In order to meet the diversified needs of high-strength dual-phase steel users in automobile manufactur-ers,two kinds of high-strength dual-phase steels with different microstructure characteristics of F/M and B/Ar were obtained,adopting reasonable chemical composition design and process control.The process design principles and microstructure characteristics of F/M and B/Ar high-strength dual-phase steels were studied by means of SEM,TEM,tensile and hole expansion tests,and the influencing factors of mechanical properties were analyzed.The results show that the annealing temperature of F/M dual-phase steel is 810℃ in the range of(AC1+AC3)/2±8℃(AC1 and AC3 are the start and end temperatures of austenite transformation during heating,respectively),which is mainly composed of 47％ferrite,46％martensite and 7％block retained austenite.The ferrite has two forms of recrystallized ferrite and proeutectoid ferrite,and the grain size is 2.5-4.0 μm and 1.0-2.5 μm,respectively.The annealing temperature of B/Ar dual-phase steel is set to 900℃ in the single-phase austenite region.The microstruc-ture is mainly composed of 84％bainite and 16％second-phase retained austenite.The bainite is based on the origi-nal γ grain.The phase transformation is formed,and the retained austenite is characterized by lamellar or discontinu-ous block.There are obvious differences in microstructure morphology between F/M and B/Ar dual-phase steels.The coordinated deformation effects of each phase structure are different during the deformation process,which affects its mechanical properties.The tensile strength can be controlled at the level of 1 000 MPa by both processes.The nano-sized VC precipitated phase particles with a diameter of 4-13 nm are dispersed in the matrix,and the pre-cipitation strengthening amount exceeds 220 MPa,which interacts with high-density dislocations,and finally improves the strength and plasticity of the material.The tensile strength of F/M dual-phase steel is 1 035 MPa,and the elongation after fracture is 18.7％.Compared with F/M dual-phase steel,the tensile strength of B/Ar dual-phase steel increases by 111 MPa to 1 146 MPa,and the product of strength and plasticity reaches 19.83 GPa·％.It has the characteristics of high yield ratio and hole expansion rate,which are 0.709 and 38％,respectively.
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