Abstract: Effects of ferrite grain size on quasi-static and dynamic deformation behavior of ferrite-martensite dual phase steel (DP980) are investigated. Two groups of experimental dual phase DP steels with the same martensite volume fraction and different ferrite grain size are obtained through performing the experiment with different austenitizing temperature. The quasi-static tensile experiment and the dynamic tensile experiment for the two groups of DP steels are carried out at strain rates ranging from 10–4 to 1 750 s–1 at room temperature using universal testing machine CMT4105 and split Hopkinson tensile bar (SHTB), respectively. Then the true stress-effective plastic strain curves of DP980 steel for five strain rates have been obtained through the data processing. Johnson-Cook (J-C) model, which is not concerned with effects of grain size, and modified Khan, Huang and Liang (KHL) model, which is concerned with effects of grain size, are used to research dynamic deformation behavior of dual phase steel. And coefficient of determination R2 is introduced to determine goodness of fit for experimental results and models. The analysis results of the experiment indicate that modified KHL model is in good agreement with the experimental results, whose R2 reaches 0.998 7, and that modified KHL model has good characterization of deformation behavior for DP980 over a wide range of strain rates, and can reflect effects of grain size on dynamic deformation behavior of DP980.

Key words: Constitutive model, Dual-phase steel, Dynamic deformation behavior, Split Hopkinson tensile bar( SHTB), Strain rate