Crystal plasticity modeling and characterization of the deformation twinning and strain hardening in Hadfield steels

The deformation and strain hardening due to dislocation slip and twinning in Hadfield steels is investigated with a crystal plasticity model. A phenomenological interaction and hardening formulation is incorporated to the numerical model based on the microscopic characterization and deformation behavior. Single and polycrystal simulations on a Hadfield steel are conducted to prove the soundness of the model in describing the deformation and hardening behavior of the steel. The competition between dislocation slip and twin dominated deformation plays an essential role in the asymmetry between tension-compression as well as in the strain hardening behavior of the steel. The simulations performed on another Hadfield alloy verifies the model's capability to represent the strain rate sensitivity of the material, when a positive strain rate dependence exists. The use of realistic 3D polycrystalline aggregates imitating the microstructure of the Hadfield steels provides new insight into the inter-grain and intra-grain behavior of austenitic microstructures exhibiting twinning, particularly revealing the nature of local stress and twin concentrations. The strain rate sensitivity of the alloyed Hadfield steel is observed also at the grain scale, intensifying twinning at higher strain rates depending on the loading direction. The local gradients were found to arise from the neighbouring grains and from the intra-grain reorientation, explaining the experimental observations of only partially twinned grains. The simulation results and the 3D aggregate approach used in this paper provide information for the validation of crystal plasticity model as well as about the local deformation behavior of Hadfield steels.