Significant impact of intercritical annealing temperature on microstructure and mechanical properties of Al substituted Si dual phase steel under ultra-rapid heating

The significant impact of ultra-rapid heating continuous annealing on microstructure and mechanical properties of Al substituted Si dual phase steel under hot-dip galvanized process was studied. The heating rate of 300 °C/s, and different annealing temperatures in the range of 750 °C to 810 °C were explored. The study indicated that the yield and tensile strengths are increased with the increase of intercritical annealing temperature during rapid heating continuous annealing. When the annealing temperature was 780 °C, the steel exhibited good comprehensive properties with yield strength of 574.9 MPa, tensile strength up to 1009 MPa, total elongation of 18.5%. This is attributed to refined microstructure, appropriate proportion of phases, high density of dislocations and finely distributed NbC precipitates. Furthermore, the variations in strength, elongation and strain-hardening behavior of the steel with thermomechanical parameters and the inherent mechanism for strengthening were further discussed in relation to the microstructural features.