En raison de leurs excellentes propriétés mécaniques, couplées à une bonne résistance à la corrosion par piqûres et à un coût modéré (basse teneur en nickel et en molybdène), les aciers inoxydables austéno-ferritiques (dits aciers inoxydables duplex) sont largement utilisés dans de nombreux secteurs industriels. Les aciers inoxydables duplex ont une microstructure complexe composée à proportion équivalente d’austénite et de ferrite. L’austénite ayant une composition chimique différente de celle de la ferrite, un film hétérogène se forme à la surface des aciers inoxydable duplex. Par ailleurs, les deux phases métalliques ayant des propriétés mécaniques différentes, un champ de contraintes hétérogènes est généré dans les grains. Sous certaines conditions, l’existence de gradients de contraintes peut conduire à des hétérogénéités du film passif. Dans cette étude, l’effet d’un vieillissement de longue durée dans un milieu contenant des chlorures sur la composition chimique du film passif a été tout d’abord étudié. Le comportement en corrosion de certains alliages duplex a été ensuite déterminé à partir d’essais TCP (détermination de la température critique de piqûration). Les résultats ont été analysés en tenant compte des informations obtenues précédemment. Après vieillissement, l’épaisseur du film passif et le rapport Cr/Fe ont significativement augmenté. La distribution des chlorures dans le film passif est hétérogène. Cette distribution a été reliée à la microstructure du matériau et au champ de contraintes résiduelles. Il a été montré qu’elle influence le comportement électrochimique du matériau. Le comportement en corrosion est ensuite analysé à l’aide des courbes de polarisation locales. Des critères métallurgiques ont été proposés pour l’amorçage de piqûres. / Duplex stainless steels (DSS) are highly important engineering materials, due to their generally high corrosion resistance combined with high strength and moderate alloy cost (lower nickel and molybdenum content). They are widely used in various industrial sectors. DSS have a complex microstructure with comparable volume of austenite and ferrite. Due to differences in chemical composition between austenite and ferrite, a heterogeneous passive film is formed on both phases. In addition, due to differences in mechanical properties, a heterogeneous stress field may be generated in metallic grains. Under certain conditions, these differences may also yield formation of a heterogeneous passive film. In this work, the influence of long-term ageing in chloride-containing media by on the chemical composition of the passive film was first studied by means of XPS and Auger at the microscale. The corrosion behaviour of some duplex stainless steels was then determined from CPT tests (determination of the critical pitting temperature). Results were analysed taking into account information obtained previously. After ageing, the thickness and the ratio Cr/Fe are significantly increased. The chloride distribution in the passive film was heterogeneous. It was related to the microstructure and the residual strain field. It was shown that this distribution modifies the electrochemical behaviour of samples. The corrosion behaviour was then analysed from local polarization curves and CPT tests. Metallurgical criteria for pitting were proposed.

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.

The thesis deals with hyper duplex stainless austenitic-ferritic steels and their mechanical and castability properties. The evaluation of resistance to pitting corrosion is divided by PRE values. Steels with a PRE value higher than 48 belong to the group of hyper duplex steels. The theoretical part contains an introduction to the chemical composition, structure and properties of these steels. The practical part is focused on the conditions of tendency to crack castings during solidification and cooling. Furthermore, there is evaluated influence of intermetallic phases on mechanical properties.

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.

Duplex stainless steel (DSS) that developed in the 1930’s is a type of steel that consists of bothaustenite and ferrite phases in an almost equal proportion. It inherits properties of both ferriticand austenitic stainless steel and so it has good mechanical and corrosion resistance propertiesthat makes it suitable material in different industries with aggressive environment. There aredifferent approaches that used to evaluate the susceptibility of stainless steels to pitting corrosionlike Pitting Resistance Equivalent Number (PREN) and electrochemical methodologies. In thisstudy, focus is on the potentiodynamic (AL 101 5170) and potentiostatic (ASTM G150) testmethods as laboratory evaluations in which standard DSS (2205) is exposed to the differentchloride concentrations 0.1 M and 1 M respectively. In these methods parameters like PittingPotential (Ep) and Critical Pitting Temperature (CPT) can be measured respectively and used topredict the susceptibility of DSS to pitting corrosion. DSS owes its good corrosion resistance tothe oxide film that protects the metal from corrosion. Pitting can be initiated as a result of anyheterogeneities on the metal surface which act as a passive film defect like non-metallicinclusions and intermetallic precipitations such as sigma phase when metal is exposed toaggressive environment and high temperature. The aim of the present work is to make acomparison between two electrochemical methods besides finding how inclusions andmicrostructure can have impact on their results and on pitting corrosion. The results of theexperiment shows that there is a positive linear relation only in longitudinal direction betweenCPT and Ep. Also, among two test methods only ASTM G150 can detect sigma phase existence(<3%). Based on investigations in this experiment, inclusion characteristics such as numberdensity and composition has compatible results in both methods so that samples with big sizeinclusions (>8 μm) have negative effect on corrosion resistance and in terms of composition,samples with nitride inclusions has lower CPT and Ep compared with those with only oxide oroxide/sulfide inclusions. It is also discovered that phase arrangement is not the same in allspecimens that produced by different production methods and samples with finer phases havehigher CPT values in both longitudinal and transvers directions. However, this shape ofmicrostructure only affect the Ep in longitudinal directions but not transvers.

Duplex stainless steels, DSS are stainless steels that consist of the two phases austenite and ferrite.  The DSS have superb properties and are widely used in industries such as nuclear power and in pressure vessels, pipes and in pipelines.  The use of DSS are limited due to embrittlement which occurs at temperatures from 250 to 550 oC. This imposes a general limited service temperature of 250 oC. The mechanism mainly responsible for the embrittlement is a phase separation occurring in the ferrite phase. Furthermore, there is a direct link between the phase separation and the mechanical properties:  the ferrite hardness increases whereas the toughness decreases under low temperature aging.  In this thesis, the low-temperature embrittlement of duplex stainless  steels  was  studied  through  machine learning  modelling  and  experimental hardness-  and  microscopy measurements.   The  resulting  model  describes  the  data with an accuracy, R-squared = 0.94.  In combination with the experimental results, nickel  was identified  as  an  important  parameter  for  the  hardness  evolution.   This work aims to provide a fundamental study for understanding the importance of alloying elements on the phase separation in DSS, and provides a new methodology via a combination of machine learning and key experiments for the material design. / Duplexa rostfria stål är rostfria stål som består av de båda faserna ferrit och austenit. De har extraordinära egenskaper och används brett inom industrin, t ex. i kärnkraftverk och  i  tryckkärl  och  pipelines.  Användningen av  duplexa  rostfria stål  är  begränsad p.g.a.  försprödning som uppstår i legeringarna vid temperaturer mellan 250-550 oC, vilket  medför  att  den  tillåtna  temperaturen  vid  användning  begränsas  till  under 250 oC.  Den  främsta  orsaken  till  försprödningen  är  en  fasseparation  i  den  ferrita fasen under åldring vid låg temperatur.  Vidare leder fasseparationen till mekaniska förändringar i ferritfasen: hårdheten  ökar  medan  segheten  minskar.   I  den här  rapporten  undersöks försprödningen  av  duplexa  rostfria  stål  vid  åldring  med hjälp av datormodellering med maskininlärning samt av experimentella hårdhets- och mikroskopiska  mätningar.   Modellen  hade  en  noggrannhet  (determinationsko- efficienten,  R2)  på  0.94.   Resultatet  från  modellen  visade  tillsammans  med de  experimentella  resultaten  att  nickel  är  ett  legeringsämne  som  har  stor betydelse  för hårdhetsökningen.  Detta  arbete  syftar  till  att  utgöra  en grundläggande  studie  för att förstå påverkan från olika legeringsämnen på fasseparationer i DSS, och bidrar med en ny metodik för materialdesign som kombinerar maskininlärning och utvaldaexperiment. / EIT RawMaterial Project ENDUREIT

Made available in DSpace on 2017-07-21T19:25:52Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-03-10 / 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.

Made available in DSpace on 2017-07-21T19:26:00Z (GMT). No. of bitstreams: 1 Andre Assmann.pdf: 3125745 bytes, checksum: 38854736eae2fcc4e8c2c21a2668f387 (MD5) Previous issue date: 2011-04-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In the present work showing the results on mechanical and tribological properties of duplex stainless steel LDX2101 nitriding by Ion Implantation (II), Plasma Immersion Ion Implantation (PI3) and Glow Discharge (GD). Nitrogen ion implantation was performed at room temperature and 350 C. The nitrogen fluencies were combined to obtain an atomic nitrogen concentration of 27 %. The PI3 was carried out with temperatures of 300 and 350 C working in N2 atmosphere during 3 hours. For GD, the working conditions were gas mixture N2/H2 (in the ratio 80%/20%, 60%/40% and 20%/80%) and N2/CH4 (in the ratio 98%/02%) during 3 hours at temperatures of 300, 350 and 380 C. Structural characterizations of the modified layers were performed by X-Ray Diffraction (XRD) with Bragg-Brentano geometry. Hardness was obtained by instrumented indentation using Oliver and Pharr method’s with Berkovich indenter. Tribological tests were evaluated by reciprocating sliding with a WC(Co) sphere (counter body). XRD patterns for II samples showing only the formation of γN, however, samples treated by GD and PI3 showed the formation of γ’Fe4N and Fe2+XN, over there γN, as a function of the working temperature and nitriding atmosphere. After the nitriding hardness values between 8 and 20 GPa in comparison to 3 GPa of the bulk was obtained. The hardness profile of samples treated by GD at 350 and 380 C exhibit plateaulike for values of hardness between 13 and 20 GPa, indicate the formation of a thicker nitrited layer. The friction coefficient for II samples showed a strong adhesive wear. PI3 samples exhibit long running-in regimes compared to II and untreated samples. GD samples showing a predominant abrasive wear because ploughing of surface for asperities and wear particles formed between the surface and counter body. The significant decrease in the wear was observed in all GD samples, with a reduction of one order of magnitude compared to untreated sample. / No presente trabalho, são apresentados os resultados sobre as propriedades mecânicas e tribológicas do aço inoxidável duplex LDX 2101 nitretado por Implantação Iônica (II), Implantação Iônica por Imersão em Plasma (3IP) e Descarga Luminosa (DL). A Implantação Iônica de nitrogênio foi realizada em temperatura ambiente e em 350 C. As fluências utilizadas foram combinadas para obter uma concentração de átomos de nitrogênio de 27 %. A nitretação 3IP, foi realizada nas temperaturas de 300 e 350 C em atmosfera de N2 durante 3 horas. Para o tratamento por DL as condições de tratamento foram em diferentes atmosferas de N2/H2 (nas proporções de 80%/20%, 60%/40% e 20%/80%) e N2/CH4 (na proporção de 98%/02%) durante 3 horas nas temperaturas de 300, 350 e 380 C. A caracterização estrutural das camadas modificadas foi obtida através de Difração de Raios-X (DRX) com geometria Bragg-Brentano. Os perfis de dureza foram obtidos por indentação instrumentada usando o método de Oliver e Pharr com indentador do tipo Berkovich. Testes tribológicos foram realizados com tribômetro do tipo pino sobre disco em movimento recíproco com uma esfera de WC(Co) de contra corpo. Os padrões de DRX para amostras tratadas por II apresentaram apenas a formação de γN, contudo, as amostras tratadas por DL e 3IP apresentaram a formação de γ’-Fe4N e Fe2+XN, além de γN, como função da temperatura de tratamento e da atmosfera de nitretação. Após as nitretações durezas entre 8 e 20 GPa em comparação a 3 GPa para o substrato foram obtidas. Perfis de dureza para amostras tratadas por DL em 350 e 380 C exibiram valores entre 13 e 20 GPa em forma de platô, indicando a formação de uma espessa camada nitretada. O coeficiente de atrito para as amostras tratadas por II apresentaram um forte desgaste adesivo. Amostras tratadas por 3IP exibiram longos regimes de acomodação comparados as amostras tratadas por II e a amostra referência. Amostras tratadas por DL apresentaram um predominante desgaste abrasivo devido à deformação plástica da superfície causada pelas asperidades e pelas partículas de desgaste formadas entre a superfície e o contra corpo. Uma significante diminuição no desgaste foi observada em todas as amostras tratadas por DL, com uma redução de uma ordem de grandeza quando comparado a amostra sem tratamento.

Welding of duplex stainless steel pipeline material for the oil and gas industry is now common practice. To date, research has been conducted primarily on the parent material and heat affected zones in terms of its susceptibility to various forms of corrosion. However, there has been little research conducted on the degree of sensitisation of the various successive weld layers, namely the root, fill and cap layers. The focus of this research study was to: (i) provide an in-depth microstructural analysis of the various weld passes, (ii) study the mechanical properties of the weld regions; (iii) determine degree of sensitisation of the various weld passes; and (iv) investigate the residual stress levels within the various regions/ phases of the welds. Four test conditions were prepared using manual Gas Tungsten Arc Welding with 'V' and 'U' bevel configuration. Structural analysis consisted of (i) optical microscopy, scanning electron microscopy and magnetic force microscopy; (ii) ferrite determination using Magna-Gauge, Fischer Ferrite-scope and Point Count method. Mechanical testing consisted of Vickers hardness measurements, Charpy impact studies and transverse tensile testing. The degree of sensitisation was determined by three test methods: a modified ASTM A262, ASTM A923 and a modified Double Loop Electrochemical Potentiodynamic Reactivation (DL-EPR) test. Residual stress levels were determined using two neutron diffraction techniques: a reactor source and a time of flight spallation source. Microstructure observed by optical microscopy and magnetic force microscopy shows the formation of both fine and coarse structures within the weld metal. There was no evidence of secondary austenite, being present in any of the weld metal conditions examined. In addition, no detrimental intermetallic phases or carbides were present. The DL-EPR test results revealed that the fill layer regions for all four conditions and the base material showed the highest values for Ir/Ia and Qr/Qa. All four test conditions passed the ASTM A262 and A923 qualitative type tests, even under restricted and modified conditions. Residual stress measurements by neutron diffraction conducted at Lucas Heights Hi-Flux Reactor revealed that the ferrite phase stress was tensile in the heat affected zones and weld, and appeared to be balanced by a local compressive austenite phase stresses in the normal and transverse directions. Residual stress measurements by neutron diffraction conducted at Los Alamos Nuclear Science Centre revealed that in the hoop direction, ferrite (211) and austenite (311) exhibit tensile strains in the weld. In the axial and radial direction, the strains for both phases were more compressive. Correlations between the degree of sensitization and microstructural changes / ferrite content were observed. Higher degrees of sensitization (Ir/Ia and Qr/Qa) were associated with reduced ferrite (increased austenite) content. Correlations between the stresses generated, the evolved microstructures and degree of sensitization were evident. Stresses within the cap region were generally shown to be of a tensile nature in the transverse and longitudinal direction. In summary, the study has shown that correlations exist between the weld microstructure, susceptibility to sensitisation and levels / distribution of internal stresses within the weld regions.

CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico / FAPEMIG - Fundação de Amparo a Pesquisa do Estado de Minas Gerais / O aumento crescente da procura por produtos que necessitam de componentes cada vez menores impulsiona o desenvolvimento da microusinagem, considerada altamente necessária para os avanços tecnológicos na área metal mecânica. Neste contexto, o microfresamento é uma alternativa viável para a fabricação destes microcomponentes, permitindo a usinagem de geometrias complexas em diversos materiais tais como: metais e ligas, compósitos, polímeros, cerâmicas e alguns aços inoxidáveis, sendo que estes últimos despertam grande interesse para a indústria devido à sua característica de grande resistência à corrosão e à oxidação. No entanto, adaptar o conhecimento do fresamento de aços inoxidáveis em escala convencional para a microescala exige o entendimento dos fenômenos específicos que surgem com a redução das dimensões envolvidas nas operações. Diante desse contexto, este trabalho tem como principal objetivo a investigação da usinabilidade do aço inoxidável duplex UNS S32205 no microfresamento. Para tanto, foram realizados ensaios para fabricação de microcanais, utilizando uma microfresadora CNC de quatro eixos, rotação máxima de 60 000 rpm e resolução de 0,1 μm, usando microfresas de metal duro com diâmetro de 200 µm e 400 µm. A partir dos dados experimentais, foram analisados a evolução do desgaste, as formas e mecanismos de desgaste da ferramenta, a formação de rebarba, a superfície microusinada, a rugosidade superficial e a formação de cavaco. Os resultados mostram que a ferramenta com diâmetro de 200 µm apresentou um excelente desempenho em relação ao comprimento usinado, no entanto o aumento da velocidade de corte levou a um desgaste excessivo e altas rebarbas. Na usinagem utilizando ferramentas de diâmetro 400 µm, o desgaste e altura das rebarbas foi atenuado através da utilização do fluído de corte. E por fim, as ferramentas com maior diâmetro apresentaram rebarbas muito menores quando comparadas às de menor diâmetro, formando cavacos contínuos, além de apresentarem um menor grau de recalque. / The increasing demand for products requiring increasingly smaller components drives the development of micromachining, which is considered to be highly necessary for technological advances in the field of mechanical engineering. In this context, micromilling is a viable alternative for the manufacture of these microcomponents, allowing the machining of complex geometries in various materials such as: metals and alloys, composites, polymers, ceramics and some stainless steels, the latter of which arouse great interest for the industry due to its characteristic of great resistance to corrosion and oxidation. However, adapting the knowledge of milling of stainless steels on a conventional scale to the microscale requires an understanding of the specific phenomena that arise with the reduction of operations. Considering this context, this work has as main objective the investigation of the machinability of duplex stainless steel UNS S32205 in the micromilling operation. For that, tests were made to manufacture microchannels, using a 4-axis CNC micromill machine tool, with maximum spindle rotation of 60 000 rpm and resolution of 0.1 μm, using 200 µm and 400 µm diameter tools. From the experimental data, it was investigated the evolution of tool wear, the forms and mechanisms of tool wear, burr formation, machined surface quality, surface roughness and chip formation. The results show that the tool with diameter 200 µm presented an excellent performance in relation to the machined length, however the increased cutting speed led to excessive wear and high burrs. In the machining tests using tools with diameter 400 µm, the wear and height of the burrs was attenuated through the use of cutting fluid. Finally, the tools with the largest diameter presented minor burrs when compared to the smaller diameter, forming continuous chips, in addition to presenting a lower chip thickness ratio of the chips. / Dissertação (Mestrado)