Le projet RESSET, dans lequel s'inscrit cette thèse, entend éviter le décyclage des ferrailles en explorant de nouvelles routes métallurgiques engendrant des propriétés mécaniques améliorées, en présence d'éléments chimiques a priori contaminants et néfastes, comme le Cu, et en utilisant des concepts de design des matériaux. On visera en priorité des séquences de précipitation pouvant renforcer le matériau, à composition contrainte, et leur couplage avec d'autres transformations de phases d'intérêt dans les aciers, à savoir la transformation martensitique ou la réversion de l'austénite. A cet effet, des outils de modélisation des cinétiques des transformations de phases seront implémentés. Des microstructures obtenues expérimentalement par des traitements thermomécaniques sur un alliage modèle avec une composition typique de ferrailles automobiles serviront d'une part à obtenir des informations sur les évolutions microstructurales aidant au développement des modèles théoriques. D'autre part, elles seront confrontées aux prédictions des simulations pour valider leur robustesse et pour pouvoir l'utiliser pour améliorer le recyclage des aciers.
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At first sight there is limited room for steel recycling improvement as the recycling rate is already quite high (90%). However, this rate does not account for downcycling aspects. Indeed, recycling a material does not mean that its application is as prestigious as originally. New alloys are thus processed to fulfill the need for structural and functional materials, generating a large part of the CO2 emission over the world. The fact that materials are not simply reused is partly related to sorting issues. The industrial technology lacks maturity to completely differentiate the huge diversity of grades ending up to scrap dealers. Consequently, steel scrap becomes a mix of grades that does not have the composition the research and material development have focused on so far. In turn, the scrap is either mixed with primary chemical elements from ores to return to a well-known composition, or transformed into material parts for which the specifications are less strict. From a sustainability perspective, it is needed to take care of this scrap.

The RESSET project, framework for this thesis, aims at avoiding steel scrap downcycling by exploring new thermomechanical routes leading to improved mechanical properties in presence of contaminants, like Cu, and using materials design concepts. The work specifically intends for precipitation sequences able to strengthen the material. To fulfill this objective, modelling tools describing phase transformation kinetics depending on processing conditions and for the constrained scrap composition will be developed. Experimentally obtained microstructure of a model alloy subjected to a thermomechanical treatment and which composition will be fixed by a typical scrap composition will be investigated to get insights into the microstructure evolution during the processing to help the fundamental model development. These microstructures will finally be compared to the modelling tool predictions in order to validate it and to use it to help steel recycling by providing new solutions.
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Début de la thèse : 01/10/2025
WEB : https://umet.univ-lille.fr/Uploads/get.php?id=242

Funding category: Autre financement public

ANR Financement d'Agences de financement de la recherche