Ultrafine grained dual phase (UFG DP) steels was produced by a new route utilizing simple cold-rolling and subsequent intercritical annealing of ferrite/martensite duplex starting structures. The effects of processing parameters such as rolling reduction, intercritical annealing temperature and time on the microstructural evaluations and mechanical properties have been studied. The ferrite grain size and martensite volume fraction were depended on the thermomechanical processing parameters. UFG DP steels with an average grain size of about 1-2 ?m and chain-networked martensite islands were achieved by short intercritical annealing of the 80% cold-rolled duplex microstructures. It is proposed that complete recrystallization of ferrite before the austenite formation leads to a large extent randomly distributed austenite in the ferrite matrix and chain-networked structure. The strength of the low carbon steel with the new UFG DP microstructure was reached over 1500 MPa (about 200% higher than that of the as-received state, e.g.540 MPa) , without loss of ductility. Tensile testing revealed good strength-elongation balance for the new DP steels (UTS×UE ? 100-150 J cm -3 ) in comparison with the previous works and commercially used high strength steels, i.e., DP600, DP800 and DP980. Keywords: Dual phase steel, Ultrafine grained, Thermomechanical processing, Mechanical characterization
