A four parameter hardening model for TWIP and TRIP steels

Abstract

The mechanical behavior of twinning- and transformation-induced plasticity steels, commonly referred to as TWIP and TRIP steels, are characterized by linear hardening followed by an abrupt decrease in the hardening rate. We develop an empirical model that captures salient features of the strain hardening behavior. The model emphasizes ease of implementation into computer codes and identifying parameters from macroscopic data over physically motivated parameters; however, parameters fit to the mechanical response of several alloys show a direct correlation between some parameters and stacking fault energy. Finite element simulations of TWIP and TRIP steels under uniaxial tension show the lack of post-necking elongation observed experimentally is directly related to how abruptly the hardening decreases after the linear hardening regime. A scheme is then proposed for computing some hardening parameters directly from composition so that the model is compositionally-sensitive. This method is demonstrated on medium to high Mn steels so that the mechanical behavior can be predicted using the stacking fault energy, which is computed as a function of composition.