5th International High Manganese Steel Conference - HMNS 2022

High manganese steels are considered to be promising alloys for light weight applications due to their high strength and good ductility based on their special microstructure. During plastic deformation the mechanisms of twinning induced plasticity (TWIP) and transformation induced plasticity (TRIP) lead to a strong microstructure refinement within the material. Previous studies have shown that the TWIP and TRIP effect both depend on the applied stress condition during plastic forming. For an applied strain under tensile stress a larger number of twins and martensite lamellae has been observed compared to a strain under compression stress. During the sheet forming process several different stress conditions are applied to the material. Hence the amount of local tensile and pressure stresses directly influences the evolution of the local microstructure and thus the local mechanical properties. In order to consider those local property evolutions in sheet forming simulations a constitutive hardening model is needed which takes the correlation of local stress condition and microstructure evolution into account. For this purpose, the constitutive hardening model introduced by Steinmetz was extended by an empirical model, which considers the dependence of microstructure evolution on the stress condition. Within this empirical model the stress condition, represented by the Lode parameter, is correlated to one of the fitting input parameters of the hardening model. This special fitting input parameter has been identified and estimated by comparing the results of a sensitivity study of the constitutive hardening model input parameters on the one hand and a parameter study with different stress conditions as input for the crystal-plasticity simulations using DAMASK on the other hand. Finally, the extended constitutive hardening model has been used to calculate the hardening of a X30MnAl23-1 steel for different stress/strain conditions (uniaxial tensile stress, plane strain, simple shear), which is in good alignment with experimental data.