Foi avaliada a influência da microestrutura na tenacidade à fratura de dois grupos de aços de Alta Resistência e Baixa Liga (ARBL), soldados, com diferentes composições microestruturais. Os metais de solda designados por A1/A2 exibiram uma microestrutura composta por ferrita acicular circundada por ferrita de contorno de grão, com alguma formação de ferrita Widmanstätten e microfases, denominada de microestrutura do tipo clássica. Os metais de solda designados por B1/B2 exibiram um microestrutura composta por bainita, martensita de baixo teor de carbono e microfases, denominada de microestrutura do tipo de ripas. Estes dois tipos de microestruturas são normalmente encontradas nas soldas de alta resistência empregadas em estruturas e componentes de grande responsabilidade. A avaliação da tenacidade à fratura foi realizada pela utilização dos conceitos da integral-J e CTOD. A técnica empregada para a medida do crescimento da trinca, foi a da variação da flexibilidade elástica em corpos de prova SE[B] e C(T). Os valores da tenacidade à fratura dos dois grupos de soldas, para ambas geometrias de corpos de prova, foram determinados e comparados. As análises microestruturais, do metal de solda e das superfícies de fratura dos corpos de prova ensaiados, foram realizadas por meio de microscopia ótica e eletrônica de varredura, com o objetivo de se correlacionar os valores de tenacidade à fratura com a microestrutura dos metais de solda. Foi verificado que os metais de solda A1/A2 que possuem uma microestrutura clássica, apresentaram tenacidade superior aos metais de solda B1/B2, que possuem uma microestrutura do tipo de ripas. / The influence of the microstructure on the fracture toughness behaviour of two groups of multipass High Strength Low Alloy (HSLA) steel weld metals, presenting different microstructure composition, was evaluated. The weld metals A1/A2 exhibited a microstructure composed by acicular ferrite, allotriomorphic ferrite, Widmanstätten ferrite and microphases, and the weld metals B1/B2 presented a microstructure composed by bainite, low carbon martensite and microphases. The fracture toughness evaluation was carried out using J-integral and CTOD concepts and the elastic compliance technique in both SE[B] and CT testpieces. The fracture toughness values for both groups of welds and testpiece geometry were determined and compared. The weld metals microstructures and fracture surfaces analysis were performed using optical and scanning electronic microscope techniques, to correlate the determined fracture toughness values, with the local microstructure around the fatigue crack tip. It was verified that the weld metals A1/A2 exhibited fracture toughness values superior to the ones obtained from weld metals B1/B2.

Este trabalho visou entender e avaliar a resistência mecânica da junção de chapas de aço obtidas pelo processo de União de Chapas por Conformação a Frio (UCCF). Esse processo é conhecido no meio industrial pelo termo em inglês: clinching ou press joining. O formato de união cilíndrico, também conhecido como Round, foi selecionado para unir os corpos de provas. As uniões metálicas ensaiadas foram fabricadas com aço de baixo teor de carbono sem camada superficial de proteção (170MPa de limite de escoamento). O material escolhido é de comum utilização na indústria automotiva. Duas espessuras diferentes foram avaliadas: 0,8mm e 1,2mm. Um completo procedimento foi criado para determinar os parâmetros ideais do processo UCCF baseado nos critérios de falha existentes na literatura e na experiência do fornecedor do equipamento. A união em estudo foi submetida, experimentalmente, a cargas multiaxiais com o auxílio de um dispositivo baseado no ensaio de Arcan para possibilitar uma condição de carga combinada, onde foi possível identificar graficamente o comportamento estrutural do corpo de prova em estados de carregamento que variam de tração (normal à superfície do ponto) até cisalhamento (perpendicular à superfície do ponto). Os valores de resistência mecânica encontrados foram de 1,13kN (mínimo) a 2,55kN (máximo) para as chapas de aço com espessura de 0,8mm e de 1,89kN (mínimo) e 3,18kN (máximo) para as chapas de 1,2mm. Um estudo comparativo com Solda Ponto por Resistência Elétrica (SPRE) foi realizado. A UCCF alcançou resultados de 47,68% dos valores obtidos para a SPRE para chapa com espessura de 0,8mm e 37,78% para chapas de 1,2mm. / The purposes of this work were understand and evaluate cold forming sheet metal joining of steel plates mechanical resistance. This process is well known as clinching or press joining. Round clinching element was selected to be used on all tested specimens due to its industry suitability. The metallic specimens were built on mid carbon steel without zinc coat protection (Yield Stress: 170MPa). This is a common material on automotive industry. Two different thicknesses were evaluated: 0.8mm and 1.2mm. A full procedure to determine ideal clinching parameters was created based on available literature information and clinching supplier know-how. All union technology was experimentally submitted to multiaxial loads using device based on Arcan concept. Joining mechanical behavior curves were plotted from traction (normal to element joint surface) to shear (perpendicular to element joint surface) loads. As a result, 0.8mm thickness steel plates achieved load values from 1.13kN (minimum) to 2.55kN (maximum), 1.2mm thickness steel plates achieved values from 1.89kN (minimum) e 3.18kN (maximum). A comparative study was made with Electric Resistance Spot Weld (ERSP). Clinching joining achieved results as 47.68% and 37.78% of ERSP loads for 0.8mm and 1.2mm thickness steel plates respectively.

L’allégement des véhicules est un objectif incontournable dans l’industrie automobile. Parmi les voies exploitées par les constructeurs, le déploiement d’alliages d’aluminium pour le pavillon permet un allégement de plusieurs kilogrammes. C’est pourquoi, le procédé de soudo-brasage laser occupe une place de choix pour l’assemblage hétérogène pavillon aluminium/caisse acier. Cependant, en plus des problèmes liés à l’hétérogénéité du joint soudé (formation de composés intermétalliques par exemple), des difficultés inhérentes à la production en grande série émergent : un environnement avec de fortes contraintes industrielles, un niveau de conformité élevé et robuste ainsi qu’une cadence de production imposant des grandes vitesses de soudo-brasage comprises entre 4 et 6 m/min et adaptée à des configurations exploitables industriellement. L’objectif de ce travail de thèse est de conduire une analyse physique et technologique du process de soudo-brasage laser pour un assemblage hétérogène allégé pavillon/caisse. Dans un premier temps, un ensemble d’hypothèses sur l’influence de la physique du procédé, des variables process et de l’environnement d’étude sur la conformité et la reproductibilité de ces assemblages furent établies. Leur validation ensuite a été réalisée par des essais à l’échelle 1 sur une installation laser de production industrielle, prolongée par des analyses de la métallurgie et de la microstructure des assemblages ainsi que d’une simulation numérique du procédé. La physique du procédé en lien avec les paramètres du process de soudo-brasage laser acier/aluminium à haute vitesse a été identifiée. Les variables énergétiques ont montrées un fort impact sur le niveau de conformité atteint ainsi que sur la dispersion des résultats. Celles-ci tendent à influencer fortement les phénomènes physiques mises en jeu et notamment la thermique à l’interface acier/aluminium, impactant directement la formation des composés intermétalliques et leurs microstructures. Différentes tailles de grains ont été observés en fonction des paramètres process, contrôlant ainsi la tenue mécanique des assemblages soudo-brasés. La modulation in fine du cycle thermique de soudo-brasage, piloté par la physique activée du process, permet de discriminer les configurations les plus optimales pour une application industrielle du procédé. / Weight reduction of vehicles is a key objective in the automotive industry. Particularly, the use of aluminum alloys for the roof is one of the most promising path studied by manufacturers to save several kilograms. Therefore, the laser brazing process has a place of choice for assembling heterogeneous aluminum roof / steel body-side. However, in addition to issues related to the heterogeneity of the welded joint (formation of intermetallic compounds, for example), issues related to the mass production emerge: an environment with strong industrial constraints, high and robust levels of compliance, a production rate involving high brazing speeds between 4 and 6 m / min and fitting with industrial configurations. The objective of this thesis is to conduct a physical and technological analysis of laser brazing process in the case of a heterogeneous lightweight roof / body-side assembly. Firstly, a set of assumptions about the influence of the physical process, the process variables and the industrial environment on the compliance and the reproducibility of these assemblies are made. Then, validation was conducted by tests at scale 1 on a laser industrial production set-up, extended by analysis of metallurgy and microstructure of assemblies and a numerical simulation of the process. The link between the physical phenomena of the process and the high speed steel-aluminium brazing process parameters has been identified. Energy variables showed a strong impact on the level of compliance achieved and on the dispersion of results. These variables tend to strongly influence the physical phenomena of the process and especially thermal behaviors at the steel / aluminum interface, directly impacting the formation of intermetallic compounds and their microstructures. Different grain sizes were observed depending on the process parameters, influencing hence the mechanical strength of assemblies. Finally, the modulation of the brazing thermal cycle, driven by the activated physical phenomenon of the process, allows bringing out the most optimal configuration for an industrial application of the process.

Neste trabalho foram estudadas as microestruturas, dureza, e resistência ao impacto em aço alta resistência e baixa liga (ARBL) na ZAC. O processo de soldagem foi por arco submerso, utilizando corrente de 600A, tensão de 25V, velocidade de soldagem de 25,5; 24; 20,94; e 19,5 cm/min. Utilizou-se chapa de aço USI-SAC-50. Os quatro aportes de calor produzidos 3,53; 3,75; 4,24; 4,61 kJ/mm, permitiram variações microestruturais na região de granulação grosseira da ZAC, promovendo variações nas medidas de durezas e nos resultados do ensaio de impacto medido à -25ºC e -10ºC. Quando realizado o tratamento térmico de alívio de tensões a 580ºC por 1 hora, as morfologias das microestruturas e medidas de dureza na região grosseira da ZAC, praticamente foram iguais, independente do aporte de calor. Os resultados do ensaio de impacto realizado à -25ºC, com e sem tratamento térmico, não sofreram alterações significativas para os valores das energias absorvidas na ZAC. Já a -10ºC a mudança foi mais significativa. O aspecto da morfologia da fratura na região de granulação grosseira da ZAC, após o ensaio de impacto, foi coerente para os quatro aportes de calor utilizados na soldagem. / It was studied in this report the microstructure, hardness and impact resistance in High Strength Low Alloyed (HSLA) steel in HAZ. The submerged are weld metals were made, using corrent of 600A, are voltage of 25V and travel speed of 25,5; 20,9; 24; and 19,5 cm/min. The USI-SAC-50 steel was used in present report. Four different heat input 3,53; 3,75; 4,24 and 4,61 kJ/mm were used to weld, produced significant changes in the coarse heat affected zone (HAZ) microstructure morphology, and this effect promoted changes on the hardness and the impact results at -25°C and -10°C. Using stress reliev treatment at 580°C for one hour, has changed the microstructure morphology in the coarse heat affected zone and the hardness measurements becames quite similar, therefore independent of the heat input. At -25°C the impact results has shown no variations with the stress reliev heat treatment. However, there were significant changes in the impact results at -10°C. After the impact test, the aspect of morphology facture in the coarse heat affected zone (HAZ), was coherent for the four different heat input, were used to weld.

The diploma thesis is dealing with the repair procedure of the cracked ram of the press – machine parts made from gray cast iron by casting. The ram is a part of the repaired forming press LET 160. The presented work contains an overview and analysis of the technologies of repair of cast iron by welding. On the basis of the theoretical part is designed the procedure of repairing. The aim of the experimental tests is selecting the most suitable additional materiál and verifying the proposed welding process. The welding method was selected by a low preheating manual metal arc. All the pWPS were prepared for the welding of all test specimens. Experimental samples were subjected to visual, macroscopic, microscopic analysis and hardness measurement. Based on the results of the experiments was suggested a welding repair procedure with a pWPS.

The topic of this diploma thesis is the design of a MIG/MAG welding machine, suitable for locksmiths and workshops. The diploma thesis includes the analysis of existing products from the design and technical point of view and deals with the design of welding machine. The proposed concept focuses on interactive and modern look of the machine and comfortable manipulation and easy operation. The design itself offers a possible direction of morphology of welding machines in the future.

The structural stability of creep-resistant steels P22, P91 and Eurofer´97 and structural stability of weld joint P22/P91 have been studied. The microstructural changes during annealing at temperatures of 500 – 900°C were examined. The state of equilibrium have been simulated using the ThermoCalc software. The computed results were compared with published data. A good agreement between the simulation and the published data was observed.

The diploma thesis deals with the problematics of weld defects of cranes localisation and check. The aim is to analyse non-destructive methods, monitor the occurence of defects and their form and also to suggest the procedure of correction. The work is divided into a theoretical and practical part. In the theoretical part, there is an analysis of individual methods of non-destructive testing that are used for weld check on a particular girder. There is also an analysis of welding technologies used when making a crane girder. The practical part deals with evaluation of weld defects using two methods of non-destructive testing. Furthermore, statistics of defects is realised. In conclusion, the statistics outcome is resumed and evaluated.

Stress relieving in the welded joints occurs when loaded of the platform lift. Critical welds of profile from steel S235JRH and of stiffener from steel S355J0 are examined in terms of flexibility, strength and safety using strength analysis method. Under different welding conditions and parameters are performed the testing welds by method MAG. Macroscopic and microscopic inspection are conducted as well as tension test. Weld created in active gas 82 %Ar + 18 %CO2, by dip transfer with low values of welding current 96 A and voltage 20,2 V became as the top evaluated sample. This weld is recommended to use in practice.

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