The effects of microstructure and prestraining on toughness of a multipass carbon-manganese (C-Mn) weld metal have been investigated. The toughness has been assessed in terms of both Charpy impact energy and Crack Tip Opening Displacement values. An extensive Charpy impact test experimental programme has been carried out on the C-Mn pressure vessel steel weld metal resulting in comprehensive databases for the weld metal in as-received and prestrained conditions. Charpy specimens were machined from multipass submerged arc weld metals with various notch tip locations and orientations relative to the weld metal. The impact energy was evaluated over a range of temperatures from -196 to 150°C. Mechanical prestraining levels of 2,9, and 12% have been applied to impact specimens to provide the trends in impact toughness that approximate some effects of irradiation embrittlement in service. Statistical interpretation of the results, in conjunction with the measurements from the fracture surfaces of Charpy specimens and fractography, has been carried out to provide a quantitative assessment of transition temperature shifts from the full and sub-populations of impact energy data pertaining to a particular notch root location relative to the weld microstructure. Impact energy values of a multipass submerged-arc C-Mn weld metal in both as-received and prestrained conditions are found to be subject to substantial scatter in the transition and upper shelf regions. Lower shelf impact energy values are found to be insensitive to microstructure and prestraining. The microstructure is found to have a significant influence on the ductile to brittle transition curve. Impact toughness for specimens with notch root locations in the reheated microstructure is greater than the impact toughness of specimens with notches located in the as-deposited microstructure. This trend is observed in both transition and upper shelf regions and is valid for both as-received and prestrained material conditions. The OT40Js hift between the transition curves corresponding to the as-received specimens with notch root locations on the centreline of the last deposited bead and in reheated microstructure has been estimated to be approximately 50°C. Prestraining (cold deformation) is found to provide the same trends in Charpy impact energy transition curve as irradiation embrittlement. Prestraining thus reduces the as-received upper shelf energy level and shifts the as-received transition curve towards higher temperatures. The magnitude of these effects depends on the amount of prestraining. The as-received and 2% prestrained datasets are found to be very similar, as are the datasets obtained after 9 and 12% prestraining.The transition curve for specimens with the notch root located in the reheated microstructure in the as-received material condition and transition curve for the specimens with notch root located on the centreline of the last deposited bead in the 9% prestrained material condition form the boundaries of the region of all possible locations for the transition curves along the temperature axis. The width of this "window" at the 40 J energy level, i. e. the OT4o4 temperature shift between the "best" (upper bound) dataset in as-received condition and the "worst" (lower bound) impact energy dataset in 9% prestrained material is estimated to be 102°C. The microstructure is also found to have a marked influence on the CTOD values of the as-received material with reheated microstructure showing better CTOD toughness across the whole temperature range examined. Prestraining at the 9% level shifts the onset of plastic collapse to lower values of the opening displacement resulting in the reduction in upper shelf CTOD values of more than 50% relative to the as-received upper shelf CTOD values. The transition region is also shifted along the temperature axis.

High entropy alloys (HEAs) are a new class of solid solution alloys that contain multiple principal elements and possess excellent mechanical properties, from corrosion resistance to fatigue and wear resistance. Even more recently, twinning induced plasticity (TWIP) and transformation induced plasticity (TRIP) non-equiatomic high entropy alloys have been engineered, promising increased strength and ductility as compared to their equiatomic counterparts. However, impact and fracture resistance of these HEAs has not been studied as much as their other mechanical properties. In this thesis, the hardness, tensile properties, and Charpy impact energy of Al0.3CoCrFeNi, a TWIP HEA, and 50Fe-30Mn-10Co-10Cr (at.%), a TRIP HEA, was explored. First, three processing conditions, (1) as-received, (2) recrystallized, and (3) peak hardness, were chosen for each alloy and verified with Vickers microhardness measurements. Next, the tensile properties of each alloy and condition were investigated. Charpy impact specimen size was then selected based on the final plate thickness, and the machined samples were tested. Plastic zone size and change in sample thickness in the deformed region of each condition after testing was measured. Post-impact test inspection of the samples in all conditions showed that the samples were in tension near the V-notch root and in compression at the impact surface. Plastic zone size is seen to change as a function of distance from the V-notch root moving towards the impact surface in conditions that exhibited higher ductility. Overall, the TWIP alloy displayed high fracture resistance, and further microstructural optimization will likely increase the fracture resistance of these alloys.

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Das Verhalten einer 3-Punkt-Biegeprobe mit Anriss unter Belastung kann mittels eines Finite-Element-Modells nachgebildet werden. Das Modell ermöglicht die Berücksichtigung von elastisch-plastischem Materialverhalten entsprechend der jeweiligen materialspezifischen Spannungs-Dehnungs-Kurve, welche mit dem Ansatz der multilinearen kinematischen Verfestigung (MKIN) umgesetzt wird. Weiterhin gestattet das Modell die Einbeziehung der realen Rollenkinematik beim Biegevorgang. Für die Beschreibung des Bruchkriteriums wird ein spezielles Damage-Modell verwendet, mit dem man in der Lage ist, das Risswachstums in geeigneter Weise wiederzugeben. Mit diesem Modell lässt sich auch das Teilentlastungs-Compliance-Verfahren nachbilden. Diese Simulation ermöglicht die Einschätzung von Korrekturansätzen zur experimentellen Risslängenbestimmung über die Compliance-Methode.

Das Verhalten einer 3-Punkt-Biegeprobe mit Anriss unter Belastung kann mittels eines Finite-Element-Modells nachgebildet werden. Das Modell ermöglicht die Berücksichtigung von elastisch-plastischem Materialverhalten entsprechend der jeweiligen materialspezifischen Spannungs-Dehnungs-Kurve, welche mit dem Ansatz der multilinearen kinematischen Verfestigung (MKIN) umgesetzt wird. Weiterhin gestattet das Modell die Einbeziehung der realen Rollenkinematik beim Biegevorgang. Für die Beschreibung des Bruchkriteriums wird ein spezielles Damage-Modell verwendet, mit dem man in der Lage ist, das Risswachstums in geeigneter Weise wiederzugeben. Mit diesem Modell lässt sich auch das Teilentlastungs-Compliance-Verfahren nachbilden. Diese Simulation ermöglicht die Einschätzung von Korrekturansätzen zur experimentellen Risslängenbestimmung über die Compliance-Methode.

The diploma thesis is focused on the behavior of new material in furniture industry under the influence of elevated temperatures and humidity in the impact test. The aim is to confirm or disprove the possible application to components for exterior furniture. Condition simulation was performed by cycling the samples prior to testing and subjecting the individual sets to specific test temperatures. The impact strength values are different from those reported in the material datasheet and lower than in HPL compact plate used for comparison and lower then wood. The measured values were statistically processed and compared with each other.

Os aços microligados representam, cada vez mais, uma parcela significativa de produção das usinas siderúrgicas para aplicações nos mais variados segmentos industriais tais como o automotivo, petróleo e gás, construção civil e agronegócio. A característica principal desses aços é a sua elevada resistência mecânica, aliada à boa tenacidade, ductilidade e soldabilidade; o que vem sendo obtido pela utilização de composições químicas específicas com teores baixos de carbono e de microligantes que conferem essas características a esses aços. Os microligantes utilizados são os mais variados, mas principalmente destaca-se a utilização do vanádio, nióbio, titânio, cobre, manganês, cromo, alumínio e nitrogênio. No presente trabalho foram estudadas as propriedades mecânicas de um aço microligado ao vanádio com 0,25%V e um aço AISI 1020. O aço microligado apresentou LRT, LE, alongamento e estricção de, respectivamente, 735,29 MPa, 559,07 MPa, 22,7% e 63,29%. O aço AISI 1020 apresentou, respectivamente, 437,42 MPa, 268,71MPa, 32,92% e 67,15%. O aço microligado apresentou propriedade mecânica superior à do aço AISI 1020 e ductilidade equivalente. Os resultados de impacto Charpy nas temperaturas de 23 °C, -20 °C e -40 °C foram, para o aço microligado, respectivamente de, 33,83 J, 12,41 J, e 6,54 J, e para aço AISI 1020 33,18 J, 5,07 J e 3,04 J, respectivamente. Observa-se tenacidade superior do aço microligado, quando comparado com o aço AISI 1020. O ensaio revelou microestruturas refinadas em ambos os aços, e tamanho de grão de 18μm n° 8 ASTM E 112 e de 25 μm n° 7 para o aço microligado e para o AISI 1020, respectivamente. Os testes eletroquímicos realizados em uma solução aquosa 3,5% em peso de NaCl revelaram que o aço microligado apresentou formação de camada passiva, e mostrou-se menos resistente à corrosão. / Microalloyed steels are representing significant portion and increasingly steelmakers production and they are being applied to several industrial market segments such as automotive, oil and gas, civil construction and agribusiness. Its main characteristics are the superior tensile strength, toughness, ductility and good weldability. These properties are obtained through specific chemical compositions as low carbon and microalloying elements contents. Several microalloying elements can be used but some of them need to be mentioned such as vanadium, niobium, titanium, cooper, manganese, chromium, aluminum and nitrogen. In this work, the mechanical properties of a vanadium microalloyed and AISI 1020 steels were studied and compared. The microalloyed steel presented LRT, LE, elongation and toughness values of, respectively, 735.29 MPa, 559.07 MPa, 22.7% and 63,29%. AISI 1020 presented, respectively, 437.41 MPa, 268.70 MPa, 32.92% and 67.15%. The microalloyed steel presented mechanical properties superior to AISI 1020 and equivalent ductility. The results of the Charpy impact tests at the temperatures of 23 ° C, -20 ° C and -40 ° C were 33.83 J, 12.41 J, 6.54 J for the microalloyed steel, and for AISI 1020 steel the values were 33,18 J, 5.07 J and 3.04 J, respectively. The superior toughness of the microalloyed steel is observed when compared to the AISI 1020 steel. The metallographic examination showed fine grain microstructures ASTM E 112 No.8 and 7.for the microalloyed and for the AISI 1020, respectively. The electrochemical tests carried out in a 3.5 wt% NaCl aqueous solution showed that the microalloyed steel is less resistant to corrosion, and that a passive layer was formed on its surface.

[pt] O presente trabalho avalia a evolução da microestrutura e as propriedades mecânicas devido à influência do aporte de calor exercido por um procedimento de soldagem que utilizou sequencialmente dois processos de soldagem sobre um tubo de aço API 5L X80, fabricado pelo processo UOE, de um aço produzido por laminação controlada sem resfriamento acelerado. A soldagem foi realizada em um tubo de 20 de diâmetro nominal e 3/4 de espessura, fixado na posição horizontal simulando condições de campo, usando o processo MAG de curtocircuito de corrente controlada com gás de proteção CO2 (100%) para o passe de raiz e o processo por Arame Tubular com proteção gasosa Ar - CO2 (80% - 20%) para os demais passes. As propriedades mecânicas foram avaliadas segundo os ensaios mecânicos exigidos na norma API 1104, além dos ensaios de microdureza Vickers e de impacto Charpy V. As mudanças microestruturais na Zona Afetada Termicamente e Material de Solda foram avaliadas por microscopia eletrônica de varredura (MEV) e microscopia óptica. A avaliação mecânica segundo a norma API 1104 foi reprovada, onde os resultados dos ensaios de tração e Nick-Break foram aceitos e o ensaio de dobramento lateral um corpo-de-prova apresentou uma trinca superior ao comprimento máximo aceitável. Os resultados da microdureza foram aceitáveis e o resultado do impacto Charpy V, segundo a norma DNV-OS-F101, para a temperatura de 0 °C foi insatisfatório na região do metal de solda dos passes de acabamento. A região da ZTA apresentou maior energia de impacto quando comparado com o material de base à temperatura de 0 °C, embora com presença do microconstituinte A-M. / [en] The present work evaluates the changes in the microstructural and mechanical properties of an API 5L X80 steel tube due to the influence of heat input exerted during a welding procedure that used two sequential welding processes. The tubes were manufactured using the UOE process, from steel that was produced by controlled rolling without accelerated cooling. The welding was carried out on a 3/4 thick and 20 nominal diameter pipe, while it was held in a horizontal position in order to simulate field conditions, using a controlled short circuit GMAW process with CO2 (100%) gas shielding for the root pass and a flux cored arc welding process with Ar-CO2 (80% - 20%) gas shielding for the other passes. The evaluation of the mechanical properties was done by means of mechanical tests according to the API 1104 standard, in addition to the Vickers microhardness and Charpy V-notch tests. The changes in the microstructure of the Heat Affected Zone (HAZ) and the welded metal were evaluated by means of scanning electronic microscopy (SEM) and optical microscopy. The mechanical evaluation was unsatisfactory according to the API 1104 standard, while the tensile and Nick-Break test results were acceptable. The side bend test showed a crack in a specimen that exceeded the maximum acceptable value. The Vickers microhardness results were acceptable and the Charpy V-notch result, according to the DNV-OS-F101 standard, at a temperature of 0 °C, was unsatisfactory in the weld metal region of the over cap. The HAZ region showed greater energy of impact absorption compared to the base metal, at a temperature of 0 °C, even with existence of the microconstituent M-A.

Com o decorrer dos anos o consumo de petróleo e seus derivados aumentou significativamente e com isso houve a necessidade de se investir em pesquisas para descobertas de novas jazidas de petróleo como o pré-sal. Porém, não apenas a localização dessas jazidas deve ser estudada, mas, também, sua forma de exploração. Essa exploração e extração, na maioria das vezes, se dão em ambientes altamente corrosivos e o transporte do produto extraído é realizado através de tubulações de aço de alta resistência e baixa liga (ARBL). Aços ARBL expostos a ambientes contendo H2S e CO2 (sour gas) sofrem corrosão generalizada que promovem a entrada de hidrogênio atômico no metal, podendo diminuir sua tenacidade e causar falha induzida pela presença de hidrogênio (Hydrogen Induced Cracking HIC), gerando falhas graves no material. Tais falhas podem ser desastrosas para o meio ambiente e para a sociedade. O objetivo deste trabalho é estudar a tenacidade, utilizando ensaio Charpy, de um tubo API 5L X65 sour após diferentes tempos de imersão em uma solução saturada com H2S. O eletrólito empregado foi a solução A (ácido acético contendo cloreto de sódio) da norma NACE TM0284 (2011), fazendo-se desaeração com injeção de N2, seguida de injeções de H2S. Os materiais foram submetidos a: ensaios de resistência a HIC segundo a norma NACE TM0284 (2011) e exames em microscópio óptico e eletrônico de varredura para caracterização microestrutural, de inclusões e trincas. As amostras foram submetidas a imersão em solução A durante 96h e 360h, sendo que, após doze dias do término da imersão, foram realizados os ensaios Charpy e exames fractográficos. Foram aplicados dois métodos: o de energia absorvida e o da expansão lateral, conforme recomendações da norma ASTM E23 (2012). As curvas obtidas, em função da temperatura de impacto, foram ajustadas pelo método da tangente hiperbólica. Esses procedimentos foram realizados nas duas seções do tubo (transversal e longitudinal) e permitiram a obtenção dos seguintes parâmetros: energias absorvidas e expansão lateral nos patamares superior e inferior e temperaturas de transição dúctil-frágil (TTDF) em suas diferentes definições, ou seja, TTDFEA, TTDFEA-DN, TTDFEA-FN, TTDFEL, TTDFEL-DN e TTDFEL-FN (identificação no item Lista de Abreviaturas e Siglas). No exame fractográfico observou-se que o material comportou-se conforme o previsto, ou seja, em temperaturas mais altas ocorreu fratura dúctil, em temperaturas próximas a TTDF obteve-se fratura mista e nas temperaturas mais baixas observou-se o aparecimento de fratura frágil. Os resultados mostraram que quanto maior o tempo de imersão na solução A, menor é a energia absorvida e a expansão lateral no patamar superior, o que pode ser explicado pelo (esperado) aumento do teor de hidrogênio em solução sólida com o tempo de imersão. Por sua vez, os resultados mostraram que há tendência à diminuição da temperatura de transição dúctil-frágil com o aumento do tempo de imersão, particularmente, as TTDFEA-DN e TTDFEL-DN das duas seções do tubo (longitudinal e transversal). Esse comportamento controverso, que pode ser denominado de tenacificação com o decorrer do tempo de imersão na solução A, foi explicado pelo aparecimento de trincas secundárias durante o impacto (Charpy). Isso indica uma limitação do ensaio Charpy para a avaliação precisa de materiais hidrogenados. / Over the years the consumption of crude oil and its derivatives increased significantly, creating the necessity to invest in research to discover new sources of pre-salt crude oil. However, not only the location of these deposits should be studied, but also its extraction. This exploration and extraction, in most cases, occur in highly corrosive environments and the transport of the extracted product is performed by high strength low alloy steel pipes (HSLA). HSLA steels exposed to environments containing CO2 and H2S (sour gas) suffer general corrosion that promotes the diffusion of atomic hydrogen into the metal structure, which may decrease its toughness and induce cracks by the presence of hydrogen (Hydrogen Induced Cracking - HIC), leading the material to severe failures. Such events can be disastrous for the environment and the society. The objective of this work is to study the toughness using Charpy Impact Tests on an API 5L X65 sour service steel pipe, submitted to different immersion times in a H2S saturated solution. The used electrolyte was the NACE TM0284 (2011) solution A (acetic acid containing sodium chloride), with deaeration by N2 injection followed by H2S injection. The materials were submitted to HIC resistance tests according to NACE TM0284 (2011) standard and examination by optical microscopy and scanning electron microscopy for microstructural inclusions and cracks characterization. The samples were immersed in the solution for 96h and 360h and after twelve days of immersion, Charpy tests and fracture analysis were performed. Two analytical methods were applied to Charpy tests results: the energy absorbed and lateral expansion, as recommended by the ASTM E23 (2012). The obtained curves, that are a function of impact temperature, were adjusted by the hyperbolic tangent method. This procedure was performed in two different orientations in the pipe (transverse and longitudinal) and allowed the determination of the following parameters: energy absorbed and lateral expansion in the upper and lower levels and ductile-to-brittle transition temperatures (DBTT) in its different definitions: DBTTAE, DBTTAE-DN, DBTTAE-FN, DBTTLE, DBTTLE-DN e DBTTLE-FN. Fracture analysis revealed that the material behaved as expected, meaning that at higher temperatures ductile fracture occurred, at temperatures near DBTT it was obtained a mixed fracture and at lower temperatures it was observed the presence of brittle fracture. Results showed that when the immersion time in the solution was higher, the energy absorbed in upper shelf decreases, and also lateral expansion in upper shelf decreases, which may be explained by the (expected) increase of hydrogen level in solid solution, induced by the immersion time. It was found that there is a tendency of the ductile-to-brittle transition temperature to be lower with the increase of immersion time, particularly the DBTTAE-DN and DBTTLE-DN of the two pipe sections (longitudinal and transversal). This controversial behavior, which may be defined as the toughening by the increase of immersion time in the solution A, was explained by the appearance of secondary cracks during impact test (Charpy). This indicates a limitation of the Charpy test for the accurate characterization of hydrogenated materials, concerning toughness.

Diversos critérios de tenacidade à fratura translaminar dinâmica foram determinados para o laminado híbrido metal-fibra TiGra, empregando-se conceitos e metodologias da Mecânica da Fratura Elástica Linear MFEL (fator-K) e da Mecânica da Fratura Elasto-Plástica MFEP (integral-J). Verificou-se que as tenacidades de iniciação elasto-plástica, Jid, e de carga máxima, Jmd, do TiGra são controladas pelo desenvolvimento, ou supressão de delaminações. Os resultados indicaram que o emprego deste material se justifica mais pela sua resistência à propagação de danos (caracterizada por Jmd) do que à iniciação da fratura dinâmica (por Jid). De modo geral, os requisitos de validade de Jid como verdadeira propriedade do material (JId) foram satisfeitos, embora para Jmd boa parte das restrições quanto ao tamanho mínimo do corpo-de-prova tenha sido violada. Mais freqüentemente, velocidades mais rápidas de impacto beneficiaram as tenacidades-J do TiGra, enquanto que temperaturas mais elevadas afetaram negativamente estas propriedades. Quanto à MFEL, a tenacidade KJd do TiGra foi beneficiada pelo incremento na taxa de carregamento sob temperaturas mais elevadas, enquanto que a tenacidade Kid foi negativamente afetada pela taxa de deformação em todas as temperaturas avaliadas. Temperaturas mais altas também degradaram as propriedades de tenacidade-K do TiGra. Em oposição às tenacidades-J, os critérios KJd e Kid não satisfizeram em absoluto os mais exigentes critérios de contenção de plasticidade estabelecidos pela MFEL, se comparados aos propostos pela MFEP. Por fim, o desempenho mecânico do laminado TiGra foi severamente comprometido quando do cômputo da densidade específica para a determinação das tenacidades J e K por unidade de massa, sendo nesta ocasião o laminado híbrido facilmente superado por vários laminados convencionais da classe dos Carbono-Epóxi. / Several dynamic translaminar fracture toughness criteria have been determined for TiGr hybrid fiber-metal laminate through Linear Elastic (K-factor) and Elastic-Plastic (J-integral) Fracture Mechanics (LEFM and EPFM, respectively) concepts and methodologies. Instrumented Charpy impact testing was carried out over a wide range of temperatures under two loading rates. It has been discovered that the elastic-plastic initiation toughness, Jid, and the toughness at maximum load, Jmd, of TiGr are controlled by either delamination favoring or suppression. Impact tests revealed that the in-service use of TiGr must rely on its resistance to dynamic fracture propagation (as characterized by Jmd) rather than on fracture initiation (by Jid). In a broad sense, the requirements for Jid data validity as a material property (JId) were fulfilled, whereas many restrictive demands in regard to the minimum testpiece size were violated by the Jmd criterion. Generally, higher impact velocities were beneficial to TiGrs J-toughnesses, inasmuch as higher temperatures impaired these properties. Regarding the LEFM approach, KJd toughness of TiGr laminate was imparted by faster impacts at higher temperatures, whilst the strain rate negatively influenced the Kid toughness over the whole temperature range tested. Higher temperatures also degraded the K-toughness properties of TiGr hybrid laminate. Differently from J-toughnesses values, the KJd e Kid criteria did not satisfy at all the more stringent criteria set forth by the LEFM approach with regard to plastic constraint, as compared to those established by EPFM. Finally, the mechanical performance of TiGr laminate was overwhelmingly compromised as the materials specific gravity was taken in account to obtain K and J toughness values by unit weight, so that TiGr was by far exceeded in this regard by conventional Carbon/Epoxy composite laminates.