PNNL

Abstract

TWinning Induced Plasticity (TWIP) steel is a typical representative of the 2nd generation of advanced high strength steel (AHSS) which exhibits a combination of high strength and excellent ductility due to the twinning mechanisms. This paper discusses the principal features of deformation twinning in faced-centered cubic austenitic steels and shows how a physiscally-based macroscopic model can be derived from microscopic considerations. In fact, a dislocation-based phenomenological model, with internal state variables such as dislocation density and micro-twins volume fraction representing the microstructure evolution during deformation process, is proposed to describe the deformation behavior of TWIP steels. The contribution of this work is the incorporation of a physically-based twin’s nucleation and volume fraction evolution model in a conventional dislocation-based approach. Microstructural level investigations, using scanning electron microscope (SEM) and transmission electron microscope (TEM) techniques, for the TWIP steel Fe–17.5 wt.% Mn–1.4 wt.% Al- 0.56 wt.% C, are used to validate and verify modeling assumptions. The model could be regarded as a semi-phenomenological approach with sufficient links between microstructure and overall properties and therefore offers good predictive capabilities. Its simplicity also allows a modular implementation in finite element-based metal forming simulations.