Effect of the random spatial distribution of nuclei on the transformation plasticity in diffusively transforming steel

Abstract

The γ → α diffusive phase transformations of steels can lead to transformation plasticity (TRIP) if accompanied of an external loading stress or a pre-hardening of the parent phase. The most current approaches of its modelling are based on the Greenwood-Johnson mechanism; they call upon hypotheses (about microstructure morphology, constitutive laws...) which are at the origin of discrepancies between predictions and experimental observations in particular loading cases. Some of these restricting hypotheses can be eliminated with a micromechanical finite elements approach, where the elastoplastic interactions between phases are determined at the micro-scale of a volume element containing hundreds of growing particles (Barbe et al., 2005(Barbe et al., , 2008. This paper deals with the effect of the spatial distribution of product phase nuclei on the global kinetics and transformation-induced plasticity (TRIP) in the volume element. Two distributions are considered: uniform random and at preferential nucleation sites of a Voronoi tesselation mimicking austenite microstructure.

A numerical modelling of 3D polycrystal-to-polycrystal diffusive phase transformations involving crystal plasticity

“…But the best qualitative agreement with experimentally measured TRIP is provided by PX2PX modelling. This is mainly related to the kinetics of transformation, as explained in Barbe et al [2008]; Hoang et al [2007]; Quey et al [2009]: whereas the volume fraction of product phase evolves proportionally to t 3 with the MH modelling, it is described by a sigmoidal function (of the form 1 − exp(−at b )) with PX2PX modelling, and thus better matchs real kinetics. It should also be recalled that the TRIP obtained from a microstructure-based modelling, i.e.…”

Return Mapping Algorithms (RMAs) for Two-Yield Surface Thermoviscoplastic Models Using the Consistent Tangent Operator

“…The two thermomechanical models presented here are able to take into account the initiation and development of these TSTs, especially in the immediate vicinity of the top of the rails on which the trains run (see [19]), based on the main assumption that the friction occurring in the wheel/rail contact area -where the thermal effects are considerable -is strongly associated with the mechanical loading mainly applied, i.e., that TSTs are due to thermomechanical coupling processes (see [17,20]). During the solid-solid phase transformations which occur under mechanical loads, an "anomalous" plastic flow, which is also known as TRIP (transformation-induced plasticity) (see [21][22][23][24][25]), generally occurs even at much lower stress levels than the initial yield stress (the softest phase) of the material in question. Indeed, this TRIP-like mechanism can be superimposed on the classical plasticity behaviour which are always present in metallic materials.…”