AgÃncia Nacional do PetrÃleo / FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico / Os aÃos inoxidÃveis duplex possuem boas propriedades mecÃnicas e excelente resistÃncia à corrosÃo, aumentando seu uso em ambientes agressivos. Estas caracterÃsticas os fazem muito utilizados principalmente na indÃstria quÃmica e petroquÃmica. Geralmente, a fabricaÃÃo e reparo destes equipamentos envolvem operaÃÃes de soldagem, sendo que à muito importante avaliar a influÃncia dos parÃmetros de soldagem multipasse no balanceamento de fases, na microestrutura e microdureza. Primeiramente, foram realizadas soldagens em aÃo ASTM A516 Gr. 60 com eletrodo revestido AWS 2209-17, empregando diversas energias, variando a velocidade e corrente de soldagem. Foi feita a caracterizaÃÃo microestrutural atravÃs de microscopia Ãptica, quantificaÃÃo do teor de ferrita utilizando ferritoscÃpio e ensaio de microdureza para avaliar o metal de solda. Posteriormente, foram selecionadas as melhores condiÃÃes da etapa anterior para soldagem do aÃo inoxidÃvel duplex UNS S31803 para avaliar o efeito da energia de soldagem no balanceamento de fases, na microestrutura e microdureza no metal de solda e ZAC. Na Ãltima etapa foram realizadas soldagens em juntas de aÃo duplex, de modo a avaliar o efeito da energia de soldagem e restriÃÃo da junta no balanceamento de fases, microestrutura, microdureza e tenacidade do metal de solda e da ZAC. Foi verificada a influÃncia da energia de soldagem no teor de ferrita, possuindo comportamentos diferentes de acordo com os parÃmetros de soldagem. As microestruturas bÃsicas da austenita formada foram alotrimÃrfica, WidmanstÃtten e intragranular. Nas regiÃes com sobreposiÃÃo de passe houve maior quantidade de austenita no metal de solda e microestrutura mais refinada na ZAC. Foi observado que quanto maior a velocidade de soldagem, maior a quantidade de WidmanstÃtten. De forma geral, foi observado menor nÃvel de microdureza no metal de solda, principalmente nas condiÃÃes com maior quantidade de austenita WidmanstÃtten. A restriÃÃo da junta soldada influenciou no balanceamento de fases e na tenacidade da ZAC. NÃo houve efeito da energia de soldagem na tenacidade do metal de solda, possuindo nÃveis menores em relaÃÃo ao material como recebido / Duplex stainless steels show good mechanical properties and excellent corrosion resistance. These qualities are increasing their use in aggressive environments. Thus, these characteristics make them very used in chemical and petrochemical, mainly. Generally, the manufacture and repair of any industrial equipment involve welding operations, even though it is very important to evaluate the influence of multipass welding parameters in phase balances, microstructure and microhardness. Firstly, the shielded metal arc welding in steel ASTN A516 Gr. 60 with electrode AWS 2209-17 had been carried through with many energies, varying welding speed and current. Microstructural characterization by optic microscopy, quantification of ferrite content using ferritscope and microhardness test has being performed to evaluate the weld metal. After that, the best conditions of the last stage for welding of duplex stainless steel UNS S31803 had been chosen to evaluate the effect of the welding energy in phase balances, microstructure, and microhardness in the weld metal and HAZ. In the last stage, the weldings in joint of duplex steel had been carried through, in order to evaluate the effect of the welding energy and restriction of joint in phase balances, microstructure, microhardness and toughness of the weld metal and HAZ. The influence of the welding energy in the ferrite content was checked, although the behavior was different according to variation of the welding parameters. The basic microstructures of formed austenitic were allotriomoph, WidmanstÃtten and intragranular. Regions with pass overlapping presented greater amount of austenite in the weld metal and microstructure more refined in the HAZ. It was observed that increasing welding speed, greater is the amount of WidmanstÃtten austenite. In general, the increase of the amount of WidmanstÃtten austenite decreases level of microhardness in the weld metal. The restriction of the welded joint influenced in phase balances and toughness of the HAZ. There was not effect of the welding energy on toughness of the weld metal and this region occurred higher levels in relation to material as received

The master’s thesis is focused on the application of the technique of oriented foils in transmission electron microscopy. Dislocation structures were identified by this technique in both phases of polycrystalline austenitic-ferritic stainless steel SAF 2507 formed during low cycle fatigue at two plastic strain amplitudes ap. In individual grains the stress axis and the Schmid factors of active slip systems were determined. In austenitic grains, the planar structures were determined at both ap. In ferritic grains, the dislocation arrangement was different for the two observed ap. Individual screw dislocations and pile-up´s of edge dislocations were found at low ap = 1x10-4. Mixture of vein and wall dislocation structures were formed at high ap = 2x10-3. Observed dislocation structures were discussed in relation with the cyclic plastic response of the duplex stainless steel.

Material selection is an important step during the design process of an object. The goal is to produce an object to meet the requirement with minimum cost. During the recent years with discovery of oil and gas in deep water, oil and gas industry facing new challenges of handling corrosive material in seabed that gives more importance and criticality to material selection of equipment for this kind of application. Hydrogen sulfide (H2S), chloride and carbon dioxide (CO2) have made the big challenges for material that handle corrosive fluids in the seabed.This report presents a brief review of material selection for two parts of deepwater gate valve, Body and Gate. It is mostly focused on mechanical properties and required corrosion resistance. Ferritic alloys with low PRE numbers and low mechanical properties and also austenitic alloys with low yield strength are not a proper option for this case. Alloy 2205 is the most common stainless steel which is used in deep water gate valve production. There are other alloys in duplex group that show better mechanical and chemical properties than alloy 2205 but because of their high expense are not used by industries.

The thesis work consists of two parts. First, the development of two-dimensional numerical models of a Bridgman unidirectional solidification furnace, and second, the construction work of the furnace at KTH. The aim is to build a Bridgman furnace which is capable of close control over temperature gradient and growth rate such that the solidification structures of a duplex stainless steel (SAF2507) could be replicated at a laboratory scale for different cooling rates.Two numerical models of Bridgman furnace are created using COMSOL Multiphysics. The models are used as predictive tools to simulate the locations of solidification front and the temperature gradients at the solidification fronts, which are parameters difficult to access during experiments. Different hot zone temperatures of the furnace (1500~1550 °C) and different sample pulling rates (0.5~10 mm/s) are studied in simulations. The major finding from modeled results is that the temperature gradient of the sample at the solidification fronts range from 5 ~ 17 K/mm, which are lower than the furnace temperature gradient of ~50 K/mm. The corresponding steady-state cooling rates range between 5 ~ 85 K/s. The next step is to validate the models with experimental temperature profiles of the furnace, and decide whether the furnace design should be modified to achieve the cooling rates of interests. / Examensarbetet består av två delar. Först utvecklingen av tvådimensionella numeriska modeller av en Bridgman enkelriktad stelningsugn, och för det andra konstruktionsarbetet för ugnen vid KTH. Syftet är att bygga en Bridgman-ugn som har förmåga att kontrollera temperaturgradienten och tillväxthastigheten så att stelningsstrukturerna i ett duplex-rostfritt stål (SAF2507) skulle kunna replikeras i laboratorieskala för olika kylningshastigheter. Två numeriska modeller av Bridgman-ugnen skapas med COMSOL Multiphysics. Modellerna används som prediktiva verktyg för att simulera placeringen av stelningsfronten och temperaturgradienterna vid stelningsfronterna, vilket är parametrar som är svåra att komma åt under experiment. Olika varmzonstemperaturer i ugnen (1500~1550 °C) och olika provdragningshastigheter (0.5~10 mm/s) studeras i simuleringar. Det viktigaste fyndet från modellerade resultat är att provets temperaturgradient vid stelningsfronterna sträcker sig från 5 ~17 K/mm, vilket är lägre än ugns temperaturgradient på ~ 50 K/mm. Motsvarande stabilitetskylningshastigheter varierar mellan 5 ~ 85 K/s. Nästa steg är att validera modellerna med experimentella temperaturprofiler för ugnen och bestämma om ugnsutformningen ska modifieras för att uppnå intressens kylningshastigheter.

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Yes / In recent years, a new low nickel content stainless steel (EN 1.4162) commonly referred as ‘lean duplex stainless steel’ has been developed, which has over two times the tensile strength of the more familiar austenitic stainless steel but at approximately half the cost. This paper presents the finite element analysis of concrete filled lean duplex stainless steel columns subjected to concentric axial compression. To predict the performance of this form of concrete filled composite columns, a finite element model was developed and finite element analyses were conducted. The finite element model was validated through comparisons of the results obtained from the experimental study. A parametric study was conducted to examine the effect of various parameters such as section size, wall thickness, infill concrete strength, etc. on the overall behaviour and compressive resistance of this form of composite columns. Through both experimental and numerical studies, the merits of using lean duplex stainless steel hollow sections in concrete filled composite columns were highlighted. In addition, a new formula based on the Eurocode 4 was proposed to predict the cross-section capacity of the concrete filled lean duplex stainless steel composite columns subjected to axial compression.

Presented in this work are the results of twelve flexural tests conducted on small-scale coupons to establish the load-deflection behavior of UNS S32003 (ATI 2003®) hot-rolled duplex stainless steel flat plates. All specimens were tested as simply supported beams loaded at the midspan. Test specimens had nominal width and thickness of 1 in. and 0.25 in., respectively. Four different span lengths of 4 in., 6 in., 9 in., and 12 in. were investigated. Analysis of the results showed that the non-linear deflection behavior can be estimated reasonably well by adopting the conventional deflection equation pertaining to an assumed linear elastic material, but after replacing the modulus of elasticity with a secant modulus corresponding to the maximum tension strain resulting from the applied load.

This thesis discusses on results of experiments carried outwith austenitic, duplex and super duplex stainless steels andTi-6Al-4V. In these it has been seen that the heat cycle duringwelding or weld simulation has a great effect on the propertiesof thematerials. The properties are related to the resultedgrain size after processing, as well as, to the chemicalcomposition of the material. The thesis discusses on the grainsize resulted after hot processing and how the properties areinfluenced by it. Also, it has been seen how large grain sizeinfluences the fracture toughness of the duplex stainlesssteel. The CTOD values become so low that an alternativeproduction method should be used instead of casting. The thesisdescribes the behavior of grain size in the hot processing ofTi-6Al-4V and impact toughness resulted by various weldingprocesses. The thesis shows correlation between grain growthbehavior of metallurgically different materials, i.e. duplexstainless steel, Ti-6Al-4V and quenced and tempered low alloysteel. Keywords:Stainless steel, Duplex Stainless Steel,Titanium Grade 5, Ti-6Al-4V microstructure, mechanicalproperties, welding, welding simulation / <p>QCR 20161026</p>

Very high cycle fatigue (VHCF) is generally considered as the domain of fatigue lifetime beyond 10 million (107) load cycles. Few examples of structural components which are subjected to 107-109 load cycles during their service life are engine parts, turbine disks, railway axles and load-carrying parts of automobiles. Therefore, the safe and reliable operation of these components depends on the knowledge of their fatigue strength and the prevalent damage/failure mechanisms. Moreover, the fatigue life of materials in the VHCF regime is controlled by the fatigue crack initiation and early growth stage of short cracks. This study was focussed on the evaluation of fatigue properties of duplex stainless steels in the VHCF regime using the ultrasonic fatigue testing equipment. The ultrasonic fatigue tests were conducted on the cold rolled duplex stainless strip steel and hot rolled duplex stainless steel grades. Two different geometries of ultrasonic fatigue test specimens were tested. Considerable attention was devoted to the evaluation of fatigue crack initiation and growth mechanisms using the high resolution scanning electron microscopy. The fatigue crack initiation was found to be surface initiated phenomena in all the tested grades, albeit different in each case. The second part of this thesis work was the development of a distributed dislocation dipole technique for the analysis of multiple straight, kinked and branched cracks in an elastic half plane. Cracks with dimensions much smaller than the overall size of the domain were considered. The main goal of the development of this technique was the evaluation of stress intensity factor at each crack tip. The comparison of results from the stress intensity factor evaluation by the developed procedure and the well-established Finite Element Method software ABAQUS showed difference of less than 1% for Jacobi polynomial expansion of sixth order in the dipole density representation. / <p>Article III was still in manuscript form at the time of the defense.</p> / Very high cycle fatigue of stainless steels