Development of a 780-MPa-class hot-rolled advanced high-strength steel with ultrahigh ductility

This study deals with the development of a 780-MPa-class hot-rolled advanced high-strength steel(AHSS) with an ultrahigh elongation at break of approximately 30% and strength-ductility product exceeding 24 GPa·%,indicating the excellent formability of the newly developed AHSS.The microstructure of the newly developed 780-MPa-class AHSS consists mainly of the triplex phase of ferrite, bainite, and retained austenite with a volume fraction of 10%±2%.The stability of the retained austenite in the newly developed AHSS is much higher than that of conventional transformation-induced plasticity steels, in which the retained austenite is prone to transformation into martensite under deformation.At a pre-strain lower than 1.2%,the volume fraction of the retained austenite and the elongation at break of the present 780-MPa-class AHSS remain almost unchanged, showing a high tolerance in the process window during leveling or straightening.Therefore, the present 780-MPa-class AHSS is particularly suitable for the production of components with complex shapes.