Temperature dependence of steel constitutive behavior: A simplified model

Increasing carmodel diversification leads to shorter production runs of which consequently the start-up phase is then a larger part. Typically, in the start-up phase the tooling heats up from ambient temperature to approximately 80 °C which is enough to markedly change the process window. The ASPECT project [1] aims to model this and although the main influence here is the change in friction with temperature still the change in material behavior cannot be neglected. For many years Tata Steel Europe has advocated the use of constitutive models based on dislocation dynamics in which the strain rate and temperature effects can be incorporated [2]. However, the model is in differential equation form and thus needs to be continuously evaluated in an FEA code, for instance in a user subroutine. The model presented in [2] is applicable to a wide range of temperature, but in the start-up phase of stamping the range of temperatures encountered is limited to 100 °C, and a simplified model may suffice. Moreover, when such a simplified solution is implemented as a hardening curve in tabular form it can be used in an arbitrary FEA code without modification. This is presented in this paper and shown to be accurate to about 5 MPa (RMSE) in the limited temperature range at hand.