Modelling Thermo-Viscoplasticity of Case-Hardening Steels Over Wide Temperature Ranges

The aim of this work is the development of a thermodynamically consistent fully coupled thermoviscoplastic material model for metals, especially for case hardening steels.
The model is based on a split of the free energy into a thermo-elastic, a purely plastic and a purely thermal part and covers nonlinear cold-work hardening and thermal softening.
Effects arising from phase transformations at austenitisation temperature are accounted for in the model as well as nonlinear temperature dependencies of the elastic moduli, the plastic hardening moduli, the thermal expansion, the heat capacity and the heat conductivity.
Moreover, strain rate dependency of the current yield stress is realized using a temperature dependent nonlinear Perzyna-type viscoplastic model. The model and its parameters are fitted against experimental data for case hardening steel 16MnCr5 (1.7131). Several numerical examples are discussed.