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 & mu;m (for the asreceived steel) to about 4 & mu;m (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 & alpha; 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 finegrained 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.

Automated summary

The effect of large-strain cold rolling followed by intercritical annealing on the microstructure and mechanical properties of plain low-carbon steel was studied. The grain size of ferrite decreased from 38 μm to about 4 μm in the dual-phase steel. A weblike structure of martensite was created in the dual-phase steel, and it exhibited continuous yield behavior without a distinct yield point phenomenon. By introducing weblike martensite and refining α grains, the yield strength, ultimate tensile strength, and tensile toughness significantly increased. The dual-phase steel composed of weblike martensite and fine-grained ferrite showed extraordinary strength-ductility-toughness balance and potential applications in the automotive industry.