Dual-phase (DP) steels have a composite-type microstructure consisting mainly of hard martensite islands embedded in a soft ferrite matrix. DP steels exhibit a characteristic combination of high strength, high work hardening rate and good ductility. Mechanical behaviour of DP steels is closely related to their microstructures. Hence, it is necessary to take into account their microstructural parameters in any attempt to estimate their flow behaviour. In this study, the flow curves of low carbon DP steels with 26.4 and 52% martensite produced by intercritical annealing processes at different temperatures were calculated using the finite element method (FEM). According to the results of microscopical observations of steel microstructures, martensite islands were assumed in the model to be spherical in shape. Moreover, in agreement with the experimental results in the literature clearly showing the possibility of martensite plastic deformation in similar steels during straining when its volume fraction is greater than about 30%, the plasticity of martensite islands in the steel microstructures was taken into account in the model by using their experimentally obtained stress-strain relations as a function of their estimated carbon contents. Having estimated the stress-strain behaviour of the ferrite phase in all steel samples using the microstructural parameters corresponding to the starting ferrite+pearlite steel, the flow curves of different DP steel samples with elastic martensite (in low martensite content steels) and elasto-plastic martensite (in high martensite content samples) were calculated. The calculated stressstrain curves exhibited reasonable agreements with the experimental stress-strain curves obtained from the tensile test.

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