É proposto e testado um modelo elementar para o processo de encruamento de aços de dupla fase (ferrita-esferoidita), em aços de baixo, médio e alto carbono, o qual parece fornecer bons resultados quanto à influência, sobre as propriedades mecânicas, da fração volumétrica, tamanho e distribuição das fases não ferríticas. / An elementary model for the work-hardening process in duplex-structures steels (ferrite-spheroidite) is proposed and tested on low, medium and high carbon content, which seems to give good results concerning the influence of the volume fraction and particle size of the second phase on the work-hardening behaviour.

É proposto e testado um modelo elementar para o processo de encruamento de aços de dupla fase (ferrita-esferoidita), em aços de baixo, médio e alto carbono, o qual parece fornecer bons resultados quanto à influência, sobre as propriedades mecânicas, da fração volumétrica, tamanho e distribuição das fases não ferríticas. / An elementary model for the work-hardening process in duplex-structures steels (ferrite-spheroidite) is proposed and tested on low, medium and high carbon content, which seems to give good results concerning the influence of the volume fraction and particle size of the second phase on the work-hardening behaviour.

É proposto e testado um modelo elementar para o processo de encruamento de aços de dupla fase (ferrita-esferoidita), em aços de baixo, médio e alto carbono, o qual parece fornecer bons resultados quanto à influência, sobre as propriedades mecânicas, da fração volumétrica, tamanho e distribuição das fases não ferríticas. / An elementary model for the work-hardening process in duplex-structures steels (ferrite-spheroidite) is proposed and tested on low, medium and high carbon content, which seems to give good results concerning the influence of the volume fraction and particle size of the second phase on the work-hardening behaviour.

Made available in DSpace on 2014-06-11T19:32:50Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-06-23Bitstream added on 2014-06-13T19:43:37Z : No. of bitstreams: 1 elisei_cca_dr_guara.pdf: 9236786 bytes, checksum: 11aa6a238a1bba073997e41684b859f2 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / As necessidades do mercado por materiais mais resistentes e econômicos resultaram na pesquisa e desenvolvimento de novos aços. Neste contexto surgiram os aços de alta resistência e baixa liga que podem ter microconstituintes diferenciados dependendo do processamento térmico ou termomecânico aplicado. Por meio desses processamentos, a formação de estruturas multifásicas, bainíticas ou bifásicas tem sido conseguida. Este trabalho tem como objetivo caracterizar o efeito de diferentes tratamentos térmicos sobre as propriedades mecânicas obtidas do ensaio de tração e impacto e microestruturais de um aço microligado com baixo teor de carbono e silício. Para isto, foi realizado um tratamento de austenitização a partir de 950ºC, seguido de tratamento isotérmico a 500ºC para a obtenção do constituinte bainítico. Para a obtenção da estrutura multifásica foram realizados dois tratamentos de recozimento intercrítico (760ºC e 800ºC) seguidos de tratamento isotérmico a 500ºC por dois tempos de permanência (3 e 10 minutos), foram também realizados dois tratamentos de têmpera intercrítica (760ºC e 800ºC) para obtenção da estrutura bifásica foram realizados. Para a caracterização microestrutural foram utilizadas a microscopia óptica, eletrônica de varredura e de força atômica. Foram necessárias a utilização de diferentes reagentes químicos (Nital a 2%, metabissulfito de sódio, LePera e a técnica de Heat tinting), para a identificação das fases por microscopia óptica. O nital foi utilizado para realçar os contornos de grão tanto para a realização da microscopia eletrônica de varredura, microscopia de força atômica, assim como para a realização das medidas de tamanho e grão ferrítico. Pelos resultados obtidos pode-se verificar a obtenção das estruturas desejadas de cada tratamento, principalmente de austenita retida partindo-se de... / The needs of the industries by more strength and economic materials have been generated research and development of new steels. In this context came the high-strength and low alloy steels that may have different constituents depending on the heat processing or thermomechanical applied. Through these processes the formation of multiphase, bainitics or dual-phases structures have been achieved. This study aimed to characterize the effect of different treatments on the mechanical properties obtained from the testing of tensile and impact of a steel and microstructural microalloy low carbon and silicon. For this was done a treatment of austempering to 950°C followed by isothermal treatment to 500ºC to obtain the bainitic constituent. To obtain the structure of multiphase two intercritical treatments (760°C and 800°C) followed by isothermal treatment to 500ºC for two times (3 and 10 minutes) were made. And two quenching treatments (760°C and 800°C) to obtain the dual phase structure were made. For the microstructural characterization were used optical microscopy, electronic scanning and atomic force. As required the use of different chemical etchants (nitric acid to 2%, sodium metabisulphite, LePera and the heat tinting technique) to identify the phases through optical microscopy, and the nitric acid was used to highlight the grain for both attainment of scanning electron microscopy, atomic force microscope, as well as to carry out the measures of grain size and ferritic. Through the results can be the achievement of desired structures of each treatment mainly the verification of obtaining retained austenite on steel with low silicon and aluminum and that small variations in microconstituents can affect the mechanical properties of the material . You can also observe and identify the phases obtained in the heat treatments with the aid of microscopy techniques already mentioned.

Orientador: Marcelo dos Santos Pereira / Banca: Herman Jacobus Cornelis Voorwald / Banca: Antonio Jorge Abdalla / Banca: Carlos de Moura Neto / Banca: Carlos Antonio Reis Pereira Baptista / Resumo: As necessidades do mercado por materiais mais resistentes e econômicos resultaram na pesquisa e desenvolvimento de novos aços. Neste contexto surgiram os aços de alta resistência e baixa liga que podem ter microconstituintes diferenciados dependendo do processamento térmico ou termomecânico aplicado. Por meio desses processamentos, a formação de estruturas multifásicas, bainíticas ou bifásicas tem sido conseguida. Este trabalho tem como objetivo caracterizar o efeito de diferentes tratamentos térmicos sobre as propriedades mecânicas obtidas do ensaio de tração e impacto e microestruturais de um aço microligado com baixo teor de carbono e silício. Para isto, foi realizado um tratamento de austenitização a partir de 950ºC, seguido de tratamento isotérmico a 500ºC para a obtenção do constituinte bainítico. Para a obtenção da estrutura multifásica foram realizados dois tratamentos de recozimento intercrítico (760ºC e 800ºC) seguidos de tratamento isotérmico a 500ºC por dois tempos de permanência (3 e 10 minutos), foram também realizados dois tratamentos de têmpera intercrítica (760ºC e 800ºC) para obtenção da estrutura bifásica foram realizados. Para a caracterização microestrutural foram utilizadas a microscopia óptica, eletrônica de varredura e de força atômica. Foram necessárias a utilização de diferentes reagentes químicos (Nital a 2%, metabissulfito de sódio, LePera e a técnica de Heat tinting), para a identificação das fases por microscopia óptica. O nital foi utilizado para realçar os contornos de grão tanto para a realização da microscopia eletrônica de varredura, microscopia de força atômica, assim como para a realização das medidas de tamanho e grão ferrítico. Pelos resultados obtidos pode-se verificar a obtenção das estruturas desejadas de cada tratamento, principalmente de austenita retida partindo-se de... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The needs of the industries by more strength and economic materials have been generated research and development of new steels. In this context came the high-strength and low alloy steels that may have different constituents depending on the heat processing or thermomechanical applied. Through these processes the formation of multiphase, bainitics or dual-phases structures have been achieved. This study aimed to characterize the effect of different treatments on the mechanical properties obtained from the testing of tensile and impact of a steel and microstructural microalloy low carbon and silicon. For this was done a treatment of austempering to 950°C followed by isothermal treatment to 500ºC to obtain the bainitic constituent. To obtain the structure of multiphase two intercritical treatments (760°C and 800°C) followed by isothermal treatment to 500ºC for two times (3 and 10 minutes) were made. And two quenching treatments (760°C and 800°C) to obtain the dual phase structure were made. For the microstructural characterization were used optical microscopy, electronic scanning and atomic force. As required the use of different chemical etchants (nitric acid to 2%, sodium metabisulphite, LePera and the heat tinting technique) to identify the phases through optical microscopy, and the nitric acid was used to highlight the grain for both attainment of scanning electron microscopy, atomic force microscope, as well as to carry out the measures of grain size and ferritic. Through the results can be the achievement of desired structures of each treatment mainly the verification of obtaining retained austenite on steel with low silicon and aluminum and that small variations in microconstituents can affect the mechanical properties of the material . You can also observe and identify the phases obtained in the heat treatments with the aid of microscopy techniques already mentioned. / Doutor

Chapas de aço bifásico (\"dual phase\") se caracterizam por apresentar microestrutura composta de matriz de ferrita poligonal com 15 a 20% de martensita dispersa, o que lhes confere alta resistência mecânica aliada a boa conformabilidade. Este tipo de material pode ser obtido diretamente após a laminação a quente através da aplicação de tratamento termomecânico. O objetivo deste trabalho foi estudar o efeito da temperatura de acabamento e velocidade de resfriamento sobre o desenvolvimento da microestrutura e propriedades mecânicas de um aço bifásico ao Mn-Si-Cr-Mo próprio para laminação a quente. A técnica experimental consistiu de ensaio de laminação a quente em cinco passes, em que foi variada a temperatura de acabamento, ou de fim de laminação. A seguir os corpos de prova foram resfriados em meios com diferentes severidades de têmpera. Procedeu-se então à análise das amostras através de metalografia quantitativa e ensaio de tração. Os resultados mostraram que quando o resfriamento foi feito de modo direto a velocidade de resfriamento é o parâmetro mais importante na determinação da microestrutura e propriedade4 mecânicas, cabendo à temperatura de acabamento um papel secundário. No caso das amostras submetidas a resfriamento escalonado a variável que influenciou decisivamente as propriedades mecânicas do material foi a temperatura em que a têmpera foi interrompida. / Dual phase steel strips show a microstructure that consists of a soft polygonal ferrite matrix with 15 to 20% of hard martensite dispersed on it, which grants high strength and good cold formability to this product. This kind of steel can be produced direct from the rolling heat through the application of a thermomechanical treatment compatible with the chemical composition of the steel. The aim of this work was to study the effect of the colling finish temperature and coolong rate on the development of the microstructure and mechanical properties of a Mn-Si-Cr-Mo dual-phase steel suitable for hot rolling. The experimental technique comprised a Five-pass hot rolling Schedule on a laboratory rollong Mill using different finish temperatures. Then the samples were copied in media with different quench severities. The samples thus obtained were analysed through quantitative metallography and tension testing. The results obtained showed that in the samples directly quenched the cooling rate is the capital parameter for the determination of the microstructure and mechanical properties, whereas the finish temperature plays a secondary role. When the samples were submitted to interrupted quenching the variable that decisively influenced the mechanical properties was the temperature on which the quench was interrupted.

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.

Dissertação (Mestrado em Engenharia Mecânica) - Centro Universitário da Fei, São Bernardo do Campo, 2014

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.

Este trabalho contém uma investigação teórico experimental do comportamento à flexão de telhas metálicas autoportantes formadas à frio. São apresentados de forma sucinta o processo de fabricação, o estado da arte, bem como as propriedades mecânicas do aço. A parte experimental do trabalho utilizou 4 espécimes ensaiados, onde cada espécime era constituído por 5 telhas autoportantes, sendo realizado um total de 16 ensaios de flexão, onde as variáveis foram o elemento de ligação das telhas denominado capa, seu sistema de fixação e o número de parafusos utilizados na referida ligação. As conclusões contidas nesta investigação estão fundamentadas na comparação entre os valores experimentais dos deslocamentos verticais e da resistência última dos espécimes ensaiados e as recomendações da “Load and Resistance Factor Design Specification for Cold-Formed Steel Structural Members”, complementadas por uma análise linear elástica com base no método de elementos finitos. / An experimental and theoretical investigation of the flexural behaviour of cold-formed steel roofs is presented in this thesis. In a brief way, the manufactoring process, the state-of-the-art and the steel mechanical properties are presented. The experimental work was carried out on 4 test specimen, having each test specimen 5 corrugated steel sheets. A total amount of 16 flexural tests was performed and the variables considered were: the influence of the top roof, the number of connecting using bolts between each neighbour panel sheet and the process of roof fixing. The flexural behaviour was analysed using the vertical displacements and the ultimate flexural strenght. Conclusions are based on the comparision between the experimental work and theorical analysis into the light of the code “Load and Resistance Factor Design Specification for Cold-Formed Steel Structural Members”, and also elastic linear analysis using the finite element method.