Le tantale est un métal très dense (d = 16,6) et fond à très haute température (2996°C), ce qui en fait un matériau potentiellement utilisable pour des creusets utilisés en pyrochimie. La littérature montre qu'il est possible de renforcer encore ces propriétés anti-corrosion par un traitement de cémentation. En effet, la corrosion intergranulaire du tantale est stoppée par la présence de précipités de Ta2C aux joints de grains. L'obtention du Ta saturé carbone avec Ta2C aux joints de grains en surface (Ta(C) + Ta2C), très pauvre en carbone, demande une bonne compréhension et une maitrise de la cémentation du tantale.La réalisation d'un cycle de cémentation sur des échantillons de tantale provoque l'apparition à la surface du tantale d'une couche de TaC (en surface) et d'une couche de Ta2C sous jacente. Un travail sur la réduction du flux de carbone à la surface du tantale a permis d'étudier les premiers stades de formation des couches de carbures de tantale. Ces conditions particulières de cémentation favorisent la croissance en épitaxie des couches de carbures sur le substrat Ta. Les analyses EBSD ont permis de mettre en évidence les relations cristallographiques entre chaque phase.Lors d'un cycle de cémentation, la croissance des couches de carbures doit être contrôlée du fait que celles-ci soient très riches en carbone. Plusieurs types de paramètres peuvent influer sur la croissance des couches : les paramètres de cycles (temps et température de cémentation) et des paramètres extérieurs aux cycles de cémentation, tels que la surface des échantillons. L'influence de ces paramètres sur la cinétique de croissance des couches a été étudiée. En complément des essais, la simulation numérique avec le logiciel CASTEM© a été utilisée afin d'étudier la diffusion du carbone dans le tantale. Les données expérimentales permettent d’ajuster les variables du modèle comme le coefficient de diffusion du carbone dans le tantale.La réalisation d'un recuit sous vide après cémentation permet d'obtenir en surface des microstructures autres que le TaC. Le recuit fait diffuser le carbone contenu en surface vers le coeur du tantale. Une étude a permis de déterminer les paramètres du traitement de recuit, pour obtenir en surface, au choix : du TaC, ou du Ta2C, ou du Ta(C) + Ta2C. / 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.

The exceptional wear resistance and work hardenability, place Hadfield steel as one of themost important materials for manufacturing cast components used in the mining, crashing,drilling, and excavation industries. In all metallic alloys used for component casting, themechanical properties are highly influenced by the microstructure of the material. Castcomponents with finer microstructural characteristics are known to present bettermechanical properties and reduced risk of defects when compared with components witha coarser microstructure. A reduced grain size in Hadfield steel can increase the strengthof the material up to 30% and reduce the risk of porosity formation during solidification.The practice of adding selected compounds or alloying elements in a metal melt to modifyand refine the microstructure is called inoculation. It is currently one of the trendingmethods utilized in light-metal alloys and cast-iron components production but has not,yet, gained adequate acceptance in the steel casting industry because researchers have notbeen able to find proper inoculants.The main objective of this work is to investigate the qualitative and quantitativecharacteristics of the by-products of deoxidation of Hadfield steel that remain in thematerial after solidification and their positive or negative effect on the coarseness of thefinal as-cast microstructure. This type of research can help to identify the type of particlesor alloying elements that are most effective for refining the microstructure of austeniticsteels and pave the way for developing new or improving conventional deoxidation andinoculation processes that will, in turn, result in the improvement of the properties of thecomponent.The precipitation of particles and the as-cast grain size are studied in aluminum andtitanium deoxidized Hadfield steel samples acquired under pilot scale experimentalconditions. In the first part of this work, the qualitative and quantitative characteristics ofparticles such as type, morphology, composition amount and size are identified. Thesequence of precipitation is established. A model for predicting particle size and growth isdeveloped. The experimental results are compared against thermodynamic equilibriumcalculations and the precipitation mechanisms for each type of particles are described. Inthe second part, the as-cast grain size of samples with varying deoxidation treatments ismeasured. Then, the grain-size is correlated with certain particle characteristic and theparticles are ranked according to their ability to refine the microstructure. The particledisregistry with austenite is calculated and compared to the experimentally acquiredranking. / Hadfieldstålen exceptionella slitstyrkan och deformationshårdnande har gjort dessa till ettav de viktigaste materialen för tillverkning av gjutna komponenter som används inomgruv-, kross-, borr-och gruvindustrin. I alla metallegeringar som används för tillverkningav gjutna komponenter styrs de mekaniska egenskaperna av materialets mikrostruktur.Gjutna komponenter med fin mikrostruktur presentera bättre mekaniska egenskaper ochminskad risk för defekter jämfört med komponenter med grov mikrostruktur. En minskadkornstorlek i Hadfieldstål kan öka materialets hållfasthet upp till 30% och minska riskenför porositetsbildning vid stelning.Tillsatsning av spårämnen eller legeringselement i en metallsmälta för att modifiera ochförbättra mikrostrukturen kallas ympning. Denna metod används i lättmetaller och vidtillverkning av gjutjärnskomponenter, men har ännu inte fått acceptans i stålindustrineftersom forskningen inte har funnit effektiva kärnbildare att användas som ympmedel.Huvudsyftet med detta arbete är att undersöka kvalitativa och kvantitativa egenskaper hosde desoxideringsprodukter som skapas under tillverkningen av Hadfield stål och hur deunder och efter stelning påverkar mikrostrukturens grovlek. Arbetet syftar till att identifierapartikeltyper och legeringselement som är effektiva för att förfina den austenitiskamikrostrukturen och bana väg för utveckling nya och förbättra desoxiderings- ochympningsprocesser som i sin tur kommer att resultera i en förbättring av den gjutnakomponentens egenskaper.Partiklarnas utskiljning och materialet resulterande kornstorlek studerades i aluminiumochtitan-desoxidiserade Hadfieldstål, tillverkade i pilotskala. Den första delen av dettaarbete var att identifiera kvalitativa och kvantitativa egenskaper hosdesoxidationspartiklar, som typ, morfologi, sammansättning och storlek.Utskiljningssekvensen fastställdes. En modell för att förutsäga partikelstorlek och derastillväxt utvecklades. De experimentella resultaten jämfördes med termodynamiskajämviktberäkningar och utskiljningen för varje typ av partikel beskrevs. I den andra delenstuderades kornstorleken och hur denna varierade desoxideringsbehandlingen. Därefterkorrelerades kornstorleken med partikeltyp och dess karaktäristika och rangordnades efterderas förmåga att förfina mikrostrukturen. Partiklarnas kristallografiska missanpassningmot austenitens kristallstruktur beräknades och jämfördes med experimentellt fastställdarangordningen. / InDeGrainS I

Les alliages de type HP constituent un matériau de choix pour l'élaboration des tubes de vaporeformage et de vapocraquage dans l'industrie pétrochimique. Exposés à des températures comprises entre 700°C et 1000°C sous des pressions gazeuses de plusieurs MPa, leur microstructure initiale associée à une fine précipitation secondaire, intervenant en cours de service, leur confèrent une excellente résistance aux mécanismes de fluage auxquels ils sont sujets. Néanmoins, à terme, la coalescence des précipités conduit à la dégradation rapide des tubes.Les effets de certains éléments d'alliages (V, Ti/W) sur la précipitation secondaire des carbures M23C6 et NbC ont été étudiés au travers de simulations via le logiciel TC-PRISMA. Sur la base de résultats prometteurs en termes d'optimisation des caractéristiques de la précipitation, deux alliages modèles ont été coulés au laboratoire et soumis à divers vieillissements dans la gamme de température correspondant aux conditions de service. Les microstructures de ces alliages ont d'abord été comparées à celle d'un alliage HP industriel de composition standard à l'état brut de coulée. La précipitation secondaire a par la suite été caractérisée au sein des trois alliages dans les différents états vieillis. Les investigations microstructurales ont permis de mettre en avant certains effets bénéfiques d'un ajout de vanadium et d'ajouts combinés de titane et de tungstène sur les caractéristiques de la précipitation secondaire. / HP alloys are typically used as steam methane reforming tubes in the petrochemical industry. During service, they are exposed to temperatures between 700°C and 1000°C under gaz pressure of several MPa. Their as-cast microstructure, together with fine in-situ secondary precipitation, provide these alloys with an excellent resistance to creep deformation. Nevertheless, after long-time ageing, coarsening of secondary carbides leads to the weakening of the tubes and therefore to an accelerated damaging.The effects of some alloying elements (V, Ti/W) on secondary precipitation of M23C6 and NbC carbides were investigated through numerical simulations performed with TC-PRISMA software. On the basis of encouraging results in terms of precipitation optimization, two model HP-type alloys were cast at the laboratory and aged in the range of temperatures corresponding to service conditions. As-cast microstructures were first compared with an industrial "standard" alloy. Then, secondary precipitation were characterized for all the alloys and all ageing temperatures. Microstructural investigation highlighted the beneficial effect of vanadium and titanium/tungsten additions on secondary precipitation characteristics.

Group IV transition metal carbides are promising materials for high temperature structural application, due to their unique sets of properties such as high melting temperature, high temperature strength, hardness, elastic modulus, wear and corrosion resistance, metal-like thermal and electrical conductivity and thermal shock resistance. This group includes zir-conium carbide, which, along with its composites, are potential candidates for applications such as nose cones for re-entry vehicle, engines, wear resistant parts and in nuclear fuel cladding. Such structural applications demand high strength material with minimal flaws, in order to achieve the required reliability. Attainment of high strength calls for fully dense material with as small a grain size as possible. Producing fully dense zirconium carbide requires very high temperature, which is a direct consequence of its high melting point. Higher processing temperatures increase grain size, thereby also causing a loss in strength, along with the increased cost. Therefore, there is always a driving force to produce such a material in fully densified form at as low a temperature as possible. There have been a number of studies on processing and densification of zirconium carbide. Pressureless sintering of zirconium carbide requires temperature of 2400oC-3000oC to reach reasonably high density. At such high temperatures, abnormal grain growth limits the final density, as pores get entrapped inside the grains. Hot pressing of zirconium carbide also requires upwards of 2000oC to reach high density and is the primary route to produce densified zirconium carbide product. Reactive hot pressing (RHP), is a relatively new processing approach. Here, the reaction between zirconium and carbon to produce zirconium carbide and the densification of the porous mass, occurs simultaneously. Study on reactive hot pressing of zirconium carbide have shown that, it is possible to achieve very high density at much lower temperatures 1600oC. Clearly, reactive processing is an exciting new technique to process zirconium carbide. However, there has been a lack of studies to understand why it provides better densification than conventional hot pressing. Such understanding is of paramount importance, as it can lead to better optimization of RHP and perhaps even lower the process temperature further. The objective of the present study is to understand the densification process in RHP of zirconium carbide through systematic and carefully designed experiments. A model of reactive hot pressing is also constructed to get more insight into the phenomenon. 0.1 Pressureless Reaction Sintering of Zirconium Car-bide Pressureless reaction sintering (RS) of zirconium carbide is studied to understand the role of stoichiometry and zirconium metal in densification. ZrC of four different stoichiometries are chosen for these sets of experiments which are conducted in vacuum at 1200oC and 1600oC for 1 hour to understand the role of stoichiometry. One sample of pure Zr is also sintered to elucidate the role of zirconium in densification. After reaction sintering, all the samples are characterized by density measurement, x-ray diffraction and microstructure, using scanning electron microscopy. After pressureless sintering at 1600oC, zirconium metal reaches the highest relative density of ~ 95%. Densification decreases monotonically with increasing stoichiometry. Zr+0.5C composition reaches the next best relative density (of 90%), while Zr+0.67C composition shows much lower densification. The other two compositions, Zr+0.8C and Zr+C, in contrast, display de-densification rather than densification. Since the pure zirconium sample reaches high density, it can, in principle, help in densification of the mixed powders before getting fully reacted. Non-stoichiometric carbides also exhibit higher diffusivity of carbon, which aids the densification and the greater the deviation from stoichiometry, the smaller the deleterious effects of de-densification from reaction. This troika of factors is responsible for the substantially better densification in non-stoichiometric carbide, compared to stoichiometric carbide. 0.2 Reactive Hot Pressing of Zirconium and Carbon Reactive hot pressing of zirconium carbide is explored with the emphasis on finding the underlying densification mechanism. The earlier proposed densification mechanism for RHP is the plastic flow of transient non-stoichiometric carbide. To differentiate the effect of transient phases from that of zirconium, RHP is carried out at 800oC. At this low temperature, transient phases cannot take part in plastic flow and subsequent densification. Thus, any densi cation at this temperature can be totally attributed to zirconium and the role of zirconium thus can be separated from that of transient phases. A combination of RHP and RS experiments are carried out at 1200oC to better understand the phenomenon. Again, ZrC carbide of four different stoichiometries are investigated in this RHP study. After RHP at 800oC, all the four different ZrC compositions reached more than 90% RD through plastic flow of the Zr leading to a continuous matrix with embedded graphite particles. Since the reaction remains incomplete at this temperature, it is clear that Zirconium alone is responsible for enabling densification at such a low temperature. It is therefore argued that any unreacted Zr would, at higher temperature, be able to drive densification even more. Thus, zirconium does not only participate in densification; it is a dominant factor enabling low temperature densification. Pressureless reaction sintering at 1200oC following the RHP at 800oC, results in de-densi fication, as the reaction between zirconium and carbon occurs with significant volume shrinkage. Since such shrinkage increases with stoichiometry of the carbide, the higher stoichiometry carbides are more susceptible to de-densification. RHP at 1200oC, mostly completes the reaction, but only ZrC0:5 reaches near theoretical density. Thus, the final density of the fully reacted mixture is arrived at through a combination of processes in which the more stoichiometric carbides suffer from not only the smaller metal content but also a greater volume shrinkage during reaction. Thus, ZrC0:5 reaches 99% RD whereas ZrC reaches only 85% RD. The interplay between these two processes may be controlled by a two step RHP begin-ning at 800oC followed by a ramp up to 1200oC. The higher RD achieved at 800 C results in a higher final density for all the four compositions. Thus, two step RHP is a novel way to get better densification in RHP of zirconium carbide. 0.3 Hot Pressing of Zirconium Carbide Powders of Different Stoichiometry In the literature, densification in RHP is mostly attributed to the presence of transient non-stoichiometric carbides. To examine this hypothesis, ZrC of three different stoichiometries are prepared and then subjected to hot pressing at the same temperature and pressure as the previous RHP experiments (i.e. 1200oC and 40MPa for 30 min). After the hot pressing experiments, ZrC0:5 composition shows significant densification (95% RD), whereas ZrC0:67 composition shows very limited densification (70% RD) and ZrC composition shows little or no densification (50% RD). Evidently, the transient phase formed with stoichiometry close to ZrC0:5 can certainly contribute substantially to densification. But for the more carbon-rich compositions, the transient phases do not appear to play a significant role and the benefit of RHP, wherein ZrC can reach 90% RD, must come from the contribution of metal plasticity. 0.4 Reactive Hot Pressing of Zirconium and Zirconium Carbide Two limiting factors for densification during RHP are, de-densification (courtesy of the reaction) and the gradual increase in volume fraction of a rigid, non-sintering phase. To investigate the role of these factors further, two compositions of mixed metal and carbide powders, namely Zr+ZrC and 0.5Zr+ZrC, are subjected to RHP. When reaction is complete, the compositions after RHP will correspond to ZrC0:5 and ZrC0:67, respectively, but with the following difference with respect to the metal-carbon mixtures investigated earlier: these new compositions do not experience de-densification due to reaction and they contain significantly more amount of hard phase (53 and 69%) in the starting composition than their zirconium and carbon mixture counterparts i.e. Zr+0.5C and Zr+0.67C (16 and 20%). These two compositions are subjected to the same process schedules, i.e., RHP at 800oC, pressureless reaction sintering at 1200oC following RHP at 800oC and two step 800oC and 1200oC RHP. After 800oC RHP, Zr+ZrC and 0.5Zr+ZrC compositions reach much lower density than Zr+0.5C and Zr+0.67C compositions as a direct consequence of the larger amount of hard phase hindering densification at the lower temperature. After the 1200oC pressureless sintering following the RHP at 1200oC, the RD of Zr+ZrC and 0.5Zr+ZrC compositions increase (which is opposite to the behaviour of Zr+0.5C and Zr+0.67C com-positions) as they do not su er from reaction derived de-densification. After two step RHP, Zr+ZrC and 0.5Zr+ZrC compositions reach a final RD that is higher than the Zr+0.5C and Zr+0.67C compositions, even though after the first RHP at 800oC, they were much less densified. Thus, the absence of de-densification during reaction is able to more than compensate for the increase in hard phase content. 0.5 Reactive Hot Pressing: Low temperature process-ing route Based on the major factors of densification identified earlier, it was investigated whether RHP temperatures could be brought down further while being supplemented by a free sintering step to complete the reaction without de-densification. From a practical standpoint, such a process would allow dense products to be made by hot pressing with low temperature dies and fixtures while carrying out a more economical pressureless sintering at higher temperatures Therefore, Metal-carbide mixtures, Zr+ZrC and Ti+ZrC, are chosen, along with a temperature of 900 C which is above the allotropic phase transformation temperature for Zr around 880oC, thereby utilizing a zirconium phase that is softer than the hexagonal Zr. For completion of reaction, pressureless reaction sintering is done at 1300oC and 1400oC. It is found that after 1400oC reaction sintering, both the compositions reach almost full density and the Ti+ZrC composition also shows a higher hardness (13 vs 10 GPa) than the Zr+ZrC composition, due to the formation of a binary carbide with consequent solid solution hardening. 0.6 Effect of Particle Size on Reactive Hot Pressing During RHP, premature exhaustion of zirconium by reaction can limit densification. One way to have better densification is to slow down the reaction, so that significant amount of densification takes place before the metal zirconium is exhausted. One way to reduce reaction rates is to increase particle size. Larger particles are expected to slow down the reaction without affecting sintering, as densification is controlled by power law creep of Zr which is grain size independent. Because of lack of availability of Zr with different particle sizes, two different graphite particle sizes, i.e. 7-10 m and 50-60 m, were studied and it was shown that after 1200oC RHP, indeed the larger particle size improves densification. 0.7 Modelling of Reactive Hot Pressing Reactive hot pressing is a complicated phenomenon, and to get an insight and also to optimize the parameters, the availability of a computational model is of paramount importance. Keeping that in mind, a model of RHP has been constructed based on four different parts, namely: 1. Densification of zirconium under pressure 2. Reaction of zirconium and carbon 3. The constraint on sintering from a rigid phase and, finally, 4. The volume contraction during reaction. The model uses published data for the 4 steps and shows reasonable qualitative and quantitative agreement with the experimental results. Further experiments are done with the model to optimize the processing parameters. Results from the virtual experiments consolidates our earlier conviction gained from experimental results, by showing zirconium is the principal factor in densification and exhaustion of zirconium coupled with reaction derived de-densification prevent the higher stoichiometric carbide from achieving full densification. It also shows, RHP gives best densification when reaction is 70-80% complete. So two step RHP where the first RHP will only complete the reaction 70-80%, and a final RHP at temperature which will complete the reaction, will possibly be the way to achieve best densification. 0.8 Conclusions The study on RHP of zirconium carbide led to the following conclusions: • Zirconium plays the most crucial role in densification. • Transient phases only play a role when the final stoichiometry of RHPed carbide is close to that of ZrC0:5. • De-densification from reaction prevents higher stoichiometric carbide from reaching full densification. • Two step RHP, with one RHP at lower temperature at which reaction will remain incomplete, and the other at higher temperature to complete the reaction, yields best densification. • For lower stoichiometric carbide (ZrC0:5,ZrC0:67), full densification can be achieved at 1200oC. For higher stoichiometric carbide, even though large amount of densification upward of 90% RD is achieved at 1200oC, full densification will be out of reach. • RHP shows better densification than conventional hot pressing for all stoichiometries.

This master‘s thesis deals with the suggestion of suitable tools for milling aluminum alloys profiles for the construction of aperture fillings and their aplication to a CNC machining center for increasing the efficiency of the cutting process. The first part of the thesis is focused on the description of the company and the workplace of production of aluminum alloys constructions. The following pages contain description of standardized products, which are used to identify the test profile that is part of the experimental verification. Next part of this thesis is characteristic of aluminum alloys and tool materials suitable for their machining. Second part of this work contains an analysis of the current state, suggestion of new cutting tools and their application to the production proces. At the end of this thesis there is the technical-economic evaluation that deals with the time and economic savings of the applied design.

This thesis deals with a summary of different types and characteristics of coatings used for increasing the lifetime of cemented carbide tools. Besides, the thesis includes solving the issue regarding edge chipping during machining interrupted pipe ends at the pipe line, selecting a new type of indexable inserts and indexable inserts holders to increase line productivity and decrease tool costs in the related operation.

The assessment of MQL technology application in reaming process was elaborated in this diploma work. The evaluation of energy intensity was carried out in terms of specific cutting force during reaming of austenitic stainless steel work piece by using HSS reamers. The comparison of economic costs in the case of the application of MQL technology in production was made. Confrontation of oil mist removal principles. At the conclusion the evaluation of ecological benefits for the environment and the positive influence on the working environment cleanness was defined.

Les matrices en carbure de Tungstène et Cobalt (WC‐Co) sont utilisées dans les procédés de frappe à froid de l’acier pour leur exceptionnelle capacité à résister aux phénomènes d’usure. Ces travaux ont pour objectif de mieux comprendre les mécanismes complexes qui entrainent finalement la dérive des matrices vers l’état usé. Cette complexité vient des liens étroits entre la microstructure et les propriétés mécaniques macroscopiques de ces matériaux. Pour la compréhension des mécanismes de dérive vers l’usure, une stratégie de travail en quatre étapes est établie. La première étape est le prélèvement de matrices de frappe, avec différentes durées de vie, directement sur la chaîne de production. La deuxième étape est l’identification de la rhéologie. Elle s’accompagne de la modélisation numérique du procédé de frappe pour calculer le champ des contraintes et des déformations plastiques. La troisième étape est la caractérisation localisée de l’évolution de la surface selon trois axes : les propriétés tribologiques, morphologiques, et mécaniques. On quantifie ainsi la dégradation progressive des conditions de contact corrélée avec une fragilisation des surfaces et la décohésion de grains de carbures WC. Pour comprendre les mécanismes qui conduisent à la décohésion de grains, une stratégie de modélisation numérique à l'échelle mésomécaniques 2D est mise en place. L’énergie de rupture entre un grain et le reste du matériau est modélisée par des éléments cohésifs. Ces modèles montrent que la sensibilité de chaque grain à l’arrachement dépend non seulement des conditions de contact et de la ténacité du matériau, mais également de la taille et de la configuration du grain au voisinage de la surface. / Tungsten carbide and Cobalt (WC‐Co) dies are used for cold forming processes of steel because of their exceptional performances in resisting wear phenomena. This work aims to a better understanding of the complex damage mechanisms that eventually cause wear. This complexity comes from the existing relationships between their microstructure and their macroscopic mechanical properties. For a better understanding of the damage mechanisms leading towards wear, a four‐step strategy is presented. The first step is the cold heading dies sampling directly on the production line. They are collected at different lifetimes. The second step is the identification of the die rheology. It is followed by numerical modeling of the forging process to calculate the stress field and plastic strain magnitude. The third step is to characterize the local evolution of the surface properties along three axes: the tribological, the morphological and mechanical aspects. These analyses quantify the progressive decrease of contact conditions correlated with surface embrittlement and WC carbide grains debonding. To understand the mechanisms that lead to the grains debonding, a set of 2D mesoscale contact models are performed. The fracture energy between a WC grain and the rest of the material is computed using cohesive elements. These models show that the sensitivity to debonding depends not only on the contact conditions and the material fracture toughness, but also on the grain size and grain configuration in the vicinity of the surface.

In this study, the goal is to predict the microstructure evolution during and after the hot working of a martensitic stainless steel with 13% chromium using a physically-based model in the form of a MATLAB toolbox. This model is based on dislocation density theory and consists of coupled sets of evolution equations for dislocation, vacancies, recovery, recrystallization, and grain growth. The focus in this work is on the flow stress calculation and the effect of second phase particles on the strengthening mechanisms in the material at elevated temperatures. Recovery and recrystallization are also studied for this alloy during deformation and following stress relaxation. The experimental part of this work was performed with a Gleeble thermo-mechanical simulator over the temperature range of 850 to 1200°C. Samples were investigated later by a light optical microscope (LOM) and a scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscope (EDS). Hardness test and phase isolation were also performed on the samples and the results are compared with the modeling results. The model can satisfactorily predict the grain growth, recovery, recrystallization, and flow stress for this alloy. Further investigation on the second phase particles showed that the measured mean size of carbides has a good agreement with what is obtained from the model and the hardness values. On the other hand, the modeled volume fraction of the carbides followed a slightly different trend comparing to hardness values, and phase isolation results at temperatures higher than 1000°C. Additionally, the Ms temperature and fraction of the martensite phase are calculated for quenched samples where the results are following the measured hardness values. Finally, the Zener-Hollomon parameter (Z) and its relation to the flow stress and the activation energy for deformation are defined. The dynamic recrystallization (DRX) kinetic is modeled and the fraction DRX was calculated at various temperatures and strain rates for this alloy. / I denna studie är målet att förutsäga mikrostrukturutvecklingen under och efter varmbearbetning i ett martensitiskt rostfritt stål med 13 % krom med hjälp av en fysisk baserad modell i form av en MATLAB verktygslåda. Denna modell är baserad på en teori för dislokationstäthet och bestårav kopplade uppsättningar av evolutionsekvationer för dislokation, vakanser, återhämtning, rekristallisation och kornstillväxt. Fokus i detta arbete är beräkning av flytespänningen och effekten av sekundärfaspartiklar på härdningsmekanismerna i materialet vid höga temperaturer. Återhämtning och rekristallisation studeras också för denna legering under deformation och efter spänningsrelaxation. Den experimentella delen av detta arbete utfördes med en Gleeble termomekanisk simulator inom temperaturområdet 850 till 1200°C. Proverna undersöktes senare med ett ljust optiskt mikroskop (LOM) och svepelektronmikroskop(SEM) utrustad med energidispersiv spektroskopi (EDS). Hårdhetstest och fasisolering utfördes också på proverna och resultaten jämförs med modelleringsresultaten. Modellen på ett tillfredsställande sätt kan förutsäga korntillväxt, återhämtning, rekristallisation och flytspänningen för denna legering. Vidare undersökning av partiklarna i sekundärfasen visade att den uppmätta medelstorleken för karbider har bra överensstämmelse med vad som erhålls från modellen och hårdhetsvärdena. Den modellerade volymfraktionen av karbiderna följde en något annorlunda trend vid temperaturerna högre än 1000°C jämfört med hårdhetsvärden och fasisoleringsresultat. Dessutom beräknas Ms temperaturen och fraktionen av martensitfasen för släckta prover där resultaten följer de uppmätta hårdhetsvärdena. Slutligen definieras Zener-Hollomon-parametern (Z) och dess förhållande till flytspänningen och aktiveringsenergin för deformation. Den kinetiska dynamiska rekristallisation (DRX) modelleras och fraktionen DRX beräknades vidolika temperaturer och töjningshastigheter för denna legering.

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