Neste trabalho, propõe-se um modelo numérico-computacional representativo dos processos de tratamento térmico, que seja uma ferramenta eficiente e forneça meios para um entendimento efetivo do mecanismo de geração de tensões residuais durante a têmpera de aços. Foram investigados os fenômenos térmicos, mecânicos e de transformação de fase observados na têmpera, bem como o acoplamento entre esses três fenômenos. O modelo utiliza o Método dos Elementos Finitos (MEF) e o programa ABAQUS®, além de rotinas numéricas em FORTRAN responsáveis pela resolução do problema termo-mecânico-microestrutural acoplado. A utilização de sub-rotinas, que implementam uma alteração na formulação (matemática e numérica) do programa de Elementos Finitos, permite incluir no modelo as informações presentes em uma curva CRC (curva de resfriamento contínuo) do aço SAE 4140, implementando o cálculo de deformações da peça simulada de modo incremental e cumulativo. Os resultados mostram que a utilização das sub-rotinas desenvolvidas neste trabalho permitiu implementar, conjuntamente com o programa ABAQUS®, o cálculo das frações volumétricas, durezas, distorções e tensões que surgem em um tratamento térmico de têmpera, simulando as transformações martensítica, perlítica, bainítica e ferrítica. Os resultados dos modelos foram equivalentes aos relatados pela literatura, principalmente no que se refere às durezas e tensões associadas a cada transformação de fase. Em particular, os resultados indicam que a transformação martensítica está sempre associada à formação de tensões compressivas. Ensaios experimentais foram realizados a fim de validar os modelos computacionais propostos, utilizando-se um teste Jominy adaptado e instrumentado, de modo a permitir a amostragem da variação de temperaturas no material. Ensaios metalográficos permitiram correlacionar as frações volumétricas transformadas durante a têmpera do corpo de prova Jominy aos valores calculados pelo modelo numérico acoplado. / The objective of this work is to analyze residual strains and stresses and volumetric expansion due to phase transformations that occur during quenching of a steel body, as well as to predict these phase transformations. The coupled thermo-mechanical-phase transformation problem was analyzed, specifically in terms of the quenching process. Different computational models were presented, based on the finite element software ABAQUS® and on the use of FORTRAN subroutines. The continuous-cooling-transformation (CCT) diagrams of SAE 4140 steel are represented differently in each model, depending on the transformed phases and correspondent volumetric expansion. These subroutines include information from the CCT diagrams of SAE 4140 into a FORTRAN code. The subroutine calculates all the microstructures resulting from quenching (ferrite, pearlite, bainite, and martensite), depending on cooling rate. The numerical analysis conducted in this work provided results in terms of the temperature and stresses developed during quenching. The properties determined in this work are hardness, yield strength, volumetric fraction and distortion. Hardness has been predicted by the use of analytical equations. The finite element analyses were able to explain and reproduce phenomena observed during quenching of a steel cylinder. In particular, numerical results indicated that martensite formation is always related to a compressive stress field. The results of the models are in qualitative agreement with data provided by literature, particularly, in relation to the stresses originated by each different phase transformation during quenching process. Experimental testing was conducted, based on the analysis of the quenching of a Jominy probe, in order to validate the computational model developed in this work.

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.

Background: Compare Goldmann applanation tonometer (GAT) prism and correcting applanation tonometry surface (CATS) prism to intracameral intraocular pressure (IOP), in vivo and in vitro. Methods: Pressure transducer intracameral IOP was measured on fifty-eight (58) eyes undergoing cataract surgery and the IOP was modulated manometrically to 10, 20, and 40 mmHg. Simultaneously, IOP was measured using a Perkins tonometer with a standard GAT prism and a CATS prism at each of the intracameral pressures. Statistical comparison was made between true intracameral pressures and the two prism measurements. Differences between the two prism measurements were correlated to central corneal thickness (CCT) and corneal resistance factor (CRF). Human cadaver eyes were used to assess measurement repeatability. Results: The CATS tonometer prism measured closer to true intracameral IOP than the GAT prism by 1.7+/-2.7 mmHg across all pressures and corneal properties. The difference in CATS and GAT measurements was greater in thin CCT corneas (2.7+/-1.9 mmHg) and low resistance (CRF) corneas (2.8+/-2.1 mmHg). The difference in prisms was negligible at high CCT and CRF values. No difference was seen in measurement repeatability between the two prisms. Conclusion: A CATS prism in Goldmann tonometer armatures significantly improve the accuracy of IOP measurement compared to true intracameral pressure across a physiologic range of IOP values. The CATS prism is significantly more accurate compared to the GAT prism in thin and less rigid corneas. The in vivo intracameral study validates mathematical models and clinical findings in IOP measurement between the GAT and CATS prisms.

Background: Goldmann applanation tonometry (GAT) error relative to intracameral intraocular pressure (IOP) has not been examined comparatively in both human cadaver eyes and in live human eyes. Futhermore, correlations to biomechanical corneal properties and positional changes have not been examined directly to intracameral IOP and GAT IOP. Methods: Intracameral IOP was measured via pressure transducer on fifty-eight (58) eyes undergoing cataract surgery and the IOP was modulated manometrically on each patient alternately to 10, 20, and 40 mmHg. IOP was measured using a Perkins tonometer in the supine position on 58 eyes and upright on a subset of 8 eyes. Twenty one (21) fresh human cadaver globes were Intracamerally IOP adjusted and measured via pressure transducer. Intracameral IOP ranged between 5 and 60 mmHg. IOP was measured in the upright position with a Goldmann Applanation Tonometer (GAT) and supine position with a Perkins tonometer. Central corneal thickness (CCT) was also measured. Results: The Goldmann-type tonometer error measured on live human eyes was 5.2 +/- 1.6 mmHg lower than intracameral IOP in the upright position and 7.9 +/- 2.3 mmHg lower in the supine position (p <.05). CCT also indicated a sloped correlation to error (correlation coeff. = 0.18). Cadaver eye IOP measurements were 3.1+/-2. 5 mmHg lower than intracameral IOP in the upright position and 5.4+/- 3.1 mmHg in the supine position (p <.05). Conclusion: Goldmann IOP measures significantly lower than true intracameral IOP by approximately 3 mmHg in vitro and 5 mmHg in vivo. The Goldmann IOP error is increased an additional 2.8 mmHg lower in the supine position. CCT appears to significantly affect the error by up to 4 mmHg over the sample size.

No description available.

More complex and bigger structures have increased the applicability of low alloy high strength steels due to weight and cost reductions in these projects. One of the requirements for the use of these materials is the preservation of performance after welding. Meanwhile, the norms on which the Welding Procedures Specifications (WPS) are based have not yet considered the development of modern steel and its new production process, resulting in unnecessary welding costs that diminish the profits of the application of this type of steel. This thesis aimed to develop and evaluate an experimental methodology to guide the creation and control of welding procedures for structural steel through a microstructural atlas of the heat affected zone (HAZ) in a thermomechanical control process (TMCP), 65 ksi steel (ASTM A572 Grade 65). This steel was used in the project of an industrial building for CBMM in Araxá, Minas Gerais, Brazil. It is proposed that through a microstructural atlas of a given steel, it is possible to determine the range of cooling rates that the steel may suffer during welding without affecting mechanical properties and without risking cold cracks. When comparing the microstructure of steel welds performed in field conditions, it is possible to determine the heat input range for a given process in the preparation of a WPS. The selected case study is from a high strength low alloy class 65 ksi steel (ASTM A572 Grade 65) that was used in the structure of an industrial building. The steel was produced using TMCP. The atlas was created via the construction of a continuous cooling transformation diagram using physical simulation (dilatometer and Gleeble) of the coarse grain HAZ (GCHAZ). The characterization of the simulated region was performed by metallography and mechanical tests. The microstructure of real welds made by a qualified WPS were compared to the atlas in order to certify the correct use of parameters and to validate the method. The methodology was also qualified and the potential economic benefits were quantified (based only on the reduction of consumables used and the increased availability of the welding process machine) for the selected industrial project. The mapped microstructures varied from martensite (at high cooling rates) to pearlite/ferrite with large grain size (at low cooling rates). There was remarkable prevalence of bainitic microstructure in a wide range of cooling rates, consistent with the chemical composition of the steel studied. Comparisons with real weld microstructures showed the atlas is compatible with them, and that it can more accurately describe the effective thermal cycle xi that occurs in the coarse grain region of the HAZ (other regions were not included). The application of this methodology in the development of new WPS would allow greater flexibility in the welding procedures, including welding without preheating. In this respect alone, it was possible to forecast savings of approximately R$200,000.00, 1,000 hours of processing and 172 tonnes of carbon equivalent emissions. / Estruturas cada vez mais complexas e de maiores dimensões vêm aumentando a aplicabilidade de aços de baixa liga e alta resistência, devido à redução de peso e custo dessas estruturas. Um dos requisitos para o uso desses materiais é a manutenção do desempenho após soldagem. Entretanto, as normas em que se baseiam as Especificações de Procedimentos de Soldagem (EPS) ainda não consideram aços mais modernos em termos de rota de fabricação, o que pode fazer com que custos desnecessários de soldagem minimizem os ganhos da aplicação desses aços. Este trabalho teve como objetivo o desenvolvimento e avaliação de uma metodologia para, experimentalmente, orientar a elaboração e o controle da aplicação de procedimentos de soldagem para aços estruturais, através de atlas microestrutural de regiões da zona afetada pelo calor (ZAC). Propõe-se que, através de um atlas microestrutural de um dado aço, seja possível determinar a faixa otimizada de energia de soldagem para um dado processo na elaboração e aplicação da EPS e, consequentemente, as velocidades de resfriamento que o aço possa sofrer durante a soldagem, sem perder as propriedades mecânicas e sem colocálo em risco quanto a trincas a frio. Tomou-se como estudo de caso o aço produzido por laminação controlada de classe de resistência de 65 ksi (ASTM A572 Grau 65), utilizado em um projeto de um prédio industrial na empresa CBMM. Trata-se de um aço fabricado pelo processo TMCP com resfriamento acelerado. A elaboração do Atlas se deu através da construção de um diagrama CCT, por simulação física (dilatômetro e Gleeble), da região de grãos grosseiros da zona afetada pelo calor (ZAC GG). Foram feitas caracterizações metalográficas e mecânicas das regiões simuladas. Microestruturas de soldas realizadas com EPS qualificadas foram comparadas com as do Atlas para se certificar da adequabilidade dos parâmetros utilizados e validação da abordagem. Foram realizadas ainda a qualificação e quantificação de potenciais benefícios econômicos no citado projeto industrial, obtidos pelo uso desta metodologia. As microestruturas apresentadas no mapa variavam de martensíta, para altas taxas de resfriamento, até perlita/ferrita de tamanho de grão elevado, para baixas taxas de resfriamento. Observou-se notável predominância da microestrutura bainítica em uma larga faixa de taxas de resfriamento, compatível com as propriedades e composição do aço estudado (alta soldabilidade). As comparações com as microestruturas de soldas reais mostraram que o Atlas pode descrever de forma precisa o ciclo térmico efetivamente imposto ix na ZAC GG. Concluiu-se que a aplicação desta metodologia na elaboração de novas EPS permitiria uma maior flexibilidade nos procedimentos de soldagem, admitindo inclusive soldagem sem pré-aquecimento. Em relação a não necessidade de pré-aquecimento, podese prever uma economia significante de custos e redução de emissão de gases que provocam efeito estufa. / Mestre em Engenharia Mecânica

Des nuances d’aciers à moyen carbone, microalliés au vanadium, ont été élaborées avec l’objectif d’obtenir de nouvelles microstructures, majoritairement constituées de ferrite aciculaire (FA). Le contrôle de la composition chimique (0.1-0.3 % V) et la vitesse de refroidissement (2.0 °Cs-1) conduit à des fractions de FA atteignant 80 %. Un paramètre empirique, le pouvoir ferritisant, P, a été introduit pour évaluer l’effet combiné de la composition chimique et de la vitesse de refroidissement sur la fraction de FA. Les caractérisations par MEB et MET montrent que la FA se développe à partir de la ferrite proeutectoïde recouvrant les inclusions de MnS. Une précipitation interphase de carbonitrures de vanadium, V(C,N), serait à l’origine d’un appauvrissement local en carbone de la matrice austénitique autour des aiguilles de FA, favorisant une germination autocatalytique. Le caractère fractal de la FA a été mis en évidence par des caractérisations morphologiques. Les dimensions fractales, D, et les longueurs de coupure ont été déterminées par la méthode de comptage de boîtes à partir d’images MEB. Des essais mécaniques isothermes-quasistatiques révèlent des propriétés mécaniques équivalentes à celles des microstructures bainitiques. Les courbes contrainte-déformation montrent un comportement mécanique de type Hollomon. Les structures de ces aciers présentent des taux de consolidation qui augmentent avec l’accroissement de la fraction de FA. Une corrélation entre les propriétés mécaniques et la dimension fractale a été établie. Ce lien s’exprime par des relations de type exponentiel : [delta]M = c exp [[alpha](D -2)] où M représente? les propriétés mécaniques (Re, Rm, etc.) et c? et ?[alpha] des constantes / Medium carbon vanadium microalloyed steels have been developed to obtain new microstructures, mainly formed of acicular ferrite (AF). Controlling the chemical composition and (0.1-0.3 % V) and the cooling rates (2.0 °Cs-1) lead to AF fractions up to 80 %. An empirical parameter, the ferritisant power, P, has been introduced to evaluate the combined effect of chemical composition and cooling conditions. Scanning (SEM) and transmission (TEM) electron microscopy investigations indicate that AF develops from proeutectoid ferrite enveloping MnS inclusions. An interphase precipitation of vanadium carbo-nitrides, V(C,N) has been identified. It is suggested that this precipitation is at the origin of carbon depletion in the austenitic matrix surrounding the AF plates. The formation of the AF is then enhanced by an autocatalytic effect. The fractal nature of AF has been determined by SEM and TEM characterisations. Fractal dimensions, D, and cut off lengths have been derived by the counting box method applied to SEM images. Mechanical tests conducted in isothermal and quasistatic conditions reveal that mechanical properties of AF are of the same grade of that of bainitic microstructures. Experimental strain-stress curves are described by the Hollomon law. The work hardening of the studied microstructures increases with the AF fraction. The mechanical properties have been linked to the fractal dimension by the following exponential relation : [delta]M = c exp [[alpha] (D -2)], where M represents the mechanical property (Re, Rm, etc.) and c and [alpha] are constants parameters