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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Soldagem TIG de tubos de aço inox AISI 316 para varetas combustíveis

Bittencourt, Marcelo de Siqueira Queiroz, Instituto de Engenharia Nuclear 03 1900 (has links)
Submitted by Marcele Costal de Castro (costalcastro@gmail.com) on 2017-09-06T14:12:21Z No. of bitstreams: 1 MARCELO BITTENCOURT- M.pdf: 4387805 bytes, checksum: 0c4443c405d67bd09a18a80758de61f8 (MD5) / Made available in DSpace on 2017-09-06T14:12:21Z (GMT). No. of bitstreams: 1 MARCELO BITTENCOURT- M.pdf: 4387805 bytes, checksum: 0c4443c405d67bd09a18a80758de61f8 (MD5) Previous issue date: 1985-03 / Foi realizado um estudo da selagem de tubos de aço inoxidável austenítico AISI 316, 20% de formado a frio, a pinos de material similar pelo processo de soldagem TIG autógeno, visando a sua utilização como vareta de combustível para reatores nucleares. Inicialmente foram executadas soldas preliminares, empregando-se dois projetos de pino tampão, que permitiram a seleção de uma solda considerada ideal. A seguir procedeu-se à confecção de corpos de prova soldados, com os parâmetros escolhidos, a fim de se averiguar o comportamento mecânico do componente. Foi também realizado um tratamento térmico na temperatura de serviço em corpos de prova soldados visando examinar o efeito causado no componente em serviço através de observações microestruturais e do comportamento mecânico. Este componente foi comparado ao como soldado. Concluiu-se que a recristalização causada pela soldagem diminuiu as propriedades mecânicas do componente. O tratamento térmico aumentou as propriedades mecânicas do componente. O tratamento térmico aumentou as propriedades mecânicas, mas diminuiu o tempo de vida do componente quanto à ruptura.
2

Estudo de suscetibilidade a trinca a frio em juntas soldadas de aço SAR-80 BT

Godoy, Antonio Fernando 15 December 1989 (has links)
Orientador : Roseana da Exaltação Trevisan / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Campinas / Made available in DSpace on 2018-07-14T02:07:40Z (GMT). No. of bitstreams: 1 Godoy_AntonioFernando_M.pdf: 2053561 bytes, checksum: c3ee13a0f69c039d3ccf91f272af374d (MD5) Previous issue date: 1989 / Resumo: Este trabalho tem como objetivo estudar a suscetibilidade a trinca a frio em juntas soldadas de aço alta resistência baixa liga, através do teste de auto restrição Tekken. Para realização deste trabalho, foram utilizadas chapas do aço SAR - 80 BT de 12,7 mm e 25,4 mm de espessura. O consumível utilizado, foi o eletrodo revestido de alta resistência E 120 18 M com 3,25 mm de diametro. O processo de soldagem utilizado, foi o processo arco elétrico com eletrodo revestido ( SAER ), polaridade Inversa. O insumo de calor e teor de hidrogênio, também foram parâmetros fixados. O único parâmetro variável foi a temperatura de pré-aquecimento. Foram analisados o número, tamanho e a propagação das trincas, além da microestrutura. Ainda foram realizadas medidas de dureza na seção transversal de cada cordão teste. O número, tamanho e localização das trincas, foram correlacionados ao tipo de microestrutura e a dureza em cada região. A principal conclusão neste trabalho, é que a temperatura de pré-aquecimento até 50°C para os corpos-de-prova de 12,7 mm de espessura, e até 100°C para os corpos-de-prova de 25,4 mm de espessura, é o fator predominante na formação da trinca a frio. Acima desta temperatura, outros fatores como a microestrutura, teor de hidrogênio, passam a influenciar de uma forma mais significativa / Abstract: The main objective of the present work is to study the cold crack incidence in high strength low alloy welded steel using the TEKKEN TEST. The experimental was carrled out in SAR-80 BT plates with 12,7 rnrn ,and 25,4 mm thickness. The E 120 18 M electrode wlth 3,25 mm diameter was used in all cases studied. The Shield Metal Arc weldlng Process with inverse polarity was used to make the weld beads. During the experiments the heat-input and the hydrogen content were fixed and the pre-heat temperature was varied. The number, size and direction of propagation of the cold cracks were correlated wlth the hardness and microstructure of each weld bead test. The main conclusion is that the pre-heating temperature, up to 50°C for plates with 12,7 mm thickness and up to 100°C for plates with 25,4 mm thickness, is the dominant factor in the cold crack formation. Above those values, other factors, as the steel microestructure and the hydrogen content, come to influence more significantly the formation of the cold crack / Mestrado / Mestre em Engenharia Mecânica
3

Monitoração e localização de defeitos na soldagem TIG utilizando técnicas de espectrometria

Bebiano, Daniel Flávio Vidal 25 July 2008 (has links)
Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Mecânica, 2008. / Submitted by Diogo Trindade Fóis (diogo_fois@hotmail.com) on 2009-09-09T18:04:08Z No. of bitstreams: 1 2008_DanielFlavioVidalBebiano.pdf: 14527938 bytes, checksum: 04f5787ddb6a9d22b7dd8cfb992a3549 (MD5) / Approved for entry into archive by Luanna Maia(luanna@bce.unb.br) on 2009-10-02T12:27:28Z (GMT) No. of bitstreams: 1 2008_DanielFlavioVidalBebiano.pdf: 14527938 bytes, checksum: 04f5787ddb6a9d22b7dd8cfb992a3549 (MD5) / Made available in DSpace on 2009-10-02T12:27:28Z (GMT). No. of bitstreams: 1 2008_DanielFlavioVidalBebiano.pdf: 14527938 bytes, checksum: 04f5787ddb6a9d22b7dd8cfb992a3549 (MD5) Previous issue date: 2008-07-25 / Há um esforço das indústrias em aumentar a qualidade dos produtos, aprimorar os métodos produtivos e reduzir o custo do processo. Dentre esses processos encontra-se a soldagem. Há vários estudos sobre controle da soldagem e utilização de sensores para monitorar a solda. Nesse sentido, este trabalho apresenta um sistema de monitoração on-line não intrusivo capaz de detectar defeitos na soldagem TIG. Desse modo, a etapa de inspeção terá seu tempo reduzido assim como os custos envolvidos. O sensor avaliado é o espectrômetro. Esse dispositivo capta perturbações no arco elétrico por meio da espectroscopia de emissão. A monitoração é feita por meio do cálculo da temperatura dos elétrons - pelo método da razão das intensidades relativas - ou pela intensidade de algumas linhas espectrais escolhidas. Alguns experimentos foram realizados para a simulação de defeitos. Foram utilizados algoritmos baseados em métodos estatísticos (estocásticos) para tratamento dos dados a fim de indicar a presença de defeitos e a sua localização. Por fim, é feita uma correlação entre a solda defeituosa, o sinal obtido e a indicação da posição dos defeitos. Demonstra-se que o sistema aplicado (sensor e algoritmos) é capaz de detectar os defeitos após a realização da solda e discute-se a possibilidade da detecção em tempo real. _______________________________________________________________ ABSTRACT / There is an effort made by industries to improve product quality and production methods, and to decrease the production costs. Welding is one of these processes. There are several studies about controlling or monitoring the welding process. This work presents a on-line non-intrusive monitoring system capable of detecting TIG weld defects. In this way, inspection step will take less time and lower costs. The sensor applied was a spectrometer. It captures perturbations on the electrical arc. Monitoriment is made by the calculation of electronic temperature of relative intensity lines or the normalized absolute intensity of chosen lines. Experiments were made to simulate weld defects. Statistical (stochastic) algorithms were tested to indicate those defects presence and their localization. The work demonstrates that the applied system composed by sensor and algorithms is capable of detecting defects after the welding process and it is discussed the possibility of real-time detection.
4

Previsão da dureza maxima na zona afetada pelo color em soldagem

Niño Bohórquez, Carlos Enrique January 1989 (has links)
Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnologico / Made available in DSpace on 2016-01-08T16:17:31Z (GMT). No. of bitstreams: 1 80571.pdf: 2695901 bytes, checksum: 895b38fb3cdfd8304523527442b05556 (MD5) Previous issue date: 1989 / Foi estudada a aplicabilidade de fórmulas de previsão da pureza máxima da ZAC em função da composição química do metal base e do tempo de resfriamento entre 800 e 500ºC. Com esse fim foram utilizados valores de dureza medidos para aços estruturais nacionais do tipo baixo C, baixa liga e outros valores coletados da literatura. Foi constatado que, embora as fórmulas tenham sucesso na previsão da dureza da martensita, que parece depender exclusivamente do teor de carbono, e na previsão da dureza da microestrutura isenta de martensita, devido a falhas na avaliação da temperabilidade, surgem desvios da ordem de 30HV, considerados altos quando comparados com os níveis de dureza de 200 a 400HV, comuns na ZAC.
5

Estudo sobre a abertura e estabilidade do arco MIG na soldagem de alumínio /

Santos, Túlio Fernandes dos January 2000 (has links)
Dissertação (Mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. / Made available in DSpace on 2012-10-17T11:17:35Z (GMT). No. of bitstreams: 0Bitstream added on 2014-09-25T17:51:45Z : No. of bitstreams: 1 170001.pdf: 14935810 bytes, checksum: b226370a2dc870b5342d5f8a72da3324 (MD5) / Na soldagem MIG do alumínio, com corrente imposta e pulsada, tem-se o risco de não ocorrer a abertura do arco, devido à boa condutibilidade térmica e elétrica do alumínio e à aleatoriedade do contato do arame-eletrodo com o metal de base. Os resultados deste trabalho indicam que a geometria da ponta do arame é o principal fator de influência na abertura, mas, mesmo na condição mais crítica deste fator, que é a ponta arredondada, a abertura pode ser assegurada com o uso de uma elevada corrente de abertura. Experimentos com diferentes níveis de corrente de pulso, para arame ER4043 de 1,2 mm de diâmetro, indicam um melhor acabamento superficial do cordão depositado, e da região próxima a este, quando empregada corrente de pulso entre 160 e 200 A, sendo que, mesmo com deslocamento da tocha no sentido puxando, considerado desfavorável, os resultados são satisfatórios. O equilíbrio entre velocidade de alimentação e velocidade de fusão do arame determina a estabilidade do comprimento do arco, que, não sendo mantida, pode ocasionar fusão do arame-eletrodo com o bico de contato e enrolamento do arame no mecanismo de alimentação, ou o mergulho do arame-eletrodo na poça de fusão, provocando curto-circuito. A estabilidade do comprimento do arco pode ser conseguida através de controle sinérgico da altura do arco, operando pela modulação da freqüência de pulsos.
6

Weldability aspects of high yield strength Q & T steels

Machado, Ivan Guerra January 1984 (has links)
A specially designed, highly restrained speciamen test (60º groove angle) was successfully used to study root run weld metal solidification cracking origins and tendencies. Thirty six submerged arc welds were made on two High Yield Strangth Quenched and Tempered base steels (HY100 and Q2N0, with two low alloy wires (LINDE 95 and OERLIKON S3 NiMo 1), two basic fluxes (OP41TT and OP121TT), and six welding parameters combination at three energy inputs, viz: 1.9, 2.8 and 4.1 KJ/mm. The weld metal solidification cracking phenomenon showed up to be extremely complex and basically dependent on chemical composition, solidification (primary) structures, microsegregation, flux type, dendrites size and orientation, and base metals stress state. The most resistant welds to this defect were those made using Q2N base steel, OP121TT flux and OERLIKON S3 NiMo 1 wire. A combination of the following properties are thought to have induced this result: high carbide-to-ferrite elements forming in the base metal; flux promoting weld centerline equiaxed structure and less microsegregation; wire chemical composition, with high Mn/Si ratio, inducing also less microsegragation at the weld centerline; lower carbon and nickel combined contetens in presence of also lower phosphorus and sulphur contents. The Q2N greater ability to relieve the strain around the weld pool at high temperature is another possibility, albeit not practically demonstrated. The welding paramenters main influence on solidification cracking tendency was found to be through change in centreline solidification macrostructure and dendrite size, but the stress fields within and around the weld pool are also thought to play a significant role. The dendrite size holds a strong relationship with weld bead geometric factors, such as weld bead height-to-width ration and, principally, external area-to-perimeter ratio. The dendrite size measured on the weld bead longitudinal section must be corrected, for it depends on the angle between the dendrite growth direction and the weld bead symmetry line in a transverse section. Thus, the actual dendrite size rate of change with welding parameters is not that observed through metallographic analysis. Four types of centreline solidification macrosturctures were identified and associated with solidification cracking tendency, viz: stray, competitive columnar, centreline and equiaxed. The former three macrostructures were found to be dependent on welding paramenters, whilst the latter was promoted by the OP121TT flux. Experiments have shown that this flux releases more than twice the amount of gas(es) released by the OP41TT flux. The time available for reactions between the weld pool liquid metal and the surrounding atmosphere was evaluated through an (approximate) weld pool retention time, given as the weld ripple lag-to-welding speed amount of fused slag and deoxidants recovery. The root run welds have shown a secondary microstructure principally composed of ferrite with aligned M-A-C, acicular ferrite and martensite. No differences were detected between weld metals deposited by both wires of fluxes, being noticed the change in microstructure size only. A good correlation was found between transformation temperature and cooling time. Evidence was found of ‘cold’ or high temperature ( not solidification) cracking propagation from existing solidification cracking, and carbides segregation along the solidification cracking path. Change in the groove angle to 0º and 120º modified the general weld bead geometry and reduced the solidification cracking tendency. Cold wire addition reduced the centreline solidification cracking tendency, with no action on transverse cracks. A device was designed to make exploratory welds with wire oscillation keeping the welding head still. Low oscillation frequencies ( below 10 Hz) in the welging direction have shown to be very effective to overcome both, transverse and centreline solidification cracks. Stress relieving the base metals considerably reduced the solidification cracking tendency. The all-weld metal mechanical properties were assessed through the use of a specimen desing which allowed the obtention of practically nil diluted wels, made with 1.9 and 4.1 KJ/mm energy inputs and the two wires and fluxes combinations. The results have shown that even at the highest energy input it is possible to obtain weld metals with relatively high yield strength and toughness, using any one of the available flux/wire combinations. The results have shown that even at the highest energy input it is possible to obtain weld metals with relatively high yield strength and toughness, using any one of the available fluz/wire combinations. The results yielded not less than 600 N/mm² Yield Strength and average Charpy V-notch energy absorbed of 80 J at -40º, with transition temperature to quasicleavage fracture mode occurring below -40ºC and at or above – 80ºC. The basic techniques utilized included metallographic analysis using light microscope, transmission Electron Microscope and Scanning Electron Microscope; weld metals ‘in situ’ thermal analysis; all-weld metal mechanical tests; hardeness.
7

Weldability aspects of high yield strength Q & T steels

Machado, Ivan Guerra January 1984 (has links)
A specially designed, highly restrained speciamen test (60º groove angle) was successfully used to study root run weld metal solidification cracking origins and tendencies. Thirty six submerged arc welds were made on two High Yield Strangth Quenched and Tempered base steels (HY100 and Q2N0, with two low alloy wires (LINDE 95 and OERLIKON S3 NiMo 1), two basic fluxes (OP41TT and OP121TT), and six welding parameters combination at three energy inputs, viz: 1.9, 2.8 and 4.1 KJ/mm. The weld metal solidification cracking phenomenon showed up to be extremely complex and basically dependent on chemical composition, solidification (primary) structures, microsegregation, flux type, dendrites size and orientation, and base metals stress state. The most resistant welds to this defect were those made using Q2N base steel, OP121TT flux and OERLIKON S3 NiMo 1 wire. A combination of the following properties are thought to have induced this result: high carbide-to-ferrite elements forming in the base metal; flux promoting weld centerline equiaxed structure and less microsegregation; wire chemical composition, with high Mn/Si ratio, inducing also less microsegragation at the weld centerline; lower carbon and nickel combined contetens in presence of also lower phosphorus and sulphur contents. The Q2N greater ability to relieve the strain around the weld pool at high temperature is another possibility, albeit not practically demonstrated. The welding paramenters main influence on solidification cracking tendency was found to be through change in centreline solidification macrostructure and dendrite size, but the stress fields within and around the weld pool are also thought to play a significant role. The dendrite size holds a strong relationship with weld bead geometric factors, such as weld bead height-to-width ration and, principally, external area-to-perimeter ratio. The dendrite size measured on the weld bead longitudinal section must be corrected, for it depends on the angle between the dendrite growth direction and the weld bead symmetry line in a transverse section. Thus, the actual dendrite size rate of change with welding parameters is not that observed through metallographic analysis. Four types of centreline solidification macrosturctures were identified and associated with solidification cracking tendency, viz: stray, competitive columnar, centreline and equiaxed. The former three macrostructures were found to be dependent on welding paramenters, whilst the latter was promoted by the OP121TT flux. Experiments have shown that this flux releases more than twice the amount of gas(es) released by the OP41TT flux. The time available for reactions between the weld pool liquid metal and the surrounding atmosphere was evaluated through an (approximate) weld pool retention time, given as the weld ripple lag-to-welding speed amount of fused slag and deoxidants recovery. The root run welds have shown a secondary microstructure principally composed of ferrite with aligned M-A-C, acicular ferrite and martensite. No differences were detected between weld metals deposited by both wires of fluxes, being noticed the change in microstructure size only. A good correlation was found between transformation temperature and cooling time. Evidence was found of ‘cold’ or high temperature ( not solidification) cracking propagation from existing solidification cracking, and carbides segregation along the solidification cracking path. Change in the groove angle to 0º and 120º modified the general weld bead geometry and reduced the solidification cracking tendency. Cold wire addition reduced the centreline solidification cracking tendency, with no action on transverse cracks. A device was designed to make exploratory welds with wire oscillation keeping the welding head still. Low oscillation frequencies ( below 10 Hz) in the welging direction have shown to be very effective to overcome both, transverse and centreline solidification cracks. Stress relieving the base metals considerably reduced the solidification cracking tendency. The all-weld metal mechanical properties were assessed through the use of a specimen desing which allowed the obtention of practically nil diluted wels, made with 1.9 and 4.1 KJ/mm energy inputs and the two wires and fluxes combinations. The results have shown that even at the highest energy input it is possible to obtain weld metals with relatively high yield strength and toughness, using any one of the available flux/wire combinations. The results have shown that even at the highest energy input it is possible to obtain weld metals with relatively high yield strength and toughness, using any one of the available fluz/wire combinations. The results yielded not less than 600 N/mm² Yield Strength and average Charpy V-notch energy absorbed of 80 J at -40º, with transition temperature to quasicleavage fracture mode occurring below -40ºC and at or above – 80ºC. The basic techniques utilized included metallographic analysis using light microscope, transmission Electron Microscope and Scanning Electron Microscope; weld metals ‘in situ’ thermal analysis; all-weld metal mechanical tests; hardeness.
8

Soldagem subaquatica com mig/mag

Almeida, Daniel Soares de January 1992 (has links)
Na produção de soldas subaquáticas são empregadas várias técnicas que podem ser classificadas em dois grandes grupos: Técnicas de soldagem em câmaras secas e Técnicas molhadas. Ambos os grupos apresentam inconvenientes: os primeiros são capazes de produzir soldas de alta qualidade, no entanto, estas soldas são de custo muito elevado. As técnicas de soldagem molhada são de custos mais reduzidos e mais versáteis. Porém, a qualidade é muito baixa e seu emprego, normalmente, se restringe à reparos. Uma solução para estes problemas é o processo MIG/MAG com cavidade local seca. Com este processo pode-se produzir soldas de qualidade superior com baixos custos. O objetivo deste trabalho foi projetar e construir um dispositivo (bocal) que permitisse a criação de uma região seca em torno do arco e poça de fusão. Com este dispositivo passou-se à investigar os parâmetros de soldagem que permitissem a obtenÇão de cordões de solda na água. Análises do aspecto, geometria e dureza destes cordões foram realizadas e comparadas com outros feitos na superficie. Juntas de topo na posição plana com chanfro em "V" simples de 60° foram realizadas à uma profundidade de 300mm em chapas de aço BS4360 e arame AWS ER70S-6. / To make underwater welds, many kinds of techniques have been proposed and used, which may be classified in two large groups: Dry Chamber Techniques and Wet Techniques. Both groups show inconveniences: Dry Chamber Techniques are able to produce high quality welds, but they are costly. Wet Welding Techniques are less expensive and more versatile; however, the welds are rather poor and their uses are generally limited to repairs. So, perhaps wet underwater GMAW with local cavity is a solution for this problem. With this process, it is possible to produce welds with high quality and low cost. Therefore, the main aim o f this work was to develop a nozzle, that allows the formation of a stable and durable dry cavity around the are and molten weld pool. Also, it was investigated the welding parameters, in a way to have sound underwater bead-on-plate and flat position groove ·welds. Analysis of geometry, hardness and mechanical properties of those welds were made, and compared with another made on land. Flat position welds.were made at a depth of 300mm on BS 4360 steel plates, single-V, 60° angle, with filler wire AWS ER70S-6.
9

Estudo da soldagem MIG/MAG pela técnica hiperbárica a seco

Baixo, Carlos Eduardo Iconomos January 1999 (has links)
Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico. / Made available in DSpace on 2012-10-18T15:24:20Z (GMT). No. of bitstreams: 0Bitstream added on 2016-01-09T01:42:13Z : No. of bitstreams: 1 174095.pdf: 15373992 bytes, checksum: cff4951cb35244716b9813490eb38baa (MD5) / Neste trabalho são apresentados os resultados de pesquisas conduzidas para a utilização do processo MIG em ambiente hiperbárico, até 6 bar, composto por argônio. Os ensaios foram direcionados para a soldagem nos modos de transferência curto-circuito e projeção axial em função destes serem aplicáveis à todas as posições de soldagem. Apesar da modulação em tensão constante ser a mais utilizada para a transferência por curto-circuito, esta não permite um controle apurado sobre corrente de soldagem durante os períodos de arco e de curto-circuito. Para contornar esta deficiência, foram desenvolvidas metodologias destinadas ao controle da forma de onda da corrente aplicadas à este modo de transferência. Além da analise do desempenho das características estáticas em imposição de corrente e tombante, neste trabalho foram desenvolvidas relações paramétricas para um controle sinérgico aplicado a transferência por curto-circuito. Os resultados permitiram identificar que na transferência por curto-circuito uma metodologia de controle baseada em três níveis de corrente permitiu produzir depósitos com geometria favorável, apesar dos efeitos adversos da pressão ambiente. Na soldagem com transferência por projeção axial, verificou-se a necessidade das variáveis de soldagem serem ajustadas para produzir uma transferência com arco curto. Apesar dos frequentes curto-circuitos, esta condição se torna necessária para a obtenção de depósitos com maior largura de cordão.
10

Weldability aspects of high yield strength Q & T steels

Machado, Ivan Guerra January 1984 (has links)
A specially designed, highly restrained speciamen test (60º groove angle) was successfully used to study root run weld metal solidification cracking origins and tendencies. Thirty six submerged arc welds were made on two High Yield Strangth Quenched and Tempered base steels (HY100 and Q2N0, with two low alloy wires (LINDE 95 and OERLIKON S3 NiMo 1), two basic fluxes (OP41TT and OP121TT), and six welding parameters combination at three energy inputs, viz: 1.9, 2.8 and 4.1 KJ/mm. The weld metal solidification cracking phenomenon showed up to be extremely complex and basically dependent on chemical composition, solidification (primary) structures, microsegregation, flux type, dendrites size and orientation, and base metals stress state. The most resistant welds to this defect were those made using Q2N base steel, OP121TT flux and OERLIKON S3 NiMo 1 wire. A combination of the following properties are thought to have induced this result: high carbide-to-ferrite elements forming in the base metal; flux promoting weld centerline equiaxed structure and less microsegregation; wire chemical composition, with high Mn/Si ratio, inducing also less microsegragation at the weld centerline; lower carbon and nickel combined contetens in presence of also lower phosphorus and sulphur contents. The Q2N greater ability to relieve the strain around the weld pool at high temperature is another possibility, albeit not practically demonstrated. The welding paramenters main influence on solidification cracking tendency was found to be through change in centreline solidification macrostructure and dendrite size, but the stress fields within and around the weld pool are also thought to play a significant role. The dendrite size holds a strong relationship with weld bead geometric factors, such as weld bead height-to-width ration and, principally, external area-to-perimeter ratio. The dendrite size measured on the weld bead longitudinal section must be corrected, for it depends on the angle between the dendrite growth direction and the weld bead symmetry line in a transverse section. Thus, the actual dendrite size rate of change with welding parameters is not that observed through metallographic analysis. Four types of centreline solidification macrosturctures were identified and associated with solidification cracking tendency, viz: stray, competitive columnar, centreline and equiaxed. The former three macrostructures were found to be dependent on welding paramenters, whilst the latter was promoted by the OP121TT flux. Experiments have shown that this flux releases more than twice the amount of gas(es) released by the OP41TT flux. The time available for reactions between the weld pool liquid metal and the surrounding atmosphere was evaluated through an (approximate) weld pool retention time, given as the weld ripple lag-to-welding speed amount of fused slag and deoxidants recovery. The root run welds have shown a secondary microstructure principally composed of ferrite with aligned M-A-C, acicular ferrite and martensite. No differences were detected between weld metals deposited by both wires of fluxes, being noticed the change in microstructure size only. A good correlation was found between transformation temperature and cooling time. Evidence was found of ‘cold’ or high temperature ( not solidification) cracking propagation from existing solidification cracking, and carbides segregation along the solidification cracking path. Change in the groove angle to 0º and 120º modified the general weld bead geometry and reduced the solidification cracking tendency. Cold wire addition reduced the centreline solidification cracking tendency, with no action on transverse cracks. A device was designed to make exploratory welds with wire oscillation keeping the welding head still. Low oscillation frequencies ( below 10 Hz) in the welging direction have shown to be very effective to overcome both, transverse and centreline solidification cracks. Stress relieving the base metals considerably reduced the solidification cracking tendency. The all-weld metal mechanical properties were assessed through the use of a specimen desing which allowed the obtention of practically nil diluted wels, made with 1.9 and 4.1 KJ/mm energy inputs and the two wires and fluxes combinations. The results have shown that even at the highest energy input it is possible to obtain weld metals with relatively high yield strength and toughness, using any one of the available flux/wire combinations. The results have shown that even at the highest energy input it is possible to obtain weld metals with relatively high yield strength and toughness, using any one of the available fluz/wire combinations. The results yielded not less than 600 N/mm² Yield Strength and average Charpy V-notch energy absorbed of 80 J at -40º, with transition temperature to quasicleavage fracture mode occurring below -40ºC and at or above – 80ºC. The basic techniques utilized included metallographic analysis using light microscope, transmission Electron Microscope and Scanning Electron Microscope; weld metals ‘in situ’ thermal analysis; all-weld metal mechanical tests; hardeness.

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