Case hardening steels modelled by thermo-viscoplasticity over a wide range of temperature

The aim of this work is the development of a thermodynamically consistent fully coupled thermo-viscoplastic material model for metals.

The model is based on a split of the free energy into a thermo-elastic, a thermo-plastic and a purely thermal part and covers nonlinear cold-work hardening and thermal softening.

Nonlinear temperature dependent effects are accounted for the elastic moduli, the plastic hardening moduli, the thermal expansion, the heat
capacity and the heat conductivity.

Furthermore, strain rate-dependency of the current yield stress is realized using a temperature dependent nonlinear Perzyna-type viscoplastic model based on an associative flow rule. The model and its parameters are fitted against experimental data for case hardening steel 16MnCr5 (1.7131).

We discuss the consistent linearisation of the proposed model and its implementation in a monolithic fully coupled finite element framework. Finally, we present results for selected boundary value problems.