京都大学 / 新制・課程博士 / 博士(工学) / 甲第24617号 / 工博第5123号 / 新制||工||1979(附属図書館) / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 田中 功, 教授 奥田 浩司, 教授 安田 秀幸 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

The classical test to confirm the performance of a given fibre design for use in reinforced concrete is the pull-out test. While attempts have been made to simulate the performance of such pull-out tests, in practice it has been found that there is a significant disparity between prediction and real-life performance. The high strength of steel reinforcing fibres is a consequence of the cold wire drawing process and subsequent fabrication. Residual stresses exist in cold drawn wire as a consequence of the elastic response to a non-uniform distribution of plastic strain. This also introduces a yield strength profile where yield strength varies radially through the wire. The question arises as to whether fibre design should use a starting material model that considers these properties. This thesis examines whether the tensile test, simple bend test and pull-out test provide enough information to define a starting material model that may be used for further design and simulation of such fibres. Since the details of the wire drawing process and material specification are proprietary and therefore unknown, a sensitivity study was conducted to determine which aspects of the wire drawing process have the greatest effect on the pull-out curve and the following were established as being significant: • Plastic strain due to wire drawing was shown to be the most important factor. • The bilinear curve was shown to be a suitable approximation for the stress-strain curve. • Replacing the plastic strain profile with a single value of average equivalent plastic strain is practical. The following were established as having negligible effect: • The consequences of the hooked-end forming process. • The residual stress profiles due to wire drawing provided that the above was also excluded. • The hardening law While inverse analysis demonstrated that all tests provide sufficient information to determine the required properties for this bilinear material model, the pull-out test was shown to provide more accurate approximations of the maximum pull-out force at the first and second peaks and the bend test was shown to produce more accurate approximations of the energy associated with pull-out. Good correlation with the baseline pull-out curve was found for both the isotropic and the kinematic hardening laws and it is concluded that behaviour during pull-out is insensitive to the hardening law. Sensitivity analysis and characterisation of the material model using an experimental pull-out curve demonstrated the importance of the coefficient of friction. Full characterisation using the pull-out curve therefore requires the solution to a three-variable problem: yield strength, tangent modulus and coefficient of friction. This was a suggested topic for further study. / Dissertation (MEng)--University of Pretoria, 2019. / Mechanical and Aeronautical Engineering / MEng (Mech) / Unrestricted

Tråddragning är en kallbearbetningsprocess där tråd dras genom en dragsten, som plastiskt deformerar materialet och reducerar tvärsnittsarean. En viktig parameter i tråddragningsprocessen är draghastigheten - en ökad draghastighet kan förbättra produktiviteten, vilket är önskvärt för företaget Suzuki Garphyttan AB då efterfrågan på produkter har ökat. Dessutom är ökad produktivitet positivt i avseende med ekonomisk hållbarhet, men får inte ske på bekostnad av trådkvaliteten. En försämrad kvalitet kan leda till en större mängd skrot vilket är negativt utifrån ett miljömässigt hållbarhetsperspektiv. I detta examensarbete har åtta olika experiment utförts med syfte att undersöka hur ökad draghastighet och ett ökat vattentryck påverkar ytkvaliteten på kolstålet Oteva 75. Data i form av temperaturmätningar, ytjämnhet och djup av defekter har samlats in för att göra jämförelser och dra slutsatser mellan ökad draghastighet och ytkvalitet. Resultatet indikerar att det uppstår mindre variationer gällande ytjämnheten vid lägre hastigheter samt att djupet på repor inte har försämrats eller förbättrats i ett specifikt mönster vid ökade hastigheter. Med ett ökat vattentryck var djupet på repor minst vid mellersta hastigheten och ytjämnheten hade marginellt större variationer vid högre hastigheter jämfört med den lägsta. För att kunna dra generella slutsatser måste fler liknande experiment göras i framtiden. Variablerna måste observeras mer noggrant genom att till exempel använda samma maskin, samma smörjmedelsförhållanden och samma leverantör. Detta kan göras genom att testa samma trådring, i samma maskin. / Wire drawing is a cold-working process in which a wire is pulled through a drawing die, resulting in plastic deformation of the material and wire diameter reduction. One important parameter in the wire drawing process is the drawing speed. An increased drawing speed can improve productivity, which is desired for the company Suzuki Garphyttan AB due to the increased demand for products. Furthermore, improved productivity is positive in terms of economic sustainability, but cannot be at the expense of wire quality. Worsen quality may lead to increased amount of scrap which is negative from a perspective of environmental sustainability. In this master thesis, eight different experiments have been performed with the aim to examine how increased drawing speed-, and pressure of cooling water, affects the surface quality of the carbon steel Oteva 75. Data in terms of temperature measurements, surface roughness and depth of defects have been collected to make comparisons and conclusions between increased drawing speed and surface quality. The result indicates that there are less variations regarding the surface roughness at lower speeds than higher speeds. The depth of defects has not deteriorated or improved in a specific pattern at increased speeds. With increased water pressure, the depth of defects was smallest at the first speed increase and the surface roughness had marginally larger variations at the highest speed. To be able to draw general conclusions, more similar experiments must be done in the future. The variables involved need to be observed more carefully by, for example, using the same shaving equipment, the same lubrication conditions, and the same supplier. This can be done by testing on the same wire ring, in the same machine.

As distorções de forma de componentes mecânicos, que ocorrem durante a fabricação, constituem um sério problema enfrentado pela indústria metal-mecânica. Neste trabalho, avaliou-se uma rota de fabricação de barras de aço ABNT 1045 envolvendo os processos de trefilação, alívio de tensões e têmpera por indução utilizando-se uma visão holística do processo. Após um estudo detalhado, variou-se 5 parâmetros do processo, sendo eles: corrida, ângulo de fieira, ângulo de endireitamento, temperatura de alívio de tensões e profundidade de camada temperada. Caracterizou-se as tensões residuais, em todas as etapas do processo, utilizando-se as técnicas de difração de raios-X, difração de nêutrons e difração de radiação Síncrotron, bem como, a microestrutura do material. Após as etapas de trefilação combinada e tratamento térmico avaliou-se as distorções de forma, utilizando-se um equipamento de medição por coordenadas e posteriormente calculou-se os vetores distorção. Os dados obtidos foram analisados utilizando-se o software Minitab® através da montagem de uma matriz DoE (Design of Experiments). A partir dos resultados obtidos, avaliou-se quais etapas do processo induzem maior "potencial de distorção" nos componentes. A partir das medições de tensões residuais foi obtida uma visão detalhada de como estas tensões residuais se distribuem no material após cada etapa do processo, os dados mostram diferenças significativas ao longo das posições periféricas nas etapas de pré-endireitamento e trefilação. Dados apontam que a distribuição da zona de segregação é responsável pelo comportamento diferente nas duas corridas analisadas em relação às distorções. As tensões residuais geradas no endireitamento do fio-máquina são responsáveis por causar heterogeneidades no material e induzem um alto “potencial de distorção”. Nos parâmetros de processo estudados as deformações induzidas no processo de trefilação não foram capazes de eliminar as distribuições heterogêneas de tensões residuais geradas no pré-endireitamento, porém utilizando-se o ângulo de fieira de 15º houve uma diminuição da distorção após a têmpera por indução. Após o processo de endireitamento por rolos cruzados (PERC) a distribuição das tensões residuais na superfície é mais homogênea para os ângulos de ferramenta avaliados neste trabalho (16º e 18º), entretanto existem diferenças significativas na distribuição de tensões residuais no núcleo do material, e estas diferenças são umas das causadoras das distorções após o processo de têmpera por indução. / Shape distortions are a serious problem in the metalworking industry, distortion due to heat treatment is responsible for additional and cost machining operations. Minimizing or even avoiding heat treatment distortion is one of the key factors to minimize production costs. In the past, investigations had focused on single effects or isolated parameters steps in a manufacturing chain. It is well established now that each step of the process chain generates a “distortion potential” and a new global approach, treating distortion as a system attribute, analyzing the entire manufacturing chain from steelmaking to heat treatment process is necessary. The main idea of distortion engineering is that all steps of the manufacturing chain together contribute to the final distortion behavior. In this work, a steel route of combined cold-drawing process to induction hardening of ABNT 1045 steel bars was investigated. The residual stresses characterizations were carried out using X-ray diffraction, neutron diffraction and synchrotron diffraction methods. The identification and interaction between factors on distortion behavior was carried out using statistical analysis, with the aid of DoE (Design of Experiments). For the DoE method the number of causes that can be considered were 5 parameters of the process, including: different batches, drawing angle, PERC angle, stress relief temperature and induction hardening depth. From the results obtained, the evaluation of which steps in the process induce higher "distortion potential" during the various steps of the process was carried out. From the measurements of residual stresses a detailed view of how these residual stresses are distributed for material in each step of the process was obtained, the results show significant differences along the peripheral positions in the pre-straightening and drawing stages. The experimental results indicate the microstructure of the material, wire rod geometry and the die angle process parameters as main "distortion potentials".

As distorções de forma de componentes mecânicos, que ocorrem durante a fabricação, constituem um sério problema enfrentado pela indústria metal-mecânica. Neste trabalho, avaliou-se uma rota de fabricação de barras de aço ABNT 1045 envolvendo os processos de trefilação, alívio de tensões e têmpera por indução utilizando-se uma visão holística do processo. Após um estudo detalhado, variou-se 5 parâmetros do processo, sendo eles: corrida, ângulo de fieira, ângulo de endireitamento, temperatura de alívio de tensões e profundidade de camada temperada. Caracterizou-se as tensões residuais, em todas as etapas do processo, utilizando-se as técnicas de difração de raios-X, difração de nêutrons e difração de radiação Síncrotron, bem como, a microestrutura do material. Após as etapas de trefilação combinada e tratamento térmico avaliou-se as distorções de forma, utilizando-se um equipamento de medição por coordenadas e posteriormente calculou-se os vetores distorção. Os dados obtidos foram analisados utilizando-se o software Minitab® através da montagem de uma matriz DoE (Design of Experiments). A partir dos resultados obtidos, avaliou-se quais etapas do processo induzem maior "potencial de distorção" nos componentes. A partir das medições de tensões residuais foi obtida uma visão detalhada de como estas tensões residuais se distribuem no material após cada etapa do processo, os dados mostram diferenças significativas ao longo das posições periféricas nas etapas de pré-endireitamento e trefilação. Dados apontam que a distribuição da zona de segregação é responsável pelo comportamento diferente nas duas corridas analisadas em relação às distorções. As tensões residuais geradas no endireitamento do fio-máquina são responsáveis por causar heterogeneidades no material e induzem um alto “potencial de distorção”. Nos parâmetros de processo estudados as deformações induzidas no processo de trefilação não foram capazes de eliminar as distribuições heterogêneas de tensões residuais geradas no pré-endireitamento, porém utilizando-se o ângulo de fieira de 15º houve uma diminuição da distorção após a têmpera por indução. Após o processo de endireitamento por rolos cruzados (PERC) a distribuição das tensões residuais na superfície é mais homogênea para os ângulos de ferramenta avaliados neste trabalho (16º e 18º), entretanto existem diferenças significativas na distribuição de tensões residuais no núcleo do material, e estas diferenças são umas das causadoras das distorções após o processo de têmpera por indução. / Shape distortions are a serious problem in the metalworking industry, distortion due to heat treatment is responsible for additional and cost machining operations. Minimizing or even avoiding heat treatment distortion is one of the key factors to minimize production costs. In the past, investigations had focused on single effects or isolated parameters steps in a manufacturing chain. It is well established now that each step of the process chain generates a “distortion potential” and a new global approach, treating distortion as a system attribute, analyzing the entire manufacturing chain from steelmaking to heat treatment process is necessary. The main idea of distortion engineering is that all steps of the manufacturing chain together contribute to the final distortion behavior. In this work, a steel route of combined cold-drawing process to induction hardening of ABNT 1045 steel bars was investigated. The residual stresses characterizations were carried out using X-ray diffraction, neutron diffraction and synchrotron diffraction methods. The identification and interaction between factors on distortion behavior was carried out using statistical analysis, with the aid of DoE (Design of Experiments). For the DoE method the number of causes that can be considered were 5 parameters of the process, including: different batches, drawing angle, PERC angle, stress relief temperature and induction hardening depth. From the results obtained, the evaluation of which steps in the process induce higher "distortion potential" during the various steps of the process was carried out. From the measurements of residual stresses a detailed view of how these residual stresses are distributed for material in each step of the process was obtained, the results show significant differences along the peripheral positions in the pre-straightening and drawing stages. The experimental results indicate the microstructure of the material, wire rod geometry and the die angle process parameters as main "distortion potentials".

As distorções de forma de componentes mecânicos, que ocorrem durante a fabricação, constituem um sério problema enfrentado pela indústria metal-mecânica. Neste trabalho, avaliou-se uma rota de fabricação de barras de aço ABNT 1045 envolvendo os processos de trefilação, alívio de tensões e têmpera por indução utilizando-se uma visão holística do processo. Após um estudo detalhado, variou-se 5 parâmetros do processo, sendo eles: corrida, ângulo de fieira, ângulo de endireitamento, temperatura de alívio de tensões e profundidade de camada temperada. Caracterizou-se as tensões residuais, em todas as etapas do processo, utilizando-se as técnicas de difração de raios-X, difração de nêutrons e difração de radiação Síncrotron, bem como, a microestrutura do material. Após as etapas de trefilação combinada e tratamento térmico avaliou-se as distorções de forma, utilizando-se um equipamento de medição por coordenadas e posteriormente calculou-se os vetores distorção. Os dados obtidos foram analisados utilizando-se o software Minitab® através da montagem de uma matriz DoE (Design of Experiments). A partir dos resultados obtidos, avaliou-se quais etapas do processo induzem maior "potencial de distorção" nos componentes. A partir das medições de tensões residuais foi obtida uma visão detalhada de como estas tensões residuais se distribuem no material após cada etapa do processo, os dados mostram diferenças significativas ao longo das posições periféricas nas etapas de pré-endireitamento e trefilação. Dados apontam que a distribuição da zona de segregação é responsável pelo comportamento diferente nas duas corridas analisadas em relação às distorções. As tensões residuais geradas no endireitamento do fio-máquina são responsáveis por causar heterogeneidades no material e induzem um alto “potencial de distorção”. Nos parâmetros de processo estudados as deformações induzidas no processo de trefilação não foram capazes de eliminar as distribuições heterogêneas de tensões residuais geradas no pré-endireitamento, porém utilizando-se o ângulo de fieira de 15º houve uma diminuição da distorção após a têmpera por indução. Após o processo de endireitamento por rolos cruzados (PERC) a distribuição das tensões residuais na superfície é mais homogênea para os ângulos de ferramenta avaliados neste trabalho (16º e 18º), entretanto existem diferenças significativas na distribuição de tensões residuais no núcleo do material, e estas diferenças são umas das causadoras das distorções após o processo de têmpera por indução. / Shape distortions are a serious problem in the metalworking industry, distortion due to heat treatment is responsible for additional and cost machining operations. Minimizing or even avoiding heat treatment distortion is one of the key factors to minimize production costs. In the past, investigations had focused on single effects or isolated parameters steps in a manufacturing chain. It is well established now that each step of the process chain generates a “distortion potential” and a new global approach, treating distortion as a system attribute, analyzing the entire manufacturing chain from steelmaking to heat treatment process is necessary. The main idea of distortion engineering is that all steps of the manufacturing chain together contribute to the final distortion behavior. In this work, a steel route of combined cold-drawing process to induction hardening of ABNT 1045 steel bars was investigated. The residual stresses characterizations were carried out using X-ray diffraction, neutron diffraction and synchrotron diffraction methods. The identification and interaction between factors on distortion behavior was carried out using statistical analysis, with the aid of DoE (Design of Experiments). For the DoE method the number of causes that can be considered were 5 parameters of the process, including: different batches, drawing angle, PERC angle, stress relief temperature and induction hardening depth. From the results obtained, the evaluation of which steps in the process induce higher "distortion potential" during the various steps of the process was carried out. From the measurements of residual stresses a detailed view of how these residual stresses are distributed for material in each step of the process was obtained, the results show significant differences along the peripheral positions in the pre-straightening and drawing stages. The experimental results indicate the microstructure of the material, wire rod geometry and the die angle process parameters as main "distortion potentials".

This thesis focuses on the tribological performance of tool surfaces in two steel working operations, namely wire drawing and hot rolling. In all forming operations dimensions and surface finish of the products are of utmost importance. Forming basically includes three parts – forming conditions excluded – that may be changed; work material, tool and (possibly) lubricant. In the interface between work material and tool, the conditions are very aggressive with – generally or locally – high temperatures and pressures. The surfaces will be worn in various ways and this will change the conditions in the process. Consequently, the surface finish as well as the dimensions of the formed product may change and in the end, the product will not fulfil the requirements of the customer. Therefore, research and development in regard to wear, and consequently tribology, of the forming tools is of great interest. The investigations of wire drawing dies focus on coating adhesion/cohesion, surface characteristics and material transfer onto the coated steel both in laboratory scale as well as in the wire drawing process. Results show that it in wire drawing is possible to enhance the tribological performance of drawing dies by using a lubricant together with a steel substrate coated by a polished, dual-layer coating containing both hard and friction-lowering layers. The investigations of hot rolling work rolls focus on microstructure and hardness as well as cracking- and surface characteristics in both laboratory scale and in the hot strip mill. Results show that an ideal hot work roll material should be made up of a matrix with high hardness and a large amount of complex, hard carbides evenly distributed in the microstructure. The surface failure mechanisms of work rolls are very complex involving plastic deformation, abrasive wear, adhesive wear, mechanical and thermal induced cracking, material transfer and oxidation. This knowledge may be used to develop new tools with higher wear resistance giving better performance, lower costs and lower environmental impact.

No description available.

Die vorliegende Arbeit zeigt einen Weg, Kupfer und einphasige Kupferlegierungen mit stark verzwillingten Gefügen durch ein technisch relevantes Umformverfahren herzustellen. Der Drahtzug bildet dabei aufgrund seines Spannungszustands und der entsprechenden Texturentwicklung in kubischflächenzentrierten Metallen ein ideales Umformverfahren, um einen Großteil des Gefüges durch mechanische Zwillingsbildung zu verfeinern. Für die Aktivierung der Zwillingsbildung in reinem Kupfer unter den untersuchten Werkstoffvarianten sind Temperaturen nahe der Temperatur des flüssigen Stickstoffs notwendig. Um den Drahtzug in flüssigem Stickstoff umzusetzen, wurden verschiedene Feststoffschmiermittel auf ihre Eignung hin getestet. Die Textur der mit Stickstoffkühlung hergestellten Halbzeuge ist durch eine dreifache Fasertextur bestehend aus <111>-, <001>- und <115>-Fasertexturkomponente charakterisiert. Anhand der strengen Orientierungsverhältnisse konnte der Volumenanteil von verzwillingtem Material bestehend aus Matrixkörnern und Verformungszwillingen auf 71 vol% durch röntgenografische Globaltexturmessungen abgeschätzt werden, wobei das Volumenverhältnis von Zwillingen zu Matrix bei knapp 0,7:1 liegt. Die Zwillinge zeigen eine breite Zwillingslamellenweitenverteilung von wenigen Nanometern bis einige 100 nm im höchstverformten Stadium. Durch die Absenkung der Umformtemperatur und die daraus resultierende Aktivierung der Zwillingsbildung kann die Zugfestigkeit von reinem Kupfer um 140 MPa im Vergleich zu einem ohne Kühlung hergestellten Draht auf 582 MPa erhöht werden. Dabei reduziert sich die elektrische Leitfähigkeit um 6,5% gegenüber einem grobkorngeglühten Kupfer. Eine Absenkung der Stapelfehlerenergie auf 30 mJ/m² in CuAl2 führt zur Aktivierung der mechanischen Zwillingsbildung beim Drahtzug ohne Kühlung. Durch diese Aktivierung der Zwillingsbildung kann bei fortschreitender Verringerung der Stapelfehlerenergie wie in CuAl7 die Zugfestigkeit des umgeformten Drahtes auf weit über 1 GPa erhöht werden. Das entsprechende Gefüge ist dabei ultrafeinkörnig.

Die Temperaturverhältnisse beim Ziehen und Wärmebehandeln von Draht werden mit mathematisch-analytischen Methoden auf der Grundlage der FOURIERschen Wärmeleitungsgleichung eingehend untersucht. Insbesondere wird unter den spezifischen Wärmeübergangsbedingungen zwischen Draht und Ziehdüse sowie zwischen Draht und Ziehtrommel deren thermische Wechselwirkung analysiert. Ein Näherungsverfahren zur Berechnung der Drahttemperaturen in Zugfolgen unter Berücksichtigung des Ziehdüseneinflusses wird angegeben und mit einem Beispiel zum Nassziehen stark verzinkten Stahldrahts illustriert. Aus geschwindigkeitsabhängig gemessenen Änderungen des Drahtdurchmessers werden unter thermoelastischer Ziehringdurchmesserkorrektur Schmierfilmdicken bestimmt. Diffusionsgleichungen werden analysiert und ein Zusammenhang zur Reaktionskinetik wird hergestellt. Ein neues reaktionskinetisches Werkstoffmodell, das insbesondere auch im Falle stärker anisothermer Verhältnisse, also bei Kurzzeitwärmebehandlung anwendbar ist, wird vorgestellt.