based on microstructural regulation was designed to address the common challenge of balancing strength and plasticity in conventional low-alloy carbon steels. By constructing a multimodal heterostructure composed of recovered, deformed, and recrystallized grains, utilizing their synergistic deformation effects to overcome the inverse strength-ductility relationship. The results indicate that Q215 steel exhibits a typical dual-mode heterostructure after 30 % cold rolling and rapid annealing at 640 °C, resulting in a yield strength, tensile strength, and elongation of 527 MPa, 563 MPa, and 14.2 %, respectively. This structure achieves superior mechanical properties through a specific strain allocation mechanism: low-defect-density recovered grains dominate initial plastic deformation, while high-hardness deformed grains participate in strain coordination and dislocation accumulation as strain increases. This material maintains low production costs while approaching the performance of advanced high-strength steel. The study also reveals differential effects of heterostructure components on crack propagation: fine recrystallized grains accelerate crack propagation due to disrupted grain boundary continuity, and deformed grains can hinder the propagation of cracks.