Métallurgie
Etude expérimentale et modélisation des cinétiques de transformation de phase dans un alliage de titane
The aim of this thesis is to experimentally study and to model the kinetics of α + β → β → αII phase transformations in Ti-6Al-4V alloy for isothermal and non-isothermal conditions. To this purpose, several technics have been performed (DSC, SEM, optical microscopy, in-situ electrical resistivity and XRD). The KM-JMA equation has been used to describe the kinetics of phase transformations during isothermal holdings. An approach based on the additivity rule has been developed to adapt the KM-JMA equation to non-isothermal phase transformations and is compared to the one using the fictitious time. Kinetics parameters (n, k and Q) have been determined using this approach and discussed based on the microstructural analysis. Mechanisms of the α + β → β → α phase transformations have been discussed by considering the microstructural analysis and the kinetics parameters already determined. Finally, the βm → αII phase transformation kinetics in isothermal conditions has been simulated with the MatCalc software and modelled using both the nucleation – growth theory and the KM-JMA equation. Voir les détails
Mots clés : Ti-6Al-4V, KM-JMA, additivity, nucleation – growth
Modélisation paramétrique de l’effet du pouvoir refroidissoir sur le comportement mécanique des alliages métalliques fonctionnels lors de leurs transformations
La connaissance de modèles de prédiction des propriétés mécaniques des alliages ferreux est utile dans de nombreuses applications. Ces applications sont celles de l’analyse de l’influence des paramètres des produits tels la composition chimique et les paramètres de déformation sur les caractéristiques finales des aciers obtenus. En pratique, les modèles de prédiction ne sont pas a priori connus et leur établissement nécessite un effort plus ou moins considérable notamment à cause de la grande variabilité des paramètres dimensionnels et chimiques des produits et de la complexité des systèmes de laminage. En particulier, cette complexité du système industriel a fait en sorte qu’au cours de la fabrication des bandes laminées à chaud en acier, on a pu constater un problème de dispersion des propriétés sur produit fini, nous avons choisi d’expérimenter la régression polynomiale c’est à dire en considérant le modèle linéaire avec contraintes métallurgiques. L'effet de la vitesse de refroidissement sur la taille du grain ferritique final a pu être évalué de façon quantitative pour plusieurs vitesses de refroidissement. La température de laminage a une certaine influence sur la taille du grain ferritique. En particulier, nous avons mis en évidence l'effet de la vitesse de refroidissement sur la taille du grain ferritique. Voir les détails
Mots clés : modèle de prédiction, vitesse de refroidissement, taille de grain, Laminage, acier
Extension de la méthode des tranches au cadre viscoplastique lors de la modélisation du laminage des tôles pour éviter les ruptures de bandes
Nous présentons dans ce travail un modèle mathématique du laminage des tôles dans les cadres elastoplastique et elastoviscoplastique.Ce modèle s’appuie sur la méthode des tranches cette dernière méthode est utilisée classiquement dans le cadre rigide plastique indépendant des vitesses. Cependant, lors du laminage à chaud les vitesses jouent un rôle primordial sur l’intensité des contraintes mise en jeux et donc sur l’effort et le couple de laminage.Pour prendre en compte des vitesses, nous avons mis au point un nouvel algorithme basé sur la méthode du tir. Techniquement nous avons utilisé la méthode de la sécante qui ajuste la position du point neutre et la méthode Runge- kutta pour la solution du problème.Nous obtenons un modèle ouvert qui nous permet d’utilisée déférentes lois de comportement et de frottement plastique et viscoplastique.Nous finalisons ce travail en testant différentes hypothèses de comportement volumique et surfacique. Voir les détails
Mots clés : rupture, modélisation, Laminage, vitesse, viscoplastique
Influence of heat treatment on the structure and abrasion wear of A105N steel
Wear is the removal of material from a surface by very different mechanisms such as abrasion, erosion, fatigue and corrosion. In the industrial sector, the cost of repairing used parts is very high; the solution in this case is to choose an anti-wear material. To choose an anti-wear material, the first factor is the identification of wear type; however, the conditions of use in the industry are complex so the choice of materials is difficult.Usually the choice of material depends on several factors such as high hardness, high resistance to abrasive wear and low friction coefficient. Thermal treatments are proposed in order to improve these properties. The objective of our work is to study the influence of heat treatment on the structure and abrasion resistance behavior of A105N steel.Samples solution treatment is carried out at a temperature of 900 °C for 2 h then quenched in water. Experimental techniques such as optical microscopy, SEM, EDX and abrasion wear test are used to highlight the effect of heat treatment on the wear resistance of the steel.The microstructural characterization shows that in the initial state, the structure is composed of ferrite and perlite, after tempering, the structure is composed of perlite and bainite. The wear tests by abrasion show a clear difference on the weight losses of up to 50% following the quenching treatment. Voir les détails
Mots clés : wear, abrasion, steel, heat treatment, A105N.
Characterization and Microstructural of Hot Rolling Mill Scale
In the IMETAL-El Hadjar complex, during the steel manufacturing process, a significant amount of scale is produced onthe surface of slabs and billets of hot-rolled steel. In the various rolling mills, the quantity of scale produced is estimated to be about0.1% of the annual production of the steel complex. The quality of the thin steel sheet during the rolling process is affected by thebehavior of the iron oxide layers formed on their surfaces (scale).This amount of scale which is a fatal by-product of the forging and rolling processes can be reused in certain areas and applied byappropriate recycling techniques such as agglomeration of iron ores in the blast furnace as a raw material. This aspect of recycling istaken into consideration.The objective of this study is to identify the microstructural properties of the scale, using different analytical methods such as X-raydiffraction and scanning microscopy.Several samples were used for characterization of the locally produced scale.The analyzes of the results given by SEM showed that hematite and magnetite, the main phases present in the scale, are stacked inthin layers of a magnitude of the order of a micron meter. These phases of iron oxides are confirmed by the analysis of the spectragiven by the X-ray diffractometer.The presence of silicon in the scale is due to the covering powder used on the wall layers of the ladles. Voir les détails
Mots clés : mill scale, Oxidation, hot rolling, Microstructural properties, SEM, X-ray.
Characterization and Microstructural of HotRolling Mill Scale
In the IMETAL-El Hadjar complex, during the steel manufacturing process, a significant amount of scale is produced on the surface of slabs and billets of hot-rolled steel. In the various rolling mills, the quantity of scale produced is estimated to be about 0.1% of the annual production of the steel complex. The quality of the thin steel sheet during the rolling process is affected by the behavior of the iron oxide layers formed on their surfaces (scale).This amount of scale which is a fatal by-product of the forging and rolling processes can be reused in certain areas and applied by appropriate recycling techniques such as agglomeration of iron ores in the blast furnace as a raw material. This aspect of recycling is taken into consideration.The objective of this study is to identify the microstructural properties of the scale, using different analytical methods such as X-ray diffraction and scanning microscopy.Several samples were used for characterization of the locally produced scale.The analyzes of the results given by SEM showed that hematite and magnetite, the main phases present in the scale, are stacked in thin layers of a magnitude of the order of a micron meter. These phases of iron oxides are confirmed by the analysis of the spectra given by the X-ray diffractometer.The presence of silicon in the scale is due to the covering powder used on the wall layers of the ladles. Voir les détails
Mots clés : mill scale, Oxidation, hot rolling, Microstructural properties, SEM, X-ray
APPROXIMATE MODEL FOR PREDICTING STATIC RECRYSTALLIZATION OF FERRITIC STAINLESS STEEL TYPE 430
An approximate model for predicting static recrystallisation of ferritic stainless steel type 430, in hot rolling is proposed. In this model, the effect of variables such as strain, strain rate, temperature and initial grain size were considered during hot rolling operations. A set of integrated mathematical models for predicting static recrystallisation evolution during hot rolling has been developed through laboratory research work experiments. It consists of many sub-models such as percentage of recovery, recrystallisation kinetics, time for 50 percent of recrystallisation, recrystallised grain size and grain growth. Some of the most important theoretic basic approaches to describe the kinetics of primary recrystallisation were first independently developed and comprehensive portrayed by Johnson and Mehl, Avrami as by Kolmogorov (Often named the JMAK-theory).The quantitative determination of the effects of these variables obtained, analysed and compared in the context of the recrystallisation kinetics of this material.The predicted results are in good agreement with measured of laboratory tests. The results of constitutive models based on semi empirical equations will be compared in the next publication to more sophisticated models based on cellular automata, vertex and Monte-Carlo-Potts methods. Voir les détails
Mots clés : ferritic stainless steel, hot rolling, Static recrystallisation, Mathematical model.
Effect of Welding Process on Microstructure and Mechanical Properties of Duplex Stainless Steel Welds
The purpose of this study is a comparison between the effect of two electrical arc welding processes, on the structural and mechanical behavior of 2205 duplex stainless steel weldments, the first one is the manual process GTAW and the second one is the automatic process SAW. This effect has been identified and examined in the different welding area namely, the base metal BM, the heat affected zone HAZ and the weld metal WM, using optical metallographic techniques and mechanical methods by hardness tests. Voir les détails
Mots clés : duplex stainless steel, welding, microstructure, mechanical properties
Tribological and Eelectrochemical Characterization of a Titanium Alloy in a Physiological Solution.
Titanium alloys are used primarily for biomedical and / or dental applications. They are characterized by a better mechanical compatibility with the tissues and a good biocompatibility in the body fluids. The alloy TA6V4 used in orthodontics is subject to degradation by wear and corrosion. In this context, we are primarily interested in the study of the dry friction wear of the TA6V4 / Al2O3 torque by means of a rotating Ball / Disc tribometer. In order to evaluate the biocompatibility of this alloy, an electrochemical study in a physiological solution was carried out using conventional electrochemical measurement methods (time-dependent monitoring of the corrosion potential, potentiodynamic curve) as well as Electrochemical impedance spectroscopy. The results of tribology, the friction of the torque TA6V4 / Al2O3 against each other, revealed a friction coefficient of 0.2 and a wear volume of the order of 22.579.10-12 mm3/N.mm. The wear mechanism studied by scanning electron microscopy revealed abrasive and adhesive degradation. From the electrochemical point of view, the TA6V4 alloy in Hank's solution exhibited good corrosion resistance with a polarization resistance of 44 540 Ω. Analysis by electrochemical impedance spectroscopy indicated that this alloy is passive in nature, following the formation of a surface-stable two-phase oxide layer composed of an internal compact layer which has good corrosion resistance And an external porous layer which is favorable to osteointegration. Voir les détails
Mots clés : Alloy TA6V4, Corrosion behavior, friction
Influence of Vanadium on the Corrosion Behavior of High Manganese Steel in 0.5 M H?SO? Solution
The effect of vanadium on the corrosion behavior of high manganese steel in 0.5 M H?SO? solution has been investigated using scanning electron microscopy, potentiodynamic polarization and impedance spectroscopy. The results have shown that the addition of vanadium to high manganese steel decreases the corrosion current density from 2.1 mA cm¯² to 1.29 mA cm¯². Impedance diagrams show the existence of a high frequency capacitive loop and a low frequency inductive loop. The addition of vanadium increases charge transfer resistance from 5.18 Ω cm² to 12.45 Ω cm². Voir les détails
Mots clés : corrosion, Manganese, EIS, Tafel