O presente estudo objetivou caracterizar as juntas soldadas de uma chapa de aço inoxidável duplex UNS S32205 soldada utilizando diferentes energias (0,5 kJ/mm, 1,0 kJ/mm e 3,5 kJ/mm) e avaliar a susceptibilidade dessas juntas à corrosão sob tensão (CST) em ambiente contendo cloreto. O ensaio por gotejamento \"drop evaporation test\" (DET) de água do mar sintética foi utilizado para avaliar a susceptibilidade à CST das juntas soldadas e investigar os efeitos da temperatura (70 ºC, 90 ºC e 110 ºC) e da tensão de tração (70%, 90% e 100 % do limite de escoamento do metal base) na resistência à CST. Os resultados da caracterização mecânica, suscetibilidade à corrosão intergranular e caracterização microestrutural das juntas soldadas não evidenciaram a presença de fases deletérias, como as fases ? e ?. A proporção da fase ferrita na zona fundida e na zona afetada pelo calor (ZAC) foi inversamente proporcional à energia de soldagem. Por exemplo, a ferrita na ZAC variou de 68% para 0,5 kJ/mm a 54% para 3,5 kJ/mm. Os resultados dos ensaios de CST mostraram houve trincamento e fratura para todos os corpos de prova ensaiados a 110 ºC (mesmo com 70% do limite de escoamento), enquanto que nenhuma trinca foi observada nos corpos de prova ensaiados a 70 ºC e 90 ºC. Os ensaios de CST realizados a 90 ºC apresentaram corrosão localizada e preferencial da fase de ferrita longe do cordão de solda, enquanto os ensaios realizados a 70 ºC não apresentaram sinais significativos de corrosão. Todos os corpos de prova ensaiados a 110 ºC apresentaram fratura abaixo do deposito de sal com aspecto de vulcão formado pela evaporação da solução gotejada. As trincas propagaram pela interface ?/? ou clivagem transgranular nas fases ferrita e austenita. Para menores tensões ensaiadas, a proporção de clivagem transgranular da fase de ferrita foi mais significativa que a fase de austenita. O ensaio de DET não foi eficiente para investigar o efeito das alterações microestruturais na ZAC na susceptibilidade à CST. A análise de distribuição de temperatura na superfície dos corpos de prova indicou que o gotejamento da água do mar sintética teve um efeito de resfriamento e a temperatura na região de gotejamento foi pelo menos 10 ºC mais baixa quando comparada a outras regiões do corpo de prova. Além disso, o pH na região gotejante foi mais básico (pH = 11) do que a solução de água do mar sintética (pH = 8,2). / The present investigation characterized the welded joints of a UNS S32205 duplex stainless steel plate using different welding energies (0.5 kJ/mm, 1.0 kJ/mm and 3.5 kJ/mm) in order to evaluate the susceptibility of these joints to stress corrosion cracking (SCC) in Cl- environments. Drop evaporation test (DET) of synthetic seawater was used to assess the SCC behavior of the welded joints and to investigate the effects of the temperature (70 ºC, 90 ºC and 110 ºC) and the tensile strength (70%, 90% and 100% of the base metal\'s yield strength) on their SCC resistance. The results of the mechanical, intergranular corrosion susceptibility and microstructural characterization of the welded joints did not show the presence of deleterious phases, such as ? and ? phases. Additionally, the proportion of ferrite phase in the molten zone and in the heat-affected zone was inversely proportional to the welding energy. For instance, the ferrite in the HAZ varied from 68% for 0.5 kJ/mm to 54% for 3.5 kJ/mm. The results of SCC testing showed the cracking and fracture for all specimens tested at 110 ºC (even at 70% of the yield strength), while no cracking was observed at 70 ºC and 90 ºC. DET performed at 90 ºC showed that there was a localized and preferential corrosion of the ferrite phase far away from the weld bead, while DET performed at 70 ºC did not show any significant sign of corrosion. All samples tested at 110 ºC presented a noteworthy salt deposition in the shape of a volcano and their cracks were formed underneath the salt layer by the pit corrosion of the ferrite phase. The cracks propagated by either ? / ? interfacial or transgranular cleavage at ferrite and austenite phases. For lower stresses, the proportion of transgranular cleavage of the ferrite phase was more significant than the austenite phase. DET was not an efficient test to investigate the effect of the microstructural changes in the HAZ on the SCC susceptibly of the welded joints as the crack took place below the salt deposit and away from the weld bead. The temperature distribution analysis on the surface of the DET samples indicated that the seawater drip has a significant cooling effect and the temperature of this region was at least 10 ºC lower when compared to other regions of the samples. Additionally, the pH on the drip region was more basic (pH = 11) than the synthetic seawater solution (pH = 8.2). Keywords: Duplex stainless steels; stress corrosion cracking; synthetic seawater; welding.

Aços inoxidáveis dúplex apresentam uma estrutura composta por ferrita e austenita. O fato de a austenita ser estável à temperatura ambiente possibilita que esses aços sejam usados no estudo da reação de formação da austenita a partir da ferrita, podendo os resultados ser aplicados a aços de baixa liga, em que a austenita se transforma em martensita no resfriamento brusco, e a outros sistemas com transformações entre fases cúbicas de corpo centrado (CCC) e cúbicas de face centrada (CFC). Foram realizados estudos em um aço inoxidável dúplex do tipo DIN W.Nr. 1.4462 (UNS 31803). As amostras foram solubilizadas no campo ferrítico a 1325°C e resfriadas em água. As amostras foram ainda tratadas isotermicamente em temperaturas entre 700°C e 1100°C por tempos entre 5.000 e 30.000 segundos. Deste modo, a formação de austenita a partir da ferrita foi estudada em seu estágio inicial e em estágios avançados da reação, com relação aos seus aspectos morfológicos e cristalográficos. As morfologias encontradas apresentaram variações dependentes dos segmentos de contorno de grão em que as partículas se formam. As partículas nucleadas nos contornos de grão podem ser adequadamente descritas pela classificação morfológica de Dubé. Além disso, essas partículas apresentaram, em geral, relações de orientação do tipo Kurdjumov-Sachs e Nishyiama-Wassermann com pelo menos um dos dois grãos, podendo ser encontradas relações intermediárias entre essas duas. . Em alguns casos, as partículas mantêm relações de orientação com os dois grãos adjacentes, apresentando pequenos desvios das relações exatas relatadas na literatura. As partículas de austenita intragranulares apresentam desvios em relação à relações exatas maiores do que os encontrados nas partículas de contornos de grão. Em alguns casos, as partículas intragranulares aparentam não apresentar relações de orientação com a matriz ferrítica. / Duplex Stainless Steels have a structure composed by ferrite and austenite. The fact that austenite, in these steels, is stable at low temperatures, allows the use of these steels in studies of austenite formation from ferrite, in such way that the results can be applied to low alloy steels, in which austenite transforms to martensite upon rapid cooling, and to other systems containing transformations between body-centred cubic (BCC) and face-centred cubic (FCC) phases. Studies were performed on a DIN W.Nr. 1.4462 (UNS 31803) duplex stainless steel. The samples were solution treated in the ferrite region at 1325°C and water cooled. Samples were then submitted to isothermal treatments at temperatures between 700°C and 1100°C for up to 30.000 seconds. In this way, austenite formation from ferrite was studied on initial and advanced stages of the reaction, concerning morphological and crystallographic aspects. The morphologies observed varied with the grain boundary segment in which the particles were formed. The grain boundary particles may be adequately described by the Dubé classification. Moreover, these particles presented Kurdjumov-Sachs and Nishyiama-Wassermann orientation relationships with at least one of the adjacent grains, with possibilities of occurrence of intermediate relationships between K-S and N-W relationships. In some cases, the particles show orientation relationships with both adjacent grains, with small deviations form the exact relationships reported in literature. Intragranular austenite particles show higher deviations from the exact relationships than grain boundary particles. In some cases, intragranular particles have no apparent orientation relationships with the ferrite matrix.

The austenitic stainless steel 316L has been compared to duplex stainless steels to be able to highlight a choice of material for manufacturing of spare tanks used for cooling water at nuclear power stations on the Swedish west coast. In this report 316L and the duplex stainless steels 2205, 2304 and LDX 2404 have been compared according to corrosion resistance, strength, manufacturing aspects and prices. The steels arranged by increasing corrosion resistance: 316L < 2304 < LDX 2404 < 2205. The steels arranged by increasing strength (considering the thickness of the plates needed for construction): 316L < 2304 < LDX 2404 and 2205. The steels arranged by increasing price/tank: 2304 < LDX 2404 < 2205 < 316L. One of the duplex stainless steels is recommended rather than the austenitic stainless steel 316L. In terms of price 2304 is preferable to 2205 and LDX 2404. When it comes to corrosion resistance 2205 is superior to 2304 and can sometimes be considered as unnecessary good and therefore not relevant for this application.

La demande croissante en énergie nécessite l'exploration de pétrole et de gaz dans des conditions plus difficiles. Ces systèmes de production exigent l'utilisation d'équipements forgés faits de nuances d'acier de plus haute résistance, comme les aciers inoxydables austéno-ferritiques (duplex). Ces composants tendent à présenter une perte de ductilité et de performance mécanique générale provoquée par l'hydrogène produit par p. ex. des systèmes de protection cathodique et des processus de corrosion. Les composants en aciers inoxydables duplex présentent une longue histoire d’endommagement par l'hydrogène à basse température provenant de diverses sources. Bien qui ce type de endommagement soit assez récurrent, diverses informations connexes restent à élucider, en raison de l'interaction complexe de l'hydrogène avec la microstructure et le caractère localisé de la production et du transport de l'hydrogène dans le matériau.Le présent travail vise à améliorer la compréhension physique de l'interaction entre l'hydrogène et la microstructure ainsi que les effets de différentes procédures de chargement d'hydrogène sur les propriétés mécaniques des composants forgés en acier inoxydable super duplex UNS S32750.Le développement d'une telle compréhension implique l'évaluation des effets de l'hydrogène sur les propriétés mécaniques du matériau au moyen d'essais de traction dans différents environnements riches en hydrogène. Basé sur des résultats d'essais de traction à vitesse de déformation faible, une relation quantitative entre la fragilisation provoquée par l'hydrogène gazeux et cathodique est proposée, et les effets possibles de la fragilisation par l’hydrogène provoquée par dislocations sont discutés.Des descriptions quantitatives et qualitatives du transport de l'hydrogène, incluant l'analyse des effets des différentes microstructures et voies de diffusion, et de sa position dans le réseau et dans la microstructure (ségrégation de l'hydrogène aux pièges) sont proposées. Ces descriptions sont obtenues en considérant les résultats de différentes techniques expérimentales: essais de perméation, spectroscopie de désorption thermique, spectroscopie de masse d'ions secondaires à temps de vol et diffusion de neutrons. / The increasing demand for energy requires the exploration of oil and gas at deeper water locations and on more severe conditions. These production systems have demanded the use of forged equipments made of higher strength steel grades, such as austenitic-ferritic (duplex) stainless steels. These components are more prone to exhibit loss of ductility and general mechanical performance caused by hydrogen generated e.g. by cathodic protection. Duplex stainless stainless steels components present a vast history of hydrogen damage at low temperatures, due to hydrogen derived from various sources. Even being this kind of damage fairly recurring, various related information remains to be elucidated, due to the complex interaction of hydrogen with the microstructure and localized character of hydrogen generation and transportation in the material. The present work aims to improve the physical understanding of the interaction between hydrogen and the microstructure as well as the effects of different hydrogen charging procedures on the mechanical properties of forged components made of the super duplex stainless steel grade UNS S32750.The development of such understanding involves the evaluation of the effects of hydrogen on the mechanical properties of the material through tensile tests in different hydrogen-rich environments. Based on results of slow-strain rate tensile tests, a quantitative relationship between embrittlement caused by gas hydrogen and cathodic charging is proposed, and possible effects of dislocation-assisted hydrogen transportation and embrittlement are discussed. Quantitative and qualitative descriptions of the hydrogen transportation, including analysis of the effects of different microstructures and diffusion paths, and of its position in the lattice and in the microstructure (hydrogen segregation to traps) are proposed. These descriptions are achieved considering results of different testing techniques: permeation tests, thermal desorption spectroscopy, time-of-flight secondary ion mass spectroscopy and neutron scattering.

Aços inoxidáveis dúplex apresentam uma estrutura composta por ferrita e austenita. O fato de a austenita ser estável à temperatura ambiente possibilita que esses aços sejam usados no estudo da reação de formação da austenita a partir da ferrita, podendo os resultados ser aplicados a aços de baixa liga, em que a austenita se transforma em martensita no resfriamento brusco, e a outros sistemas com transformações entre fases cúbicas de corpo centrado (CCC) e cúbicas de face centrada (CFC). Foram realizados estudos em um aço inoxidável dúplex do tipo DIN W.Nr. 1.4462 (UNS 31803). As amostras foram solubilizadas no campo ferrítico a 1325°C e resfriadas em água. As amostras foram ainda tratadas isotermicamente em temperaturas entre 700°C e 1100°C por tempos entre 5.000 e 30.000 segundos. Deste modo, a formação de austenita a partir da ferrita foi estudada em seu estágio inicial e em estágios avançados da reação, com relação aos seus aspectos morfológicos e cristalográficos. As morfologias encontradas apresentaram variações dependentes dos segmentos de contorno de grão em que as partículas se formam. As partículas nucleadas nos contornos de grão podem ser adequadamente descritas pela classificação morfológica de Dubé. Além disso, essas partículas apresentaram, em geral, relações de orientação do tipo Kurdjumov-Sachs e Nishyiama-Wassermann com pelo menos um dos dois grãos, podendo ser encontradas relações intermediárias entre essas duas. . Em alguns casos, as partículas mantêm relações de orientação com os dois grãos adjacentes, apresentando pequenos desvios das relações exatas relatadas na literatura. As partículas de austenita intragranulares apresentam desvios em relação à relações exatas maiores do que os encontrados nas partículas de contornos de grão. Em alguns casos, as partículas intragranulares aparentam não apresentar relações de orientação com a matriz ferrítica. / Duplex Stainless Steels have a structure composed by ferrite and austenite. The fact that austenite, in these steels, is stable at low temperatures, allows the use of these steels in studies of austenite formation from ferrite, in such way that the results can be applied to low alloy steels, in which austenite transforms to martensite upon rapid cooling, and to other systems containing transformations between body-centred cubic (BCC) and face-centred cubic (FCC) phases. Studies were performed on a DIN W.Nr. 1.4462 (UNS 31803) duplex stainless steel. The samples were solution treated in the ferrite region at 1325°C and water cooled. Samples were then submitted to isothermal treatments at temperatures between 700°C and 1100°C for up to 30.000 seconds. In this way, austenite formation from ferrite was studied on initial and advanced stages of the reaction, concerning morphological and crystallographic aspects. The morphologies observed varied with the grain boundary segment in which the particles were formed. The grain boundary particles may be adequately described by the Dubé classification. Moreover, these particles presented Kurdjumov-Sachs and Nishyiama-Wassermann orientation relationships with at least one of the adjacent grains, with possibilities of occurrence of intermediate relationships between K-S and N-W relationships. In some cases, the particles show orientation relationships with both adjacent grains, with small deviations form the exact relationships reported in literature. Intragranular austenite particles show higher deviations from the exact relationships than grain boundary particles. In some cases, intragranular particles have no apparent orientation relationships with the ferrite matrix.

Super duplex stainless steels are applied in highly corrosive environments. To withstand such conditions, they designed with increased content of alloying elements and a duplex microstructure consisting of austenitic and ferritic phases. The result of this combination is the desired improvement in corrosion resistance, but also, the enhancement of mechanical properties. Machining super duplex stainless steels involves strain hardening of the workpiece, intense adhesive wear and elevated temperatures within the cutting zone leading to rapid tool wear and poor machined surface integrity. This research pertains to the application of commercially available PVD coatings to minimize the detrimental effects when turning super duplex stainless steel S32750. The selected coatings for this study were Alcronos (AlCrN), Alnova (AlCrN + AlCrSiN), Formera (CrN + CrAlTiN), Croma Plus (Cr + CrN + OX), Fortiphy (CrN) and Certiphy (TiAlN). The wear behavior and mechanisms in two distinct machining experiments were evaluated, and all tools failed by chipping preceded by intense adhesive wear and BUE formation. The use of AlCrN coatings improved tool life significantly. Data on the cutting force, chip formation, and workpiece surface integrity indicate less workpiece strain hardening effects, improved friction conditions at the tool/chip interface, as well as thinner chips being formed when machining with Alcronos coated carbide inserts. The micro-mechanical properties of the selected coatings were assessed and Alcronos combined high hardness and elastic modulus with a high plasticity index value that allows this coating to better manage the friction in the cutting zone and better dissipate the energy generated during cutting. / Thesis / Master of Applied Science (MASc) / Super duplex stainless steels are designed to be applied in highly corrosive environments. Like any other stainless steels, processing the super duplex grade can be challenging, especially when it comes to machining. The major causes of poor machined surface quality and rapid tool wear are high temperature, the workpiece enhanced mechanical properties, surface hardening and the tendency to stick to the cutting tool causing adhesive wear. This research explores the application of coated cutting tools to improve the machinability of the super duplex stainless steel UNS S32750. Different commercially available coatings were tested and two, Alcronos and Alnova, improved tool life significantly. These two coatings were capable of improving the friction conditions within the cutting zone which, in turn, helps with the formation of the chips and leads to a better machined surface integrity and an approximately 5 to 6 times longer tool life.

[pt] Os aços inoxidáveis Duplex são materiais metálicos que tendem a aliar uma excelente resistência à corrosão em meios agressivos com elevada resistência mecânica devido à sua microestrutura bifásica. Essa microestrutura é composta por uma matriz ferrítica e ilhas de austenita, a temperatura ambiente, com frações volumétricas aproximadamente iguais dessas duas fases. Com isso, estas ligas costumam ser utilizadas em tubulações e equipamentos industriais onde se requer elevada relação resistência/peso, especialmente em empreendimentos de construção e montagem off-shore. Este trabalho apresenta uma metodologia desenvolvida com a utilização de um modelo numérico parametrizado baseado no método de elementos finitos para analisar o efeito dos ciclos térmicos de soldagem nos aços duplex e leanduplex. O modelo desenvolvido faz uso da análise térmica transiente da soldagem, em que as propriedades térmicas dos materiais envolvidos são termo dependentes, e grandes gradientes térmicos são gerados entre a região da solda e as áreas afastadas dela. Procedimentos experimentais para medição dos ciclos térmicos empregados sob determinados regimes de soldagem são utilizados para calibrar o modelo numérico. A metodologia é aplicada ao estudo do comportamento de uma solda na forma de cordão sob chapa contendo um único passe, realizada com o processo GMAW, em chapas planas de 10mm de espessura dos aços duplex UNS32205 e leanduplex UNS32304, através de um modelo de elementos finitos. Os resultados mostram uma boa correspondência entre o modelo numérico e o resultado experimental. / [en] Duplex stainless steels are metallic materials that tend to combine excellent corrosion resistance in aggressive environment with high mechanical strength due to their biphasic microstructure. This microstructure is composed of a ferritic matrix and austenite islands, at room temperature, with approximately equal volume fractions of these two phases. As a result, these alloys are often used in pipes and industrial equipment where high resistance / weight ratio is required, especially in offshore assembly and construction field. This work presents a methodology developed with the use of a parameterized numerical model based on the finite element method to analyze the effect of thermal welding cycles on duplex and leanduplex stainless steels. The developed model uses the transient thermal analysis of welding, in which the thermal properties of the materials involved are thermo-dependent, and large thermal gradients are generated between the region of the weld and the areas away from it. Experimental procedures for measuring the thermal cycles employed under certain welding conditions are used to calibrate the numerical model. The methodology is applied to the study of the behavior of a weld in the form of a strand in sheet form containing a single pass, realized with the GMAW process, in flat plates of 10mm thickness of the duplex steels UNS32205 and leanduplex UNS32304, through a finite element model. The results show a good correspondence between the numerical model and the experimental result.

Advanced alloys often present precipitated carbides and nitrides in their microstructure following exposure to elevated temperatures. These secondary phases are usually undesirable, because potentially deleterious for the corrosion and mechanical performances of the material. Carbides and nitrides are enriched in key alloying elements that are subtracted from their surrounding matrix areas, creating alloying element depleted zones, which might become initial sites for corrosion initiation. In this study, the influence of micro- and nano-sized precipitated carbides and nitrides on the corrosion initiation of biomedical CoCrMo alloys and duplex stainless steels has been investigated at microscopic scale, by using a combination of local probing techniques. The microstructures of the alloys were first characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and magnetic force microscopy (MFM). The Volta potential mapping of carbides and nitrides revealed their higher nobility compared to the matrix, and particularly compared to their surrounding areas, suggesting the occurrence of some alloying element depletion in the latter locations, which may lead to a higher susceptibility for corrosion initiation. In-situ electrochemical AFM studies performed at room temperature showed passive behavior for large potential ranges for both alloy families, despite the presence of the precipitated carbides or nitrides. At high anodic applied potential, at which transpassive dissolution occurs, preferential dissolution started from the areas adjacent to the precipitated carbides and nitrides, in accordance with the Volta potential results. Thus, the presence of carbides and nitrides doesn’t largely affect the corrosion resistance of the tested advanced alloys, which maintain passive behavior when exposed to highly concentrated chloride solutions at room temperature with no applied potential. The effect of nitrides on the corrosion initiation of duplex stainless steels was investigated also at temperatures above the critical pitting temperature (CPT). Depending on the type, distribution and size range of the precipitated nitrides different corrosion behaviors were observed. Intragranular (quenched-in) nano-sized nitrides (ca. 50-100 nm) finely dispersed in the ferrite grains have a minor influence on the corrosion resistance of the material at temperatures above the CPT, while larger intergranular (isothermal) nitrides (ca. 80-250 nm) precipitated along the phase boundaries cause a detrimental reduction of the corrosion resistance of the material, in particular of the austenite phase / <p>QC 20130927</p>

Submitted by OTACILIO DONISETE FRANZINI null (otaciliodf@hotmail.com) on 2016-12-21T11:37:28Z No. of bitstreams: 1 APLICAÇÃO DE LASER PULSADO Nd YAG NA SOLDAGEM DO AÇO SUPER DUPLEX UNS S32750.pdf: 3133785 bytes, checksum: 7f73ce4a1615cca31edb63d392f368f2 (MD5) / Approved for entry into archive by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br) on 2016-12-22T12:59:13Z (GMT) No. of bitstreams: 1 franzini_od_me_ilha.pdf: 3133785 bytes, checksum: 7f73ce4a1615cca31edb63d392f368f2 (MD5) / Made available in DSpace on 2016-12-22T12:59:13Z (GMT). No. of bitstreams: 1 franzini_od_me_ilha.pdf: 3133785 bytes, checksum: 7f73ce4a1615cca31edb63d392f368f2 (MD5) Previous issue date: 2016-12-13 / Os aços inoxidáveis Duplex e Super Duplex, 50% austenita e 50% ferrita, combinam as características mais desejáveis dos aços ferríticos e austeníticos, possuem excelente resistência mecânica e à corrosão para uma ampla variedade de meios, com expressiva resistência à corrosão em água do mar e outros ambientes contendo cloreto, devido a seu elevado nível de cromo, molibdênio, e nitrogênio. Quando soldado a região do metal de solda desses aços perdem suas características de resistência mecânica e à corrosão devido ao desbalanceamento das fases ferrita e austenita. No presente trabalho foi analisado a influência do processo de soldagem autógena a laser Pulsado Nd:YAG nas características mecânicas e microestruturais da junta soldada, variando a taxa de sobreposição dos pulsos de 40 a 90% em chapas de aço inoxidável Super Duplex UNS S32750 com 1,5 mm de espessura. Utilizou-se uma fonte laser pulsada Nd.YAG, United Winner 150A, com potência máxima de 150 W. A energia do pulso de soldagem foi fixada em 10J, potência de pico de 2 kW, largura temporal de 5 ms e frequência variando entre 1,5 e 9,0 Hz. Como gás de proteção utilizou-se argônio puro com vazão de 10 l/min. A caracterização microestrutural foi realizada através de microscopia ótica e microscopia eletrônica de varredura. Os resultados mostraram que o aumento da taxa de sobreposição da junta de 40% até 90% aumenta a resistência mecânica e a dureza do metal de solda. Em relação à microestrutura do metal de solda observou-se uma ferritização da mesma com pequena fração volumétrica de austenita nas regiões de contorno de grão. Não foi observada a presença de fases frágeis no metal de solda. / Duplex Stainless steels and Super Duplex 50% austenite and 50% ferrite, combine the most desirable traits of ferritic and austenitic steels possess excellent mechanical strength and corrosion resistance to a wide variety of ways, with substantial corrosion resistance in seawater and other environments containing chloride, due to its high level of chromium, molybdenum, and nitrogen. When welded to the weld metal region of these steels lose their mechanical strength features and corrosion due to the imbalance of the ferrite and austenite phases. In this paper we analyzed the influence of the welding process autogenous laser Pulsed Nd: YAG laser on the mechanical and microstructural features of the welded joint, by varying the overlap rate of pulses from 40 to 90% in stainless steel plates Super Duplex UNS S32750 with 1.5 mm thick. We used a pulsed laser source Nd.YAG, United Winner 150A, with maximum power of 150 W. The power of the welding pulse was set at 10 J, peak power of 2 kW, temporal width of 5 ms and frequency ranging from 1.5 and 9.0 Hz. As shielding gas used is pure argon with a flow rate of 10 l / min. Microstructural characterization was performed by optical microscopy and scanning electron microscopy. The results showed that increasing the overlap rate of 40% to 90% joint strength increases and the hardness of the weld metal. Regarding the welding ferritização observed a metal microstructure thereof with small volume fraction of the austenite grain boundary regions. It was observed the presence of brittle phases in the weld metal.

Orientador: Vicente Afonso Ventrella / Resumo: Os aços inoxidáveis Duplex e Super Duplex, 50% austenita e 50% ferrita, combinam as características mais desejáveis dos aços ferríticos e austeníticos, possuem excelente resistência mecânica e à corrosão para uma ampla variedade de meios, com expressiva resistência à corrosão em água do mar e outros ambientes contendo cloreto, devido a seu elevado nível de cromo, molibdênio, e nitrogênio. Quando soldado a região do metal de solda desses aços perdem suas características de resistência mecânica e à corrosão devido ao desbalanceamento das fases ferrita e austenita. No presente trabalho foi analisado a influência do processo de soldagem autógena a laser Pulsado Nd:YAG nas características mecânicas e microestruturais da junta soldada, variando a taxa de sobreposição dos pulsos de 40 a 90% em chapas de aço inoxidável Super Duplex UNS S32750 com 1,5 mm de espessura. Utilizou-se uma fonte laser pulsada Nd.YAG, United Winner 150A, com potência máxima de 150 W. A energia do pulso de soldagem foi fixada em 10J, potência de pico de 2 kW, largura temporal de 5 ms e frequência variando entre 1,5 e 9,0 Hz. Como gás de proteção utilizou-se argônio puro com vazão de 10 l/min. A caracterização microestrutural foi realizada através de microscopia ótica e microscopia eletrônica de varredura. Os resultados mostraram que o aumento da taxa de sobreposição da junta de 40% até 90% aumenta a resistência mecânica e a dureza do metal de solda. Em relação à microestrutura do metal de solda observou-se u... (Resumo completo, clicar acesso eletrônico abaixo) / Mestre