Plastic deformation behavior and construction of constitutive model in a wide range of strain rates of 800 MPa grade dual phase steel

Abstract In order to investigate deformation character of 800 MPa grade dual phase steel (DP800) as is loaded in different circumstances, the nine strain rates are selected respectively including 10 −4  s −1 , 10 −3  s −1 , 10 −2  s −1 , 10 −1  s −1 , 1 s −1 , 10 s −1 , 100 s −1 , 500 s −1 and 1000 s −1 . Based on the summary of strain rate sensitivity, yield strength and tensile strength are different in terms of increment rate as strain rate rises, as can be identified by dynamic factor. Besides, plasticity has also been improved in dynamic regime. Strengthening mechanism with three different stages in tensile test is also researched, which is associated with making a microstructure analysis via optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). In addition, through the observation of fracture appearances in SEM and the calculation of fracture energy absorption, it is indicated that the capacity of energy absorption increases alongside strain rate. Lastly, the constitutive model is established based on a holistic review of ferrite grain size, strain rate sensitivity, as well as the coupling effects of strain, strain rate and temperature, ultimately for an excellent fitting degree.