Добірка наукової літератури з теми "Cémentation gazeuse basse pression"
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Дисертації з теми "Cémentation gazeuse basse pression":
Matamoros, Marin Fatima. "Modélisation et optimisation des fours de cémentation gazeuse basse pression." Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0288.
This PhD work deals with the development of an optimization methodology for low-pressure gas carburizing furnaces. The objective is to determine the optimal operating conditions allowing operators exposed to the toxic by-products generated (polycyclic aromatic hydrocarbons (PAHs) and soot in this case) to work in safer conditions. A first-principles model of the process based on mass balance equations as well as equations derived from a detailed kinetic mechanism of gas-phase acetylene pyrolysis is first developed. The kinetic model is then reduced in order to reduce the size of the differential system; then completed by a model of soot formation, a pyrolytic carbon formation reaction and heterogeneous phenomena occurring on the surface of the steel parts to be cemented which are described by means of Langmuir-Hinshelwood-Hougen-Watson model. Experiments conducted on a laboratory scale tubular reactor and a jet stirred reactor are carried out without steel parts. The results are then compared to the results of simulations of acetylene pyrolysis, soot and pyrolytic carbon formation in a plug flow reactor and in a perfectly stirred tank reactor. The results show the importance of the role played by the formation of pyrolytic carbon and soot on the formation of PAH. Experiments on an industrial low-pressure gas-carburizing furnace are conducted as well; they consist in the carburization of steel parts using an industrial "recipe", i.e. predetermined operating conditions obtained by trial-and-error basis in order to meet the desired carburizing depth. The experimental results are used to estimate the parameters of the heterogeneous surface reaction by assuming a complete model of low-pressure gas carburizing in a perfectly stirred tank reactor. The model is then used in the formulation of the dynamic constrained optimization problem which aims to minimize the production of toxic compounds while ensuring the industrial quality of the carburized steel parts. Optimal operating conditions allowing to obtain steel parts of the same quality as those obtained with the industrial recipe are then determined by solving the optimization problem and experiments using the new operating conditions are conducted in the industrial furnace. The results corroborate that the optimized recipe leads to steel parts of the same quality as the industrial recipe, while reducing the process toxicity
Bensabath, Tsilla. "Approche préventive pour une réduction des Hydrocarbures Aromatiques Polycycliques (HAP) dans les fours à pyrolyse : application à la cémentation gazeuse à basse pression." Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0064/document.
Low-pressure gas carburizing is a heat treatment process used to harden surface of steel by enriching the metal with carbon atoms coming from pyrolysis of hydrocarbons. At the same time, a wide variety of molecules and radicals are also formed in the gas phase. They react together, leading to the formation of PAHs. PAHs are toxic and even carcinogenic, and activities such as furnace maintenance may thus represent a risk to workers. Experiments of acetylene pyrolysis were carried out in conditions close to low-pressure gas carburizing processes, at 900°C and 8 kPa. Two kinds of reactors were used: a jet stirred reactor and tubular reactors. At the outlet of the reaction zone, products of pyrolysis were analyzed. Among other products, 16 PAHs classified as priority pollutants by the United States Environmental Protection Agency (US EPA) were observed. Influence of residence time and of reactant dilution was studied. Experimental results were compared to those obtained with a detailed kinetic model. This model was developed in order to describe PAH formation during light hydrocarbon pyrolysis. The focus was placed on formation pathways of the first aromatic rings and of the 16 EPA-PAHs. In addition to the experimental data obtained in this study, the model was validated using experimental data from the literature. The aim of the study is to understand the phenomena of PAH formation and growth in order to find operating conditions to make safer the low-pressure gas carburizing processes
Eyzop, Daniel. "Caractérisation de couches cémentées en basse pression." Lille 1, 1996. https://pepite-depot.univ-lille.fr/LIBRE/Th_Num/1996/50376-1996-232.pdf.
Les résultats sont discutés en fonction des corrélations possibles entre ces différents paramètres. L'influence de l'austénite retenue ou des carbures est étudiée. Nous montrons, notamment, l'effet de la structure a cur sur le point d'annulation des contraintes. Pour quelques cas d'étude, on caractérise la résistance à la fatigue de flexion rotative par la détermination de la limite d'endurance et des paramètres de la loi de bastenaire. Modéliser la répartition des contraintes résiduelles après traitement de cémentation est l'objectif de nombre de chercheurs. Le but est d'intégrer ces contraintes résiduelles aux calculs prévisionnels de comportement de pièces mécaniques. Bien qu'il existe des modèles de calcul des contraintes résiduelles prenant en compte les effets thermiques mécaniques et métallurgiques, nous avons choisi de comparer nos résultats aux prévisions déduites de modèles simples, purement élastiques, bases sur les seules variations volumiques locales. L'intégration de l'effet d'un revenu à basse température complète cette approche. L'ensemble de ces résultats constitue une banque de données pour l'industriel et pour le chercheur et confirme l'intérêt du traitement de cémentation sous basse pression
Douce, Jean-François. "Modélisation de la trempe gazeuse haute pression : application aux aciers de cémentation et de trempe." Thesis, Vandoeuvre-les-Nancy, INPL, 2008. http://www.theses.fr/2008INPL085N/document.
The use of non vaporizable fluids such as gas to quench steel bodies makes the simulation of all the coupled physical phenomena involved in this heat treatment possible thanks to current numerical simulation tools. It gives access to the prediction of thermal, metallurgical and mechanical behaviour of steel pieces during quenching operation. Several authors have tried and build such kind of models in order to promote gas quenching use either by trying to replace less environmental friendly oil treatments or by trying to control distortions during or after quenching. In our work a model describing the physical coupled phenomena, from gas flow to distortion has been built step by step by coupling both commercial numerical codes Fluent and Sysweld. Simulation results have then been compared to gas flow velocities measurements (by PIV), temperature measurements and in situ distortions measurements (contour’s detection method). This confrontation revealed a very good agreement between calculated and experimental data despite some slight differences, which have been analysed in detail. This validated the calculation method used in the model. One of the perspectives of this work could be the validation of the model for higher quenching rate. However, some industrial applications (tridimensional more complex bodies quenching simulation, quenching of full loads, …) can be run from now on with confidence
Turpin, Thierry. "Etude des transferts de matière et des transformations de phases au cours de la cémentation en phase gazeuse à la pression atmosphérique d'aciers inoxydables fortement alliés." Vandoeuvre-les-Nancy, INPL, 2002. http://www.theses.fr/2002INPL046N.
Carette, Laurent. "Etude des mécanismes de formation des carbures obtenus par cémentation basse pression d'un alliage de tantale, application à la pyrochimie." Thesis, Paris, ENSAM, 2019. http://www.theses.fr/2019ENAM0029.
Tantalum is a metal with a good corrosion resistance. However, tantalum pyrochemical crucibles are damaged by the molten metals they contain, especially by diffusion at the tantalum grain boundaries. A solution is to carburize the crucibles. During carburizing, two carbides are formed: TaCx and Ta2Cx in the form of two homogeneous surface layers. During cooling, a layer of Ta2Cx precipitates is also formed.In this study, the low pressure carburizing process is applied to the TaW2.5% alloy (Ta97.5wt.%-W2.5wt.%). The aim is to benefit from the advantages of tungsten addition: limitation of the grain growth during the treatment and an increase of the carbide precipitation at the grain boundaries. However, these carbides differ from those of pure tantalum by their nature and their morphology (lamellar layer).A CALPHAD study was performed to obtain a thermodynamic database and thus improve the understanding of MC and M2C carbide formation (with M=Ta,W). In addition, EBSD analyzes have shown the crystallographic relationships {110}Ta//{0001}Ta2Cx and {111}TaCx//{0001}Ta2Cx.Finally, the layer growth kinetics were studied according to the different parameters (duration of carburizing and diffusion, temperature, surface state and microstructural state). This study thus made possible to obtain different phases on the surface of crucibles: MC, M2C or TaW + M2C precipitates. Then, these surface microstructures were evaluated against attack by liquid metals (Al, Bi) and salts (CaCl2)
Cotton, Dominique. "Etude de formation d'hémicarbure de tantale (Ta2C) par l'intermédiaire d'un procédé de cémentation sous pression réduite." Thesis, Dijon, 2015. http://www.theses.fr/2015DIJOS010/document.
Tantalum is a very dense metal (d = 16.6) and has a very high melting temperature of 2996°C. This material is particularly required for crucibles used for pyrochemical applications. Early studies show that a carburizing treatment enhances corrosion resistance from liquid metals. Indeed, the intergranular attack of tantalum is stopped by Ta2C precipitates, which occupy the grain boundary regions. The production of the carbon saturated tantalum with Ta2C precipitates requires a good understanding of tantalum carburizing.A carburizing treatment on tantalum sample causes the emergence of a TaC layer on surface and Ta2C layer just below. A reduction of carbon flow has enabled the study of the first steps of tantalum carbides formation. This specific condition of carburizing leads to an epitaxic growth of carbide layers on tantalum substrate. EBSD analysis highlights the crystallographic relations between each phase.Tantalum carbide layers are highly carbon concentrated. So the growth of carbide layers has to be controlled during the carburizing treatment. Several parameters may affect carbide layers growth : process parameters (time and temperature of carburizing treatment) and external parameters such as the reactive surface of the samples. The influence of these parameters on tantalum carbide growth kinetics has been studied. In addition, the diffusion of carbon in tantalum has been modeled with CASTEM© software. Experimental data are used to compute parameters of the model, such as carbon diffusion coefficient in tantalum.Other microstructures than TaC can be obtained on surface by applying an annealing treatment after carburizing. With this treatment, the carbon contained on surface diffuses to the bulk of the metal. Annealing treatment parameters have been determined to get on surface TaC, or Ta2C, or carbon saturated tantalum with Ta2C precipitates
Petit-Etienne, Camille. "Dépôt d'oxyde de silicium par procédé plasma hors équilibre à basse pression et à pression atmosphérique sur de l'acier : application aux propriétés anticorrosion." Phd thesis, Paris 6, 2007. http://tel.archives-ouvertes.fr/tel-00367151.
Gasnot, Laurent. "Application du couplage de la fluorescence induite par laser et de la chromatographie à l'étude de la formation de NO dans des flammes basse pression méthane/air." Lille 1, 1995. http://www.theses.fr/1995LIL10140.
Le, Thi Kim Cuong. "Raman spectroscopy of soot produced in low pressure flames : ex situ Analyses and Online Gas Phase Studies." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS068/document.
Every year, an amount of 107 tons of soot is produced on the world scale. Soot, as part of atmospheric black carbon, has serious impacts on climate change and human health. The impacts depend on many factors including adsorbed compounds, aging and mixing processes. Therefore in order to reduce the soot amount, besides considering these mentioned factors, the study of formation kinetics, structure and optical properties is also essential. There are several methods applied in soot investigations. Raman spectroscopy plays a particular role as it is a powerful tool for structural investigation of the carbon-based materials because it is sensitive to molecular structures. In this work, differential Raman cross sections of soot and some other carbonaceous particles were measured to progress toward quantitative Raman spectroscopy. Soot particles produced by premixed ethylene flames at a low pressure were investigated by ex-situ Raman measurement on deposited films and in-situ(online) Raman measurement in the gas phase. Combination of the Raman spectroscopy of soot sampled on substrates with infrared and optical spectroscopy and transmission electron microscopy allowed progressing on the interpretation of soot Raman spectra. The online gas phase measurements provided a novel view on soot birth and structures in low pressure flames with, for instance, the detection of a large amount of sp hybrized carbon atoms during nascent soot growth. These studies pave the way to soot detection and analysis directly and quantitatively in the atmosphere