Modelling of the mechanical properties of dual phase steels based on microstructure

An approach is presented which describes the strain hardening behaviour of Dual Phase steels in experiments as well as in simulation based on microstructure. Therefore different types of microstructures with different contents of hard martensite phase and soft ferrite matrix were produced by intercritical annealing in salt bath followed by fast water cooling. An increase of strength level of the Dual Phase steels with increasing martensite contents was observed in quasistatic tensile tests as well as in dynamic tensile tests. In order to describe the influence of strain rate the model of thermal activated dislocation glide was applied including adiabatic heating measured by thermography. Strain rate sensitivity in absolute values is independent on microstructure. Higher temperatures are observed with increasing strength of the material which corresponds with the martensite content of the Dual Phase steel. Carbon partitioning during intercritical annealing, calculated by thermodynamic simulations, was taken into account for the calculation of flow curves of single phases for the Finite Element simulation (FE simulation) in Abaqus by using a Representative Volume Element based on microstructure of the Dual Phase steel. By application of different parameters for simulation quite accurate predictions of mechanical properties and quasistatic strain hardening behaviour are achieved. Simulation results are compared with experimental results of tensile tests and bulge tests. For validation of the developed model an industrial produced DP500 steel grade was chosen. The model application for industrial Dual Phase steels is limited probably due to the more complex microstructure. Therefore in future some modifications in input data for FE simulation are necessary in order to predict the correct strength level of industrial materials.