Dissertations / Theses: 'Duplex and super duplex stainless steel'

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Rieder, Ester Schmidt. "The passivity of a super duplex stainless steel." Thesis, University of Birmingham, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.272490.

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Sharafi, Shahriar. "Microstructure of super-duplex stainless steels." Thesis, University of Cambridge, 1993. https://www.repository.cam.ac.uk/handle/1810/221879.

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Fang, Peijun. "Weldability and hydrogen relationships in super duplex stainless steel." Thesis, Robert Gordon University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260057.

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Wang, Huei-Sen. "Thermal modelling of zeron 100 super duplex stainless steel." Thesis, Robert Gordon University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287771.

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Renton, N. C. "Time-variant reliability of super-duplex stainless steel tubulars." Thesis, University of Aberdeen, 2007. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU239879.

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The development of high pressure-high temperature oil wells in the U.K.'s north sea province has led to the application of high-strength, corrosion resistant alloys for production tubulars. One such alloy is super-duplex stainless steel (SDSS). The cold-worked material combines high strength with excellent corrosion resistance properties as a result of its chromium, molybdenum, tungsten and nitrogen content. The material's macro properties are a function of its two-phase microstructure made up of roughly equal parts austenite and ferrite. Recent in-service failures of SDSS tubulars have identified gaps in the understanding of the material's properties. The study investigated the link between the microstructure of the material and its mechanical and corrosion behaviours. The results revealed that the microstructure of the material was highly anisotropic and varied through the pipe-wall as a result of manufacturing techniques. A method of measuring the crack resistance of the material was developed, with the results showing that the spatial arrangement of the microstrucure determined the crack resistance of the fracture plane. The properties of ferrite were identified as the limiting factor on the crack resistance of the material. The investigation also revealed that a small difference in chemical composition between the two phases led to the preferential dissolution of ferrite in aqueous oxygen bearing chloride environments.

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Alsarraf, Jalal. "Hydrogen embrittlement susceptibility of super duplex stainless steels." Thesis, Cranfield University, 2010. http://dspace.lib.cranfield.ac.uk/handle/1826/4562.

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This thesis describes the metallurgical and environmental factors that influence hydrogen embrittlement of super duplex stainless steels and presents a model to predict the rate at which embrittlement occurs. Super duplex stainless steel has an austenite and ferrite microstructure with an average fraction of each phase of approximately 50%. An investigation was carried out on the metallurgical and environmental factors that influence hydrogen embrittlement of super duplex stainless steels. Tensile specimens of super duplex stainless steel were pre-charged with hydrogen for two weeks in 3.5% NaCl solution at 50º C at a range of applied potentials to simulate the conditions that exist when subsea oilfield components are cathodically protected in seawater. The pre-charged specimens were then tested in a slow strain rate tensile test and their susceptibility to hydrogen embrittlement was assessed by the failure time, reduction in cross-sectional area and examination of the fracture surface. The ferrite and austenite in the duplex microstructures were identified by analysing their Cr, Ni, Mo and N contents in an electron microscope, as these elements partition in different concentrations in the two phases. It was shown that hydrogen embrittlement occurred in the ferrite phase, whereas the austenite failed in a ductile manner. An embrittled region existed around the circumference of each fracture surface and the depth of this embrittlement depended on the hydrogen charging time and the potential at which the charging had been carried out. The depth of embrittlement was shown to correlate with the rate of hydrogen diffusion in the alloy, which was measured electrochemically using hydrogen permeation and galvanostatic methods. A two-dimensional diffusion model was used to calculate the hydrogen distribution profiles for each experimental condition and the model could be employed to provide predictions of expected failure times in stressed engineering components.

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Martins, Alessandra Souza. "Estudo comparativo da resistÃncia Ã corrosÃo dos aÃos inoxidÃveis super duplex ASTM A890 / A890M grau 5A e 6A." Universidade Federal do CearÃ, 2014. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=12591.

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CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior
Uma liga metÃlica que vem apresentando um desempenho satisfatÃrio em ambientes de maior agressividade Ã o aÃo inoxidÃvel super duplex. Esse tipo de aÃo possui boas propriedades de resistÃncia mecÃnica, resistÃncia Ã corrosÃo e tenacidade ao impacto. Mesmo apresentando desempenho satisfatÃrio, esses aÃos podem apresentar problemas de corrosÃo quando sofrem algum tratamento tÃrmico devido Ã precipitaÃÃo de uma fase deletÃria chamada de alfa linha (â), a qual precipita em temperaturas entre 300 ⁰C e 550 ⁰C e pode ocasionar uma diminuiÃÃo da resistÃncia Ã corrosÃo e tenacidade do material. Portanto, o objetivo deste trabalho Ã avaliar a resistÃncia Ã corrosÃo dos aÃos inoxidÃveis super duplex fundidos de grau 5A e 6A apÃs sofrerem tratamento tÃrmico a 475 ⁰C. O grau 6A se difere do 5A pela presenÃa de cobre e tungstÃnio na sua composiÃÃo quÃmica. A resistÃncia Ã corrosÃo dos corpos de prova foi avaliada por meio das seguintes tÃcnicas eletroquÃmicas: monitoramento do potencial de circuito aberto, polarizaÃÃo anÃdica, polarizaÃÃo cÃclica, espectroscopia de impedÃncia eletroquÃmica e temperatura crÃtica de pite. Foi realizada a caraterizaÃÃo microestrutural dos materiais, onde foi possÃvel observar sua estrutura bifÃsica composta por uma matriz ferrÃtica e ilhas de austenita em proporÃÃes coerentes. O ensaio de dureza Brinell mostrou que a dureza aumenta nas primeiras horas de tratamento tÃrmico e, depois, hÃ uma diminuiÃÃo nessa taxa de aumento da dureza. Os resultados eletroquÃmicos indicaram que, para os dois tipos de aÃo estudados, as amostras com 10 horas de tratamento tÃrmico apresentaram uma maior resistÃncia Ã corrosÃo.

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Al-Rabie, Mohammed. "Observations of stress corrosion cracking behaviour in super duplex stainless steel." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/observations-of-stress-corrosion-cracking-behaviour-in-super-duplex-stainless-steel(51f53ed4-7bdc-469a-8ff7-7dfd9ff56339).html.

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The new generation of highly alloyed super duplex stainless steels such as Zeron 100 are preferable materials for industrial applications demanding high strength, toughness and superior corrosion resistance, especially against stress corrosion cracking (SCC). SCC is an environmentally assisted failure mechanism that occurs due to exposure to an aggressive environment while under a tensile stress. The mechanism by which SCC of duplex stainless steel is expected to suffer depends on the combination of electrochemical and the mechanical interaction between austenite and ferrite in the duplex alloys. The main aims of this work are to study the suitability of digital image correlation (DIC) to monitor the initiation and propagation of SCC and to understand how the microstructure of duplex stainless steel influences the kinetics of crack initiation and growth. The combined analysis of DIC, SEM and EBSD was used to study the relative crack propagation and the effect of interphase boundaries on crack growth as well. Cracking was initiated beneath saturated MgCl2 droplets in an atmospheric environment at 80°C and relative humidity of 30-33%. As-received and 10% cold rolled samples (with two orientations transverse and longitudinal to the loading direction) were subjected to an applied strain of 0.03 under displacement controlled tests. Regular optical observations were recorded of the droplets and their surrounding area. DIC analyses used the differentiation of the displacement fields to obtain the apparent surface strains used to detect crack initiation and propagation, and to measure crack opening displacements. It was found that DIC was efficiently observed the strain developments and the displacements in observed surfaces outside of the droplets but it could not identify or quantify the initiation of the cracks inside the droplets because of the mobility of the salt film and the high amount of the corrosion products formed which obscure the vision under the droplets. In addition, results showed that early stage microcracks were initiated in α phase and α/γ interfaces and propagated preferentially in the ferrite phase. Also, SCC initiation and propagation was accelerated by cold rolling and the grains orientations were of major effects on the retardation of crack propagation which was more severe in the transverse rolling direction. Also, there was no relation established between the strain level and the density of pitting in either phase.

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Alhoud, Abdulrezeg M. A. "Effect of process variables on the corrosion resistance of super duplex stainless steel." Thesis, University of Aberdeen, 2010. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=128219.

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The title of this research suggests the importance of manufacturing variables and their influence on the behavior of super duplex stainless steel (SDSS) alloy when exposed to corrosive aqueous environments. Studies show that SDSS alloys have many applications due to their good physical, mechanical and corrosion resistance properties. However, there are a number of cases of in-service failures of SDSS alloys, such as pitting corrosion, stress corrosion cracking and environmentally assisted cracking failures. The root cause of these failures was due to the impact of one or more manufacturing variables such as surface finish, microstructure defects or deficiencies after deformation. From this concept, a detailed study into the effect of manufacturing variables on the corrosion resistance of a UNS S39274 super duplex stainless steel has been carried out. The manufacturing variables studied are as follows: Effect of surface condition; The corrosion resistance of stainless steel components is very sensitive to the final surface condition. The effect of surface condition on the corrosion resistance was investigated by measuring the critical pitting temperature (CPT) and the pitting potential (Epit) of in-service UNS S39274 super duplex stainless steel tubular sections with three different surface roughness values of Ra =2.8, 3.2 and 3.5m. Experimental results confirmed that the surface roughness parameter Ra is a useful parameter as a general and basic guideline of surface texture but it’s not sufficient on its own to predict the likely effect of surface roughness on the in-service corrosion behaviour of SDSS materials. The manufacturer of super duplex stainless steel products should include the electrochemical corrosion evaluation such as the CPT or Epit values beside the surface roughness average value Ra and PRENs in SDSS alloy assessment. Effect of microstructure; The thermo-mechanical handling of super duplex stainless steels is an important factor in their performance. This is due to the complex nature of the material which is highly alloyed with Cr, Ni, Mo, and N. Exposure to certain temperature ranges leads to undesired secondary phases formation. The presence of intermetallic phases has been found to be harmful to super duplex stainless steel properties. A study was undertaken to evaluate the effect of thermal exposure of a solution annealed UNS S39274 super duplex stainless steel to temperatures of 850C, 1000ºC and 1300ºC on its microstructure and its localised corrosion resistance. Heat treatment at 850ºC and 1000C caused formation of intermetallics such as sigma () and chi () while at 1300C caused precipitation of secondary austenite and enlarged grains and percentage of ferrite was observed. The formation of intermetallics of sigma () and chi () had a drastic effect on the corrosion resistance of the super duplex stainless steel. Electrochemical measurements confirmed that the intermetallics affected the corrosion resistance by reducing the pitting potential by around 80% in the active direction. Evaluation of the corrosion morphology using SEM revealed depletion at the ferrite/austenite interfaces created intergranular corrosion path with preferential attack of the ferrite phase. The present results confirmed that PRENs is not suitable for corrosion assessment of SDSS after exposure to intermetallic temperature ranges. Effect of cold work; Cold work introduces metallurgical changes like dislocations and deformation bands which affect the corrosion resistance of stainless steel components. Cold work is still a complicated phenomenon for ferritic/austenitic alloys such SDSS. The effect of cold work (0%, 4%, 8%, 12% and 16% plastic strain) on the pitting corrosion behaviour of UNS S39274 SDSS was evaluated. The Ferrite phase of the material exhibits greater degrees of plastic deformation under straining providing a greater number of initiation sites than the austenite phase. The hydrogen embrittelement of the cold worked specimens was investigated after 48 hours cathodic charging in 0.1M H2SO4. Experimental results indicated that the increase in cold work caused reduction in mechanical properties such as elongation and strain to failure. The depth of embrittlement increased as the degree of cold work increased and revealed brittle surfaces of cleavage fracture mode. Manufacturer and users should consider the degree of plastic strain when cold worked SDSS components going to work in corrosive environments or hydrogen containing environments. The main conclusion of the work is that the interactions between corrosive environments and SDSS components containing one or more of the manufacturing variables evaluated must be considered if reductions in in-service life are to be avoided.

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Obi, Udoka. "Effect of ageing on phase evolution, mechanical and corrosion properties of a high tungsten super-duplex stainless steel." Thesis, University of Aberdeen, 2015. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=225950.

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Super duplex stainless steels (SDSSs) with lower nickel content are cost effective substitutes for higher alloyed austenitics and nickel alloys in demanding environments such as oil and gas production tubulars and pipelines due to their excellent corrosion resistance and high strength. The overall properties of SDSS are derived from its dual microstructure of equal ferrite and austenite, higher alloying additions of chromium, molybdenum, nitrogen and tungsten and its thermomechanical history. Higher alloying renders SDSS prone to secondary phase precipitation such as sigma phase during improper welding operations or fabrication, affecting the materials properties. Reports suggest that tungsten additions in SDSS delays sigma phase precipitation, hence the development of tungsten based SDSS such as UNS S39274. However, secondary phases cannot be entirely avoided in SDSS. Secondary phase evolution in DSS and the mechanical properties/corrosion behaviour of SDSS has been studied extensively yet their interaction is still not clear. In-service failures of SDSS components have identified gaps in the understanding of the link between secondary phase evolution and material properties, thus limiting the safe and efficient use of SDSS. The work presented in this thesis explored and quantified experimentally the role of aging on secondary phase evolution and ensuing effects on the mechanical properties, corrosion behaviour and toughness of UNS S39274 SDSS. The results revealed that chi phase precipitation occurred preferentially before the sigma phase, although chi phase was metastable in the studied alloy. Numerical modelling established that the measured concentration of the precipitated sigma phase follows the prediction by the Johnson-Mehl-Avrami kinetic model. The time-temperature -transformation was computed using experimental data, the results were compared with theoretical predictions. Results established that increase in both sigma and chi phase led to significant drop in the uniform strain and enhancement of the modulus, hardness and yield and tensile strengths. We note that the sigma phase was attacked by corrosion in comparison to other grades of 25Cr SDSS where the sigma phase remains inert to corrosion attack. Pitting corrosion resistance was influenced more by sigma phase than the chi phase composition. Chi phase was more damaging on the toughness than sigma phase. Another key finding is that the corrosion behaviour and fracture behaviour is more sensitive to lower secondary phase volume fraction than the tensile properties.

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Smuk, Olena. "Microstructure and properties of modern P/M super duplex stainless steels." Doctoral thesis, KTH, Materials Science and Engineering, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3758.

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Humphreys, Alan Owen. "The low temperature fracture behaviour of the super duplex stainless steel Zeron 100." Thesis, University of Birmingham, 1998. http://etheses.bham.ac.uk//id/eprint/1427/.

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The micromechanisms of fracture in an austenitic/ferritic super-duplex stainless steel (Zeron 100) have been studied for a range of product forms, including cross-rolled plate, conventional (ingot) route and powder route extruded pipe, hot isostatically pressed (HIP'd) powder, and weldments produced using both tungsten inert gas (TIG) and manual metal arc (MMA) techniques. The rolled plate material was also investigated after heat treatments at temperatures of 425 and 850°C, which were known to embrittle the material.

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Liang, Xingzhong. "Microstructure evolution and hydrogen embrittlement in super duplex stainless steels." Thesis, University of Leicester, 2018. http://hdl.handle.net/2381/42527.

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Super duplex stainless steel has a wide range of applications in chemical transport and processing facilities, especially in subsea oil and gas pipelines. A desirable combination of corrosion resistance and mechanical properties can be delivered by a balanced duplex microstructure. However, the microstructure of steel can be altered during processing, which can result in degradation of mechanical properties and corrosion resistance. In offshore environment, cathodic protection is widely used to improve corrosion resistance of gas and oil transportation pipelines. However, the application of cathodic protection can trigger the evolution of atomic hydrogen, which can adversely affect the macroscopic mechanical properties. Solute hydrogen induces premature failure, which is known as hydrogen embrittlement. In this project, microstructure evolution in super duplex stainless steel was first investigated. A new Cr2N precipitation mechanism has been proposed that a nano size lamellar M23C6 facilitates Cr2N rods precipitation in super duplex stainless steel. To study Cr2N precipitates in super duplex stainless steel weldment, transmission Kikuchi diffraction (TKD) was used to measure the geometrically necessary dislocation distribution (GND) around Cr2N. The TKD-GND results suggest a high GND density can be measured in nano-sized regions adjacent to Cr2N. The effect of hydrogen charging on dislocation multiplication in super duplex stainless steel was investigated and it is found that dislocation density multiplies by about one order of magnitude in steels with under 5% pre-strain, but dislocation density remains the same in steel with pre-strain at 10% and above. EBSD was used to study the effect of hydrogen on crack propagation. Hydrogen assists crack propagation through ferrite but can be trapped by both ferrite and austenite. It is found that austenite traps cracks by emitting dislocations or forming secondary grain boundaries ahead of crack tips, while in ferrite grains, the grain boundaries can impede crack propagation. The above findings provide new insight into microstructure evolution and hydrogen induced failure in super duplex stainless steel.

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Kumara, Chamara. "Modelling of the temperature field in TIG arc heat treated super duplex stainless steel samples." Thesis, Högskolan Väst, Avdelningen för maskinteknik och naturvetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-9590.

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Super Duplex Stainless Steels have superior corrosion resistance properties and strength compared to conventional steels. However, these properties are influenced by the different phases that precipitate during the heat treatment process. The conventional way of studying the time and temperature effects on the properties and micro-structure of SDSS is to prepare many samples at different temperatures and holding times. The welding research group at Production Technology Center, Trollhättan, Sweden, has recently developed a unique heat treatment method to produce a wide range of temperature by using a stationary TIG arc heat source. It results in a graded micro-structure in a single sample at a specific time period. The accuracy of the results ob-ained from this process is highly related to the accuracy of the temperature field model next to weld pool. In this work, a model was developed by using OpenFOAM CDF code, to predict the temperature field of the super duplex stainless steel samples that have been subjected to this novel TIG arc heat treatment process. The developed model was able to capture the trend in the overall temperature field in the heat affected zone. However, there was some mismatch between the modelled and experimental temperature profiles in certain locations in the heat affected zone. Further improvements have to be done to the developed model in order to take the phase transformation effect into account. A preliminary investigation has been carried out on how to implement this in the current model and reported in the thesis.

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Oliveira, Junior Carlos Ancelmo 1981. "Torneamento do aço inoxidável super duplex UNS S32750 e influência na resistência à corrosão." [s.n.], 2013. http://repositorio.unicamp.br/jspui/handle/REPOSIP/264188.

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Orientador: Anselmo Eduardo Diniz
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
Made available in DSpace on 2018-08-22T09:27:39Z (GMT). No. of bitstreams: 1 OliveiraJunior_CarlosAncelmo_M.pdf: 7354499 bytes, checksum: 05a6c099baa7c4f194f916c8e418d4db (MD5) Previous issue date: 2013
Resumo: Os aços inoxidáveis super duplex são ligas extremamente resistentes à corrosão, desenvolvidas para aplicações com altos níveis de exigência, em que as peças terão contato com ambientes corrosivos como a água do mar, por exemplo. Devido à sua composição química e microestrutura, que proporcionam alta resistência mecânica, alta resistência ao calor e também alta ductilidade, que são fatores positivos para a aplicação, a usinabilidade dessas ligas é geralmente muito baixa o que resulta em longos ciclos de produção e alto custo de ferramental. Este trabalho trata do torneamento da liga UNS 32750 comercialmente conhecida como SAF2507 e sua consequente influência na resistência à corrosão apresentada ao longo da aplicação. Durante os ensaios, houve variação de velocidade de corte, classe e cobertura da ferramenta, além da condição de refrigeração com alternativas de alta e baixa pressão. Os resultados indicam que as pastilhas com cobertura PVD são mais resistentes ao desgaste e, combinadas ao uso de refrigeração de alta pressão, podem melhorar o seu desempenho em relação à vida útil e rugosidade bem como à posterior resistência à corrosão do material. Desgaste de entalhe e aderência encontrados na usinagem com pastilhas PVD, juntamente com lascamentos e quebras que ocorreram nas pastilhas CVD, foram os tipos e mecanismos de desgaste/avaria da ferramenta mais encontrados durante os ensaios
Abstract: Super duplex stainless steels are extremely corrosion-resistant alloys that were developed to work in very demanding applications, in which the workpieces are exposed to corrosive environments like sea water, for example. Due to their chemical composition and microstructure, that provide high mechanical and heat resistance besides high ductility, which are favorable factors for the application, the machinability of these alloys is generally poor and results in long production cycles and high tool costs. The goal of this research is to study turning operation of the UNS 32750 alloy, commercially called SAF2507, and its consequent influence in the corrosion resistance for application situations. During the tests, the input variables were cutting speed, grade and coating of the inserts, besides the cooling conditions with low and high pressure options. The results indicate that the PVD coated inserts are more wear-resistant than the CVD inserts and when they are combined with high pressure cooling, their performance related to tool life and workpiece roughness as well as the corrosion resistance of the material after machining is improved. Notch wear and attrition found in machining with PVD inserts, together with chipping and tool breakage that occurred in machining with CVD inserts, were the most frequent types of wear/damage and wear mechanism found during the tests
Mestrado
Materiais e Processos de Fabricação
Mestre em Engenharia Mecânica

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Martins, Marcelo. "Caracterização microestrutural-mecânica e resistência à corrosão do aço inoxidável super duplex ASTM A890 / A890M grau 6A." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-25102007-152307/.

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Este trabalho foi desenvolvido com o intuito principal de adquirir \"know how\" na fabricação de componentes fundidos e usinados de bombas centrífugas, para aplicações em plataformas \"offshore\". Os materiais utilizados para esse destino - aços inoxidáveis super duplex - constituem sistemas termodinamicamente meta estáveis, que buscam o estado de estabilidade termodinâmica quando excitados termicamente. Por outro lado, esses materiais apresentam uma grande instabilidade dimensional, devido às tensões residuais desenvolvidas no resfriamento do tratamento térmico e durante o processo de usinagem, principalmente quando se trabalha com tolerâncias extremamente pequenas (10 m a 15 μm). Nesse contexto, foram realizados tratamentos térmicos a partir de 520°C, variando-se de 20°C em 20°C até a temperatura limite de 1180°C, com o objetivo de verificar-se a influência dessas temperaturas na microestrutura, dureza e tenacidade ao impacto do material. O enfoque principal foi dado na dinâmica de precipitação da fase sigma, que é o intermetálico mais conhecido e estudado nessa categoria de aços. Sua precipitação é inevitável, durante o processo de solidificação, porém, pode ser minimizada controlando-se a composição química e a taxa de resfriamento. Partindo-se de uma estrutura solubilizada, foi possível determinar as temperaturas a partir das quais a fase sigma começa a precipitar e dissolve-se por completo, bem como a influência de sua presença na dureza e na energia absorvida no ensaio de impacto Charpy. Técnicas de microscopias óptica, eletrônica de varredura, eletrônica de transmissão e difração de raios-x foram utilizadas para caracterização microestrutural do material nas várias condições de tratamento térmico. Ensaios eletroquímicos utilizando-se água do mar sintética, aerada e saturada com C02, contendo 20000ppm, 40000ppm e 80000ppm de íons cloreto, a temperaturas de 5OC, 25OC e 60°C foram realizados somente para o material solubilizado a 1130°C, 1160°C e solubilizado a 1130°C, seguido por alívio de tensões a 520°C. Os resultados mostraram que o tratamento térmico de alivio de tensões a 520°C, não promoveu precipitação de fases intermetálicas na microestrutura e tampouco prejudicou a resistência a corrosão do material, indicando a possibilidade prática de seu uso.
The present work was developed to acquire know how in manufacturing of castings and machined components for centrifugal pumps for offshore platform applications. Normally, the materials used to do them are the super duplex stainless steels that are thermodynamically metastable systems which tend to equilibrium when thermally activated. On the other hand, these materials show a great dimensional instability due to the residual stresses developed during the cooling from heat treatment process and also after machining process. This is crucial when working with very small dimensional tolerances, typical for these components. It were made stress relief heat treatments from 520°C, increasing the temperatures in 20°C steps until 1180°C to check the influence of these temperatures on microstructures, hardness and absorbed energy in Charpy test of this materials. The main focus was given on sigma phase precipitation dynamic, because it is the most common and studied intermetalic in this kind of stainless steels. It is impossible to avoid its precipitation during the cooling from solidification process, but it can be minimized by controlling the chemical composition and the cooling rate from solidification. Starting with a solution annealed structure, it was possible to determine the temperature where the sigma phase begins to precipitate and also its dissolution temperature. The influence of sigma phase content on hardness and absorbed energy in impact test was evaluated. Microstructure characterization was made using optical, scanning and transmission electron microscopy, as well as X-ray diffraction analysis for each different temperature. The electrochemical corrosion tests using synthetic sea water with 20000ppm, 40000ppm and 80000ppm of chlorine ions, at 5oC, 25°C and 60°C were made. Samples solution annealed such at 1130°C and at 1160°C and solution annealed at 1130°C followed by aging at 520°C were tested electrochemically. The results showed that the stress relief heat treatment at 520°C did not promote the intermetalic phase precipitation on material\'s microstructure and also, did not diminish the material\'s corrosion resistance.

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Hosseini, Vahid. "Influence of multiple welding cycles on microstructure and corrosion resistance of a super duplex stainless steel." Licentiate thesis, Högskolan Väst, Avdelningen för svetsteknologi (SV), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-10151.

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Super duplex stainless steel (SDSS) has found a wide use in demanding applications such as offshore, chemical and petrochemical industries thanks to its excellent combination of mechanical properties and corrosion resistance. Welding of SDSS, however, is associated with the risk of precipitation of secondary phases and formation of excessive amounts of ferrite in the weld metal and heat affected zone. The present study was therefore aimed at gaining knowledge about the effect of multiple welding thermal cycles on the microstructure and possible sensitization to corrosion of welds in SDSS.Controlled and repeatable thermal cycles were produced by robotic welding. Oneto four autogenous TIG-remelting passes were applied on 2507 type SDSS plates using low or high heat inputs with pure argon as shielding gas. Thermal cycles were recorded using several thermocouples attached to the plates. Thermodynamic calculations and temperature field modelling were performed in order to understand the microstructural development and to predict the pitting corrosion resistance. Etching revealed the formation of different zones with characteristic microstructures: the fused weld zone (WZ) and the heat affected zone composed of the fusion boundary zone (FBZ), next to the fusion boundary, and further out Zone 1 (Z1) and Zone 2 (Z2). The WZ had a high content of ferrite and often nitrides which increased with increasing number of passes and decreasing heati nput. Nitrogen content of the WZ decreased from 0.28 wt.% to 0.17 wt.% after four passes of low heat input and to 0.10 wt.% after four passes of high heatinput. The FBZ was reheated to high peak temperatures (near melting point) and contained equiaxed ferrite grains with austenite and nitrides. Zone 1 was free from precipitates and the ferrite content was similar to that of the unaffected base material. Sigma phase precipitated only in zone 2, which was heated to peak temperatures in the range of approximately 828°C to 1028°C. The content of sigma phase increased with the number of passes and increasing heat input. All locations, except Z1, were susceptible to local corrosion after multiplere heating. Thermodynamic calculations predicted that a post weld heat treatment could restore the corrosion resistance of the FBZ and Z2. However, the pitting resistance of the WZ cannot be improved significantly due to the nitrogen loss. Steady state and linear fitting approaches were therefore employed to predict nitrogen loss in autogenous TIG welding with argon as shielding gas. Two practical formulas were derived giving nitrogen loss as functions of initial nitrogen content and arc energy both predicting a larger loss for higher heat input and higher base material nitrogen content. A practical recommendation based on the present study is that it is beneficial to perform welding with a minimum number of passes even if this results in a higherheat input as multiple reheating strongly promotes formation of deleterious phases.

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Suma, Emeric Emmanuel. "Using Duplex Stainless Steel to Join X65 Pipe Internally Clad with Alloy 625 for Subsea Applications." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1492696298842902.

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Da, Silva Craidy Pedro. "Interactions Hydrogène-Microstructure-Propriétés Mécaniques dans les Composants en Acier Inoxydable Super Suplex." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAI041.

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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

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20

Næss, Monika. "EFFECT OF MICROSTRUCTURE AND SURFACE FINISH ON LOCALIZED CORROSION PERFORMANCE OF SUPER DUPLEX STAINLESS STEEL IN SEAWATER." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for produksjons- og kvalitetsteknikk, 2014. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-25741.

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Corrosion resistant alloys (CRAs) used in subsea pressure-retaining components must be compatible with production fluids and resistant to pitting and crevice corrosion in seawater. Whereas materials selection in production environments is governed by well-established international standards such as ISO 15156, much debate still exists as of how to determine the seawater localized corrosion resistance of higher grade CRAs such as duplex super duplex stainless steels (DSS and SDSS, respectively). While most industry specifications rely on the ASTM G48 standard to determine localized corrosion resistance, for duplex and super-duplex stainless steels there is no consensus on surface finish prior testing (e.g. polishing or pickling) and test temperature (e.g. 50 °C in NORSOK 630 versus 40 °C in ASTM A923). Moreover, it is unclear whether existing procedures are sensitive enough to determine the onset of deleterious phases such as σ-phase and chromium nitrides. The objective of this investigation was to quantify the seawater pitting corrosion resistance of a type 25Cr SDSS (UNS S32750) and its correlation with microstructure and surface finish before testing. Cyclic potentiodynamic polarization (CPP) testing was used to determine the effect σ-phase on the corrosion response of the system. CPP results were then compared against industry standard practices based on the ASTM G48 Method A test. In addition, CPP tests were conducted at various temperatures, ranging from 25 to 90°C, to determine the effect of deleterious phases on critical pitting temperature (CPT) and overall localized corrosion resistance.The results from this project indicate that the Critical Pitting temperature for standard solution annealed Super Duplex Stainless Steel is 60-70°C. It is also shown that the corrosion resistance is reduced for material that contains sigma phase showing a Critical Pitting Temperature of 40-50°C. The surface treatments seem to have less effect on the values, but pickled surfaces gave a more repeatable result.

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Poinsot, Jocelin. "Influence des éléments cuivre et tungstène sur les mécanismes de corrosion localisée des super-duplex." Thesis, Bourgogne Franche-Comté, 2017. http://www.theses.fr/2017UBFCK013.

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Les aciers inoxydables super-duplex (SDSS) sont des matériaux d’ingénierie intéressants, du fait de leur structure biphasé qui leur confère généralement une grande résistance à la corrosion combinée à une haute résistance mécanique. Ils sont utilisés dans de nombreux secteurs industriels, tels que l’oil & gas (pipelines et réservoirs de stockage), le dessalement (évaporateurs et pompes), la géothermie, la dépollution (épurateur) et l’industrie des pâtes et papiers (digesteurs et réacteurs de blanchissement).Dans cette thèse, l’influence de l’addition de cuivre et de tungstène dans les SDSS sur la résistance à la corrosion localisée (piqûration) a été évaluée. Les trois nuances étudiées ont été : UR2507, UR2507Cu (1,6 %mass. Cu) et UR2507W (0,6%mass. Cu et 0,6%mass. W).L’épaisseur et la composition chimique des films passifs formés après un état de surface optimisés ont été étudiées par spectrométrie photoélectronique X et par spectrométrie Auger avant et après immersion dans 5 M NaCl 90°C. La résistance à la corrosion par piqûres a ensuite été évaluée dans des milieux NaCl en utilisant la méthode de la détermination de la température critique de piqûration (CPT) combinée à la microcellule électrochimique (capillaire d’un diamètre de 300 microns environ) et la méthode pulsée (PPT). Les analyses locales de CPT ont été utilisées pour comparer les mécanismes d’amorçage des piqûres sur les trois nuances alors que la PPT a permis de comparer la taille des piqûres formées. En complément, les potentiels critiques de piqûration ont été mesurés à une échelle plus globale (5 cm²) dans des solutions de différentes concentrations en NaCl et de différentes températures. Ces conditions sont plus proches des conditions réelles d’utilisation des SDSS. Il a été montré que l’effet du cuivre et du tungstène sur la résistance à la corrosion localisée dans les SDSS dépend du milieu d’utilisation (T,[Cl-]) et que les phases d’amorçage et de début de propagation peuvent aussi être influencés par des paramètres non liés à la composition tel que le pH local et l’état de surface (écrouissage)
Super duplex stainless steels (SDSS) are interesting engineering materials, due to their generally high corrosion resistance combined with high strength. They are widely used in various industrial sectors, such as oil & gas (pipelines and storage tanks), desalination (evaporators and pumps), geothermal, pollution control (scrubber) and pulp and paper (digester and bleaching reactors) industries.In this PhD thesis, the influence of the addition of copper and tungsten in SDSS on their localised corrosion resistance (pitting) was investigated. Three alloys studied were: UR2507, UR2507Cu (1.6 %wt. Cu) and UR2507W (0.6%wt. Cu and 0.6%wt. W).The thickness and chemical composition of the passive film formed on the three alloys after optimised surface preparation was first investigated by means of X ray photoelectron spectroscopy and Auger electron spectroscopy before and after immersion in highly concentrated NaCl solutions. Pitting corrosion resistance was then investigated in NaCl-based media using the critical pitting temperature testing method combined with the electrochemical microcell technique (capillary diameter of about 300 microns) and potentiostatic pulse technique (PPT). Local CPT measurements were used to compare the resistance of the three different alloys to pitting while PPT enables to compare the size of the pits formed. In addition, pitting potentials were measured in samples with 5 cm² area in solutions of different NaCl concentrations and temperatures. These measurements are closer to the real using conditions of the alloys.It was showed that copper and tungsten effects on localised corrosion resistance in SDSS depend on the using media (T, [Cl-]) and the initiation and start of the propagation phases can also be influenced by parameters not linked to composition such as local pH and surface conditions (cold-work layer)

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22

Aguiar, Denilson José Marcolino de. "Estudo da formação e reversão de martensita induzida por deformação na austenita de dois aços inoxidáveis dúplex." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-03072013-112618/.

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No presente trabalho foram estudados os fenômenos de encruamento e, principalmente, a formação e reversão da martensita alfa-linha (a\', cúbica de corpo centrado, CCC, ferromagnética) induzida por deformação em um aço inoxidável dúplex UNS S31803 e um super dúplex UNS S32520. Inicialmente, as microestruturas dos dois materiais na condição solubilizada foram caracterizadas com auxílio de várias técnicas complementares de análise microestrutural. Foram determinadas fração volumétrica, estrutura cristalina, composição química, tamanho e morfologia das duas fases (ferrita e austenita). Posteriormente, os dois aços foram deformados por dois métodos: a laminação a frio, dividida em vários estágios, com menores graus de deformação e a limagem, sendo que o cavaco limado resultante apresenta altos graus de deformação. Algumas amostras deformadas foram recozidas. Os fenômenos de encruamento, formação e reversão de martensita induzida por deformação na austenita, recuperação, recristalização da austenita e da ferrita no cavaco limado foram estudados predominantemente por difratometria de raios X e usando o método de Rietveld. A difratometria de raios X também foi utilizada para determinação das microdeformações residuais e tamanhos de cristalito (subgrão), calculadas a partir do alargamento dos picos de difração causado pelas deformações. Desta forma, puderam-se comparar os níveis de deformação da laminação e limagem. Qualitativamente, a formação e reversão da martensita induzida por deformação também foi estudada por meio de medidas magnéticas utilizando-se dados de saturação magnética das curvas de histerese obtidas com o auxílio de um magnetômetro de amostra vibrante. Observou-se que para o aço inoxidável dúplex, tanto a laminação quanto a limagem causaram a formação de martensita induzida por deformação e para o aço inoxidável super dúplex, apenas a limagem promoveu essa transformação. Em comparação com o aço dúplex, o aço super dúplex apresentou maior resistência à formação de martensita induzida por deformação, pois apresenta uma austenita mais rica em nitrogênio e uma maior propensão à formação de fase sigma durante o recozimento, pois apresenta uma ferrita mais rica em cromo e nitrogênio.
In the present work the phenomena of strain hardening, formation and reversion of the strain induced alpha-prime martensite (a\', body centered cubic, BCC, Ferromagnetic) in an UNS S31803 duplex and UNS S32520 super duplex stainless steels have been studied. Firstly, the microstructures of both materials in the solution annealed condition were characterized with the aid of several microstructural analysis complementary techniques. The volume fraction, crystalline structure, chemical composition, size and morphology of the two phases (ferrite and austenite) have been determined. Further, both steels were deformed by two methods: cold rolling, divided into several stages, with lower strain levels than filing, which the chips resulting had higher strain levels. The phenomena of strain hardening, formation and reversion of strain induced martensite in the austenite phase, recovery and recrystallization of austenite and ferrite phases have been studied, mainly using X-ray diffraction and the Rietveld method. X-ray diffraction was also used to determine the residual microstrain and crystallite size (sub grain), calculated from the diffraction peak broadening caused by straining. Thus, the levels of cold rolling and filing strains could be compared. Qualitatively, the formation and reversion of strain induced martensite was also studied by magnetic measurements using data from magnetic saturation of hysteresis curves obtained with the aid of a vibrating sample magnetometer. It has been observed that for the duplex stainless steel, both filing as well as cold rolling promoted strain induced martensite. On the other hand, for the super duplex stainless steel, just filing promoted this transformation. In the comparing with duplex, the super duplex stainless steel austenite is more stable that is why is richer in nitrogen, so, the strain induced martensite formation is more difficult. The easier sigma phase precipitation during annealing as well in the super duplex stainless steel is due higher levels of chrome and molybdenum than the duplex stainless steel.

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Bordinassi, Éd Claudio. "Contribuição ao estudo da integridade superficial de um aço inoxidável super-duplex após usinagem." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/3/3151/tde-22042007-135903/.

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Este trabalho teve por objetivo estudar os efeitos da operação de torneamento na integridade superficial do aço inoxidável super-duplex ASTM A890 - Gr 6A. O foco do trabalho foram as operações de acabamento, porém também foram realizados alguns estudos com operações de desbaste, ambas utilizando planejamentos fatoriais completos com 2 níveis e 5 fatores. Os ensaios foram realizados em centros de torneamento com ferramentas de metal duro e tiveram como variáveis: a geometria da ferramenta / classe da pastilha, avanço, profundidade de corte, velocidade de corte e utilização ou não de fluido de corte. As respostas estudadas foram: análise microestrutural óptica e por difração de raios-X, medição de forças através de um dinamômetro piezoelétrico, rugosidade superficial, micro-dureza, tensão residual através de difração de raios-x e estabilidade dimensional. Os resultados não mostraram alterações microestruturais no material mesmo nas operações de desbaste que foram as mais severas. As outras respostas foram correlacionadas com os parâmetros de corte e a melhor combinação destes foi encontrada para a obtenção da melhor integridade superficial. O menor avanço (0,1mm/v), a menor velocidade de corte (110m/min) e a maior profundidade de corte (0,5mm) obtiveram os menores valores para a tensão residual, a menor rugosidade e o maior valor de micro-dureza. A correlação entre as respostas foi bastante difícil de ser estabelecida, uma vez que as interações tiveram grande influência nas análises, porém para algumas combinações estas correlações se mostraram possíveis de serem estabelecidas.
The objective of this work was to study the effects of the turning operations in the surface integrity in a super duplex stainless steel (SDSS) ASTM A890-Gr6A. The focus of the work was the finishing operations but some tests in rough operations were carried out. A complete factorial planning was used for both, with 2 levels and 5 factors. The tests were conducted on turning centers with carbide tools and the main input variables were: tool geometry / tool material class, feed rate, cutting depth, cutting speed and the cutting fluid utilization. The analyzed answers were: microstructure analysis by optical microscopy and x-ray diffraction, cutting measurements by a piezoelectric dynamometer, surface roughness, micro-hardness, residual stress by x-ray diffraction technique and dimensional stability. The results do not showed any changes in the microstructure of the material, even when the greater cutting values were used. All the other answers were correlated with the cutting parameters and the best combination of cutting parameters was founded for the best surface integrity. The smaller feed rate (0,1mm/v), smaller cutting speed (110m/min) and greater cutting depth (0,5mm) provided the smaller values for the tension residual stress, the smaller roughness and the greater micro-hardness. The correlation between all the answers was very difficult to analyze because there was great interaction between the factors, but for some data groups it was possible.

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Lasebikan, B. A. "Mechanical behaviour and stress corrosion cracking of super duplex stainless steel pipes in high pressure and high temperature environment." Thesis, University of Aberdeen, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.540314.

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The oil and gas industry is constantly looking at ways to keep costs down in high temperature and high pressure (HPHT) well completions. The use of duplex or super duplex stainless steel (DSS or SDSS) for production tubing rather than high alloy (austenitics or nickel based) steels is one way to achieve this. An effective use of DSS or SDSS requires an understanding of the effects of environmental and metallurgical variables on the general and localised corrosion behaviour and resistance to environment assisted cracking (EAC) in HPHT well conditions. This research investigates the behaviour of small scale SDSS pipes subject to combined loads in a chloride and sulphide environment which are commonly found in the non-production annulus of oil and gas well completions. The effects of H₂S (which can sometimes leak from the production fluid) on the chloride-based fluid and ammonium bisulphite in the non-production environment is examined. This is used to provide a realistic assessment of the type of fluid that SDSS production tubing may be exposed to in service. Experimental results are presented for the failure envelope under combined internal pressure and axial tension, and mechanical properties of SDSS pipe over a range of temperatures. A standalone autoclave was designed and commissioned to study the initiation of EAC in SDSS pipes in several aqueous solutions under a range of loading conditions: internal pressure, axial load, and a combination of internal pressure and axial load. The work presented in this thesis shows that corrosion tests can be carried out using small scale pipes for better understanding of the effects of stress state on corrosion behaviour. In particular, the safe working envelope of SDSS in terms of load combination, chloride-sulphide environment and temperature is determined in this thesis. This would help the end user understand and gain better in-service performance of SDSS in oil and gas HPHT environment.

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GirÃo, Daniel de Castro. "Influence of sigma phase in the corrosion resistance of super duplex stainless steel ASTM A890 grade 1C after isothermal treatment." Universidade Federal do CearÃ, 2015. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=15245.

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The super duplex stainless steels are often used in applications where high mechanical strength is required, combined with corrosion resistance, especially in highly aggressive environments. However, when certain manufacturing processes are involved (hot forming or welding, for example) can occur the precipitation of undesirable phases, causing reduction of both mechanical properties as well as corrosion resistance. Particularly between 700 and 900 ÂC may occur sigma phase formation. This phase is responsible for the reduction of corrosion and mechanical resistance of super duplex steels. Through computer simulation in Thermo-CalCÂ program, the phase diagram of ASTM A890 GRADE 1C super duplex stainless steel showed higher precipitated fraction of this phase in 830 ÂC temperature. Thus, this essay aims to evaluate the influence of isothermal treatment time in regards to this material aging, the corrosion resistance due to the formation of sigma phase. The evaluation of corrosion resistance was performed through open circuit potential monitoring, electrochemical impedance and potentiodynamic polarization tests (anodic branch) in 0.5 M H2SO4 solution, 0.5 M H2SO4 + 0.5M HCl and 0.5 M HCl at temperatures of 25, 35 and 45 ÂC. Additionally, a microstructural characterization of this material was performed by quantification phase through optical microscopy, morphological analysis by Scanning and Transmission Electron Microscopy, coupled techniques Electron backscattered diffraction and Electron Energy Dispersion Spectroscopy, and Vickers microhardness measures. The microstructural and morphological characterization confirmed the presence of sigma phase in super duplex stainless steel 1C and that the amount of this phase increases with aging heat treatment time. This phase showed a greater microhardness than the ferrite and austenite phases. The aging heat treatment influenced negatively on corrosion resistance of the steel when exposed to acidic solutions of H2SO4 and HCl at 25 ÂC, mainly when these are present in the same solution, probably due to their low pH. In this solution (H2SO4 + HCl), both increasing the aging heat treatment time as well as the temperature (35 and 45 ÂC), affects negatively the sample corrosion resistance, decreasing acoording a higher content of this phase.
Os aÃos inoxidÃveis super duplex sÃo frequentemente utilizados em aplicaÃÃes onde Ã necessÃria uma grande resistÃncia mecÃnica, combinada a resistÃncia Ã corrosÃo, especialmente em ambientes de elevada agressividade. Entretanto, ao sofrer determinados processos de fabricaÃÃo (conformaÃÃo a quente ou soldagem, por exemplo), pode ocorrer Ã precipitaÃÃo de fases indesejÃveis, que causam tanto reduÃÃo de propriedades mecÃnicas quanto afetam a resistÃncia Ã corrosÃo. Particularmente entre 700 ÂC e 900 ÂC pode ocorrer Ã formaÃÃo de fase sigma. Esta fase Ã responsÃvel pela reduÃÃo da resistÃncia Ã corrosÃo e mecÃnica dos aÃos inoxidÃveis super duplex. Por meio de simulaÃÃo computacional no programa Thermo-CalCÂ, o diagrama de fases do aÃo inoxidÃvel super duplex ASTM A890 GRAU 1C apresentou maior fraÃÃo precipitada desta fase na temperatura de 830 ÂC. Assim, o presente trabalho tem por objetivo avaliar a influÃncia do tempo de tratamento isotÃrmico de envelhecimento deste material, na resistÃncia Ã corrosÃo devido Ã formaÃÃo da fase sigma. A avaliaÃÃo da resistÃncia Ã corrosÃo foi realizada por meio do monitoramento do potencial de circuito aberto, impedÃncia eletroquÃmica e de ensaios de polarizaÃÃo potenciodinÃmica (ramo anÃdico) em soluÃÃo de H2SO4 0,5 M, H2SO4 0,5 M + HCl 0,5 M e HCl 0,5 M, nas temperaturas de 25, 35 e 45 ÂC. Adicionalmente, foi realizada a caracterizaÃÃo microestrutural desse material atravÃs de quantificaÃÃo de fases por microscopia Ãtica, anÃlise morfolÃgica por Microscopia EletrÃnica de Varredura e TransmissÃo, acoplados as tÃcnicas de DifraÃÃo de ElÃtrons Retroespalhados e Espectroscopia de DispersÃo de Energia de ElÃtrons, alÃm de medidas de microdureza vickers. A caracterizaÃÃo microestrutural e morfolÃgica confirmou a presenÃa de fase sigma no aÃo inoxidÃvel super duplex 1C e que a quantidade desta fase aumenta com o tempo de tratamento tÃrmico de envelhecimento. Esta fase apresentou microdureza maior que as fases ferrita e austenita. O tratamento tÃrmico de envelhecimento influenciou de maneira negativa na resistÃncia a corrosÃo desse aÃo quando exposto a soluÃÃes Ãcidas de H2SO4 e HCl a 25Â C, principalmente quando este estÃo presentes na mesma soluÃÃo, devido provavelmente ao seu baixo pH. Nesta soluÃÃo (H2SO4 + HCl), tanto o aumento do tempo de tratamento tÃrmico de envelhecimento quanto o aumento da temperatura (35 e 45 ÂC), afetam negativamente na resistÃncia Ã corrosÃo do material estudado, diminuindo Ã medida que se tem um maior conteÃdo de fase sigma.

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Franzini, Otacilio Donisete [UNESP]. "Aplicação de laser pulsado Nd:YAG na soldagem do aço super duplex UNS S32750." Universidade Estadual Paulista (UNESP), 2016. http://hdl.handle.net/11449/146743.

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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.

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Franzini, Otacilio Donisete. "Aplicação de laser pulsado Nd:YAG na soldagem do aço super duplex UNS S32750 /." Ilha Solteira, 2016. http://hdl.handle.net/11449/146743.

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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

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Sawczen, Tiago. "Caracterização eletroquímica e proposta de metodologia para a determinação da temperatura crítica de pite de aços inoxidáveis super duplex UNS S32760." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/46/46136/tde-30092014-113605/.

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O Aço Inoxidável Super Duplex UNS S32760 é um aço de alta liga com estrutura composta por uma matriz ferrítica com ilhas austeníticas, em proporções aproximadamente iguais. Esta estrutura lhe confere boas propriedades como: resistência à corrosão, em particular à corrosão por pite e por fresta, excelentes propriedades mecânicas, boa soldabilidade, alta condutividade térmica, baixo coeficiente de expansão térmica e excelente tenacidade. Suas principais aplicações geralmente ocorrem em ambientes com alta concentração de cloreto, como por exemplo, em tubos para transporte de óleo e gás, equipamentos para transporte ou em contato com materiais rico sem cloretos, em tanques e vasos para a indústria química e petroquímica. Estas aplicações tornam importante a determinação da temperatura crítica de pite (TCP). A ASTM normatiza essa determinação com as normas G-150 e G-48, que abrangem aços inoxidáveis austeníticos comuns e ligas à base de níquel, não existindo uma condição especifica para o teste em aços super duplex. O objetivo deste trabalho é a caracterização eletroquímica e o desenvolvimento de uma metodologia para a determinação da temperatura crítica de pite de aços super duplex UNS S32760. Devido à falta de normatização para estes materiais uma combinação das normas ASTM G-48 e G-150 foi empregada neste trabalho. Utilizou-se como meio uma solução contendo FeCl3 6% e HCl 1%, em massa. Foram empregadas como técnicas medidas de potencial de circuito aberto em função do tempo de imersão, curvas de polarização potenciostática anódica, cronoamperometria, espectroscopia de impedância eletroquímica (EIE), microscopia ótica (MO), microscopia eletrônica de varredura (MEV) e espectroscopia por dispersão de energia (EDS). Foram realizados tratamentos dos dados experimentais, abordando-os de maneiras diferentes para que a melhor resposta fosse obtida na determinação da TCP das ligas. Duas amostras diferentes deste material foram estudadas, uma amostra comercial e uma amostra desenvolvida pelo laboratório de pesquisa e desenvolvimento da Villares Metals, com diferentes teores de cromo e molibdênio. Apesar da variação na composição química das amostras, nas análises por MEV e EDS, as mesmas se mostraram semelhantes, quando apenas polidas, apresentando os mesmos tipos de precipitado. A microscopia ótica possibilitou visualizar a diferença na proporção de fases entre as duas ligas e as características morfológicas das mesmas. Analisando mais detalhada e minuciosamente os dados eletroquímicos, foi determinado que o melhor valor de densidade de corrente a ser utilizada como parâmetro na determinação da TCP , é 25±5 µAcm-2. Utilizando este parâmetro foi mostrado que a TCP determinada é menor, quando comparada com a obtida pelas normas convencionais. A combinação das diferentes técnicas permite afirmar que a metodologia empregada determina de maneira bem mais precisa a TCP.
UNS S32760 super duplex stainless steel is a high alloy steel, containing a ferrítica matrix and austenitic islands as structure at equal proportions approximately. This structure results in good properties as high resistance to corrosion, particularly to pitting and crevice corrosion, excellent mechanical properties, good weldability, high thermic conductivity, low thermic expansion coefficient, and excellent tenacity. Their principal applications are in high chloride concentration media, for example in tubes for oil and gas, in transport equipment when in contact with high chloride concentration materials, tanks and vases for chemical and petrochemical industries. Due to these applications the evaluation of the pitting critical temperature is mandatory for these materials. G-150 and G-48 ASTM Standards are recommended for conventional stainless steels and nickel alloys, but there is not any specific standard for super duplex stainless steels. The main of this work is the characterization and the development of a methodology to evaluate the critical pitting temperature for USS S32760 super duplex stainless steels. Due to the absence of standard analyses for this materials, a combination of G-48 and G-150 standards were employed. The medium was 6% FeCl3 by mass and 1% HCl by mass solution. Open circuit potential measurements, anodic potentiostatic polarization curves, chronoamperometry, electrochemical impedance spectroscopy (EIS), optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS) were used as techniques. Different treatments for the experimental results were used in order to obtain the best value for TCP of these alloys. Two different samples of this material were studied: a commercial sample and a new composition developed at P&D Villares Metals industry, with different contents in chromium and molybdenum. The materials studied presented the same kinds of inclusions, according to SEM and EDS analyses. OM analysis showed the proportionality between the ferritic and austenitic phases and their morphological characteristics. The electrochemical studies suggest the 25 ± 5 µAcm-2 value for current density to be used in the CPT e valuation. The CPT obtained is lower when compared to those one using conventional standards. The combination of different techniques permits to conclude that the proposed methodology evaluates the CPT w ith higher precision.

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Oliveira, Caroliny Gomes de. "Assessment of susceptibility corrosion of stainless steel super duplex UNS S32750 (SAF 2507) AND UNS S32760 (ZERON100) using a EPR portable cell." Universidade Federal do CearÃ, 2014. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=13348.

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CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior
The great demand for techniques that can detect and determine the degree of susceptibility to corrosion motivated thedevelopment of a research project that resulted in the construction of a portable electrochemical cell that has been validated according to ASTM A262. The success of this technique for nondestructive evaluation has motivated the expansion of this technique to other materials and phenomena of precipitation. In this work it was evaluated the use of this EPR-DL portable cell used applied for assessing the susceptibility to corrosion in super duplex stainless steels UNSS32750 and UNSS32760.Those materials were heat treated at 475ÂC and 850ÂC at different time of creating different patterns precipitation of deleterious phases to be detected by the cell. The solutions used were: 2M H2SO4 +0.01 M KSCN +0.5 M NaCl (solution 1 ) and 2M H2SO4 +0.01 M KSCN +1.0 M NaCl (solution 2) and the speedsscanswerestudied: 1.67 mV / s , 3.0 mV / s and 6.0 mV / s. To prove the presence of deleterious phases precipitation and associate them with the electrochemical behavior presentedby the electrochemical cell, the sampleshad theirmicrostructuresanalyzedby optical microscopy (OM), scanning electron microscopy (SEM), and energy dispersive of X-ray spectroscopy (EDS). Also the consumption of ferrite magnetic phase was assessed with ferrite scope and performed Vickers hardness tests to analyze the increasing in hardness due to precipitation of deleterious phases. It was observed by OM, SEM / EDS, ferrite scope, EPR- DL and Vickers hardness, that as much longer the heat treatment the amount of deleterious phasesprecipitated was increased. The results demonstrated that the solution 2 was the most effective in detecting susceptibility to corrosion, being capable to detect the depletion of chromium even in conditions of low precipitation and obtaining greater values of Ir/Ia as the scanning speed was reduced to the same condition of heat treatment. All these analyzes has confirmed that the EPR- DL portable cell was able to detect the depletionof chromium caused by the presence of deleterious phases, and reflecting the degree of susceptibility to corrosion of SDSS which were studied
A grande demanda por tÃcnicas que consigam detectar e determinar o grau de susceptibilidade Ã corrosÃo motivou o desenvolvimento de um projeto que resultou na construÃÃo de uma cÃlula portÃtil para a determinaÃÃo do fenÃmeno da sensitizaÃÃo em aÃos inoxidÃveis austenÃticos, a qual foi validada seguindo a norma ASTM A262. O sucesso desta tÃcnica nÃo destrutiva em campo tem motivado a expansÃo dessa tÃcnica de anÃlise para outros materiais e fenÃmenos de precipitaÃÃo. O presente trabalho apresenta a avaliaÃÃo dessa cÃlula portÃtil utilizada em ensaios de EPRâDL para avaliaÃÃo de susceptibilidade a corrosÃo nos AISD UNS S32750 e UNS S32760. Estes materiais foram tratados termicamente a 475ÂC e a 850ÂCem diferentes tempos, criando diferentes padrÃes de precipitaÃÃes de fases deletÃrias para serem detectados pela cÃlula. As soluÃÃes utilizadas foram: 2M de H2SO4+0,01M de KSCN+0,5 M de NaCl (soluÃÃo 1) e 2M de H2SO4+0,01M de KSCN+1,0 M de NaCl (soluÃÃo2) e as velocidades de varreduras estudadas foram de 1,67mV/s, 3,0mV/s e 6,0mV/s. Para comprovar a presenÃa da precipitaÃÃo de fases deletÃrias e associÃ-las ao comportamento eletroquÃmico apresentado pela cÃlula, as amostras tiveram suas microestruturas analisadas por microscopia Ãtica (MO), microscopia eletrÃnica de varredura (MEV),e ensaios com energia dispersiva de raios-X (EDS).TambÃm foram avaliados o consumo da fase ferrita por analise magnÃtica com ferritoscÃpio e realizados ensaios de dureza Vickers para analisar o aumento da dureza devido a precipitaÃÃo das fases deletÃrias. Foi observado por MO, MEV/ EDS, ferritoscÃpio, EPR-DL e por dureza Vickers que quando maior o tempo de tratamento tÃrmico maior foi a quantidade de fases deletÃrias precipitadas. Quanto maior foi o nÃvel de precipitaÃÃo, maiores foram os valores de Ir/Ia e maiores valores de dureza foram obtidos. Os resultados mostraram que a soluÃÃo 2 foi a mais eficaz na detecÃÃo da susceptibilidade a corrosÃo, conseguindo detectar o empobrecimento de cromo mesmo em condiÃÃes de baixa precipitaÃÃo, e obtendo maior valores de Ir/Ia conforme a velocidade de varredura era diminuÃda para uma mesma condiÃÃo de tratamento. Todas essas anÃlises comprovaram que a cÃlula portÃtil de EPR- DL foi capaz de detectar o empobrecimento de cromo ocasionado pela presenÃa das fases deletÃrias, e refletindo o grau de susceptibilidade a corrosÃo dos AISD estudados.

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INVERNIZZI, BRUNO P. "Soldagem circunferencial do aço inoxidável super duplex UNS S32750 pelo processo MIG com controle CMT®." reponame:Repositório Institucional do IPEN, 2017. http://repositorio.ipen.br:8080/xmlui/handle/123456789/28014.

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Neste trabalho foram realizados experimentos de soldagem circunferencial em tubos de aço inoxidável super duplex UNS S32750, com diâmetros de 19,05 mm e 48,20 mm. Foram executadas soldas utilizando-se diversos parâmetros de soldagem num equipamento MIG com controle CMT® Cold Metal Transfer. Os cordões de solda foram avaliados por inspeção visual e dimensional, além dos ensaios de tração e microdureza Vickers, bem como a análise microestrutural em conjunto com análise de precipitação de fases, a qual foi realizada em acordo com a prática A da norma ASTM A923, e ensaio de corrosão conforme a prática A da norma ASTM G48 em conjunto com a norma ASTM A923. Os resultados indicaram que a soldagem do tubo com diâmetro de 19,05 mm apresentou cordão de solda com dimensões inaceitáveis conforme norma, tendo sido esta condição atribuída a utilização de um elevado diâmetro do arame para as condições (parâmetros) usadas de soldagem. A soldagem do tubo com diâmetro de 48,20 mm apresentou falta de penetração nas condições empregadas, quando soldado pelo processo CMT® convencional. No caso da utilização do CMT® combinado com arco pulsado, em condições que geraram maior aporte de calor durante a soldagem, assim obteve-se penetração total da junta e acabamento superficial adequado. Os resultados indicaram que a soldagem utilizando o processo CMT® combinado com arco pulsado, nas condições (parâmetros) empregados geraram bom acabamento superficial, aliado propriedades mecânicas compatíveis, atendendo exigências de normas, bem como uma microestrutura balanceada e alta resistência à corrosão.
Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

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Invernizzi, Bruno Pizol. "Soldagem circunferencial do aço inoxidável super duplex UNS S32750 pelo processo MIG com controle CMT®." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-23052017-152804/.

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Neste trabalho foram realizados experimentos de soldagem circunferencial em tubos de aço inoxidável super duplex UNS S32750, com diâmetros de 19,05 mm e 48,20 mm. Foram executadas soldas utilizando-se diversos parâmetros de soldagem num equipamento MIG com controle CMT® Cold Metal Transfer. Os cordões de solda foram avaliados por inspeção visual e dimensional, além dos ensaios de tração e microdureza Vickers, bem como a análise microestrutural em conjunto com análise de precipitação de fases, a qual foi realizada em acordo com a prática A da norma ASTM A923, e ensaio de corrosão conforme a prática A da norma ASTM G48 em conjunto com a norma ASTM A923. Os resultados indicaram que a soldagem do tubo com diâmetro de 19,05 mm apresentou cordão de solda com dimensões inaceitáveis conforme norma, tendo sido esta condição atribuída a utilização de um elevado diâmetro do arame para as condições (parâmetros) usadas de soldagem. A soldagem do tubo com diâmetro de 48,20 mm apresentou falta de penetração nas condições empregadas, quando soldado pelo processo CMT® convencional. No caso da utilização do CMT® combinado com arco pulsado, em condições que geraram maior aporte de calor durante a soldagem, assim obteve-se penetração total da junta e acabamento superficial adequado. Os resultados indicaram que a soldagem utilizando o processo CMT® combinado com arco pulsado, nas condições (parâmetros) empregados geraram bom acabamento superficial, aliado propriedades mecânicas compatíveis, atendendo exigências de normas, bem como uma microestrutura balanceada e alta resistência à corrosão.
This study carried out circumferential welding experiments in UNS S32750 Super Duplex Stainless Steel tubes using diameters of 19,05 mm and 48,20 mm. Welds were performed using various welding parameters on a MIG machine with Cold Metal Transfer® CMT control. The weld joints were evaluated by visual and dimensional inspection in addition to the Vickers microhardness and traction tests, as well as the microstructural analysis in conjunction with phase precipitation analysis, which was performed according to practice A of ASTM A923, and corrosion test in accordance with practice A of ASTM G48 in conjunction with ASTM A923. The results indicated that welds performed in pipes with a diameter of 19.05 mm showed a weld joint with unacceptable dimensions according to the standard, this condition being attributed the use of a high wire diameter for the welding conditions used. Welding performed for pipes with a diameter of 48.20 mm showed a lack of penetration under the conditions employed when welded by the conventional CMT® process. In the case of the use of CMT® combined with pulsed arc, under conditions that generated greater heat input during welding, this resulted in total penetration of the joint and adequate surface finish. The results indicated that welding using the CMT® process combined with pulsed arc, under the conditions (parameters) employed generated good surface finish, combined mechanical properties, meeting standards requirements, as well as a balanced microstructure and high resistance to corrosion.

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Andersen, Kjetil. "HISC in Super Duplex Stainless Steels : A study of the relation between microstructure and susceptibility to hydrogen induced stress cracking." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-22418.

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Testing of susceptibility to hydrogen induced stress cracking (HISC) in two 25% Cr Super Duplex Stainless Steels (SDSS) has been carried out. These were a forged material and a hot isostatically pressed (HIP) material with austenite spacing 51.5 µm and 12.9 µm, respectively. The tests were carried out on both smooth and notched samples by stepwise increasing load in Cortest proof rings on hydrogen pre-charged samples until fracture. The fracture surfaces were examined in scanning electron microscopes (SEM) and the hydrogen contents were measured. The microstructures of the materials were examined with the electron backscattered diffraction technique (EBSD) and assessed in relation to the results from the HISC testing.The results indicated that both SDSS materials are prone to HISC and that the HIP material has a higher threshold for HISC. The fracture surface on samples of both materials showed features indicating reduced ductility from HISC. The HIP samples indicated ductile fracture in the centre, implying that hydrogen influence was primarily in close proximity of the sample surfaces. This observation, and considerably higher hydrogen content measured in the forged material, indicates slower hydrogen diffusion in the HIP material than in the forged material.The results obtained were discussed against the literature reviewed and compared to the requirements in DNV-RP-F112. Indication of low temperature creep was observed on smooth samples by relaxation of the load determining ring deflection. The results from smooth samples indicated a threshold for HISC fracture (after one day of low temperature creep) at 112.6% ± 3.9% of yield strength (YS) and 104.8% ± 3.1% for HIP and forged material, respectively. No ring relaxation occurred for the notched samples. Therefore the results from these samples indicated higher threshold for HISC than the smooth samples, namely at 117.1% ± 2.2% and 113.8% ± 2.2\% of YS for HIP and forged samples, respectively.

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Oliveira, Willian Rafael de. "INFLUÊNCIA DOS PARÂMETROS DE IMPLANTAÇÃO IÔNICA POR IMERSÃO EM PLASMA NA EFICIÊNCIA DA NITRETAÇÃO DO AÇO INOXIDÁVEL SUPER DUPLEX." UNIVERSIDADE ESTADUAL DE PONTA GROSSA, 2016. http://tede2.uepg.br/jspui/handle/prefix/858.

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This work aimed at study the correlation of variables in a plasma immersion ion implantation (PIII) system, as well as their synergistic combination for the nitriding of the UNS S32750 super duplex stainless steel ( SD 2507). The research comprised two phases, as follows. (i) Study of the system. The interconnection of variables, namely voltage (V), pulse width (L), frequency (f) and current (I), were systematically analyzed with respect to the cathode heating. A mathematical formulation was proposed for the ion average energy and the substrate temperature, which took into consideration the energy conservation in the system, and the basic theories for plasma and sheaths and the ion interaction with matter. Hereafter, such model is thought to be experimentally demonstrated, allowing inferring the actual PIII fraction of energy that is converted to heat. (ii) N-PIII of the SD. Mirror-like samples were nitrided under different V, f and L combinations, leading to the temperatures 295, 325, 355 and 400 oC. The surface characterization methods were the optical, field emission electron, and atomic force microscopies, X-ray diffraction, energy dispersive X-ray spectroscopy, backscattered electron diffraction, and instrumented indentation. The austenite and ferrite fraction in the as received material amounted to 43,7 % and 56,3 %, respectively. After nitriding, the modified layers were 0,5-1,5 m thick. Up to 355 ºC, the expanded phase N was produced in originally austenite grains, whereas Fe2-3N e Fe4N precipitates were formed in ferrite grains. The hardness profiles were similar among different temperatures and between the two phases in the same sample. However, in ferritic regions, the mechanism for plastic deformation changed from ductile to brittle. In the 400 ºC treatments, only N was formed. Finally, a correlation for the production of the expanded phase in PIII and the mean pulse energy Ei was attained, given by and . Where IN and I are the integrated intensities of diffraction peaks for austenite and expanded austenite, respectively.
O objetivo deste trabalho foi estudar o comportamento de um sistema de implantação iônica por imersão em plasma (PIII: “plasma immersion ion implantation”), em função de suas variáveis, bem como a influência destas na nitretação de superfícies do aço super duplex UNS S32750 (ou SD 2507). O trabalho foi dividido em dois momentos, como segue. (i) Estudo do sistema. O comportamento das variáveis associadas à implantação iônica, especificamente tensão (V), largura de pulsos (L), frequência (f) e corrente (I), foi sistematicamente analisado com relação ao aquecimento do cátodo. Com base na conservação de energia, física de plasmas e bainhas catódicas e interação de íons com a matéria, propôs-se uma formulação matemática relacionado a energia média dos íons à temperatura do substrato, a qual poderá, futuramente, ser posta à prova experimental, mensurando-se a fração de energia que é, de fato, transformada em calor. (ii) Nitretação por PIII do SD. Amostras com superfície especular foram nitretadas sob diferentes combinações de V, f e L, em temperaturas de 295, 325, 355 e 400 oC. As superfícies foram caracterizadas por métodos de microscopia (ótica, eletrônica com efeito de campo, de força atômica), difração de raios X, espectroscopia de raios X por energia dispersiva, difração de elétrons retroespalhados, e indentação instrumentada. O SD apresenta estrutura cristalina de austenita e ferrita na proporção de 43,7/56,3. A nitretação produziu camadas modificadas com espessura de 0,5 a 1,5 m. Observou-se, nos tratamentos até 355 ºC, a formação da fase expandida N nos grãos que originalmente eram austenita, e de precipitados de nitretos -Fe2-3N e -Fe4N em grãos de ferrita. Embora não houve diferenças significativas nos perfis de dureza, tanto entre as temperaturas quanto entre as fases em uma mesma amostra, o mecanismo de deformação plástica nas regiões ferríticas transitou de dúctil para frágil. Nas nitretações em 400 ºC, houve apenas a formação de N. Finalmente, determinou-se que a obtenção da fase expandida por PIII no SD se relaciona com a energia média por pulso Ei por e . Onde I e I são as intensidades integradas dos picos de difração da austenita expandida e da austenita, respectivamente.

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Rossitti, Sergio Mazzer. "Efeito do Nióbio na Microestrutura e nas Propriedades Mecânicas do Aço Inoxidável Superduplex Fundido SEW 410 W.Nr. 1.4517." Universidade de São Paulo, 2000. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-26102005-142234/.

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A produção economicamente viável dos aços inoxidáveis duplex, pressupõe a utilização de sucatas e retornos de ligas contendo altos teores de elementos como Cr, Ni e Mo. O aproveitamento destes materiais pode entretanto, introduzir na composição química outros elementos não previstos pela norma do material sendo produzido. Este trabalho estudou a influência do Nb na microestrutura e nas propriedades mecânicas do aço inoxidável superduplex fundido SEW 410 W. Nr. 1.4517, bem como sobre as etapas de fabricação de um produto fundido. Os teores de Nb estudados foram 0%, 0,2%, 0,5% e 1,5% (% em peso). Foi dado ênfase às microestruturas e propriedades no estado bruto de fundição, após tratamento térmico de solubilização e finalmente, após envelhecimento das amostras solubilizadas. Foram utilizadas diversas técnicas de avaliação microestrutural: microscopia ótica, metalografia quantitativa, microscopia eletrônica de varredura e de transmissão, análise química de microregiões com microssonda eletrônica, ensaios magnéticos via ferritoscópio e ensaios dilatométricos. Os ensaios mecânicos realizados foram: dureza, ensaio de tração e ensaio Charpy. A análise dos resultados demonstrou que o Nb causou uma sensível alteração na microestrutura e nas propriedades mecânicas da liga, dificultando o processo de produção de uma peça fundida.
To produce duplex stainless steel in an economic way it is necessary to use scrap and process returns containing high Cr, Ni and Mo contents. This procedure can result in an unexpected alloy chemical composition with some elements not included in the material standard. This work studied the Nb influence on the microstructure and mechanical properties of cast super duplex stainless steel SEW 410 W. Nr. 1.4517, as well as the influence over the fabrication process of a casting. The Nb contents studied were 0%, 0,2%, 0,5% and 1,5% (weight %). Emphasis was given to the microstructures and mechanical properties in as cast condition, after solution heat treatment and finally after aging of previous solution heat treated samples. Several microstructural analysis techniques were used: optical microscopy, quantitative metallography, scanning electron microscopy, transmission electron microscopy, chemical microanalysis using energy dispersive spectrometry, magnetic phase detection using feritscope and dilatometry. The mechanical testing realized were hardness testing, tension testing and Charpy impact testing. Results analysis demonstrated that Nb caused an appreciable change on microstructure and mechanical properties of the material, making difficult the fabrication process of a casting.

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Hutchings, D. "Hydrogen embrittlement of duplex stainless steel." Thesis, University of Manchester, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.631722.

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Duplex stainless steels (DSS's) are frequently used in oil and gas production and are subsequently subjected to cathodic protection. There is now growing concern about the cathodic evolution of hydrogen produced from this protection system, which may diffuse into the alloy and cause an embrittled condition. DSS's have a microstructure that is a mixture of austenite and ferrite and combines the advantages of these grades, whilst minimising their deficiences. In this research, Zeron 100 DSS was studied in six conditions to investigate the effects of hydrogen embrittlement (HE) on the various strengths and microstructures. The six conditions wer~ as follows: as-received, cold worked, age-hardened (475°C embrittlement), high temperature heat treated, rod and powder. To simulate service environments, 3.5% wt NaCI solution at ambient temperature with an applied potential of -1.1 V (SCE) was used. The effect of pre-charging for up to 550 hours at 80°C was also investigated. Test methods included slow strain rate testing (SSRT), monitoring of transient crack propagation (TCP) using circumferentially notched tensile specimens using a DC potential drop method, acoustic emission CAE) and some conventional bolt loaded fracture mechanics specimens. Test results were correlated with the varying microstructures and environmental conditions and consisted of mechanical properties, threshold crack growth including transient effects and AE data. In this work transgranular cleavage cracks were obtained in the susceptible ferrite phase as a direct result of HE; the depth of these cracks implied a high hydrogen concentration throughout the specimen. The austenite failed by ductile tearing and acted as a physical barrier to the propagation of cleavage cracks. As a result of SSR testing the best material was found to be the powder material; the fine equally dispersed austenite phase caused a lowering of the effective K value. The worst material was the high temperature heat treated type because it contained more ferrite (11:1 72%). The age-hardened material was also susceptible because of the hard and brittle ex' phase. However, regardless of the environment the UTS remained virtua]]y unchanged for each individual material, indicating that most cracking occurred in the post-UTS stage of the test. With the TCP test a lowering of the fracture load was found when an HE environment was used; daldt vs Kq curves were produced, however the DC potential drop equipment could not accurately measure crack growth because of the bridging effect of the austenite phase. The most susceptible microstructures were again the age-hardened and heat treated types. The hydrogen evolution reaction (HER) was also investigated by creating a fresh surface on the as-received DSS and studying the changes in the HER. This work showed that the effect of scratching is irreversible. Also the oxide film can not be totaHy reduced electrochemica]]y and only mechanical methods can remove the oxide films entirely. Fina]]y a means of detecting "475°C embrittlement" of DSS's was investigated using an electrochemical technique in 5M HCI. i-E curves were produced which showed the reactivation of the ferrite and austenite phases in the as-received material. By age-hardening at 475°C the two reactivation peaks merged.

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36

Santos, Poliana Rochele F?lix dos. "Estudo da viabilidade t?cnica para obten??o de superf?cie duplex em a?o inoxid?vel martens?tico AISI 410 atrav?s do processo de deposi??o a plasma por gaiola cat?dica." Universidade Federal do Rio Grande do Norte, 2013. http://repositorio.ufrn.br:8080/jspui/handle/123456789/12773.

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The technique of plasma nitriding by the cathode cage mainly stands out for its ability to produce uniform layers, even on parts with complex geometries. In this study, it was investigated the efficiency of this technique for obtaining duplex surface, when used, simultaneously, to nitriding treatment and thin film deposition at temperatures below 500?C. For this, were used samples of AISI 41 0 Martensitic Stainless Steel and performed plasma treatment, combining nitriding and deposition of thin films of Ti and/or TiN in a plasma atmosphere containing N2-H2. It was used a cathodic cage of titanium pure grade II, cylindrical with 70 mm diameter and 34 mm height. Samples were treated at temperature 420?C for 2 and 12 hours in different working pressures. Optical Microscopy (OM), Scanning Electron Microscopy (SEM) with micro-analysis by Energy Dispersive Spectroscopy (EDS), X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM) and analysis of Vickers Microhardness were used to investigate coating properties such as homogeneity and surface topography, chemical composition, layer thickness, crystalline phase, roughness and surface microhardness. The results showed there is a direct proportionality between the presence of H2 in plasma atmosphere and the quantity of titanium in surface chemical composition. It was also observed that the plasma treatment at lowpressure is more effective in formation of TiN thin film
A t?cnica de nitreta??o a plasma por gaiola cat?dica vem se destacando, principalmente, pela sua capacidade de produzir camadas uniformes mesmo em pe?as com geometria complexa. Neste trabalho, investigou-se a efici?ncia desta t?cnica para obten??o de superf?cie duplex, quando utilizada, simultaneamente, para tratamento de nitreta??o e deposi??o de filmes finos em temperaturas inferiores a 500?C. Para tal, foram utilizadas amostras do a?o inoxid?vel martens?tico AISI 410 e realizados tratamentos a plasma, combinando a nitreta??o e deposi??o de filmes finos de Ti e/ou TiN, em uma atmosfera contendo N2-H2. Foi utilizada uma gaiola cat?dica de tit?nio puro grau II em forma cil?ndrica, com 70 mm de di?metro e 34 mm de altura. As amostras foram tratadas numa temperatura de 420?C, com dura??o de 2 e 12 horas e em diferentes press?es de trabalho. Microscopia ?ptica (MO), Microscopia Eletr?nica de Varredura (MEV) com microan?lise por Espectroscopia de Energia Dispersiva (EDS), Difra??o de Raios-X (DRX), Microscopia de For?a At?mica (MFA) e ensaio de Microdureza Vickers foram empregados para investigar as propriedades do revestimento, tais como homogeneidade e topografia superficial, composi??o qu?mica, espessura da camada, fases cristalinas, rugosidade e microdureza superficial. Os resultados mostraram existir uma proporcionalidade direta entre a presen?a de H2 na atmosfera do plasma e a quantidade do elemento qu?mico tit?nio na composi??o qu?mica superficial. Observou-se, tamb?m, que o tratamento a plasma em baixa press?o ? mais eficaz na forma??o do filme fino de nitreto de tit?nio

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37

Sture, Henrik. "Integrity Evaluation of Duplex Stainless Steel Flanges." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for produktutvikling og materialer, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-19055.

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Duplex stainless steel flanges are normally forged to form, as required by the ASTM A182/A182M standard, but may also potentially be machined directly from forged stainless steel bar. In order to evaluate the integrity of such flanges, axisymmetric elastic-plastic finite element models have been developed, considering static effects such as bolt load and internal pressure. Additionally, tensile testing of a sample forged bar (UNS S31803) has been conducted. The stress distribution in a flange during gasket seating and operating conditions has been determined, as well as the degree of plastic strain caused by the bolt loads. The maximum stresses have been found to be around the same values as the minimum yield strength requirement of the studied material (UNS S31803), and the location of the maximum stress concentrations have been identified as the gasket groove. The tensile tests of the forged bar (UNS S31803) have shown that the yield and tensile strength properties are considerably higher than the standardized minimum requirements. The elastic modulus of the forged bar has also been determined, and was found to be lower than anticipated in the axisymmetric models. Some specimens have also been found to exhibit highly non-linear elastic properties.

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38

Dalton, John Christian. "Surface Hardening of Duplex Stainless Steel 2205." Case Western Reserve University School of Graduate Studies / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=case1480696856644048.

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39

Marrow, Thomas James. "Fatigue mechanisms in an embrittled duplex stainless steel." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386998.

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40

Farrell, J. "Hyperbaric welding of duplex stainless steel pipelines offshore." Thesis, Cranfield University, 1996. http://dspace.lib.cranfield.ac.uk/handle/1826/4513.

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Three duplex stainless steels (Avesta 2205, Sandvik SAF2507 and Zeron 100) were successfully welded automatically at a range of pressures from 1 to 32bar. The gas tungsten arc (GTA) welding process was chosen as it allows a high degree of control to be exercised during welding. Initial autogenous bead on plate welds established the effects of pressure on the welding process and allowed the process parameters to be determined for subsequent experiments. Analysis of the effects of pressure on the weld thermal cycle showed that at higher pressures the precipitation of phases deleterious to the weld quality was less likely than at ambient pressure. It was also found that the arc melting efficiency increased as the pressure increased, which was taken into account when the process parameters for the joints were selected. A V-butt design with a 'land' on each side was chosen for the joints to counteract any tendency for the welding arc to wander at higher welding pressures. The root welds were performed using pulsed current welding techniques to overcome the difficulties in achieving consistent penetration that were encountered when welding at lower pressures. It was found that by employing standard welding consumables commonly used for welding duplex steels at ambient pressure satisfactory austenite-ferrite phase balances could be achieved in the weld metal at all pressures. Metallographic examination of the welds showed that the joints did not have any microstructural complications that were related to pressure and mechanical testing revealed that, in terms of impact toughness, the weld metal and heat affected zone (HAZ) performed as well as, if not better than, the parent plate material. This work shows that welding of duplex stainless steels using the hyperbaric welding method is a viable option for subsea operations up to a depth of at least 320m, automated hyperbaric welding being advantageous at depths greater than 40m.

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41

Haddad, Naseem Issa Abdallah. "The development of microstructure in duplex stainless steel welds." Thesis, University of Cambridge, 1990. https://www.repository.cam.ac.uk/handle/1810/221890.

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42

Sieurin, Henrik. "Fracture toughness properties of duplex stainless steels." Doctoral thesis, Stockholm, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3964.

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43

Iversen, Torunn Hjulstad. "Intragranular Chromium Nitride Precipitates in Duplex and Superduplex Stainless Steel." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18904.

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Intragranular chromium nitrides is a phenomenon with detrimental effects on material properties in superduplex stainless steels which have not received much attention. Precipitation of nitrides occurs when the ferritic phase becomes supersaturated with nitrogen and there is insufficient time during cooling for diffusion of nitrogen into austenite. Heat treatment was carried out at between 1060◦C and 1160◦C to study the materials susceptibility to nitride precipitation with varying heat treatment temperature, nitrogen content and microstructure. Microhardness tests and Charpy v-notch tests were also carried out to investigate the nitrides effect on material properties. No standard method of quantification of nitrides exist. A method of quantifying the precipitation based on area fraction of nitrides was therefore introduced. The results show an increased amount of nitride precipitation with increased heat treatment temperature. A coarse microstructure with a large austenite spacing was found to promote higher fractions of nitride precipitation while nitrogen content was found to affect the amount of precipitation in less extent. The intragranular nitrides cause precipitation hardening in the ferrite and the precipitation was found to be at its most severe in the center of the ferritic regions, with precipitation free zones close to the phase boundaries. The microhardness of the phase was affected accordingly, with increasing hardness towards the center. Charpy v-notch test results show that nitride precipitation causes an embrittlement of the steel while intragranular secondary austenite improves the impact toughness of the material as it shortens the dif- fusion distance of nitrogen, decreasing the materials susceptibility to intragranular nitride precipitation.

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44

McKenzie, S. G. "The effect of platinum group metals on duplex stainless steel." Thesis, Imperial College London, 1985. http://hdl.handle.net/10044/1/37782.

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45

Ávila, Braz Thaís. "Shrinkage Calculation in the Continuous Casting of Duplex Stainless Steel." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-76516.

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46

Saliba, Najib. "Structural behaviour of lean duplex stainless steel welded I-sections." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/39853.

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Despite growing interest in the use of stainless steel in the construction industry and the development of a number of national and regional design codes, stainless steel is often regarded as only suitable for specialised applications. This is attributed largely to the high initial material cost associated with the most commonly adopted austenitic grades of stainless steel, as well as some conservatism embedded in current stainless steel guidance. A recently developed grade, known as lean duplex stainless steel (EN 1.4162), possesses higher strength than the common austenitic grades and has a lower cost, along with good corrosion resistance and adequate weldability and fracture toughness. The structural performance of lean duplex stainless steel remains relatively unexplored to date with only a few studies having been performed. The main aim of this study is to examine the structural behaviour of lean duplex stainless steel welded I-sections, and to assess the applicability of the current European stainless steel design guidance. As part of this research, a total of fifty two material tests, four stub column tests, eight 3-point and 4-point bending tests, eight continuous beam tests and nine shear buckling tests were carried out. The experimental programme was complemented by a parallel numerical investigation, in which finite element models were initially validated against the test results and subsequently used for parametric studies. These test and numerical results were used in conjunction with existing test data on stainless steel welded I-sections to characterise the basic material properties, assess the codified slenderness limits for cross-section classification, investigate the applicability of plastic design to indeterminate stainless steel structures, and establish new shear resistance design equations for stainless steel plate girders. Based on the findings, it was concluded that the present European design provisions can be safely applied to lean duplex but are rather conservative in some areas. To rectify this, modifications have been proposed for cross-section classification, plastic design and shear resistance calculations. These proposals, together with additional developments to the strain based continuous strength method of design, are suitable for incorporation into future revisions of Eurocode 3.

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Bhattacharya, Ananya. "Stress corrosion cracking of duplex stainless steels in caustic solutions." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26491.

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Thesis (Ph.D)--Materials Science and Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Singh, Preet M.; Committee Member: Carter, W. Brent; Committee Member: Gokhale, Arun, M.; Committee Member: Neu, Richard; Committee Member: Sanders, Thomas H., Jr.. Part of the SMARTech Electronic Thesis and Dissertation Collection.

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48

Elsherief, Ahmed Fathy Abd Elshafi. "The structure, mechanical and corrosion properties of duplex stainless weldments." Thesis, University of Southampton, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303482.

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49

Olden, Vigdis. "FE modelling of hydrogeninduced stress crackingin 25% Cr duplex stainless steel." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for produktutvikling og materialer, 2008. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-5026.

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50

Payares, Rios de Asprino M. C. "Numerical modelling of optimum microstructure behaviour in duplex stainless steel weldments." Thesis, Swansea University, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638433.

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A comprehensive study of DSS SAF 2205 weldments and nature of weld metal and heat-affected zones has been undertaken. Several DSSs SAF 2205 welds were fabricated using GMAW welding process at different welding conditions. The investigation focuses on the effect of the welding parameters are current, arc voltage, welding speed and heat input on the weld geometry, microstructure and mechanical properties. Also, the technique of the determination of “Response Surface” for the welding parameters was focused to optimise the effects on them each dependent. Variable. All weldments had the UTS, the yield strength and elongation in the range of weld mechanical according to ASTM A240. The welding parameters appeared to have much effect on the tensile properties of DSS weldments tested along transverse direction than the weldment tested along rolling direction. The hardness values vary with welding parameters employed. The trends show that HAZ hardness is slightly lower than base metal when 0.53 to 1.19 kJ/mm is used. However, the hardness in WM is higher than base metal for welding conditions with HI lower than 1.30 kJ/mm. DSS weldments showed no ductile to brittle transition. The fracture location for weld TST with head-off varied between HAZ and base metal. On the contrary, the fracture location along LT was generally at the base metal. SEM photographs shows that the mode of fracture of DSS welds is because microvoids coalescence (simples). Hence the fracture is ductile in DSS specimens. AS the heat input increases the simple size also increases.

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