2D RVE based micro-mechanical modeling with real microstructures of heat-treated 20MnMoNi55 steel

Abstract

Macro-mechanical response of multi-phase steel depends on its morphological composition with respect to volume fraction of constituent phases, phase distribution, grain size etc. To address these micro-structural inhomogeneity, a RVE (Representative Volume Element) based micro-mechanical model was incorporated in our current analysis. 20MnMoNi55 steel is basically composed of ferrite and bainite as its constituent phases. To introduce variation in constituent phases and its volume fraction, different inter-critical heat cycles were designed based on the inter-critical temperature range obtained by means of dilatometric testing of 20MnMoNi55 steel. Heat treated samples were then characterized to confirm that the variation is achieved with respect to different set of ferrite-martensite volume fraction. The experimental flow curves obtained through tensile testing for different heat treated samples were primarily correlated with respect to volume fraction of martensite in terms of flow stress of the material. 2D RVEs were constructed based on real microstructure obtained through different heat cycles with the help of Python Scripting interface in Abaqus. The flow curve obtained by means of RVE based finite element simulation closely matches with the experimental results. The stress-strain response obtained from the finite element model output database shows inhomogeneity in its distribution between softer ferrite matrix and harder martensite islands. The deformation localizations, evolved in softer ferrite matrix, are hindered by neighboring martensite islands which causes the stress triaxiality buildup in ferrite matrix. A detailed comparison of stress triaxiality distribution between ferrite and martensite matrix has been established with proper justification.