Mechanical behavior of DP780 dual phase steel at a wide range of strain rates

Abstract

The mechanical behavior of DP780 cold-rolled dual phase steel was studied by means of high-speed tensile testing machine. The constitutive relation and strain hardening behavior was analyzed by modified Johnson-Cook (JC) model and modified Crussard-Jaoul (C-J) method, respectively. Results indicated that strain rates have significant effect on mechanical properties and plastic deformation of dual phase steel. Moreover, the modified JC model can well describe the experimental results. The plastic deformation of DP780 can be divided into two stages: the first low strain stage with stronger strain hardening capacity and the second high strain stage with weaker strain hardening capacity. Strain hardening behavior was influenced by strain rate, dislocations, plastic deformation of martensite and thermal softening; the strain hardening rate of DP780 steel was not sensitive to the strain rates. Micro-voids in the tensile samples were formed at ferrite/martensite interface or formed by the fracture of martensite.