Abstract
In situ multiaxial loading during neutron diffraction tests were undertaken on a low-alloyed Quenched and Partitioning (Q&P) Transformation Induced Plasticity (TRIP) Bainitic Ferrite (TBF) steel with dispersed austenite particles. The effect of stress triaxiality on the evolution of the deformation-induced martensite is investigated under uniaxial- and equibiaxial-tension as well as tension/compression with a ratio of −1:6. It is shown that transformation is not a monotonic function of stress triaxiality; the amount of deformation-induced martensite is similar under uniaxial and equibiaxial tension but it is significantly smaller under tension/compression. The transformation kinetics are modeled using a recently developed kinetic model that accounts for the stress state and the stability and size of the austenite particles. The larger austenite particles transform first and the mean volume of the austenite particles decreases with increasing strain; the decreasing austenite particle size impedes the phase transformation as the deformation proceeds. It is concluded that stress triaxiality alone cannot account for the differences in the transformation kinetics between different loading states and that the number of potential nucleation sites depends on the stress state.
Highlights
The transformation induced plasticity (TRIP)-assisted steels are a grade of low-alloyed steels that have been widely used in the automotive industry
Isothermal bainitic transformation of TRIP Bainitic Ferritic (TBF) steels is undertaken above the martensite start (Ms) temperature, resulting in a microstructure that consists of a bainitic matrix and dispersed particles of retained austenite [17,18]
In this study we report on a series of experiments un dertaken for validating the kinetic model by Haidemenopoulos et al [37] and understanding the mechanisms that control the deformation-induced phase transformations under different loading states
Summary
The transformation induced plasticity (TRIP)-assisted steels are a grade of low-alloyed steels that have been widely used in the automotive industry. A new Materials Science & Engineering A 800 (2021) 140321 variation of the classical Olson-Cohen model was coupled with crystal plasticity to model the mechanical behavior of metastable austenitic steels under different stress states [28] This coupled kinetic model and crystal plasticity framework accounts for i) the effect of stress state on the nucleation of martensite, ii) the evolution of the deformation texture, and iii) the SFE. Haidemenopoulos et al [37] developed recently a kinetic model for the martensitic transformation in TRIP-assisted steels with a relatively small fraction of metastable austenite in the form of dispersed particles in a ferrite/bainite/martensite matrix This model describes two modes of transformation, i.e. the stress-assisted and strain-induced trans formation and it is based on the modification of the nucleation site po tency distribution by the applied stress and plastic strain. The evolving austenite size is used as model parameter and it is seen that it affects the transformation kinetics significantly
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