Abstract
Austenitic Stainless Steels and High-Strength Low-Alloy (HSLA) steels show significant dynamic recovery and dynamic recrystallization (DRX) during hot forming. In order to design optimal and safe hot-formed products, a good understanding and constitutive description of the material behavior is vital. A new continuum model is presented and validated on a wide range of deformation conditions including high strain rate deformation. The model is presented in rate form to allow for the prediction of material behavior in transient process conditions. The proposed model is capable of accurately describing the stress–strain behavior of AISI 316LN in hot forming conditions, also the high strain rate DRX-induced softening observed during hot torsion of HSLA is accurately predicted. It is shown that the increase in recrystallization rate at high strain rates observed in experiments can be captured by including the elastic energy due to the dynamic stress in the driving pressure for recrystallization. Furthermore, the predicted resulting grain sizes follow the power-law dependence with steady state stress that is often reported in literature and the evolution during hot deformation shows the expected trend.
Highlights
In the mass-manufacturing industry there is an ongoing drive to improve product quality or reduce costs by reducing finishing steps
A new continuum model was proposed to account for the effect of DRX on the stress–strain evolution during hot forming
The model is capable of accurately describing the stress–strain behavior of AISI 316LN over a wide range of temperatures and strain rates
Summary
In the mass-manufacturing industry there is an ongoing drive to improve product quality or reduce costs by reducing finishing steps. The previously discussed physically-based models are quite good at representing some of the key features of DRX like resulting grain size, the initiation of DRX and the transition from single to multiple peak behavior They are currently not ready for predicting the behavior of industrial hot forming processes in full-scale Finite Element (FE) process simulations, because they are usually validated on a limited amount of stress–strain curves within a narrow range of deformation conditions [8,22,23,26,34]. One of these is the model presented by Cram et al It is one of the more ‘complete’ multi-grain models taking a wide range of local microstructural-characteristics into account Despite of this, it under predicts the recrystallization softening at higher strain rate [32]. Calibration and validation is performed on the experiments presented by Zhang et al [16] which pertain hot compression tests of AISI316LN for a wide range of temperatures and strain rates, the hot torsion experiments on HSLA-steel presented by Roucoules et al are considered which show significant stress-softening at high strain rates [29] to validate the proposed addition to the driving pressure for grain boundary migration
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