the effect of intercritical annealing time on the microstructures and mechanical properties of an ultrafine grained dual phase steel containing niobium

an ultrafine grained dual phase (ufg dp) steel containing niobium was produced by a new routeutilizing simple cold-rolling and subsequent intercritical annealing of ferrite/martensite duplex startingstructures. the effects of intercritical holding time on the microstructural evolutions and mechanicalproperties were studied. the results showed that increasing intercritical holding time enhnaced thevolume fraction of martensite and decreased the grain size of ferrite. tensile testing also revealedgood strength–elongation balance for ufg dp steels (uts×ue > 100 jcm-3), in comparison with thecommercially used high strength steels. the variations of strength, elongation and fracture behavior withintercritical holding time were correlated with the microstructural features.