Effects of Strain Rate on the Mechanical Properties and Fracture Characteristics of a Dual Phase 980 Steel

Dual phase (DP) steels are being increasingly used as structural components in the automotive industry owing to their combination of high strength and moderate ductility. Formability and crash resistance are important mechanical properties that expose the steel to high strain rates. Fracture characteristics of a DP steel at strain rates spanning seven orders of magnitude are investigated using quantitative fractography. The DP steel investigated in this study is comprised of a continuous matrix of martensite with interspersed ferrite islands. The data reveal that the flow stress, uniform strain, and ductility are substantially higher at the higher strain rates. Quantitative fractography, employed to understand the fracture characteristics, shows an increase in the extent of ductile fracture at high strain rates. In this presentation, the results demonstrating high strain rates facilitating dimpled ductile fracture and/or increased resistance to faceted fracture are discussed.