No description available.

No description available.

Master of Science

Artefacts known as amulet rings, a kind of Viking age jewellery, have often been encountered during archaeological excavations of Viking Age sites. The rings do not appear to have any practical use, but are rather considered to be of cultural or religious importance. Their exact function is however unclear, as are the details regarding the production and material choices for the rings.This study mainly examines the microstructure of samples from Viking Age amulet rings found in Dalecarlia, Sweden. To be able to conclude how much effort that was put into the rings a comparison with medieval cutting tools was conducted. Thus, the knives were made with more care in order to obtain the material properties required to give the knives the sharpness and hardness they need to function. The analysis shows that the amulet rings were made from heterogeneous low-carbon steel, indicating little or no welding and a poor-quality starting material. Were as the microstructure of the knives had homogeneous microstructures often involving perlite, showing decent carbon content.Thus, it appears that the Viking Age smiths forged the amulet rings without putting too much effort into the process.This study also involved the manufacturing of a new knife from low-carbon steel, this was done to see if it was possible to redeem carbon into the surface while forging. This however, was difficult when not having todays technical equipment at hand, thus the result was insufficient. / Historiska föremål, kallade amulett ringar vilket är ett slags vikingatida smycken, har hittats vid arkeologiska utgrävningar av vikingatida boplatser. Man har inte hittat något praktiskt användningsområde för ringarna, utan de tros vara av kulturell eller religiös betydelse. Deras funktion är dock oklar, likaså detaljerna angående tillverkningen och materialvalet för ringarna.Denna studie undersöker mikrostrukturen av amulett ringar från Dalarna i Sverige. För att kunna dra slutsatser om hur mycket arbete som lades på ringarna genomförs en jämförelse med medeltida eggverktyg. Eftersom eggverktyg gjordes med omsorg för att få rätt materialegenskaper för att vara vassa och hårda kan man jämföra dessa med ringarna. Analyserna visade att amulett ringarna var gjorda av lågkolhaltigt heterogent stål som indikerar enbart lite eller ingen vällning och ett dåligt utgångsmaterial. Tillskillnad från eggverktygen som uppvisade en homogen mikrostruktur som ofta innehöll perlit vilket tyder på relativt hög kolhalt. Följaktligen framstår det som att vikingatida smeder inte la ned särskilt mycket tid i smidesprocessen vid tillverkningen av amulett ringar.Denna studie innefattar också smidet av en ny kniv från ett lågkolhaltigt stål för att se om det är möjligt att lösa in kol i ytan genom smidet. Detta var dock svårt att göra utan dagens tekniska utrustning vilket gjorde att resultatet inte visade någon uppkolning.

This diploma thesis deals with the generation of the different drope stampings in industrial process in MBNS Kovárna Company. The main purpose of this thesis is analysis of the industrial process and finding the main factors influences on the process. It especially deals with forgings of the shafts and also flanges with the similar quality of material 42CrMo4. Reasons of the disagreements are focused on surface insensibilities of the forging - crack. First theoretic part introduces company, meaning of the quality of material and describes tools used for finding reasons of the generation of disagreements. In the second practical part is described the whole industrial process and determination of the reasons of disagreements. In concluding part the results are analyzed and some correctional recommendations are suggested.

The work presented has the ultimate aim to increase dynamic mechanical properties by improvements in density and optimisation of microstructure of ultra high carbon PM steels by careful selection of processes, i.e. mixing, binding, alloying, heating profile and intelligent heat treatment. ThermoCalc modelling was employed to predict liquid phase amounts for two different powder grades, Astaloy 85Mo or Astaloy CrL with additive elements such as (0.4-0.6wt%)Si, (1.2-1.4wt%)C and (1-1.5wt%)Mn, in the sintering temperature range 1285-1300ºC and such powder mixes were pressed and liquid phase sintered. In high-C steels carbide networks form at the prior particle boundaries, leading to brittleness, unless the steel is heat-treated. To assist the breaking up of these continuous carbide networks, 0.4-0.6% silicon, in the form of silicon carbide, was added. The water gas shift reaction (C + H2O = CO + H2, start from ~500ºC) and Boudouard reaction (from ~500ºC complete ~930ºC) form CO gas in the early part of sintering and can lead to large porosity, which lowers mechanical properties. With the use of careful powder drying, low dew point atmospheres and optimisation of heating profiles, densities in excess of 7.70g/cm3 were attained. The brittle microstructure, containing carbide networks and free of cracks, is transformed by intelligent heat treatment to a tougher one of ferrite plus sub-micron spheroidised carbides. This gives the potential for production of components, which are both tough and suitable for sizing to improve dimensional tolerance. Yield strengths up to 410 MPa, fracture strengths up to 950 MPa and strains of up to 16 % were attained. Forging experiments were subsequently carried out for spheroidised specimens of Fe-0.85Mo+06Si+1.4C, for different strain rates of 10-3, 10-2, 10-1 and 1sec-1 and heated in argon to 700ºC, density ~7.8g/cm3 and 769 MPa yield strength were obtained.

Au cours de leur mise en forme, les alliages de titane destinés à la fabrication de pièces tournantes pour moteurs d'avions suivent un schéma thermomécanique complexe constitué généralement de plusieurs opérations de forgeage. L'étape de forgeage dans le domaine monophasé β joue un rôle important, car elle conditionne la transformation de phases qui s'opère au cours du refroidissement ou du traitement thermique consécutif dans le domaine biphasé α-β, et donc les propriétés mécaniques finales de la pièce. La maîtrise de l'évolution de la microstructure et de la texture cristallographique au cours du forgeage dans le domaine β est donc indispensable pour optimiser l'ensemble du procédé de mise en forme. Pour cela, il est important de bien comprendre les mécanismes de recristallisation dynamique (continue et géométrique) se produisant dans ce type de matériau.Dans cette étude, les effets de la température, de la déformation et de la vitesse de déformation ont été étudiés au moyen d'essais de compression uniaxiale et de torsion à chaud. Les microstructures et textures de déformation ont été caractérisées par diffraction des électrons rétrodiffusés (EBSD). Ces approches expérimentales sont associées à un travail de modélisation, pour lequel le schéma de recristallisation dynamique "continue" (ou CDRX), consistant en une fragmentation progressive des grains β initiaux par la formation de nouveaux joints de grains, a été adapté à partir d'études antérieures. Les paramètres caractérisant les mécanismes élémentaires de la CDRX (écrouissage, restauration dynamique, migration des joints) ont été déterminés par ajustement sur les données expérimentales.Ces travaux ont pour objectif l'élaboration d'un post-processeur métallurgique dédié au forgeage des alliages de titane en phase β. / Titanium alloys used for the manufacture of rotating parts of aircraft engines undergo complex thermomechanical processing schedules, involving usually several forging operations. The forging step in the single -phase domain plays an important role, because it governs the phase transformation that occurs during cooling or subsequent heat treatment in the two-phase α+β range, and therefore the final mechanical properties of the workpiece. Controlling the microstructural evolutions during forging in the β-domain is of prime interest to optimize the entire process of disks manufacture. A full understanding of the (continuous and geometric) dynamic recrystallization mechanisms occurring in this type of material is therefore required.In this study, the effects of temperature, strain and strain rate were investigated by hot uniaxial compression and torsion tests. The microstructures and textures were characterized using backscattering electron diffraction (EBSD). These experimental approaches were associated with the development of a physical model. In the latter, the mechanism of "continuous" dynamic recrystallization (CDRX), consisting of a progressive initial fragmentation of the grains leading to the formation of new grain boundaries, was adapted from former studies. The parameters characterizing the elementary mechanisms of CDRX (strain hardening, dynamic recovery, grain boundary migration) were determined by fitting the experimental data.The final objective of this work is to develop a metallurgical post-processor dedicated to forging operations of titanium alloys in the -phase range.

Les alliages à base Nickel polycristallins sont largement utilisés pour les pièces aéronautiques soumises à des sollicitations extrêmes en service. Des objectifs toujours plus ambitieux en termes de rendement énergétique des moteurs d’avions ont conduit les constructeurs à augmenter leur température de fonctionnement. Les nuances utilisées jusqu’alors dans les parties chaudes, tels que l’Inconel 718, n’ont pas une tenue mécanique suffisante à ces températures. Le René 65 est un nouvel alliage à microstructure γ-γ’ élaboré spécifiquement pour ces applications. Il a été retenu par Safran Aircraft Engines comme constituant des disques de turbine basse pression du nouveau turboréacteur LEAP. Pour garantir la bonne tenue des disques, une microstructure fine et homogène est requise. Le procédé de forgeage de ces pièces est une séquence d’étapes de déformation à chaud et de traitements thermiques, durant lesquelles la microstructure évolue. Si les phénomènes physiques gouvernant les évolutions microstructurales sont connus, leurs mécanismes exacts et leurs cinétiques varient d’un alliage à l’autre.Des essais de déformation à chaud ont été réalisés en laboratoire dans différentes conditions de température, vitesse et taux de déformation représentatifs des procédés industriels. L’étude précise des mécanismes de recristallisation dynamique, ainsi que de leurs cinétiques, constitue la première partie de ce travail. La caractérisation fine des microstructures déformées a permis de mettre en évidence un nouveau mécanisme de recristallisation, dit de recristallisation en hétéroépitaxie, qui se superpose aux autres mécanismes conventionnels. L’interaction entre ces différents mécanismes ainsi que leurs cinétiques relatives ont été établies dans une vaste gamme de conditions de déformation. Il est démontré que ce mécanisme de recristallisation s'applique également à d'autres alliages γ-γ’. La deuxième partie de l’étude est consacrée à la stabilité des microstructures déformées lors de leur exposition à haute température. L'alliage René 65, comme d’autres alliages à base Nickel, est sensible à un phénomène indésirable dit de croissance sélective de grains. Ses conditions de déclenchement ont été déterminées, de manière à délimiter une fenêtre de forgeage critique. Les mécanismes microstructuraux à l’origine de ce phénomène ont été discutés, ainsi que la possibilité d’une solution préventive. / Polycrystalline Nickel-based alloys are widely used as components for rotative parts of jet engines submitted to extreme conditions. Endlessly increasing objectives in terms of energy efficiency have led the engine manufacturers to increase their service temperature. As a consequence, Inconel 718 and similar alloys -that were used until now- cannot withstand such severe conditions anymore, and lack mechanical resistance at the increased temperature. René 65 is a new γ-γ’ superalloy which has been designed specifically for that purpose by General Electric. It has been selected by Safran Aircraft Engines as the material for low-pressure turbine disks in the new LEAP engine. To reach the desired mechanical properties, a fine and homogeneous microstructure is required. The forging process is a complex sequence which involves various hot deformation stages and thermal treatments, during which the microstructure evolves. Although the underlying mechanisms governing the microstructure evolutions are quite known, their specific mechanism and kinetics may vary depending on the alloy.Interrupted compression tests were conducted at laboratory scale under thermomechanical conditions (temperature, strain and strain rate) in accordance with the industrial process. In the first part, the focus is placed on the dynamic recrystallization mechanisms. Accurate characterization of the deformed microstructures has enabled to highlight a new recrystallization mechanism which superimposes with more conventional ones. It was named heteroepitaxial recrystallization. The interactions between those mechanisms as well as their relative kinetics have been established in a wide range of deformation conditions. . It is demonstrated that this mechanism occurs in other γ-γ’ Nickel-based alloys. The second part of the study is dedicated to the stability of deformed microstructures when exposed to high temperature thermal treatments. René 65, as many other Nickel-based alloys, is subjected to the undesirable phenomenon of selective grain growth, which leads to very heterogeneous microstructures containing abnormally large grains in a fine matrix. Critical deformation conditions leading to heterogeneous microstructures during subsequent annealing have been determined in an aim to identify the critical forging window which should be avoided. The microstructural mechanisms responsible of this phenomenon have been investigated, and the possibility of a preventive solution is discussed.

<p>Sammandrag</p><p>Detta examensarbete utförs i samarbete med företaget Componenta Wirsbo AB. Componenta smider detaljer till den tunga fordonsindustrin. Företaget använder sig av sänksmide där materialet formas genom slag från två rörliga verktyg. Smitt material har mycket goda hållfasthets egenskaper samt en mycket homogen struktur.</p><p>Företaget har som miljömål att minska sin uppvärmningsenergi med 5 %. Componenta arbetar även med ett Leanprojekt som ska leda till en mer kontinuerlig produktion. Det föreslagna värmeåtervinningssystemet kommer även att avsevärt korta avkylningstiden för detaljerna och på så sätt bidra till en mer störningsfri produktion. Detta projekt går ut på att dimensionera en anläggning för värmeåtervinning av kylvattnet från de färdigsmidda detaljerna. Det uppvärmda vattnet kan sedan användas till att värma tappvarmvatten och lokaluppvärmning. För dimensionering av anläggningen genomfördes praktiska test. I dessa test nedsänktes korgar med de smidda detaljerna i vatten och temperaturändringen på detaljerna och vattnet uppmättes. Resultatet av testerna visade att det går att utvinna ca 65 kWh energi ur varje korg med detaljer. Med värmeåtervinning av detaljerna från den mekaniska pressen kan i stort sett endast företagets varmvattenbehov täckas. Om hela produktionen värmeåtervinns kan utöver tappvarmvattenbehovet, ca 50 % av lokaluppvärmningsbehovet tillgodoses. De praktiska testerna visade att korgarna behöver ca 4 - 6 minuter i vattenbadet för att uppnå önskad avkylning. Det beräknade massflödet som pump och värmeväxlare dimensionerats efter är 2 - 9 kg/s.</p><p>Återbetalningstiden för den investering som behövs för att bygga systemet har beräknats. Om detaljerna från den mekaniska pressen värmeåtervinns återbetalar sig systemet på ca 20 månader. Värmeåtervinning från hela produktionen resulterar i en återbetalningstid på ca 7 månader.</p> / <p>Abstract</p><p>This diploma work is performed in cooperation with Componenta Wirsbo AB. Componenta are a company specialized in forging parts for the vehicle industry. The company uses drop forging where the material is moulded through hammering by two separated tools. Forged material has very good tensile properties and a very homogenous structure. The environmental goal for the company is to reduce their heating energy with 5%. Componenta are also involved in a Lean project to obtain a more continuous production. The suggested heat recycling system will also shorten the cooling time for the products and thereby contribute to a more non-stop production. The goal of this diploma work is to dimension a system for heat recycling of the cooling water from the forged details. The heated water can then be used for hot water and heating.</p><p>For dimensioning the system practically testing was performed. In these test's baskets with forged details was dipped in water and the temperature changes on the details and the water was measured. The results from these testes showed that it is possible to extract approximately 65 kWh of energy from each basket. With heat recycling of the details from the mechanical press it is possible to cover the total need of hot water for the company. If the Componenta decides to heat recycle the total production it is possible to cover the hot water need and about 50 % of the heating. The practical testing showed that the baskets needed about 4 – 6 minutes in the water to obtain the desired cooling effect. The pump and the heat exchanger are dimensioned for a flow of 2-9 kg/s.</p><p>The payoff time for this investment has been calculated. If the company heat recycles the details from the mechanical press the payoff time will be approximately 20 months. Heat recycling of the whole productions will reduce the payoff time too approximately 7 months.</p>

The thesis is focussed on improving the material yield in closed-die forging and rolling. The former is restricted to the manufacturing of heavy crown wheels and front axle beams and the latter to the hot rolling of steel slabs. To enhance the yield the commercial FE-codes Form2D and Dyna3D are used. Results from forging simulations are strengthened by full scale experiments. The research is carried out in near contact with the Swedish steel and engineering industry. In closed die forging, two bulk forming problems are treated: How to improve the tool design and how to change the pre-form geometry for decreasing the amount of material exiting the flash gap? In slab rolling, two problems related to material defects are considered: How to eliminate existing surface cracks and how to prevent the formation of voids around macro-inclusions embedded in the steel matrix? Internal voids might be the reason for scrapping the whole workpiece. Considering the forging of crown wheels, a new concept is proposed. For making the central hole of the product, the traditional method was forging a thin circular plate which was then sheared off and scrapped. Using the new technique this operation is replaced by forging a conical tap in the centre, which is then discarded. Doing so, the inner scrap material decreased with about 15%. The idea has been used in production for seven years. – Regarding the forging of front axle beams, a quasi-3D method is used comprising full scale measurements of the axial material flow. Here the theoretical material yield increased 2-7%. Regarding rolling, the initial surface cracks in the simulations are V-shaped with a crack angle of 6o and of depth 5-20 mm. The inclusions are cylindrical and either three times harder or three times softer than the matrix. The behaviour of the cracks and the inclusions are studied as influenced by process parameters. Current industrial input data are used as a reference. – It is concluded that longitudinal cracks cannot be totally eliminated. During rolling their V-shape gradually changes to Y-shape and a remaining oxide flake separates the crack bottom surfaces. For minimizing the detrimental influence of the entrapped oxide, an early closure of the crack bottom is important. Throughout the remaining rolling schedule the entrapped oxide is then torn to pieces with large areas of virgin metal in between ensuring a strong bond. The following recommendations are given for the longitudinal cracks: Light drafts/pass at the beginning of the rolling schedule followed by heavy ones. – Contradictory to longitudinal cracks it is concluded that transversal cracks are possible to eliminate. When eliminated, the initial bottom of the crack coincides with the slab surface. No folds are formed. For the transversal cracks light drafts/pass are proposed together with reversal rolling, the latter for avoiding crack folding. – Voids are easiest formed around hard macro-inclusions in the centre of the slab. Large rolls and heavy drafts are recommended to avoid this. / QC 20100720