Abstract: The presented research sought an optimized way of producing dual-phase (DP) steels with ultrahigh strength (UTS > 1280 MPa), decent global ductility (TE > 18%) and excellent sheared-edge ductility (HER>35%). In certain cases, the product of UTS × TE can conform to the properties of Generation III steels. Hot band coiling temperature, cold reduction, intercritical annealing temperature and annealing path were altered to investigate these effects on the structure-property relationships of microalloyed DP steels. The results showed the combination of a low coiling temperature, high cold reduction, high intercritical annealing temperature and standard galvanizing process can result in high tensile strengths, since these conditions lead to high stored energy, providing more driving force and more rapid kinetics for the formation of austenite during the intercritical anneal. In addition, the sheared-edge ductility was found to be controlled by the nanohardness ratio of martensite/ferrite phases, as well as the amount of retained austenite. These two factors can explain how the supercooling annealing path process can improve the sheared edge ductility of DP steels.
Authors: Yingjie Wu and Anthony J. DeArdo
Keywords: Dual-phase steels, Ultra-high strength, High hole expansion ratio, Continuousgalvanizing lines