A constitutive model for the formation of martensite in austenitic steels under large strain plasticity

Abstract

A constitutive model for diffusionless phase transitions in elastoplastic materials undergoing large deformations has been developed. The model is formulated with starting-point in basic thermodynamic relations and the phase transition is treated through an internal variable (i.e. the phase fractions) approach. The usual yield potential is used together with a transformation potential to describe the evolution of the new phase. A numerical implementation of the model is presented, complete with the derivation of a consistent algorithmic tangent moduli. Simulations based on the presented model are compared to experimental findings with good agreement. The proposed model offers a robust tool, suitable for large-scale simulations of phase transformations in austenitic steels undergoing extensive deformations. This is demonstrated in simulations of the necking of a bar under tensile loading and also in simulations of a cup deep-drawing process.

A constitutive model for analyzing martensite formation in austenitic steels deforming at high strain rates

“…Garion et al (2006) proposed a model to describe the FCC to BCC phase transformation in austenitic stainless steels based on the assumption of linearization of the most intensive part of the transformation curve. Hallberg et al (2007) presented a model that takes basic thermodynamic relations as its starting point and treats the phase transition through an internal variable (the phase fractions) approach. Wolff et al (2008) contributed to the numerical simulation of martensitic transformation laying a thermodynamic founda tion in the context of macroscopic continuum mechanics.…”

Model Describing Material-Dependent Deformation Behavior in High-Velocity Metal Forming Processes

“…Since the development of a martensitic phase occurs without any time-consuming diffusion of carbon atoms, microstructural changes can appear very rapidly, cf. Hallberg et al (2007). The observations just described can be seen as providing the rationale for the dependency of the strength of the QT material on temperature as shown in Fig.…”

“…The remainder of the internally expended energy is stored in the material at a microscopic level through micro-cracking and the creation and rearrangement of such material imperfections as point defects, stacking faults, twins and dislocation pile-ups. These microstructural alterations can also include phase transformations, as discussed by Hallberg et al (2007). The stored energy of cold work is related mainly to changes in dislocation density within the material.…”

A computational two scaled model for the simulation of micro‐heterogeneous low‐alloyed TRIP steels

“…The material model in [3], originally proposed for high-alloyed TRIP steels, has been adopted here and suited for application to the retained austenite phase in low-alloyed TRIP steels. The hyperelastic-plastic formulation at large strains uses a multiplicative decomposition of the deformation gradient, F = F e F in where F in represents all inelastic processes.…”

“…Thereby, also computational costs associated with FE 2 calculations can be significantly reduced at a comparable prediction quality. The material model used here to capture the above mentioned microstructural phase transformation is based on [3] which was proposed for high alloyed TRIP steels, see also e.g. [8].…”