Annealing softening behaviour of cold-rolled low-carbon steel with a dual-phase structure and the resulting tensile properties

The softening behaviour of cold-rolled dual-phase low-carbon steel during annealing and the resulting microstructure and tensile properties were investigated. Ferrite–martensite dual-phase structures were produced by intercritical heat treatments (IHT): (A) intercritical quenching at 760 °C after quenching at 1000 °C; (B) furnace cooling from 1000 to 760 °C and immediate quenching. The results show that an excellent strength–ductility balance is achieved by the cold rolling and appropriate annealing of these two IHT samples. Completely recrystallized ultrafine-grained ferrite with a bimodal distribution and dispersively nanoscale carbide particles are obtained. The annealing softening activation energy of cold-rolled sample (A) is far less than that of cold-rolled sample (B). In addition, the effect of IHT on the softening behaviour, resulting microstructure and tensile properties was discussed.