Esta dissertação apresenta um estudo da modelagem de experimentos aplicados a um processo industrial de tratamento térmico. A motivação deste trabalho surgiu diante das dificuldades associadas aos processos de recozimento industrial de aços do tipo baixa liga, na tentativa de encontrar temperaturas nas quais as durezas superficiais dos aços atingissem valores suficientemente baixos, adequados para etapas posteriores de fabricação, em especial a usinagem. Inicialmente forem realizados diversos experimentos com diferentes aços, onde a dureza superficial é obtida em função da temperatura de recozimento e dos teores de carbono e silício das amostras utilizadas. Em seguida propôs-se um modelo quadrático para modelar a dureza superficial como função dessas três variáveis. A estimação de parâmetros do modelo proposto foi realizada com o emprego do algoritmo Simulated Annealing, uma meta-heurística para otimização global que procura imitar o processo de recozimento de um material sólido. Finalmente, usando-se o modelo proposto, foi resolvido o chamado problema inverso, o qual consiste na estimação da temperatura de recozimento em função dos teores de carbono e silício e da dureza desejada. / This dissertation presents a study for experiments modeling applied for a heat treatment industrial process. The driving force to this work have raised from usual difficulties while low-alloy steels annealing industrial processes get on, trying to find out temperatures which the superficial hardness measurements reaches low values enough and suitable for the following stages, in special focus, the machining. At the first time, some experiments have been done with several steel grades, where superficial hardness is achieved as a function by annealing temperature, percent carbon content and percent silicon content of the samples. There was purposed a quadratic model for modeling the hardness as a function of that three parameters. The parameter estimation of the purposed model was done by the simulated annealing algorithm, a metaheuristic for global optimization which can be as the same as annealing of a solid material. Starting at the purposed model, the inverse problem was solved, where the estimated annealing temperature was achieved by the carbon and silicon percent contents and the suitable hardness.

O presente trabalho avalia e compara os resultados da tenacidade à fratura da zona termicamente afetada (ZTA) de soldas múltiplos passes por meio de ensaios de CTOD. Para este estudo, foi utilizado um aço alta resistência e baixa liga (ARBL) resistente à corrosão ambiental. As soldas foram realizadas com insumo de calor de 30 e 50 kJ/cm em um chanfro 1/2 K. Os resultados dos ensaios de CTOD mostraram que a solda produzida com maior insumo de calor apresenta tenacidade à fratura mais elevada. A análise microestrutural revelou que as microestruturas de elevada dureza e baixa tenacidade, formadas na ZTA de granulação grosseira, para a condição de 30 kJ/cm, deram lugar às microestruturas de tenacidade mais elevada, para o insumo de calor de 50 kJ/cm. / In this work the fracture toughness results of the heat affected zone (HAZ) in a multiple pass welds using a crack tip opening displacement (CTOD) concept were evaluated and compared. It was used an ambiental resistent high strengh low alloy steel. The welds were carried out using a heat input of 30 and 50 kJ/cm in a bevel preparation 1/2 K. The results of CTOD testing showed that increasing heat input, caused an improvement in the weldments fracture toughness. Microstructural analysis revealed that the high hardness and low toughness microstructures formed at coarse grain HAZ, near fusion line, for welding condition 30 kJ/cm were changed to higher toughness microstructure using a heat input of 50 kJ/cm.

Les manilles utilisées pour l'assemblage et l'amarrage des plates-formes pétrolières nécessitent des propriétés mécaniques de plus en plus élevées. Mais les défauts de fabrication de ces manilles, responsables de leur rupture prématurée, engendrent des coûts d'intervention très élevés. Afin de comprendre et d'anticiper ces défauts de fabrication, trois outils numériques ont été développés permettant de simuler (i) le procédé de fabrication, (ii) le traitement thermique et (iii) le chargement mécanique de la manille. Le procédé de fabrication des manilles est constitué d'une succession de différentes étapes de forgeage à chaud et a été caractérisé avec des mesures de température, géométrie et efforts durant toutes les étapes. Un modèle numérique thermo- mécanique du procédé de fabrication a été développé en 3D et permet de prédire tous les paramètres de forge. Une étude numérique d'influence de certains paramètres du procédé a permis de comprendre les différentes causes de mise au rebut. Des mesures de température, des observations métallographiques au microscope et au MEB ainsi que des essais mécaniques ont été effectués sur des lopins après différents cycles de traitement thermique. Un modèle numérique de traitement thermique a été développé en 1D et permet de simuler les changements de phases pendant la normalisation et la trempe, et ainsi d'obtenir la dureté résultante en tout point du lopin. Finalement, une cartographie des propriétés mécaniques d'une manille a été obtenue et les modes de déformation de la manille en condition de chargement ont été évalués par le biais d'un essai de tension sur banc. Le modèle numérique de la manille sous tension a été développé en 3D et permet d'évaluer la charge maximale en service, la charge à rupture ainsi que la zone critique de la manille étudiée / Shackles used for the assembly or the mooring of petroleum platforms require constantly higher mechanical properties. But the manufacturing defects often lead to premature failure which can cost 1M€/day. Thus, in order to understand and anticipate those manufacturing defects, three numerical tools have been developed to simulate (i) the manufacturing process, (ii) the heat treatment and (iii) the mechanical behavior of the shackle. A shackle is manufactured via a sequence of hot forming stages and the manufacturing process has been characterized during all the stages, with measures of temperature, geometry and loads. The numerical thermo-mechanical model has been developed in 3D and gives a very good prediction of each forging parameters. A numerical study of influence of some process parameters has led to a better understanding of scrapping. Temperature measurements, metallographic observations as well as mechanical testing have been carried out on cylindrical rods after various heat treatment cycles. The numerical heat treatment model has been developed in 1D and predicts phase transformations during normalizing and quenching, as well as the hardness at each point of the rod. Finally, the distribution of the mechanical properties over a shackle has been characterized and the deformation modes of the shackle were evaluated via a load test on a dedicated bench. The numerical model of the shackle under tension has been developed in 3D and allows to evaluate the working load limit, the break load as well as the critical zone of the shackle.

No description available.

No description available.

Ageing of low alloy steel in nuclear applications commonly takes the form as a hardening and an embrittlement of the material. This is due to the evolution of the microstructure during irradiation and at purely thermal conditions, as a combination or separate. Irradiation introduces evenly distributed solute clusters, while thermal ageing has been shown to yield a more inhomogeneous distribution. These clusters affect the dislocation motion within the material and results in a hardening and in more severe cases of ageing, also a decreased work hardening slope due to plastic strain localization into bands/channels. Embrittlement corresponds to decreased fracture toughness due to microstructural changes resulting from ageing. The thesis presents a possible framework for modeling of ageing effects in low alloy steels.In Paper I, a strain gradient plasticity framework is applied in order to capture length scale effects. The constitutive length scale is assumed to be related to the dislocation mean free path and the changes this undergoes during plastic deformation. Several evolution laws for the length scale were developed and implemented in a FEM-code considering 2D plane strain. This was used to solve a test problem of pure bending in order to investigate the effects of the length scale evolution. As all length scale evolution laws considered in this study results in a decreasing length scale; this leads to a loss of non-locality which causes an overall softening at cases where the strain gradient is dominating the solution. The results are in tentative agreement with phenomena of strain localization that is occurring in highly irradiated materials.In Paper II, the scalar stress measure for cleavage fracture is developed and generalized, here called the effective normal stress measure. This is used in a non-local weakest link model which is applied to two datasets from the literature in order to study the effects of the effective normal stress measure, as well as new experiments considering four-point bending of specimens containing a semi-elliptical surface crack. The model is shown to reproduce the failure probability of all considered datasets, i.e. well capable of transferring toughness information between different geometries. / Åldring av låglegerade stål i kärntekniska användningsområden framträder typiskt som ett hårdnande och en försprödning av materialet. Detta på grund av utvecklingen av mikrostrukturen under bestrålning och under rent termiska förhållanden. Bestrålning introducerar jämt fördelade kluster av legeringsämnen. Termisk åldring har däremot visats ge upphov till en mer ojämn fördelning. Klustren hämmar dislokationsrörelsen i materialet och ger därigenom upphov till en ökning av materialets sträckgräns, vid en mer påtaglig åldring det även leda till ett sänkt arbetshårdnande på grund av lokalisering av plastisk töjning i s.k. kanaler/band. Försprödning är en sänkning av materialets brottseghet som en följd av de mikrostrukturella förändringar som sker vid åldring. Arbetet som presenteras i den här avhandlingen har gjorts i syfte till att ta fram ett möjligt ramverk för modellering av låglegerade stål.I Artikel I, används en töjningsgradientbaserad plasticitetsteori för att kunna fånga längdskalebeteenden. Längdskalan i teorin antas vara relaterad till dislokationernas medelfria väg och den förändring den genomgår vid plastisk deformation. Flera utvecklingslagar för längdskalan har analyserats och implementerats i en finita element kod för 2D plan deformation. Denna implementering har använts för att lösa ett testproblem bestående av ren böjning med syfte att undersöka effekterna av utvecklingen hos längdskalan. Alla de utvecklingslagar som presenteras i artikeln ger en minskande längdskala, vilket leder till vad som valt att kallas förlust av icke-lokalitet. Fenomenet leder till ett övergripande mjuknande vid fall där den plastiska töjningsgradienten har stor inverkan på lösningen. Resultaten är i preliminär överenstämmelse med de typer av lokalisering av plastisk töjning som observerats i starkt bestrålade material.I Artikel II utvecklas ett generaliserat spänningsmått i syfte att beskriva klyvbrott, här benämnt effektivt normalspänningsmått. Detta har använts i samband med en icke-lokal svagaste länk modell, som har applicerats på två experimentella studier från den öppna litteraturen i syfte att studera effekterna av det effektiva normalspänningsmåttet. Utöver detta presenteras även nya experiment på ytspruckna provstavar under fyrpunktsböj. I artikeln visas att modellen återskapar sannolikheten för brott för alla undersökta experimentuppställningar, d.v.s. modellen visas vara väl duglig för att överföra brottseghet mellan geometrier. / <p>QC 20190312</p>

Este trabalho tem por objetivo caracterizar e comparar as microestruturas de diferentes regiões de uma chapa de aço microligado para tubo API 5L X65, empregado no transporte de gás natural e petróleo, como recebido e submetido a tratamentos térmicos de austenitização e resfriamento contínuo sob diferentes taxas de resfriamento. O aço em estudo apresenta uma linha de segregação central, originada durante o processo de produção do aço. Corpos de prova de dilatometria foram usinados da região central e de outras regiões da chapa. As amostras foram previamente austenitizadas a 1200°C e temperadas em água, visando solubilizar grande parte dos precipitados presentes no aço. Após este tratamento, as amostras foram austenitizadas em um dilatômetro de têmpera a 950°C por 180s, e em seguida resfriadas nas seguintes taxas de resfriamento: 0,5°C/s, 1°C/s, 5°C/s, 10°C/s, 20°C/s, 30°C/s, 40°C/s, 50ºC/s e 60ºC/s. Valores de temperatura e tempo correspondentes a inflexões da curva dilatométrica foram obtidas e correlacionadas com a microestrutura, para cada taxa de resfriamento. Com base nesta análise foi traçado um diagrama de Transformação por Resfriamento Contínuo (TRC) do material. / This work aims to characterize and compare the microstructures of different regions of a plate of microalloyed pipeline steel that conforms to API 5L X65, employed in the transportation of natural gas and oil, as received and after being subjected to heat treatments of austenitization and continuous cooling under different cooling rates. The steel under study presents a central line of segregation that was originated during production. Specimens for dilatometry were machined from the central region and from different regions of the plate. The samples were austenitized at 1200°C and in quenched in water, with the purpose of solubilizing most of the precipitates in the steel. After the preliminary heat treatment, the specimens were austenitized at 950°C for 180s and cooled under the cooling rates: 0.5°C/s, 1°C/s, 5°C/s, 10°C/s, 20°C/s, 30°C/s, 40°C/s, 50ºC/s and 60ºC/s in a quench dilatometer. Values of temperature and time correspond of transformation for each rate of cooling were used for the determination of the Continuous Cooling Transformation (CCT) diagram.

L'exploitation des champs de pétrole et de gaz sous haute pression (HP) et haute température (HT) a augmenté ces dernières années, nécessitant de réévaluer les risques de corrosion dans ces milieux de plus en plus sévères. Afin de contribuer à une meilleure évaluation des risques de rupture différée des aciers en présence d'H2S (SSC, Sulfide Stress Cracking) dans ces conditions, trois axes de recherche ont été suivis. Nous avons d'abord identifié un besoin d'amélioration de prédiction des conditions corrosives sous haute pression et haute température, et en particulier pour le calcul du pH in situ. Un modèle a été développé ; il prend en compte le comportement non-idéal des phases en équilibre, et permet un calcul plus précis du pH et de la fugacité des gaz acides à haute pression et haute température. Dans un deuxième temps, nous avons étudié l'effet de la pression partielle de CO2 (PCO2) sur les réactions de surface et sur les risques de SSC. Cette étude, réalisée à l'aide de mesures électrochimiques en l’absence d’un film de sulfure de fer, a permis de montrer que la présence de CO2 augmente sensiblement les cinétiques des réactions cathodiques à la surface de l'acier ainsi que le chargement en hydrogène, en particulier lorsque la pression partielle en H2S (PH2S) est faible. Enfin, des essais SSC ont été mis en œuvre dans des conditions fixes de pH et de PH2S, en faisant varier PCO2 entre zéro et 100 bar. L'objectif était de vérifier que la présence de CO2 sous forte pression augmentait bien les risques de fissuration, comme prévu par les résultats des essais électrochimiques. Les difficultés liées à la mise en œuvre d'essais en autoclave sous pression n'ont pas permis d'apporter une conclusion définitive. Néanmoins, ces travaux montrent qu'il peut exister un risque de sous-estimation de la sévérité des milieux dans les pratiques conventionnelles, lorsque PCO2 est significativement plus élevée que PH2S. Dans ces conditions spécifiques, les résultats de ce travail peuvent servir à améliorer les critères de choix de matériaux pour les milieux HP/HT. / The production of high pressure (HP) and high temperature (HT) wells has considerably increased in the last decade. It is therefore needed to reassess the risks of corrosion in always more severe environments. This work was three fold to better assess the risk of Sulfide Stress Cracking (SSC) in these environments. Firstly, there was a need to improve prediction methods for the evaluation of HP/HT environments severity, especially the in situ pH calculation. A model was which taking into account the non-ideal behaviour of gas and liquid phases in equilibrium. The determination of the in situ pH and the acid gas fugacity at high pressure and high temperature is more accurate. In a second part of the work, the impact of CO2 partial pressure (PCO2) on surface reactions and hence on the risk of SSC was examined. Electrochemical and hydrogen permeation measurements in the absence of an iron sulphide film showed that CO2 induces an increase of both cathodic reactions kinetics and hydrogen charging in the steel, especially at low H2S partial pressure (PH2S). In the last part of this work, SSC tests were performed at constant pH and constant PH2S, with various PCO2 from 0 to 100 bar. The objective was to experimentally confirm that increasing PCO2 increases the SSC risk, as inferred from the electrochemical study. Unfortunately, experimental artefacts linked with autoclave test conditions did not lead to clear conclusions on this point. However, this work shows that conventional tools might lead to underestimate SSC risks at high PCO2 and low PH2S. In these specific conditions, the new results presented in this report may contribute to improve materials selection criteria for high pressure and high temperature conditions.

Foram estudados dois tipos de aços, aço convencional ZAR 230 (ZAR - Zincagem de alta resistência) e aço microligado ZSTE 380 (segundo norma SEW 093), sendo que foram avaliadas as suas propriedades mecânicas visando a substituição do aço convencional por aço microligado na estrutura tubular de uma carroceria para veículos de transporte coletivo de passageiros. O aço convencional vem sendo utilizado pela indústria de carrocerias há vários anos, já o aço microligado é utilizado basicamente em estruturas específicas que requeiram boas propriedades mecânicas e conseqüentemente redução de peso. A análise de viabilidade para a substituição de aço convencional por aço microligado em um módulo estrutural completo requereu uma série de ensaios: ensaios padronizados em laboratório foram executados para avaliação de suas principais propriedades mecânicas e químicas; ensaios de nós estruturais submetidos a uma carga forneceram informações para o uso em software de elementos finitos tanto para execução de cálculos estruturais, quanto para calibração de resultados. Os módulos estruturais foram preparados de acordo com as regulamentações ECE R66-00 (mercado europeu) e CONTRAN 811/96 (mercado brasileiro) e foram ensaiados exaustivamente até se obter o melhor resultado de deslocamento comparativamente aos dois materiais analisados. A validação da estrutura tubular foi obtida com a utilização do software Ansys Workbench 9.0 e a confecção de estrutura representativa de uma carroceria ensaiada conforme regulamentação CONTRAN 811/96. / Submitted by Marcelo Teixeira (mvteixeira@ucs.br) on 2014-05-05T19:51:22Z No. of bitstreams: 1 Dissertacao Magnus Geder Henz Cruz.pdf: 4706762 bytes, checksum: 44526b5417018356b3a33f57c828c75e (MD5) / Made available in DSpace on 2014-05-05T19:51:22Z (GMT). No. of bitstreams: 1 Dissertacao Magnus Geder Henz Cruz.pdf: 4706762 bytes, checksum: 44526b5417018356b3a33f57c828c75e (MD5) / Two kinds of steel were studied, conventional steel ZAR 230 (a standard for high strength galvanizing) and microalloyed steel ZSTE 380 (according to the regulation SEW 093). The study of its mechanical properties aimed to replace the steel for microalloyed steel in bodywork s tubular structure for collective transport vehicles of passengers. The conventional steel has been used for the bodywork industry for years, and the microalloyed steel is basically used in specific structures, those who require good mechanical properties and mass reduction. The analysis of the feasibility for the replacement of conventional steel for microalloyed steel in a complete structural model requires a series of tests. Lab tests were done to evaluate their main mechanical and chemical properties. The tests of the structural nodes and the structural behaviour when subjected to a load provided information to be used in the finite elements method software to do structural calculation and to calibrate the results. The structural modules were prepared according to the regulations ECE R66-00 (European market) and CONTRAN 811/96 (Brazilian market) and these modules were tested exhaustively to achieve the best displacement between the two materials that were analysed comparatively. The validation of the tubular structure was obtained using the software Ansys Workbench 9.0 and the production of the representative structure of a bodywork tested according the regulation CONTRAN 811/96.

Este trabalho tem por objetivo caracterizar e comparar as microestruturas de diferentes regiões de uma chapa de aço microligado para tubo API 5L X65, empregado no transporte de gás natural e petróleo, como recebido e submetido a tratamentos térmicos de austenitização e resfriamento contínuo sob diferentes taxas de resfriamento. O aço em estudo apresenta uma linha de segregação central, originada durante o processo de produção do aço. Corpos de prova de dilatometria foram usinados da região central e de outras regiões da chapa. As amostras foram previamente austenitizadas a 1200°C e temperadas em água, visando solubilizar grande parte dos precipitados presentes no aço. Após este tratamento, as amostras foram austenitizadas em um dilatômetro de têmpera a 950°C por 180s, e em seguida resfriadas nas seguintes taxas de resfriamento: 0,5°C/s, 1°C/s, 5°C/s, 10°C/s, 20°C/s, 30°C/s, 40°C/s, 50ºC/s e 60ºC/s. Valores de temperatura e tempo correspondentes a inflexões da curva dilatométrica foram obtidas e correlacionadas com a microestrutura, para cada taxa de resfriamento. Com base nesta análise foi traçado um diagrama de Transformação por Resfriamento Contínuo (TRC) do material. / This work aims to characterize and compare the microstructures of different regions of a plate of microalloyed pipeline steel that conforms to API 5L X65, employed in the transportation of natural gas and oil, as received and after being subjected to heat treatments of austenitization and continuous cooling under different cooling rates. The steel under study presents a central line of segregation that was originated during production. Specimens for dilatometry were machined from the central region and from different regions of the plate. The samples were austenitized at 1200°C and in quenched in water, with the purpose of solubilizing most of the precipitates in the steel. After the preliminary heat treatment, the specimens were austenitized at 950°C for 180s and cooled under the cooling rates: 0.5°C/s, 1°C/s, 5°C/s, 10°C/s, 20°C/s, 30°C/s, 40°C/s, 50ºC/s and 60ºC/s in a quench dilatometer. Values of temperature and time correspond of transformation for each rate of cooling were used for the determination of the Continuous Cooling Transformation (CCT) diagram.