Strengthening and ductilization of laminate dual-phase steels with high martensite content.

• The laminate HMDP steels are produced by a combination of warm rolling and intercritical annealing. • Warm rolling accelerates cementite spheroidization, which enhances the kinetics of austenite formation. • The laminate HMDP steels present superior strength-ductility synergy than the non-laminate counterpart. • The high ductility of laminate HMDP steels is owed to the heterostructure with laminate ferrite surrounded by martensite. The steels with excellent strength and ductility are expected to be achieved by tailoring the microstructural features. In this work, laminate dual-phase (DP) steels with high martensite content (laminate HMDP steels) were produced by a combination of warm rolling and intercritical annealing. Influence of rolling strain and annealing temperature on the microstructural evolution and mechanical properties of laminate HMDP steels were systematically studied. The strength of HMDP steels was significantly improved to ∼1.6 GPa associated with a high uniform elongation of 7%, as long as the laminate structure is maintained. The strengthening and ductilizing mechanisms of laminate HMDP steels are discussed based on the influence of laminate structure and the high martensite content, which promote the development of internal stresses and can be correlated to the Bauschinger effect as measured by the cyclic loading-unloading-reloading experiments. Detailed transmission electron microscopy (TEM) observation was applied to characterize the dislocation structure in the deformed ferrite. [ABSTRACT FROM AUTHOR]