Atualmente, no setor de máquinas agrícolas o uso de aços de alta resistência está começando a ganhar espaço e cada vez mais lembrado nos projetos estruturais; para atender as necessidades citadas acima e também para redução de emissão de poluentes. A utilização dos aços de alta resistência na indústria de implementos agrícolas está focada nos aços DP (Dual Phase), sendo este o objeto de estudo desta presente pesquisa. Este trabalho visa analisar o comportamento mecânico, priorizando a análise de resistência à fadiga em flexão de uniões soldadas através do processo de soldagem de metal de gás ativo (GMAW) utilizando dois tipos de arames como material de adição. Neste estudo foram utilizadas chapas metálicas de aços de alta resistência da marca DOCOL 1000 fabricado pela SSAB e os arames de adição fornecidos pela ESAB, sendo um usado largamente na indústria de maquinas agrícolas e o outro um fio especial desenvolvido para soldagem de aços de alta resistência e baixa liga. O processo de solda robotizada foi adotado para assegurar a homogeneidade dos cordões das juntas durante a obtenção das amostras. Para a análise das características mecânicas das amostras foi realizado o ensaio de flexão estático, caracterização macroestrutural, perfil de microdureza e ensaios de fadiga de flexão em quatro pontos. Os resultados mostraram que a vida em fadiga, por flexão em quatro pontos, nas juntas soldadas com o material de adição para aço carbono comum obteve uma melhor resposta em relação ao material de adição especial para soldagem de aços de alta resistência, porém pode-se verificar que ambas as curvas de fadiga respeitaram a curva de projeto conforme norma. / Nowadays, in the agricultural industry the use of high strength steels is being used each day more and more as well and increasingly coming in our mind in structural designs, to meet the requirements mentioned above and also to reduce the emission of pollutants. The highstrength steels application in the agricultural machinery industry is focused on the DP steels (Dual Phase), which is the subject of this present study. The focus of this work is analyze the mechanical behavior, prioritizing the deflection fatigue strength analysis on welded joints by Gas Metal Arc Welding (GMAW) process using two welding wire types. In this study it was used high strength steels sheet metal called DOCOL 1000, manufactured by SSAB and solder wires supplied by ESAB, and one widely used in the agricultural machinery industry for carbon steel welding and other a special wire developed for high strength. The robotic welding process was used to ensure the homogeneity of the weld bead on the samples manufacture process. For the mechanical characteristics analysis was done the static bending test, macrography, microhardness profile and deflection fatigue tests by four points. The results showed that the fatigue life, four-point bending, at welded joint used welding wire to carbon steel achieved a better result regarding a special welding wire to high strength steel, however, both fatigue curve respected project curve as British Standard.

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Atlas Copco Secoroc AB are searching after new bulk materials for drill heads that are used in percussive drilling in order to improve their strength and durability. The aim of this project is to assist Atlas Copco in this search and provide them with further information regarding material properties, alloying elements, suppliers, etc. A literary study was carried out in order to identify materials that had UTS and KIC more than or equal to 1700 MPa and 70 MPa*m1/2, respectively. Materials that fulfilled these criteria were T250 grade maraging steel, Cobalt free maraging steel, High cobalt maraging steel, 300 grade maraging steel, AerMet 100, AF1410, S53, M54, 300M, 4340M and PremoMet. These were categorized into maraging steels, high alloy secondary hardened steels, and low alloy steels, and were then further researched.  The material with the highest combination of UTS and KIC was M54 followed by AerMet 100; while AF1410 had the highest KIC but a low UTS, and PremoMet had the highest UTS but a low KIC. Maraging steels and HASH steels have a similar price range, while low alloy steels are much cheaper.

Atlas Copco Secoroc AB are searching after new bulk materials for drill heads that are used in percussive drilling in order to improve their strength and durability. The aim of this project is to assist Atlas Copco in this search and provide them with further information regarding material properties, alloying elements, suppliers, etc. A literary study was carried out in order to identify materials that had UTS and KIC more than or equal to 1700 MPa and 70 MPa*m^1/2, respectively. Materials that fulfilled these criteria were T250 grade maraging steel, Cobalt free maraging steel, High cobalt maraging steel, 300 grade maraging steel, AerMet 100, AF1410, S53, M54, 300M, 4340M and PremoMet. These were categorized into maraging steels, high alloy secondary hardened steels, and low alloy steels, and were then further researched. The material with the highest combination of UTS and KIC was M54 followed by AerMet 100; while AF1410 had the highest KIC but a low UTS, and PremoMet had the highest UTS but a low KIC. Maraging steels and HASH steels have a similar price range, while low alloy steels are much cheaper.

O presente trabalho de pesquisa avalia os efeitos das temperaturas de austenitização plena e intercrítica, associado ao tratamento térmico de têmpera interrompida e partição, realizada em banho de sais fundidos e sua influência no comportamento mecânico e microestrutural do aço de alta resistência e baixa liga AISI300M. Para os ensaios de caracterização mecânica foram realizados ensaios de dureza cujos resultados variaram de (35HRC a 55HRC) dependendo do tratamento; ensaios de tração, que atingiram o limite de resistência máximo de 2272 MPa com 6% de alongamento; ensaios de tenacidade ao impacto Charpy que superaram os tratamentos convencionais de têmpera atingindo 38J de energia absorvida; além dos ensaios de tenacidade à fratura linear-elástica, método (KIC) que ficaram entre (35 e 67 MPa√m). Para a caracterização microestrutural foram realizadas análises por microscopia óptica, microscopia eletrônica de varredura (MEV), além da investigação microestrutural pela técnica de microscopia eletrônica de transmissão (MET) que elucidaram os microconstituintes multifásicos presentes como martensita, ferrita e bainita. Para quantificar as frações de fases presentes utilizou-se a técnica de difração por raios-X e método de refinamento Rietveld, mostrando até 20% de austenita retida na condição de partição em 400ºC. Para auxiliar e mapear as fases presentes foram utilizadas as técnicas de MEV-EBSD e EBSD acoplada ao microscópio eletrônico de transmissão MET-EBSD com indexação via software ASTAR. Após os ensaios mecânicos, as superfícies de fratura foram examinadas via MEV e exibiram em geral um modo misto de fratura om a presença de dimples, coalescimento de microcavidades e quase-clivagem. / The present research work evaluates the effects of the complete and intercritical austenitization temperatures associated with interrupted quenching and partitioning performed in molten salt baths and its influence in the mechanical behavior and microstructural of AISI 300M high strength low alloy steel. Hardness tests with range from 55HRC to 35HRC were obtained depending on the heat treatment. Tensile tests have shown maximum strength limit of 2272 MPa and 6% elongation. Toughness parameters by instrumented Charpy impact tests exceeded values obtained in the conventional heat treatments providing 38J of absorbed energy. In addition, results from linear-elastic fracture toughness tests (KIC), values among 67 and 35MPa√m were found. Microstructure characterization was performed by optical microscopy, scanning electron microscopy (SEM) and microstructural research by transmission electron microscopy (TEM), which optimized the multiphase microconstituents with the presence of martensite, ferrite and bainite. In order to quantify the phases volume fractions present, it was used a X-ray diffraction technique and \"Rietveld\" refinement method that obtained up to 20% of retained austenite in the partitioning condition at 400°C. To assist and map the present phases, it was used MEV-EBSD and EBSD techniques coupled to the transmission electron microscope MET-EBSD with indexing via ASTAR software. After the mechanical tests, fracture surfaces were analyzed by SEM and showed in general, a mixed mode of fracture with the presence of dimples, microcoalescence and quasi-cleavage.

A importância das indústrias de cana-de-açúcar no cenário nacional cresce exponencialmente, desde sua origem. Porém nas últimas três décadas este tipo de indústria deixou de ser tipicamente familiar e passou a produzir em grande escala açúcar, etanol, produtos químicos derivados, levedura e planta de CO2 (para indústria de bebida e ou alimentos), além da venda do excedente da energia que é gerada na própria indústria. Um dos principais equipamentos em uma usina de açúcar e álcool é a caldeira, nome popular dado ao vaso de pressão que gera vapor a partir do aquecimento da água em um ambiente de alta pressão. Este calor é usado como fonte para produção de energia. Os aços ligados ao Cr e Mo têm sido cada vez mais aplicada neste tipo de equipamento. O presente trabalho tem por objetivo entender a influência dos parâmetros de tratamento térmico pós-soldagem nas propriedades mecânicas e na microestrutura de um tubo sem costura de aço ASTM A 335 Gr P91, através da determinação dos valores de: resistência à tração, limite de escoamento, percentual de alongamento, dureza, tenacidade à fratura e CTOD do material base, metal de solda e zona termicamente afetada (ZTA) da região soldada de tubos unidos por solda. Para a realização desta pesquisa serão aplicados os conceitos da teoria da mecânica da fratura elasto-plástica (Crack Tip Open Displacement, CTOD) e os conceitos de comportamento mecânico dos materiais, para o estudo da influência dos parâmetros de tratamento térmico pós-soldagem. / The importance of sugar cane industries on the national scene grows exponentially since its origin. But in the last three decades these became from cottage industries to large-scale production of Ethanol, Chemicals derivatives, yeast and plant CO2 (for food or drink industry). One of the main equipment in a sugar and alcohol plant is the boiler, popular name given to the pressure vessel that generates steam from the heating of water in a high pressure environment. This is used as heat source for energy production. One of the alloy that has been increasingly applied in projects of this equipment are martensitic steels (Cr Mo alloys). The present study aims to understand the influence of post weld heat treatment parameter´s on mechanical properties and microstructure of a seamless tube, steel ASTM 335 Gr P91, the determination of values of tensile strength, yield strength, percentage of elongation, hardness, fracture toughness and CTOD of the base material, weld metal and heat affected zone (HAZ) of the welded region of tubes welded together. In this research the concepts of the theory of mechanics of elastic-plastic fracture (Crack Tip Open Displacement, CTOD) and the concepts of mechanical behavior of materials will be applied.

A aplicação de aços de alta resistência está fortemente difundida na indústria mecânica, principalmente em aplicações onde a redução de peso é importante, como por exemplo, a indústria de implementos rodoviários e maquinários agrícolas. Esta dissertação visa analisar a influência de diferentes aportes térmicos no comportamento microestrutural e mecânico de juntas soldadas através do processo MAG de modo a obter juntas com propriedades otimizadas. Para este estudo foram utilizadas chapas metálicas com espessura de 3 mm do aço de alta resistência e baixa liga USI LNE700. Os parâmetros nominais de energia de soldagem foram variados de acordo com os valores descritos pelo fornecedor SSAB. O processo de soldagem foi realizado com o auxílio de um sistema robotizado para manter a homogeneidade ao longo da junta, distância e posicionamento correto no comprimento total da junta soldada. Os ensaios para verificação do comportamento microestrutural e mecânico foram realizados com auxílio de microscopia ótica, perfis de microdureza e ensaios de tração. Buscaram-se utilizar aportes térmicos reduzidos para minimizar os efeitos de revenimento da martensita presente no metal de base, um dos principais responsáveis pela redução das propriedades mecânicas da junta soldada. Os resultados não mostraram significativa variações na microestrutura e propriedades de tração do material, porém o preenchimento da junta soldada formada apresenta um comportamento diretamente proporcional à energia de soldagem. / The application of high strength steels is strongly diffused in the engineering industry, especially in applications where weight reduction is important, such as the industry of agricultural machines and trailers industry. This investigation aims to analyze the influence of different heat inputs on microstructural and mechanical behavior of joint welded by GMAW in order to obtain joints with optimized properties. Sheet metal with a thickness of 3 mm high strength low alloy steel LNE700 (supplier Usiminas) were used. The welding energy was varied around the nominal value informed by the steel supplier SSAB for this study. The welding process was made using robotic system to maintain homogeneity along the joint, right distance and position during the total weld joint length. The microstructural and mechanical behaviors were performed with the optical microscope, microhardness profile and traction test. We attempted to use lower heat inputs to minimize the effects of tempering of martensite present in the base metal, a major contributor to the reduction of the mechanical properties of the welded joint. The results did not show significant microestructural and tensile properties variation, however, when the welding energy is increased, the welded joint penetration formed was increased as well.

Este trabalho estuda as fases presentes na solda de Inconel 625 utilizadas para unir tubos de uma serpentina de forno de uma refinaria de petrÃleo, fabricada com material de aÃo liga tipo 9Cr-1Mo e revestida internamente com alumÃnio. Para a realizaÃÃo do estudo, foi fabricado um corpo dee prova em conformidade com os procedimentos de fabricaÃÃo da serpentina tubular do forno. Amostras da junta soldada foram cortadas e submetidas a ensaios de microdureza, estudos da variaÃÃo da composiÃÃo quÃmica pelo EDS, avaliaÃÃo de fases por difraÃÃo de raios-X e pela tÃcnica por difraÃÃo de elÃtrons retroespalhados (EBSD), assim como detalhes da microestrutura foram observados por microscopia Ãtica e microscopia eletrÃnica de varredura. Os resultados mostram a provÃvel presenÃa de carbonetos de Ti, Nb e fase Laves na solda de Inconel 625. A quantidade de fase Laves à maior no revestimento de Inconel do que no passe raiz. Foram observados tambÃm descontinuidades e defeitos. Um destes defeitos estava localizado na interface entre o Inconel 625 e o primeiro passe com eletrodo AWS E-505, em regiÃo provavelmente rica em precipitados de fase Laves. Os resultados indicam a necessidade de uma melhor avaliaÃÃo do processo de soldagem, incluindo um estudo do comportamento do Inconel 625 na temperatura de operaÃÃo do forno entre 500 e 700ÂC. / This work studies the phases present in Inconel 625 weld used to join tubes of a coil of furnace oil refinery, made ​​of alloy steel material type 9Cr-1mo and lined with aluminum. For the study was made ​​a test dee body in accordance with the manufacturing procedures of the tubular coil of the furnace. Samples of the weld were cut and subjected to microhardness tests, studies of variation of chemical composition by SDS evaluation phase diffraction X-ray diffraction technique, and backscattered electrons (EBSD) as well as details of the microstructure was observed by optical microscopy and scanning electron microscopy. The results show the probable presence of carbides of Ti, Nb and Laves phase in Inconel 625 weld. The amount of Laves phase in the coating is greater than Inconel the root pass. It was also observed discontinuities and defects. One of these defects was located at the interface between the Inconel 625 and the first electrode pass AWS E-505 in rich region probably Laves phase precipitate. The results indicate the need for better assessment of the welding process, including a study of the behavior of Inconel 625 in the temperature of the furnace between 500  and 700  C.

The objective of this thesis is to further understand the austenite Abnormal Grain Growth (AGG) phenomenon in relation with precipitation state in a low alloy steel. The abnormal grain growth is addressed from both experimental and numerical modeling point of view. Prior austenite grain size distribution, precipitation volume fraction and size distribution evolution of the different heat treated states are experimentally determined for two different industrial alloys (steel-A and steel-B) in different heat treated states and experimental results are compared with model predictions. A two-step modeling technique is adopted in this study: precipitation modeling and abnormal/normal grain growth modeling. The abnormal/normal grain growth modeling is done using a simplified analytical model where the grain growth is assumed to be driven by the decrease in interfacial energy. Both the conventional Zener pinning and corner pinning by precipitate is considered as boundary movement retarding forces. The precipitation model is based on the Classical Nucleation and Growth Theories. The assumption of homogeneous precipitate nucleation and growth gave a good prediction of volume fraction, mean radius and size distribution in comparison with the experimental results. Two coupled modeling approaches of abnormal grain growth and precipitation model: ①Soft coupling and ②Dynamic coupling; shed light on the different physical parameters controlling the grain growth condition in a particular material's state. A reasonable prediction of AGG and NGG is obtained from both approaches. The dynamic coupled modeling enabled us to paint a comprehensive time-temperature mechanism map of grain growth conditions. It is found that AGG in the austenitic state depends strongly on the initial grain size distribution and precipitation state. The modeling and the experimental results showed that the precipitation state evolution (increasing or decreasing volume fraction) also impact normal/abnormal grain growth. Plausible explanations in relation with the mean austenite grain size and the precipitation state are derived for the AGG phenomenon from the present work.

High strain rate plastic deformation of metals results in the formation of localized zones of severe shear strain known as adiabatic shear bands (ASBs), which are a precursor to shear failure. The formation of ASBs in a high-strength low alloy steel, namely AISI 4340, was examined based on prior heat treatments (using different austenization and tempering temperatures), testing temperatures, and impact strain rates in order to map out grain size and grain deformation behaviour during the formation of ASBs. In the current experimental investigation, ASB formation was shown to be a microstructural phenomenon which depends on microstructural properties such as grain size, shape, orientation, and distribution of phases and hard particles—all controlled by the heat treatment process. Each grain is unique and its material properties are heterogeneous (based on its size, shape, and the complexity of the microstructure within the grain). Using measurements of grain size at various heat treatments as well as dynamic stress-strain data, a finite element model was developed using Matlab and explicit dynamic software LSDYNA to simulate the microstructural deformation of grains during the formation of ASBs. The model simulates the geometrical grain microstructure of steel in 2D using the Voronoi Tessellation algorithm and takes into account grain size, shape, orientation, and microstructural material property inhomogeneity between the grains and grain boundaries. The model takes advantage of the Smooth Particle Hydrodynamics (SPH) meshless method to simulate highly localized deformation as well as the Johnson-Cook Plasticity material model for defining the behavior of the steel at various heat treatments under high strain rate deformation.The Grain Model provides a superior representation of the kinematics of ASB formation on the microstructural level, based on grain size, shape and orientation. It is able to simulate the microstructural mechanism of ASB formation and grain refinement in AISI 4340 steel, more accurately and realistically than traditional macroscopic models, for a wide range of heat treatment and testing conditions.