Extraordinary strength–ductility–toughness in Fe–0.08C plain low-carbon steel via introducing weblike martensite: Towards the third generation

The effect of large-strain cold rolling followed by intercritical annealing on the microstructure and mechanical properties of plain low-carbon steel was investigated. The grain size of ferrite reduced from 38 μm (for the as-received steel) to about 4 μm (for the dual-phase steel). The martensite phase was connected in 3D space in the dual-phase steel and a weblike structure of martensite was created. The stress-strain curve of dual-phase steel represents the continuous yield behavior without any distinct evidence of the yield point phenomenon. By introducing weblike martensite into the microstructure and refining α grains, the yield strength, ultimate tensile strength, and tensile toughness significantly increased to 740 MPa, 1062 MPa, and 193 J cm−3, respectively. The fracture surface of the DP sample had a dimpled appearance, indicating a ductile fracture mode. The results of the present work indicated that a low-cost plain low-carbon DP steel composed of weblike martensite and fine-grained ferrite exhibits extraordinary strength–ductility–toughness balance. Therefore, the dual-phase steel produced in the present work, by moving towards the third generation, can find wide applications in the automotive industry. •The martensite was connected in 3D space and a weblike structure was created.•The yield strength, ultimate tensile strength, and toughness of DP steel significantly increased.•Weblike martensite induced an extra strain hardening, which was useful to increase the ductility.•The fracture surface of the dual-phase sample had a dimpled appearance.