Enhanced ductility of strong cold-rolled ribbed rebar through intermediate frequency induction heat treatment based on recrystallization

In this study, intermediate frequency induction heat treatment (IFIHT) is applied to cold-rolled ribbed steel rebar with low-cost Q235 as raw material, and a combination of excellent ductility and high strength has been achieved, which surmounts the bottleneck of cold-rolled rebar. To reveal the mechanisms behind the excellent mechanical properties, multi-scale characterizations are carried out to study the microstructure and the micro-strain. The results suggest that IFIHT after cold deformation not only facilitates partial recrystallization and dislocation annihilation, but also restricts grain coarsening. High proportion of high angle grain boundaries improve the dislocation accumulation ability, the defect-free recrystallized grains and the sub-grains with a high degree of dislocation annihilation facilitate dislocations slipping, therefore good ductility is achieved. In addition, the high angle grain boundaries formed through recrystallization and dislocations left after partial recrystallization ensures high strength. The enhancement of dislocation storage capacity of grains leads to the improvement of work hardening ability, which reflects in the form of high uniform elongation in the stress-strain curves.