Microstructure-based model for the static mechanical behaviour of multiphase steels

Low-alloy multiphase transformation -induced plasticity (TRIP) steels offer an excellent combination of a large uniform elongation and high strength. This results from the composite behaviour of the different constituent phases that are present in these steels: polygonal ferrite, bainitic ferrite, and martensite/austenite. The different constituents were prepared separately in order to obtain a clear understanding of their individual behaviour within the multiphase steel. The stress-strain relationships of these different types of single- and multiphase steels were simulated by physically based micromechanical models. The model used for the simulations of the stress-strain curves of the separate phases is based on the Mecking-Kocks theory and utilizes physical properties such as the microstructural parameters, the dislocation density, and the chemical composition of the different phases. Strain-induced transformation kinetics, based on a generalized form of the Olson-Cohen law, are utilized in order to include the influence of the transformation of the metastable austenite on the mechanical properties of the TRIP steels. Static stress-strain properties of multiphase steels were modelled by the successive application of a Gladman-type mixture law for two-phase steels. The model yields detailed information of stress and strain partitioning between the different phases during a static tensile test. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.