Ziel des BMWi-Fördervorhabens 1501393 ist es, durch den Einsatz von Untersuchungsmethoden auf der nm-Skala einen Beitrag zur Aufklärung von Flusseffekten und von Late-Blooming-Effekten in bestrahlten RDB-Stählen zu leisten. Zur Untersuchung dieser Effekte wurde auf RDB-Stähle deutscher Reaktoren aus zwei bei der AREVA GmbH abgeschlossenen Vorhaben zurückgegriffen. Die Auswahl der Grundwerkstoffe und Schweißgüter erfolgte so, dass sich optimale Voraussetzungen für das Erreichen des Gesamtziels des Vorhabens ergeben. Die ausgewählten Untersuchungsmethoden umfassen mit der Neutronenkleinwinkelstreuung, der Atomsondentomographie und der Positronen-annihilationsspektroskopie solche Techniken, die die nm-skaligen bestrahlungsinduzierten Defekt-Fremdatom-Cluster bestmöglich und in komplementärer Weise zu detektieren und zu charakterisieren gestatten. Es wurde ein Flusseffekt auf die Größe der bestrahlungsinduzierten Fremdatomcluster, jedoch nicht auf den Volumenanteil und die mechanischen Eigenschaften gefunden. In einem Cu-armen RDB-Schweißgut wurde ein Late-Blooming-Effekt nachgewiesen, der sich in einem steilen Anstieg des Clustervolumenanteils und der Übergangstemperaturverschiebung nach einer Phase schwacher oder fehlender Zunahme niederschlägt. The BMWi project 1501393 aimed at contributing to the clarification of flux effects and late blooming effects in irradiated RPV steels by means of experimental techniques of sensitivity at the nm scale. The investigation of these effects was focussed on RPV steels, both base metal and weld of German reactors selected according to the objectives of the present project from two previous projects performed at AREVA GmbH. The complementary techniques of small-angle neutron scattering, atom probe tomography and positron annihilation spectroscopy were applied to detect and characterize the irradiation-induced nm-scale defect-solute clusters. A flux effect on the size of the irradiation-induced clusters but no flux effect on both cluster volume fraction and mechanical properties was found. For a low-Cu RPV weld, a late blooming effect was observed, which results in a steep slope of both cluster volume fraction and transition temperature shift after an initial stage of small or no change.

Orientador: Juno Gallego / Banca: Ruís Camargo Tokimatsu / Banca: Itamar Ferreira / Resumo: No Brasil, a maior parte da energia elétrica disponível é gerada por usinas hidrelétricas as quais contam com grande número de turbinas hidráulicas. Durante sua operação estas turbinas sofrem sérios danos provenientes tanto de natureza mecânica como também hidráulica. Fenômenos de perda de massa e também trincas e rachaduras são alguns dos principais problemas que ocorrem devido a um fenômeno chamado de erosão cavitacional, que comumente é recuperado por soldagem. Sendo assim, grandes níveis de resistência à cavitação vêm sendo obtidos com a deposição de aços inoxidáveis com a presença de cobalto pelo processo de soldagem a arco com proteção gasosa. Neste trabalho, seis amostras feitas de aço-carbono ASTM A36, as quais foram extraídas de retalhos de turbinas, foram usadas como metal de base para as amostras. Usando um processo a arco elétrico com proteção gasosa (GMAW) em posição plana, duas camadas de aço AWS E70-S6 (1,2 mm de diâmetro) foi depositada em todas as amostras, e, somente em três das amostras foram depositadas duas camadas de amanteigamento com o arame de aço inoxidável AWS E309-T1 (1,6 mm de diâmetro) usando o mesmo processo, onde foi utilizado como proteção gasosa uma mistura de 75% de dióxido de carbono e 25% de argônio. A energia de soldagem nominal nestes casos foi de 0,5 kJ/mm. Por final, mais duas camadas de aço inoxidável com cobalto, liga resistente à cavitação foram depositadas por arco pulsado, com energia de soldagem nominal de 0,5 a 0,8kJ/mm, com uma mistura de gases de 98% de argônio e 2% de oxigênio como proteção. Secções transversais das amostras foram preparadas, devidamente lixadas e depois polidas com alumina 1,0μm, seguido de ataque químico moderado com Villela para observação de microestruturas. Foi feito o estudo de microdureza Vickers com carga padrão de 0,4 N e espaçamento regular (0,4 mm) ...(Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Nowadays most of the power supply used in Brazil is provided for a large number of hydraulic turbines. During its operation in hydroelectric power plants, these turbines usually have been damaged either mechanical or hydraulic reasons. So, catastrophic cracking and loss-of-mass due to cavitation erosion are main problems which are commonly repaired by welding. Higher levels of resistance to cavitation erosion have been attained with surface deposition of a cobalt-alloyed stainless steel coating by gas-protected arc welding techniques. In the present work six plates, which were machined from blades of hydraulic turbines made with ASTM A36 carbon steel grade, were used as base metal. Using manual gas-metal arc welding (GMAW) in flat weld position two layers of AWS E70-S6 carbon steel (1.2 mm diameter) were deposited on all samples. Only 3 samples two buttering layers were deposited with AWS E309-T1 flux-cored wire (1.6 mm diameter) using same processing, where were applied a 75% carbon dioxide - 25% argon mixture as protection gas. The nominal heat input used in all layers was approximately 0.5 kJ/mm. At the last welding deposition another two cobalt-alloyed, cavitation resistant, stainless steel cladding layers were deposited under pulsed arc with a nominal heat input of 0.5 to 0.8kJ/mm, being used for them a protective gas mixture of 98% argon - 2% oxygen. Transverse sections of weld deposit were prepared according standard grinding method (up to 1200-grit SiC paper) and final mechanical polishing using 1.0μm alumina, followed by moderate etching in Villela reagent for microstructural observation. Vickers microhardness measurements were carried out at standard load (0.4 N) and regular spacings (0,4mm) from surface to base metal. Light microscopy (LM) was used to determine average size of inclusions, which was measured from digitalized images using a freeware image analysis ...(Complete abstract, click electronic access below) / Mestre

Ziel des BMWi-Fördervorhabens 1501393 ist es, durch den Einsatz von Untersuchungsmethoden auf der nm-Skala einen Beitrag zur Aufklärung von Flusseffekten und von Late-Blooming-Effekten in bestrahlten RDB-Stählen zu leisten. Zur Untersuchung dieser Effekte wurde auf RDB-Stähle deutscher Reaktoren aus zwei bei der AREVA GmbH abgeschlossenen Vorhaben zurückgegriffen. Die Auswahl der Grundwerkstoffe und Schweißgüter erfolgte so, dass sich optimale Voraussetzungen für das Erreichen des Gesamtziels des Vorhabens ergeben. Die ausgewählten Untersuchungsmethoden umfassen mit der Neutronenkleinwinkelstreuung, der Atomsondentomographie und der Positronen-annihilationsspektroskopie solche Techniken, die die nm-skaligen bestrahlungsinduzierten Defekt-Fremdatom-Cluster bestmöglich und in komplementärer Weise zu detektieren und zu charakterisieren gestatten. Es wurde ein Flusseffekt auf die Größe der bestrahlungsinduzierten Fremdatomcluster, jedoch nicht auf den Volumenanteil und die mechanischen Eigenschaften gefunden. In einem Cu-armen RDB-Schweißgut wurde ein Late-Blooming-Effekt nachgewiesen, der sich in einem steilen Anstieg des Clustervolumenanteils und der Übergangstemperaturverschiebung nach einer Phase schwacher oder fehlender Zunahme niederschlägt. The BMWi project 1501393 aimed at contributing to the clarification of flux effects and late blooming effects in irradiated RPV steels by means of experimental techniques of sensitivity at the nm scale. The investigation of these effects was focussed on RPV steels, both base metal and weld of German reactors selected according to the objectives of the present project from two previous projects performed at AREVA GmbH. The complementary techniques of small-angle neutron scattering, atom probe tomography and positron annihilation spectroscopy were applied to detect and characterize the irradiation-induced nm-scale defect-solute clusters. A flux effect on the size of the irradiation-induced clusters but no flux effect on both cluster volume fraction and mechanical properties was found. For a low-Cu RPV weld, a late blooming effect was observed, which results in a steep slope of both cluster volume fraction and transition temperature shift after an initial stage of small or no change.

Ageing of low alloy steel in nuclear applications commonly takes the form as a hardening and an embrittlement of the material. This is due to the evolution of the microstructure during irradiation and at purely thermal conditions, as a combination or separate. Irradiation introduces evenly distributed solute clusters, while thermal ageing has been shown to yield a more inhomogeneous distribution. These clusters affect the dislocation motion within the material and results in a hardening and in more severe cases of ageing, also a decreased work hardening slope due to plastic strain localization into bands/channels. Embrittlement corresponds to decreased fracture toughness due to microstructural changes resulting from ageing. The thesis presents a possible framework for modeling of ageing effects in low alloy steels.In Paper I, a strain gradient plasticity framework is applied in order to capture length scale effects. The constitutive length scale is assumed to be related to the dislocation mean free path and the changes this undergoes during plastic deformation. Several evolution laws for the length scale were developed and implemented in a FEM-code considering 2D plane strain. This was used to solve a test problem of pure bending in order to investigate the effects of the length scale evolution. As all length scale evolution laws considered in this study results in a decreasing length scale; this leads to a loss of non-locality which causes an overall softening at cases where the strain gradient is dominating the solution. The results are in tentative agreement with phenomena of strain localization that is occurring in highly irradiated materials.In Paper II, the scalar stress measure for cleavage fracture is developed and generalized, here called the effective normal stress measure. This is used in a non-local weakest link model which is applied to two datasets from the literature in order to study the effects of the effective normal stress measure, as well as new experiments considering four-point bending of specimens containing a semi-elliptical surface crack. The model is shown to reproduce the failure probability of all considered datasets, i.e. well capable of transferring toughness information between different geometries. / Åldring av låglegerade stål i kärntekniska användningsområden framträder typiskt som ett hårdnande och en försprödning av materialet. Detta på grund av utvecklingen av mikrostrukturen under bestrålning och under rent termiska förhållanden. Bestrålning introducerar jämt fördelade kluster av legeringsämnen. Termisk åldring har däremot visats ge upphov till en mer ojämn fördelning. Klustren hämmar dislokationsrörelsen i materialet och ger därigenom upphov till en ökning av materialets sträckgräns, vid en mer påtaglig åldring det även leda till ett sänkt arbetshårdnande på grund av lokalisering av plastisk töjning i s.k. kanaler/band. Försprödning är en sänkning av materialets brottseghet som en följd av de mikrostrukturella förändringar som sker vid åldring. Arbetet som presenteras i den här avhandlingen har gjorts i syfte till att ta fram ett möjligt ramverk för modellering av låglegerade stål.I Artikel I, används en töjningsgradientbaserad plasticitetsteori för att kunna fånga längdskalebeteenden. Längdskalan i teorin antas vara relaterad till dislokationernas medelfria väg och den förändring den genomgår vid plastisk deformation. Flera utvecklingslagar för längdskalan har analyserats och implementerats i en finita element kod för 2D plan deformation. Denna implementering har använts för att lösa ett testproblem bestående av ren böjning med syfte att undersöka effekterna av utvecklingen hos längdskalan. Alla de utvecklingslagar som presenteras i artikeln ger en minskande längdskala, vilket leder till vad som valt att kallas förlust av icke-lokalitet. Fenomenet leder till ett övergripande mjuknande vid fall där den plastiska töjningsgradienten har stor inverkan på lösningen. Resultaten är i preliminär överenstämmelse med de typer av lokalisering av plastisk töjning som observerats i starkt bestrålade material.I Artikel II utvecklas ett generaliserat spänningsmått i syfte att beskriva klyvbrott, här benämnt effektivt normalspänningsmått. Detta har använts i samband med en icke-lokal svagaste länk modell, som har applicerats på två experimentella studier från den öppna litteraturen i syfte att studera effekterna av det effektiva normalspänningsmåttet. Utöver detta presenteras även nya experiment på ytspruckna provstavar under fyrpunktsböj. I artikeln visas att modellen återskapar sannolikheten för brott för alla undersökta experimentuppställningar, d.v.s. modellen visas vara väl duglig för att överföra brottseghet mellan geometrier. / <p>QC 20190312</p>

Neste trabalho foi feito o estudo sobre o efeito de elementos microligantes na composição química, microestrutura e propriedades mecânicas de metais como soldado produzidos por arco submerso com adição de pó de ferro em aço de alta resistência e baixa liga (ARBL). Foram feitos dois cordões de solda utilizando os aços BS - 4360 - 50 e USI - SAC - 50, o arame EM - 12K, o pó de ferro ESAB 400 e o fluxo experimental 10.71P. Utilizando-se a corrente de 600 A, tensão de 34 V, velocidade de soldagem de 30 cm/min e vazão de pó de ferro de 6,7 Kg/h foram produzidos os metais como soldado com um único passe e chanfro em \"V\", que mostraram características de boa temperabilidade e estrutura refinada. O microconstituinte em maior porcentagem nos dois cordões de solda foi a ferrita acicular. Os ensaios mecânicos realizados foram a dureza, tração e impacto. O cordão de solda com nióbio e vanádio obteve maiores valores de dureza e resistência à tração em relação ao cordão com cobre, cromo e níquel. Entretanto os altos teores de manganês presentes fizeram com que o endurecimento por solução sólida reduzisse significativamente a resistência ao impacto dos dois cordões de solda. A natureza das inclusões não metálicas foi investigada por microscopia eletrônica e análise por EDAX. / The study of the effect of microalloying elements in the chemical composition, microstructure and mechanical properties of the as-welded metaIs obtained by submerged are welding with iron powder addition in High Strength Low Alloy (HSLA) steel were done. Two weld metaIs were made using, BS - 4360 - 50 and USI - SAC - 50 steels, EM - 12K wire, ESAB 400 iron powder and 10.71P experimental flux. Using welding current of 600 A, arc voltage of 34 V, travel speed of 30 cm/min and iron powder flow of 6,7 Kg/h were obtained as-welded metals by single pass into V - groove, that showed good hardenability and refined microstructure. The higher percentage microstructure in the two weld metals was the acicular ferrite. The mechanical tests done were hardness, tensile strength and impact. The weld metal with niobium and vanadium achieve better values of hardness and yield strength than with copper, chromium and nickel weld metal. However, the hardening by solid solution, induced by the high levels of manganese, decreased the impact strength of the two weld metaIs. The non - metallic inclusions nature was investigated by electronic microscopy and EDAX analysis.

Neste trabalho foi feito o estudo sobre o efeito de elementos microligantes na composição química, microestrutura e propriedades mecânicas de metais como soldado produzidos por arco submerso com adição de pó de ferro em aço de alta resistência e baixa liga (ARBL). Foram feitos dois cordões de solda utilizando os aços BS - 4360 - 50 e USI - SAC - 50, o arame EM - 12K, o pó de ferro ESAB 400 e o fluxo experimental 10.71P. Utilizando-se a corrente de 600 A, tensão de 34 V, velocidade de soldagem de 30 cm/min e vazão de pó de ferro de 6,7 Kg/h foram produzidos os metais como soldado com um único passe e chanfro em \"V\", que mostraram características de boa temperabilidade e estrutura refinada. O microconstituinte em maior porcentagem nos dois cordões de solda foi a ferrita acicular. Os ensaios mecânicos realizados foram a dureza, tração e impacto. O cordão de solda com nióbio e vanádio obteve maiores valores de dureza e resistência à tração em relação ao cordão com cobre, cromo e níquel. Entretanto os altos teores de manganês presentes fizeram com que o endurecimento por solução sólida reduzisse significativamente a resistência ao impacto dos dois cordões de solda. A natureza das inclusões não metálicas foi investigada por microscopia eletrônica e análise por EDAX. / The study of the effect of microalloying elements in the chemical composition, microstructure and mechanical properties of the as-welded metaIs obtained by submerged are welding with iron powder addition in High Strength Low Alloy (HSLA) steel were done. Two weld metaIs were made using, BS - 4360 - 50 and USI - SAC - 50 steels, EM - 12K wire, ESAB 400 iron powder and 10.71P experimental flux. Using welding current of 600 A, arc voltage of 34 V, travel speed of 30 cm/min and iron powder flow of 6,7 Kg/h were obtained as-welded metals by single pass into V - groove, that showed good hardenability and refined microstructure. The higher percentage microstructure in the two weld metals was the acicular ferrite. The mechanical tests done were hardness, tensile strength and impact. The weld metal with niobium and vanadium achieve better values of hardness and yield strength than with copper, chromium and nickel weld metal. However, the hardening by solid solution, induced by the high levels of manganese, decreased the impact strength of the two weld metaIs. The non - metallic inclusions nature was investigated by electronic microscopy and EDAX analysis.

<p>Duplex stainless steels are a very attractive alternative to austenitic grades due to their higher strength and good corrosion performance. The austenitic grades can often be welded autogenously, while the duplex grades normally require addition of filler metal. This is to counteract segregation of important alloying elements and to give sufficient austenite formation to prevent precipitation of chromium nitrides that could have a negative effect on impact toughness and pitting resistance. The corrosion performance of the recently-developed lean duplex stainless steel LDX 2101 is higher than that of 304 and can reach the level of 316. This thesis summarises pitting resistance tests performed on laser and gas tungsten arc (GTA) welded LDX 2101. It is shown here that this material can be autogenously welded, but additions of filler metal, nitrogen in the shielding gas and use of hybrid methods increases the austenite formation and the pitting resistance by further suppressing formation of chromium nitride precipitates in the weld metal. If the weld metal austenite formation is sufficient, the chromium nitride precipitates in the heat-affected zone (HAZ) could cause local pitting, however, this was not seen in this work. Instead, pitting occurred 1–3 mm from the fusion line, in the parent metal rather than in the high temperature HAZ (HTHAZ). This is suggested here to be controlled by the heat tint, and the effect of residual weld oxides on the pitting resistance is studied. The composition and the thickness of weld oxide formed on LDX 2101 and 2304 were determined using X-ray photoelectron spectroscopy (XPS). The heat tint on these lean duplex grades proved to contain significantly more manganese than what has been reported for standard austenitic stainless steels in the 300 series. A new approach on heat tint formation is consequently presented. Evaporation of material from the weld metal and subsequent deposition on the weld oxide are suggested to contribute to weld oxide formation. This is supported by element loss in LDX 2101 weld metal, and nitrogen additions to the GTA shielding gas further increase the evaporation.</p><p> </p>

Duplex stainless steels are a very attractive alternative to austenitic grades due to their higher strength and good corrosion performance. The austenitic grades can often be welded autogenously, while the duplex grades normally require addition of filler metal. This is to counteract segregation of important alloying elements and to give sufficient austenite formation to prevent precipitation of chromium nitrides that could have a negative effect on impact toughness and pitting resistance. The corrosion performance of the recently-developed lean duplex stainless steel LDX 2101 is higher than that of 304 and can reach the level of 316. This thesis summarises pitting resistance tests performed on laser and gas tungsten arc (GTA) welded LDX 2101. It is shown here that this material can be autogenously welded, but additions of filler metal, nitrogen in the shielding gas and use of hybrid methods increases the austenite formation and the pitting resistance by further suppressing formation of chromium nitride precipitates in the weld metal. If the weld metal austenite formation is sufficient, the chromium nitride precipitates in the heat-affected zone (HAZ) could cause local pitting, however, this was not seen in this work. Instead, pitting occurred 1–3 mm from the fusion line, in the parent metal rather than in the high temperature HAZ (HTHAZ). This is suggested here to be controlled by the heat tint, and the effect of residual weld oxides on the pitting resistance is studied. The composition and the thickness of weld oxide formed on LDX 2101 and 2304 were determined using X-ray photoelectron spectroscopy (XPS). The heat tint on these lean duplex grades proved to contain significantly more manganese than what has been reported for standard austenitic stainless steels in the 300 series. A new approach on heat tint formation is consequently presented. Evaporation of material from the weld metal and subsequent deposition on the weld oxide are suggested to contribute to weld oxide formation. This is supported by element loss in LDX 2101 weld metal, and nitrogen additions to the GTA shielding gas further increase the evaporation. / QC 20101126