To decrease vehicle masses (reduction of CO2 emission), steels with improved formability are developed using alloying elements such as aluminium, silicon or manganese. During the recrystallization annealing of steel strips at ~ 1070 K under reductive atmosphere (N2 + H2), those elements are prone enough to oxidation leading to oxygen-induced segregation at the steel surface. A strong industrial concern is that the bad wetting of these oxides by zinc degrades the efficiency of galvanization, which is the historical method to prevent corrosion whose principle is that zinc being less noble to iron, it sacrificially corrodes to protect the substrate steel. Therefore, galvanization faces a new paradigm since it switches from what is close to a reactive interface with bare iron to a high-energy interface with wide bandgap oxides. To improve the coatability of steel by zinc, a strategy consists in trying to control upstream the surface oxidation of the steel. A detailed analysis of alloyed steel and environment being far out of grasp, the present SURFOX project, focuses on the oxidation of Fe-Al alloy, a common alternative to Al-alloyed steel. It involves two partners, University Pierre and Marie Curie and ArcelorMittal Maizières Research represented by two groups, “Low-dimensional oxides” (Paris group) and “Physical Chemistry and Surfaces” (Maizières group). Three contributions are foreseen, experiments on single crystals and numerical simulation from Paris group, experiments on polycrystalline FeAl plates from Maizières group. It has been chosen to study Fe-15at.%Al samples since at annealing temperature (around 1 070 K) the alloy matrix corresponds to the ferrite phase as in the case of industrial Al-alloyed grade. There is some suggestion that local arrangements in supported aluminium oxide layers mildly depend on the nature and orientation of the support and of the Al-content of the alloy, although long-range structures and oxidation kinetics are different. This suggests to define common fingerprints to all orientations prior to examining on this basis the parameters (orientation, environment) which affect the oxidation of FeAl samples. • Toward common fingerprints of all Fe-15at.%Al oxidized surfaces - By analysis relying on surface science methods in ultra-high vacuum conditions, including electron and ion spectroscopies, electron diffraction and near-field microscopy, the objective of Paris experimental group is (i) to determine the structures of the Al oxide layers formed at the Fe-15at.%Al(110), (100) and (111) surfaces, considered herein as reference data, and (ii) to explore the exciting issue of the representation of all structures by similar short-range arrangements. These will be defined with the support of numerical simulations. The structure of the oxide layers formed on Fe-15at.%Al polycrystalline plates, second series of reference data as studied by surface and material science methods (Maizières group) including electron spectroscopies and microscopies, will then be compared to those fingerprints in order to achieve an unified picture. • Orientation and environment-dependent oxidation – On the basis of this picture and by combining numerical simulation (Paris group) and experiments in various atmospheres (O2, H2O, H2O/H2, Maizières and Paris group), it is foreseen to examine the rationale of (i) the way the oxidation during recrystallization annealing depends on the dew point of the atmosphere in which the process is operated, in particular to lead to external and internal oxidation, and of (ii) the orientation-dependent oxidation anisotropy of the ferrite grains (kinetics, stability) which is of paramount importance in the industrial context. The challenging issue is to set up a unique structural model for oxide adlayers formed at the surface of FeAl alloys and to use it to get insights into the behaviour of these oxide layers as a function of both environment and crystallographic orientations

Residual gases with low heating values resulting from steel production plants are presently poorly valorised, although they represent an important energetic reservoir. These gases exhibit specific combustion characteristics as compared to conventional gases. These untypical properties make necessary transposing the combustion techniques which are presently used. The proposed project aims at identifying, by means of experimental and numerical techniques, technological solutions for exploiting in an optimal way these gases in steel reheating furnaces, over a large spectrum of operating conditions. Experimental databases will be acquired at laboratory and semi-industrial scales. In parallel, fundamental numerical studies will allow characterising the interactions between chemistry and turbulence for these gases. This will feed the development of a micro-physical model, which will be validated and implemented in a three-dimensional simulation code used for designing and optimising industrial installations. The obtained numerical tool, which will be able to characterise in detail the interactions between chemistry, turbulence and radiation will be used by the industrial partner for identifying technological evolutions of burners and industrial furnaces, with the final objective of minimising pollutant and greenhouse gas emissions.

In this project we propose a research on a new process with the aim of its industrialization. This is a new hyper-deformation process that is applicable to metallic tubes. During this process, the microstructure of the material is fragmented by an extreme plastic deformation (torsion) and develops an ultra-fine microstructure that approaches nano-structure. This transformation attributes to the material exceptional mechanical properties. Namely, the elastic limit of the material can be multiplied by approaching the maximum theoretical limit. During this process, the tube is twisted by severe plastic deformation under a high hydrostatic pressure. The dimensions of the tube do not change during the test. The material is sheared around the axis of the tube. This process was invented recently by the partners of the present project and published in the journal Scripta Materialia [Severe plastic deformation of metals by high pressure tube twisting "by L.S. Tóth, M. Arzaghi, J.J. Fundenberger, B. Beausir, O. Bouaziz, R. Arruffat-Massion, Scripta Materialia, Volume 60, Issue 3 (2009), pp 175-177] and was received very favourably by the scientific community of the field. The process was called 'HPTT' (High Pressure Tube Twisting). The first tests were conducted on aluminium and copper. In collaboration with our industrial partner - ARCELOR MITTAL - we propose in this extensive research project a detailed study on the feasibility of the process on steel tubes for industrial HPTT process. While it is well known in the literature that hyper-deformation is an effective method to obtain nano-structured materials, a massive industrialization of the various processes proposed in this area still remains to be done (see State of the art section in document B). Our ambition is to develop an equipment suitable for HPTT hyper-deformation of low alloyed IF steel tubes. Microstructural studies will be carried out to control the microstructure. Various mechanical tests will be needed to test the properties obtained on the hyper-deformed materials. In addition, simulations will help the understanding and control of the various process parameters.

Spray cooling is used in an increasing numbers of industrial applications. In the steel industry, during heat treatment of alloys, very high quenching rates are required to obtain strong and hard bonding in the metallurgical microstructure. The main purpose of this project is to deliver new models of spray cooling of solid surfaces at very high temperatures, typically around the Leidenfrost temperature and beyond. Compared to other cooling methods like jet impingement and pool boiling, spray cooling can potentially achieve very high heat dissipation rates while enforcing uniform and controlled cooling and reducing water consumption. However, despite its advantages, integration of spray cooling is still limited because of incomplete understanding of the complex fluid flow and heat transfer characteristics of sprays interacting with the hot surface. In particular, at high surface temperatures, an insulating vapour film quickly develops at the contact between a drop and the solid surface. The presence of this vapour layer modifies the dynamic of the impinging drops and reduces heat transfer considerably. When considering a practical spray, cooling is the most important beneath the centre of the spray, where droplet concentration is generally the highest, which results in a rewetting of the solid surface. A liquid film is then created and supplied with the incoming droplets; the heat flux extracted from the wall is also considerably enhanced. The present project has the ambition to combine advanced experiments, direct numerical simulation, Euler-Lagrange simulation and a large scale industrial experiment. To infer new and efficient models of spray cooling, experiments will be performed at different scales with a graded complexity. In this purpose, this project will rely on two distinct experiments. The first one will be devoted to the study of the impingement of a monodisperse and well-controlled droplet chain or of an array of parallel droplets chains in order to feature the space and time interaction phenomena occurring in sprays. These impingements will occur on a plate heated by induction with a constant flux. Significant efforts will be made to achieve experiments with a high-performance instrumentation. Non-intrusive innovative diagnostics will be specially developed and adapted in this project. Experiments dedicated to droplets chains will benefit from one of the largest range of experimental techniques never implemented yet in such a configuration. For instance, temperature droplets (before and after impingement on the wall) will be measured by two colors planar laser induced fluorescence, their sizes by forward scattering interferometry and their velocities by laser Doppler velocimetry. The heat flux removed from the hot solid surface will be inferred from infrared thermography combined with inverse conduction. In close interactions with the experimental accomplishments on droplet chains, direct numerical simulations (DNS) with interface tracking using the level-set technique will be achieved. This task implies taking into account phase change, Marangoni effect and radiative heating. DNS will help to assess the influence of many physical parameters especially when the experiment is not possible. The impingement of a single droplet chain or of an array of droplets chains on a heated wall will be studied experimentally and also numerically, using DNS, which will highlight the effect of successive impingements or of the spatial proximity of the impingements. Data coming from both experiments and DNS will be used to develop sub-models of droplet-heated wall interactions, taking into account heat and mass transfers. Euler-Lagrange numerical simulations will also be implemented: the sub-models developed for the bouncing and splashing regimes with inclusion of thermal transfer at the wall will be integrated in the code. A liquid film model will be also developed and integrated in the Euler-Lagrange code, which will be combined to a heat transfer solver to account for the heat conduction within the solid wall. The second experiment will focus on polydisperse sprays cooling with well controlled laboratory conditions. Here investigations will rely on a fine characterization of the statistical distribution of physical parameters like droplets diameter, velocity and number concentration through Phase Doppler Anemometry (PDA). Relevant PDA data will be supplied to initiate the numerical simulations of the spray/solid surface interaction that will be compared to the heat flux extracted from the wall, measured by IR thermography associated with inverse conduction. In a last step, an industrial cooling pilot unit of steel products at unit scale will be used in order to provide the extracted fluxes for previously characterized spraying conditions. The data coming from these experiments will be compared to the results of the Euler-Lagrange simulation code.