Dissertations / Theses: 'Metallic stents'

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AL-Mangour, Bandar. "The use of cold sprayed alloys for metallic stents." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=107900.

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With the invention of the coronary stent, which is a wire metal mesh tube designed to keep the arteries open in the treatment of heart diseases, promising clinical outcomes were generated. However, the long term successes of stents have been delayed by significant in-stent restenosis (blockages) and stent fracture. In this research work, it has been proposed to use Cold Gas Dynamic Spraying (CGDS) coating material as an alternative choice to manufacture metallic stent. In CGDS, fine particles are accelerated to a high velocity and undergo solid-state plastic deformation upon impact on the substrate, which leads to particle-particle bonding. The feature of CGDS distinct from other thermal spray techniques is that the processing gas temperature is below the melting point of the feedstock. Therefore, unwanted effects of high temperatures, such as oxidation, grain growth and thermal stresses, are absent. In response to the fact that the majority of stents are made from stainless steel (316L) or Co-Cr alloy (L605), this study specifically addresses the development and characterization of 316L and 316L mixed with L605 coatings produced by the CGDS process. Scanning electron microscopy and electron backscatter diffraction were used to investigate the microstructural changes of these coatings before and after annealing. The effect of gas type on the microstructure of 316L coatings and the role of post-heat treatment in the microstructure and properties are also studied. Of particular interest are grain refinement, heat treatment, mechanical properties and corrosion behavior of the cold sprayed material.
L'invention du stent coronaire, est un tube en treillis métallique conçu pour maintenir les artères ouvertes dans le traitement des maladies cardiovasculaires. Des résultats cliniques prometteurs ont été rapportés. Cependant, le succès à long terme des stents est problématique à cause des resténoses intra-stent et des fractures de stent par fatigue. Dans ce travail de recherche, il est proposé d'utiliser la technologie de pulvérisation dynamique des gaz à froid (CGDS) comme une alternative pour la fabrication de stents métalliques. En CGDS, de fines particules sont accélérées avec une vitesse élevée et subissent une déformation plastique à l'impact sur un substrat. La particularité du CGDS parmi les autres techniques de pulvérisation thermique est que la température des gaz dans le processus est bien en dessous du point de fusion de la matière. Par conséquent, les effets indésirables des températures élevées, telles que l'oxydation, la croissance du grain et les contraintes thermiques, sont absents. Comme la majorité des stents sont faits en acier inoxydable 316L et en alliage Co-Cr, cette étude porte spécifiquement sur le développement et la caractérisation de l'acier inoxydable et l'acier inoxydable 316L mélangé avec revêtements d'alliages Co-Cr produite par le procédé CGDS. Les techniques de microscopie électronique à balayage et à diffraction d'électrons rétrodiffusés ont été utilisées pour étudier les changements de microstructures de ces revêtements avant et après recuit. L'effet du type de gaz sur la microstructure des revêtements 316L et le rôle du post-traitement thermique à froid par pulvérisation dans la microstructure et les propriétés mécaniques et électrochimiques ont été également étudiées.

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Mousselli, Jad. "On surface electropolishing for the development of metallic stents." Master's thesis, Université Laval, 2019. http://hdl.handle.net/20.500.11794/36574.

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Les maladies cardiovasculaires sont responsables d'environ le tiers de tous les cas de décès au Canada. L'une des solutions utilisées pour résoudre ce problème consiste à utiliser un dispositif métallique constitué d'un maillage ayant une forme d’un filet et appelé stent. Les stents sont de petits dispositifs implantés dans des vaisseaux sanguins rétrécis pour rétablir la circulation sanguine et éviter une crise cardiaque ou un accident vasculaire cérébral et pour traiter les anévrismes du cerveau. Un contrôle précis de la surface de ces stents est nécessaire pour assurer la compatibilité de l'alliage choisi avec le milieu biologique dont il va être en contact avec. Les stents métalliques doivent satisfaire à des conditions précises définies en fonction de leur application finale. Ils doivent respecter des exigences strictes en termes de propriétés mécaniques, d'interaction électrochimique (corrosion) et de cytocompatibilité. Les alliages suivants sont traditionnellement utilisés dans les applications biomédicales et plus précisément pour les applications cardiovasculaires: l'alliage AISI316L est considéré comme une référence dans ce domaine, mais l'alliage L605, un alliage à base de Cobalt, prend de plus en plus d'importance grâce à ses propriétés mécaniques élevées (haute ductilité et haute résistance à la traction) et résistance élevée à la corrosion. L'utilisation d'alliages de titane est la nouvelle frontière pour les biomatériaux dans les applications cardiovasculaires, il est considéré comme un nouveau candidat potentiel pour les stents cardiovasculaires. Les alliages de titane présentent une combinaison unique de haute résistance et de grande ductilité (résistance à la traction et déformation uniforme supérieures à 1000 MPa et 30% respectivement). L’électropolissage est une étape de prétraitement appliquée à ces alliages métalliques pour obtenir des surfaces chimiquement homogènes, recouvertes d'une couche d'oxyde uniforme et amorphe, généralement de rugosité très lisse. Ce processus permet non seulement de contrôler les propriétés physiques de la surface, mais également celles chimiques. Le processus d'électropolissage comporte certaines variables, telles que le courant, la tension, la solution électrolytique et la température de l'électrolyte. En les contrôlant, il est possible de comprendre et d'améliorer les propriétés de la surface. Le but de ce projet est d’étudier les effets des différents variables d’électropolissage (courant, tension, solution électrolytique) sur les caractéristiques / propriétés de surface (morphologie, composition chimique et mouillabilité) des alliages utilisés pour la fabrication de stents.
Cardiovascular diseases (CVD) are responsible for about one-third of all death cases in Canada. One of the solutions used to solve this problem is using a metallic device made of a mesh and called a stent. Stents are small devices that are implanted in narrowed blood vessels to restore blood flow and to avoid a heart attack or stroke and to treat brain aneurysms. An accurate surface control is needed to assure the cytocompatibility of the chosen alloy with its biologic environment. Metallic stents must satisfy precise conditions defined according to their final application. They need to respect strict requirements, in terms of mechanical properties, electrochemical interaction (corrosion) and cytocompatibility. The following alloys are traditionally used in biomedical applications and more precisely for cardiovascular applications: the alloy AISI316L is considered a reference in this field, but the alloy L605, a Co-based material, is gaining more and more importance, due to its high mechanical properties (high ductility and high ultimate tensile strength) and high corrosion resistance. The use of Titanium alloys is the new frontier for biomaterials in cardiovascular applications, it is considered as a new potential candidate for cardiovascular stents. Titanium alloys, shows a unique combination of high strength and high ductility (ultimate tensile strength and uniform deformation higher than 1000 MPa and 30%, respectively). Electropolishing is a pre-treatment step applied to these alloys to obtain chemically homogeneous surfaces, covered with a uniform and amorphous oxide layer, generally with a very smooth roughness. This process not only makes it possible to control the physical properties of the surface, but also the chemical ones. The electropolishing process has some changeable variables, such as current, voltage, electrolytic solution and temperature of electrolyte. By controlling them, it is possible to understand and improve the surface properties. This work is aimed at studying the effects of electropolishing changeable variables (current, voltage, electrolytic solution) on surface characteristics/properties (morphology, chemical composition and wettability) of those alloys used for the manufacture of stents.

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Halwani, Dina. "Metal-tissue interactions in early stage biocorrosion of metallic stents." Birmingham, Ala. : University of Alabama at Birmingham, 2007. https://www.mhsl.uab.edu/dt/2007m/halwani.pdf.

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Thesis (M.S.)--University of Alabama at Birmingham, 2007.
Additional advisors: Peter G. Anderson, Brigitta C. Brott, Jack E. Lemons. Description based on contents viewed Feb. 4, 2008; title from title screen. Includes bibliographical references (p. 69-70).

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Oikarinen, H. (Heljä). "Imaging of biliary carcinoma, fistula and primary sclerosing cholangitis and percutaneous metallic stenting in malignant biliary obstruction." Doctoral thesis, University of Oulu, 2001. http://urn.fi/urn:isbn:9514259173.

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Abstract Biliary carcinoma, biliary fistula with occasional gallstone ileus and primary sclerosing cholangitis (PSC) are serious diseases and present specific diagnostic and therapeutic challenges. Stenting of biliary obstruction has also involved problems, but the reports are contradictory and partly limited. The aim of the present work was to evaluate and compare various imaging modalities in biliary diseases. The study also aimed to evaluate the usefulness of metallic stents in malignant biliary obstruction. The study population consisted of 210 patients with gallbladder carcinoma, bile duct carcinoma, biliary fistula, PSC or malignant biliary obstruction and eight control patients with various hepatobiliary diseases. The imaging findings of 80 patients with gallbladder carcinoma, 58 patients with bile duct carcinoma, and 16 patients with biliary fistula were reviewed. Nine patients with PSC underwent magnetic resonance cholangiography (MRC) and magnetic resonance imaging (MRI) of the liver, ultrasonography (US) of the liver and the bile ducts and endoscopic retrograde cholangiography (ERC). Eight control patients had had MRC and MRI of the liver and ERC. The medical records and radiographs of 39 patients with malignant biliary obstruction treated with percutaneously inserted metallic stents were also analysed. The stents included 48 Wallstents and seven Memotherm stents. In cases of gallbladder carcinoma, US visualised the primary tumour in 68 % and computed tomography (CT) in 57 % of the cases examined, but both methods were insufficient for accurate staging. In bile duct carcinoma, US revealed the primary tumour in 63 % and CT in 44 % of the cases examined. Both methods were sensitive in diagnosing peripheral intrahepatic cholangiocarcinoma, but inaccurate for more distal bile duct carcinoma or abdominal spread. The infiltrating type of gallbladder carcinoma and bile duct carcinoma were difficult to detect. US and CT were sensitive in revealing bile duct obstruction. The patients with biliary fistula and gallstone ileus had undergone various examinations with pathological, but not diagnostic results, and there was often a delay to diagnosis. Imaging did not reveal any of the ten spontaneous fistulas, but CT showed one of the five cases of gallstone ileus, and Gastrografin® meal revealed the single case of Bouveret's syndrome. Fistulography or cholangiography revealed all but one of the six iatrogenic fistulas. A nonvisualised or shrunken gallbladder at US should raise a suspicion of biliary enteric fistula in an appropriate clinical setting. MRC-MRI depicted the changes of PSC correctly in nine patients (radiologist 1) and in eight patients with one false positive finding (radiologist 2) in a blinded analysis. In the segmental comparison MRC missed especially bile duct dilatations. MRC was too pessimistic in the evaluation of the predictors of poor outcome. US detected features suggestive of PSC in eight patients (radiologist 3). US was unable to indicate the predictors of poor outcome. Of the patients with metallic stents in malignant biliary obstruction, 30 % had early and 66 % late complications, including stent obstructions, which occurred in 27 % of the patients at a mean of 4.4 months. The cause was mostly tumour ingrowth or overgrowth. The 25-week and 50-week patency rates were 71 % and 42 %. The patency rates of the patients with cholangiocarcinoma were significantly the lowest. There was also a tendency towards lower patency with less dilatation of the stents, an increasing number of the stents, longer strictures and hilar strictures. Many other complications were infectious. 31 % of the patients had late reinterventions.

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Dorri, Megan Mahrokh. "Study for the optimization of interfacial properties between metallic substrates and polymeric coatings by plasma-based surface modification methods to improve performance of vascular stents." Doctoral thesis, Université Laval, 2017. http://hdl.handle.net/20.500.11794/28229.

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Au cours de 15 dernières années, les maladies coronariennes et les accidents vasculaires cérébraux demeurent les causes principales de décès dans le monde. Selon l'Organisation Mondiale de la Santé, en 2015, ces deux maladies ont causé 15 millions des décès sur les 56,4 millions dans le monde. Des traitements chirurgicaux ont été élaborés et améliorés pour soigner ces maladies en maintenant les vaisseaux sanguins ouverts. Parmi les traitements chirurgicaux, l'angioplastie avec utilisation d’un stent est le traitement le plus populaire et le moins invasif. Les stents, qui sont des tubes métalliques en treillis, vont soutenir mécaniquement les vaisseaux sanguins après l’implantation et les maintenir ouverts pour améliorer le flux sanguin. Ceux-ci sont principalement composés d’acier inoxydable AISI316L (SS316L), d'alliage de cobalt-chrome et d'alliage de titane. Depuis plus d'un demi-siècle, lorsqu'un stent a été implanté pour la première fois, ils ont été considérablement améliorés. Cependant, la libération d'ions métalliques, potentiellement toxiques, et la détérioration des propriétés mécaniques à cause de la corrosion ainsi que la diminution de l'adhérence des revêtements, dans le cas de stents avec les revêtements en polymère, constituent encore des préoccupations majeures lors de l’utilisation des stents. Dans le cas des stents en SS316L, afin d’éviter la libération d'ions métalliques, au laboratoire de biomatériaux et de bioingénierie de l'Université Laval (LBB), lors de précédentes recherches, un revêtement fluorocarboné (CFx) a été étudié pour isoler complètement le stent de l'environnement biologique. Ce revêtement permet également le greffage ultérieur de molécules bioactives pour améliorer son intégration dans le corps. Cependant, l'interface de SS316L / CFx devait être améliorée pour augmenter l’adhésion du revêtement CFx sur le SS316L. Dans mon projet de doctorat, l’oxydation au plasma a été utilisé pour élaborer une nouvelle interface entre le substrat SS316L et le revêtement. Les propriétés de cette nouvelle interface, qui est composée d’une couche d'oxyde, ont été modifiées en faisant varier les paramètres du procédé plasma afin de préserver les propriétés de cette couche d’oxyde lorsqu’elle subit une déformation plastique de 25%, c’est-à-dire le pourcentage de déformation maximale que subira le stent lors de son implantation. Cette interface a permis de diminuer la libération des ions du substrat SS316L en réduisant son taux de corrosion plus que trois fois et d’améliorer l’adhérence adéquate du revêtement CFx sur le substrat, après déformation et après immersion dans une solution aqueuse saline. La nouvelle couche d'oxyde sur SS316L est une couche d'oxyde amorphe avec une épaisseur d'environ 6 nm qui se distincte bien de la microstructure polycristalline du substrat. L'amélioration des propriétés de l'interface a été attribuée à cette couche d'oxyde amorphe nano-épaisse, qui est résistante aux déformations plastiques. Cette couche d'oxyde peut être appliquée sur des stents métalliques nus composés de métaux passivables. En outre, elle crée une interface favorable pour les revêtements en polymère, qui sont utilisés pour les stents à relargage de principes actifs ainsi que pour améliorer l'intégration des stents dans le corps humain.
Over the past 15 years, ischemic heart disease and stroke have remained the leading causes of death, worldwide. According to the World Health Organization, 15 million of the 56.4 million global deaths, in 2015, were caused only by ischemic heart disease or stroke. For the treatment of these diseases, surgical treatments have been introduced and improved to hold the blood vessels open. Among the surgical treatments, angioplasty with stenting is the most popular and the least invasive treatments. Stents, which are wire mesh tubes, prepare a mechanical support for blood vessels and hold them open to restore the blood flow. They are mostly made up of AISI316L stainless steel (SS316L), cobalt-chromium, and titanium alloys. More than half a century ago, when a stent first used, it has considerably evolved. However, release of potentially-toxic metallic ions and deterioration of mechanical properties due to corrosion, and decrease of polymeric coatings adhesion, in case of coated stents, still constitute major concerns in SS316L stents. In the case of SS316L stents, to circumvent the release of metallic ions, in the laboratory for biomaterials and bioengineering of Université Laval (LBB), a fluorocarbon (CFx) coating was previously investigated to isolate the stent completely from the biological environment. The coating also enables subsequent grafting of bioactive molecules to improve its integration in the body. The results were promising; however, the interface of SS316L/CFx needed to be modified to improve the adhesion of the CFx coating. In this Ph.D. research project, a new interface between the SS316L substrate and the CFx coating was created by plasma oxidation. The properties of this new interface, which was an oxide layer, was modified by varying the plasma-process parameters in order to preserve its properties after a 25% plastic deformation. This deformation is the maximum plastic deformation that imposes on a stent during its implantation. The new interface decreased the release of ions by decreasing the corrosion rate of the SS316L substrate by a factor of three. It was also found that the new interface produced an adequate adhesion of the CFx coating to the substrate after deformation as well as after immersion in an aqueous saline solution. The new oxide layer on SS316L was an amorphous oxide layer with an approximately 6 nm thickness, which was clearly distinguished from the polycrystalline microstructure of the substrate. The enhancement of the interface properties was ascribed to this nano-thick amorphous oxide layer, which was found to be more resistant to plastic deformation. This new oxide layer can be produced on bare-metal stents made of passivating metals. Moreover, it can create a favorable interface for coated stents, which have been used in drug-eluting stents, and also to improve stents integration in the human body.

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Sullivan, J. H. "Metallic runoff from coated steels." Thesis, Swansea University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.639132.

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An investigation was carried out to assess levels of metallic runoff, particularly zinc, from the surface and cut-edges of a variety of commercial coated steels in order to ascertain potential environmental effects in line with the ongoing EU risk assessment into zinc (1995). Zinc runoff was monitored from the surfaces of a range of zinc-coated steels with sealed edges over 19 months at two UK weathering sites. The composition of the zinc coating is crucial in determining materials performance and rainfall levels are critical in determining runoff quantity. Observed zinc runoff levels are generally below the permissible drinking water level for humans but runoff levels in the harshest environment exceed this maximum for some materials during the exposure. A range of organically coated galvanised steels were exposed for 27 months at three UK weathering sites with a large cut-edge length to assess runoff from such edges. Runoff was high in initial months with zinc levels reducing with time due to the build up/action of corrosion products and corrosion inhibitors. Zinc levels were below the permissible drinking water level. Zinc runoff measured over 3 months can more accurately predict long-term organic coating delamination than salt spray and prohesion testing. Accelerated laboratory tests using a distilled water electrolyte were developed that predict long-term external weathering runoff from panels of a range of coated steels. The angle of panel, electrolyte flow rate and wet/dry cycles affect the runoff levels of such tests. The corrosion mechanisms of a variety of zinc-coated steels have been examined using the scanning vibrating electrode technique (SVET) in 0.1%NaCl. The corrosion behaviour of a coating is related to its structure and composition. The SVET has been used to assess total zinc loss from coatings during corrosion and has been confirmed using ICP-MS analysis. The predicted zinc losses from the SVET were used to model up to 12 months external weathering behaviour for the zinc-coated steels.

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Minata, Mauricio Kazuyoshi. "Próteses metálicas ou gastrojejunoanastomose no tratamento paliativo da obstrução gastroduodenal: revisão sistemática e metanálise." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/5/5168/tde-28092018-115210/.

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Introdução: obstrução gastroduodenal maligna é uma condição frequente em neoplasias gástricas e pancreáticas em estágio avançado. O tratamento paliativo visa a melhora dos sintomas e da qualidade de vida, sendo realizado pelas técnicas cirúrgicas ou endoscópicas. Embora a terapêutica cirúrgica seja consagrada, as complicações relacionadas ao procedimento e as condições clínicas desfavoráveis dos pacientes devem ser consideradas. Apesar dos avanços do tratamento endoscópico e da possibilidade de oferecer um tratamento menos invasivo, deve-se considerar as complicações e a taxa de reintervenção desta modalidade terapêutica. Novas tecnologias foram desenvolvidas para minimizar as complicações relacionadas ao uso de próteses e demandam uma análise pormenorizada. O objetivo desta revisão sistemática é comparar o tratamento endoscópico com próteses cobertas e não cobertas e o cirúrgico com gastrojejunoanastomose para obstrução gastroduodenal. Métodos: ensaios clínicos randomizados foram identificados nas bases de dados do MEDLINE, Embase, Cochrane, LILACS, SCOPUS e CINAHL. A comparação entre as próteses metálicas cobertas e não cobertas incluiu o sucesso técnico, sucesso clínico, complicações, obstrução, migração, sangramento, perfuração, fratura das próteses e reintervenção. Os desfechos usados na comparação da terapêutica cirúrgica com gastrojejunoanastomose e endoscópica com próteses foram o sucesso técnico, complicações e reintervenção. A avaliação da patência não pode ser incluída devido à falta de uniformidade dos dados extraídos. Resultados: oito artigos foram selecionados, três comparando gastrojejunostomia e próteses e cinco comparando próteses cobertas e não cobertas. A metanálise dos estudos sobre gastroenteroanastomose e próteses não demonstrou diferença significativa no sucesso técnico e número absoluto de complicações. O tratamento com próteses apresentou uma maior taxa de reintervenção que a terapêutica cirúrgica (DR = 0,26, IC 95% = 0,05 a 0,47, NNH = 4). A metanálise que comparou próteses metálicas cobertas e não cobertas não demonstrou diferença estatística significativa considerando o sucesso técnico, sucesso clínico, complicações, fratura das próteses, perfuração, sangramento e necessidade de reintervenção. Uma maior taxa de migração foi atribuída à terapêutica com próteses cobertas (DR = 0,09, IC 95% = 0,04 a 0,14, NNH = 11). Entretanto, o tratamento com próteses cobertas apresenta menor taxa de obstrução em relação às não cobertas (DR = -0,21, IC 95% = -0,27 a -0,15, NNT = 5). Uma análise de subgrupo de estudos com próteses metálicas que incluíram apenas pacientes com câncer gástrico demonstrou resultado semelhante à metanálise com todos os artigos. Conclusões: o tratamento endoscópico paliativo da obstrução gastroduodenal maligna com próteses cobertas apresenta maior taxa de migração e menor número de obstruções quando comparado com o uso de próteses não cobertas. A terapêutica cirúrgica com gastrojejunoanastomose associa-se a uma menor taxa de reintervenção em relação ao uso de próteses
Introduction: malignant gastric outlet obstruction is a frequent condition in advanced gastric and pancreatic neoplasms. Palliative treatment can be performed by endoscopic or surgical techniques. Palliation aims to relief symptoms and increase quality of life. Although surgical therapy is the established treatment, the complication rate of the procedure and the unfavorable clinical conditions must be considered. Despite the advances in the endoscopic treatment and the possibility to offer a minimally invasive therapy, complication rate and need of reintervention must be reminded. New technologies have been developed to minimize the complications related to the use of stents and require a detailed analysis. This systematic review aims to compare surgery and covered and uncovered stent treatments for gastric outlet obstruction. Methods: randomized clinical trials were identified in MEDLINE, Embase, Cochrane, LILACs, BVS, SCOPUS and CINAHL databases. Comparison of covered and uncovered stents included: technical success, clinical success, complications, obstruction, migration, bleeding, perforation, stent fracture and reintervention. The outcomes used to compare Gastrojejunostomy and stents were technical success, complications and reintervention. Patency rate could not be included because of lack of uniformity of the extracted data. Results: eight studies were selected, three comparing gastrojejunostomy and stents and five comparing covered and uncovered stents. The meta-analysis of surgical and endoscopic stent treatment showed no difference in the technical success and overall number of complications. Stents had higher reintervention rates than surgery (RD: 0.26, 95% CI [0.05, 0.47], NNH: 4). There is no significant difference in technical success, clinical success, complications, stent fractures, perforation, bleeding and the need for reintervention in the analyses of covered and uncovered stents. There is a higher migration rate in the covered stent therapy compared to uncovered self-expanding metallic stents in the palliation of malignant gastric outlet obstruction (RD: 0.09, 95% CI [0.04, 0.14], NNH: 11). Nevertheless, covered stents had lower obstruction rates (RD: -0.21, 95% CI [-0.27, - 0.15], NNT: 5). A subgroup analysis with studies that included only patients with gastric cancer showed similar results when compared with the analysis with all trials. Conclusions: in the palliation of malignant gastric outlet obstruction, covered stents had higher migration and lower obstruction rates when compared with uncovered stents. Gastrojejunostomy is associated with lower reintervention rates than stents

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KASAI, KENJI, SADAYUKI SAKUMA, SHIGEKI ITOH, HIROSHI FUKATSU, MITSUHIKO HIROSE, TSUNEO ISHIGUCHI, SANJAY S. BAIJAL, and SUMIT ROY. "Esophageal Stenting with a Self-expandable Metallic Device: A Preliminary Study." Nagoya University School of Medicine, 1992. http://hdl.handle.net/2237/17522.

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Brikas, Marijus. "Microprocessing of silicon and metals with high pulse repetition rate picosecond lasers." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2011. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2011~D_20110324_161348-78636.

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The objective of the thesis is to investigate applicability of high pulse repetition rate picosecond lasers for microfabrication and to clarify high repetition rate pulse interaction with metals and silicon. The ablation threshold and accumulation rate dependence on the laser pulse duration for silicon and metals has been experimentally studied. The model of optimal focus conditions for the maximum ablation rate was developed and experimentally confirmed. The material evaporation rate decreases duo to plasma screening for high pulse energies. Various pulse length lasers have been used for cutting and drilling of silicon. In this work key properties of laser radiation, radiation absorption, ablation and plasma formation are discussed. Surface spectroscopy methods have shown that laser cutting of silicon in the air leads to the cut surface doping with carbon atoms up to 5 µm depth from carbon dioxide in the atmosphere, and the resulting silicon carbide influences the laser cut quality. Testing of applicability of high pulse repetition rate picosecond lasers for the production of complex shapes, relationships between surface roughness and process parameters were determined. Heat abstraction from the workpiece, during laser cutting of stents from nitinol, limits the potential use of the average laser power and the effective cutting speed The silver and gold picosecond laser ablation in the liquid medium generates a narrow size distribution of nanoparticles, which form a stable... [to full text]
Disertacijos tikslas yra ištirti didelio impulsų pasikartojimo dažnio pikosekundinių lazerių pritaikomumą medžiagų mikroapdirbimui, bei išaiškinti tokių lazerių spinduliuotės sąveikos su metalais ir siliciu ypatybes. Eksperimentiškai buvo ištirta abliacijos slenksčio ir akumuliacijos koeficiento priklausomybė nuo lazerio impulso trukmės siliciui ir metalams. Sukurtas ir eksperimentiškai patvirtintas modelis optimalioms fokusavimo sąlygoms surasti, siekiant maksimalios abliacijos spartos. Didelei impulso energijai, medžiagos nugarinimo efektyvumas mažėja dėl ekranuojančio plazmos poveikio. Įvairių impulso trukmių lazeriai buvo panaudoti silicio gręžimui bei pjovimui. Paviršiaus spektroskopijos metodais, nustatyta, kad pjovimo metu silicis yra legiruojamas anglimi iki 5 µm gylio iš atmosferoje esančio anglies dvideginio, o susidariusi silicio karbido fazė įtakoja lazerinio pjovimo kokybę silicio bandinio gylyje. Taikant didelio impulsų pasikartojimo dažnio pikosekundinius lazerius sudėtingos formos detalių gamybai, rasti sąryšiai tarp paviršiaus šiurkštumo bei proceso parametrų. Pjaunant lazeriu stentus iš Nitinolio, šilumos nukreipimas nuo ruošinio riboja galimą panaudoti lazerio vidutinę galią ir tuo pačiu pasiekiamą efektyvųjį pjovimo greitį; Vykdant sidabro ir aukso abliaciją pikosekundiniu lazeriu skystyje, generuojamos siauro dydžių skirstinio nanodalelės, kurios sudaro stabilius koloidinius tirpalus.

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Brikas, Marijus. "Silicio ir metalų mikroapdirbimas didelio impulsų pasikartojimo dažnio pikosekundiniais lazeriais." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2011. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2011~D_20110324_161301-79480.

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Disertacijos tikslas yra ištirti didelio impulsų pasikartojimo dažnio pikosekundinių lazerių pritaikomumą medžiagų mikroapdirbimui, bei išaiškinti tokių lazerių spinduliuotės sąveikos su metalais ir siliciu ypatybes. Eksperimentiškai buvo ištirta abliacijos slenksčio ir akumuliacijos koeficiento priklausomybė nuo lazerio impulso trukmės siliciui ir metalams. Sukurtas ir eksperimentiškai patvirtintas modelis optimalioms fokusavimo sąlygoms surasti, siekiant maksimalios abliacijos spartos. Didelei impulso energijai, medžiagos nugarinimo efektyvumas mažėja dėl ekranuojančio plazmos poveikio. Įvairių impulso trukmių lazeriai buvo panaudoti silicio gręžimui bei pjovimui. Paviršiaus spektroskopijos metodais, nustatyta, kad pjovimo metu silicis yra legiruojamas anglimi iki 5 µm gylio iš atmosferoje esančio anglies dvideginio, o susidariusi silicio karbido fazė įtakoja lazerinio pjovimo kokybę silicio bandinio gylyje. Taikant didelio impulsų pasikartojimo dažnio pikosekundinius lazerius sudėtingos formos detalių gamybai, rasti sąryšiai tarp paviršiaus šiurkštumo bei proceso parametrų. Pjaunant lazeriu stentus iš Nitinolio, šilumos nukreipimas nuo ruošinio riboja galimą panaudoti lazerio vidutinę galią ir tuo pačiu pasiekiamą efektyvųjį pjovimo greitį; Vykdant sidabro ir aukso abliaciją pikosekundiniu lazeriu skystyje, generuojamos siauro dydžių skirstinio nanodalelės, kurios sudaro stabilius koloidinius tirpalus.
The objective of the thesis is to investigate applicability of high pulse repetition rate picosecond lasers for microfabrication and to clarify high repetition rate pulse interaction with metals and silicon. The ablation threshold and accumulation rate dependence on the laser pulse duration for silicon and metals has been experimentally studied. The model of optimal focus conditions for the maximum ablation rate was developed and experimentally confirmed. The material evaporation rate decreases duo to plasma screening for high pulse energies. Various pulse length lasers have been used for cutting and drilling of silicon. In this work key properties of laser radiation, radiation absorption, ablation and plasma formation are discussed. Surface spectroscopy methods have shown that laser cutting of silicon in the air leads to the cut surface doping with carbon atoms up to 5 µm depth from carbon dioxide in the atmosphere, and the resulting silicon carbide influences the laser cut quality. Testing of applicability of high pulse repetition rate picosecond lasers for the production of complex shapes, relationships between surface roughness and process parameters were determined. Heat abstraction from the workpiece, during laser cutting of stents from nitinol, limits the potential use of the average laser power and the effective cutting speed The silver and gold picosecond laser ablation in the liquid medium generates a narrow size distribution of nanoparticles, which form a stable... [to full text]

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11

Hekkanen, Mikko. "Inclusion Rating of Clean Steels." Thesis, Örebro University, Department of Technology, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:oru:diva-7786.

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The main part of this work has been a literature survey, reviewing scientifical reports forinformation on how steel cleanness is evaluated today, and also how the steel cleanness is related tothe fatigue performance of clean steels.

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12

Taylor, Christopher James. "Metallic and organic coating development for high performance pre-finished steels." Thesis, Swansea University, 2009. https://cronfa.swan.ac.uk/Record/cronfa42304.

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Organic coated steels are extremely popular in the construction industry due to their flexibility, cost, ease of construction and aesthetic nature. However the fact that they can be produced in many colours and finishes in large volumes slightly belies the complexity of the system itself. Many of the components have a degree of environmental sensitivity and therefore with the introduction and implementation of strict environmental legislation constant improvement is needed to keep in line or ahead of such directives. Improvement of the coating system from the substrate up is presented in this thesis. Initial work was undertaken to understand the species that would be released from an organic coating. To this end PVC based model coatings were produced and subjected to natural weathering for one year, the coatings were designed to degrade by addition of a U grade TiO2 to ensure that results were obtained during the period. The leachate species were monitored on a monthly basis and identified using inductively coupled plasma mass spectrometry (ICPMS). From this work it was found that pigmentation has an effect on the degradation of coatings. It was shown that monitoring of metallic run off is important as it provides details on species type, while some species can be identified as markers to photo-degradation of the coating. The comparison of stabilisers historic, present and novel using the same natural weathering method and testing period. Hydrotalcite was identified as a potential novel stabiliser for PVC based coatings. When compared to organotin based stabilisers as used in the past or Barium/Zinc based stabilisers that are currently used Hydrotalcite performed favourably both from a chemical and physical point of view. With regard to improving the coating system as a whole the next phase of work involved the identification of an optimum galvanised coating weight. Samples of Zn/Al galvanised steels with increasing coating weight were subjected to natural weathering for one year and the amount of zinc monitored monthly. Conventional hot dipped galvanised steel and Zalutite coatings were included in the sample field to provide further comparison points. A coating weight of 255 gm-2 was found to be the optimum with respect to the natural weathering, while Zalutite which contains a high aluminium addition performed best overall. This gave rise to the next section of work that involved used of the Scanning Vibrating Electrode Technique (SVET) to characterise the corrosion performance of galvanised coatings with aluminium additions greater than 4.8%. It was found that increasing the aluminium content improved both surface and cut edge corrosion. Under the parameters under which the samples were produced a wholly eutectic structure was achieved at a target addition of 6.1%. The final phase of work was a study on reducing the coating thickness of the high aluminium coatings to see if the improvement in corrosion performance attributed to increased aluminium addition carried across to thinner coatings. The samples were again tested using the SVET. The results suggest that there is some scope for reducing the coating thickness at certain aluminium levels.

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Röttinger, Michael Heinrich. "Metall-Stent-Implantation bei Tracheomalazie Früh- und Langzeitergebnisse /." [S.l.] : [s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=963428403.

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14

Hill, Daryl P. "The influence of non-metallic inclusions upon the properties of linepipe steels." Thesis, Aston University, 1986. http://publications.aston.ac.uk/11902/.

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The principal aim of this work was to determine the role of non-metallic inclusions in the process of hydrogen stepwise cracking (SWC). Additionally, the influence of inclusions upon the notch ductility of hydrogen charged (HC) and uncharged (UN) tensile specimens was examined. To obtain a basis for experiment a series of low carbon-manganese steels were prepared by induction melting. In order to produce variations in the composition, morphology, volume fraction, size and distribution of the inclusions the steel chemistry was adjusted prior to casting by additions of deoxidiser and Ca-Si injection. Sections of each ingot were hot rolled. Metallography, image analysis, mechanical tests and hydrogen SWC tests were then carried out. The volume fraction, morphology, and shape of inclusions influenced the tensile ductility of the steels. Marked anisotropy was found in the steels containing type II MnS inclusions at all rolling temperatures, whereas the fully Ca treated steel was isotropic. It was found that several inclusion parameters (projected length PL, mean free distance MFD, nearest-neighbour distance NND) correlated with fracture strain. An increase in inclusion volume fraction and/or the dimension of inclusions on a plane parallel to the plane of fracture led to a decrease in fracture strain. The inclusion parameters did not correlate with the fracture strains for the HC tensile specimens. However, large or clusters of inclusions acted as the principal sites for crack initiation. `Fisheyes' or areas of `flat' fracture were often found on these fracture surfaces. The criteria for SWC initiation was found to be either large inclusions or clusters of inclusions. As the PL of inclusions increased the probability of large SWCs occurring increased. SWC initiation at inclusions was believed to occur at a critical concentration of hydrogen. Factors which assisted the concentration of hydrogen at inclusions were discussed. None of the proposed mechanisms of hydrogen embrittlement could be identified as the single cause of SWC.

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15

Morata, Royes Joan. "Wear resistance of heat-treated Advanced High Strength Steels and casting." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-80526.

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The necessity to improve the durability of the machinery used in the milling industry has lead to several types of research. One study is focused on the plates that are located in the stationary and moving jaws of crushers to diminish particles sizes of Gneiss and Diabase rocks. Thus, one type of approach to increase its durability is by reducing the material loss of the plates. Amongst all the parameters to reduce the wear ratio that includes inputs from geometry to load, just the hardness input of the material can be in constant development. Consequently, there are two well-known types of heat treatment that can produce this change in hardness and are named Carbide Free Bainite (CFB) and Quenching and Partitioning (QP). In this master thesis the topic is to perform the QP heat treatments for two compositions A and B to obtain the microstructure of the steels that consist in a mix of austenite, bainite and martensite which considerably increase the hardness while the toughness is not drastically reduced due to the austenite soft phase. Five samples have been studied at four different partitioning temperatures: QP250 A, QP180 B, QP210 B, QP240 B and Mn Steel as it is the composition most used nowadays in the industry. In order to characterise both mechanical properties and microstructural features, different analysis had been performed with Micro-indentations, Charpy-V, Gouging Abrasion Tests, Optical Microscopy, Scanning Electron Microscopy and X-Ray Diffraction. These analysis had been done in the samples before and after wear as a result in change of the microstructure. As the abrasive-impact of the rocks collide with the sample, austenite transforms to martensite by induced plasticity called TRIP effect. Thus, the surface of the alloy is harder than the bulk material as no austenite is found and the wear ratio is seen to be improved. The results have shown several behaviours. Austenite transforms in its majority to fresh martensite which is an unstable martensitic phase but harder than tempered martensite that is the stable martensitic phase. Moreover, the difference in hardness between the bulk and the surface produce an affected depth layer as a consequence of the abrasive-impact penetration of rocks in which the microstructure has fully transformed to martensite on the surface and the austenite phase increases as it goes further inside the steel. The thinner this layer is, the better wear ratio presents the alloy. From all the samples, the best combination of hardness and toughness is for QP210 B.

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Guo, Shuo. "Evaluation of deformed MnS in different industrial steels by using electrolytic extraction." Thesis, KTH, Materialvetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-217880.

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The inclusions have a different chemical composition and give the steel different mechanical properties. These inclusions affect several properties of steel. In order to understand how the inclusions will affect the steel properties, the electrolytic extraction of 3D investigate method is applied on the steel grade of 42CrMo4. Then follow with Scanning Electron Microscope (SEM) observation. Steel samples from both ingot and rolling with and without heat treatment are observed and compared with different ratios. The result shown that, heat treatment can be applied for removing carbides successfully. And most inclusions are belonging to Type RS which is rod like MnS. The percentage of broken particles can be up to 80%, which means that the reason for the inclusions broken should be find. And heat treatment can affect the characteristics of elongated MnS.

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17

Zhou, Haipo. "Modification of non-metallic inclusions to improve the fatigue properties of nitriding steels." Thesis, University of Canterbury. Mechanical Engineering, 1993. http://hdl.handle.net/10092/6768.

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Nitriding processes are widely used to improve the fatigue properties of steel. Fatigue failures in nitriding steels initiate from sub-surface non-metallic inclusions, which are usually oxide inclusions. It is known that duplex oxysulphide inclusions are less harmful to the fatigue properties of steel than oxide inclusions alone, since the sulphide outer phase acts as a buffer to the oxide in the core, and thus reduces the fatigue-initiating stress influence of oxide inclusions. Twelve nitriding steel melts were produced, and non-metallic inclusions, modified by adding CaSi cored wire, were investigated. Since calcium has a high vapour pressure and a low solubility in molten steel, it is difficult to effectively modify non-metallic inclusions by the addition of CaSi cored wire in small furnaces. However, it was found that the addition of CaSi cored wire at a lower temperature was favourable to higher calcium injection yield in a small furnace, and it was also observed that the reaction with liquid steel was less violent, resulting in the effective modification of non-metallic inclusions. Analysis by a scanning electron microscope with energy dispersive X-ray technique showed a proportion of duplex oxysulphide inclusions formed in ingots from 11A, with the remainder being predominantly globular calcium aluminate inclusions. Specimens for direct stress fatigue testing were produced from steels containing both modified and unmodified inclusions, and the fatigue properties were compared. It was found that calcium aluminate inclusions had a more deleterious effect on the fatigue properties of steel than alumina inclusions. In calcium modified steels, at lifetimes of more than 5x10⁵ cycles, fatigue cracks always initiated from calcium aluminate inclusions, which were partly or completely debonded from the matrix. The fatigue properties of the calcium modified steel was found to be inferior to those of the unmodified steel. No duplex oxysulphide inclusions were found among those inclusions which produced fatigue crack initiations, and this indicated that when they were present calcium aluminate inclusions governed the fatigue properties of steel whether or not duplex oxysulphide inclusions were present in the steel. It is inferred that the fatigue properties of steel can be improved if all large calcium aluminate inclusions are modified to duplex oxysulphide inclusions.

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18

Englund, Hanna, and Henrietta Isaksson. "Regulation of Nitrogen Content in High Alloyed Stainless Steels during the AOD Process." Thesis, KTH, Materialvetenskap, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-254419.

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As a final step in the argon oxygen decarburisation (AOD) process, argon- and nitrogen gas is blown through the melt. To regulate the nitrogen content in the steel melt during this step a reliable model is needed. With data from 31 heats of the duplex stainless steel SAF2507 collected at Sandvik Materials Technology (SMT), different models are investigated. This is done by looking at the partial pressure of the nitrogen gas and the nitrogen content achieved during each heat. By calculating the nitrogen solubility in the steel melt with different models and then using Sieverts’s law, a partial pressure for the nitrogen gas is obtained for each heat and compared with the data. With adjustments done for a model obtained from J. Kijac et al., more reliable results are attained than by the model used today at SMT. It should be kept in mind that this model is based on the theory with diluted solution and is therefore not optimal for high alloyed steels, and it is suggested to develop a model from a software based on real solution such as Thermo-Calc.
I slutskedet av AOD-processen blåses argon- och kvävgas genom stålsmältan. En pålitlig modell behövs för att reglera kvävehalten i stålsmältan under det här steget. Olika modeller undersöks med data från 31 charger av det duplexa rostfria stålet SAF2507 samlad från Sandvik Materials Technology (SMT). Undersökningen sker genom att titta på partialtrycket av kvävgasen och kvävehalten som uppnåddes för varje charge. Genom att beräkna kvävelösligheten i stålsmältan med olika modeller och sedan använda Sieverts lag, kan ett partialtryck för kvävgas räknas ut för varje charge och jämföras med datan. Mer exakta resultat är uppnådda med en justerad modell hämtad från J. Kijac et al. jämfört med den modell använd på SMT idag. Att ha i åtanke är att denna modell är baserad på teori med antagande om utspädd lösning, vilket inte är optimalt för höglegerade stål och ett förslag är att utveckla en modell med hjälp av ett mjukvaruprogram som baseras på äkta lösning såsom Thermo-Calc.

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19

Schmiedt, Anja Bettina [Verfasser]. "Statistical modeling of non-metallic inclusions in steels and extreme value analysis / Anja Bettina Schmiedt." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2013. http://d-nb.info/1047230615/34.

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20

Bubenko, Clara, Karl Magnil, and Melker Olofsson. "An Investigation of Stainless Steels for Long-term Use in Liquid Sodium at up to 700°C." Thesis, KTH, Materialvetenskap, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-254324.

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The Swedish company Azelio has developed a high-efficient Stirling engine which is powered by solar energy. Since the access of solar power is limited to day-time, Azelio has also developed their own Thermal Energy Storage (TES), which collects and stores solar energy and thereby provides the engine with energy also during night-time. The engine runs a generator which produces electricity, around the clock. Liquid sodium is used as Heat Transfer Fluid (HTF) from the TES to the engine, and the temperature reaches above 600°C. At these temperatures, sodium is highly reactive and surrounding materials could strain from phenomena such as corrosion and creep. By comparing the commonly known high-temperature classified steel 253 MA to other commercially available steels, a suitable and affordable option that can withstand liquid sodium is sought. From literature studies, a list of candidates was produced. The materials were then mainly analysed upon ingoing alloying elements’ influence on material properties. The austenitic steel 153 MA has some great advantages to 253 MA at these temperatures, such as a more stable microstructure. 153 MA is therefore, from this work, recommended for further investigation.
Det svenska företaget Azelio har utvecklat en stirlingmotor som drivs av solenergi. Då tillgången på solenergi är begränsad till dagtid har Azelio också utvecklat en termisk lagringsenhet (TES). Den termiska lagringsenheten absorberar och lagrar solenergi och kan därmed förse stirlingmotorn med värme även under natten. Stirlingmotorn driver i sin tur en generator vilken producerar elektricitet under hela dygnet. Natrium används som värmeledningsfluid (HTF) mellan TES och stirlingmotorn, vid temperaturer över 600°C. Vid dessa temperaturer är natrium högreaktivt och fenomen såsom kryp och korrosion kan uppstå, vilka kan påverka egenskaperna hos omgivande material. Genom att jämföra högtemperaturstålet 253 MA med andra kommersiella stål, eftersöks en kvalificerad och prisvärd legering som kan motstå flytande natrium vid dessa temperaturer. Från en omfattande litteraturstudie skapades en lista med möjliga kandidater. Materialen analyserades sedan i huvudsak utifrån ingående legeringselements påverkan på dess egenskaper. Analysen visar på att 153 MA har några betydande fördelar jämfört med 253 MA, såsom en mer stabil mikrostruktur vid de angivna temperaturerna. Detta arbete rekommenderar därför 153 MA för vidare undersökning och testning.

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21

Yin, Jiaqing. "Formation of Bainite in Steels." Doctoral thesis, KTH, Metallografi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-207596.

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A systematic survey of morphology of bainite and proeutectoid ferrite was carried out in order to validate some old thoughts of bainite transformation mechanism. It is confirmed that there is no morphological evidence supporting a sharp change neither between Widmanstätten ferrite and the ferritic component of upper bainite, nor between upper and lower bainite. Both Widmanstätten ferrite and upper bainite start with precipitation of ferrite plates at a grain boundary while lower bainite starts with intragranular nucleation. In case of grain boundary nucleation, a group of parallel plates with same crystallographic orientation to the parent austenite grain forms. This process is followed by a second stage of decomposition of the austenitic interspace, which remained in between the primary ferrite plates. At high temperature, the austenitic interspace would either retain as thin slabs or transform into pearlite through a nodule originated from a grain boundary. At lower temperature, cementite precipitation starts to be possible and initiates simultaneous growth of ferrite. Generally, there are two modes of such eutectoid reactions operating in the second stage, i.e. a degenerate and a cooperative mode, which would lead to typical upper and lower bainite, respectively, in definition of carbides morphology. Both upper and lower bainite according to this definition are observed in a wide temperature range. A sharp temperature between the upper and lower bainite structures thus exists only when the definition is based on their nucleation sites, i.e. grain boundary nucleation for upper bainite and intragranular nucleation for lower bainite. Supposing that the first stage is a diffusionless process it should have a high growth rate to prevent carbon diffusion. This is not supported by lengthening rate obtained in current study as well as data from literature for Fe-C alloys. Finally, it is shown that the “subunits” play no role in the lengthening process of bainite.

QC 20170523

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Ånmark, Niclas. "Inclusion Characteristics and Their Link to Tool wear in Metal Cutting of Clean Steels Suitable for Automotive Applications." Licentiate thesis, KTH, Tillämpad processmetallurgi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-164875.

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This thesis covers some aspects of hard part turning of carburised steels using a poly‑crystalline cubic boron nitride (PCBN) cutting tool during fine machining. The emphasis is on the influence of the steel cleanliness and the characteristics of non‑metallic inclusions in the workpiece on the active wear mechanisms of the cutting tool. Four carburising steel grades suitable for automotive applications were included, including one that was Ca‑treated. A superior tool life was obtained when turning the Ca-treated steel. The superior machinability is associated with the deposition of lubricating (Mn,Ca)S and (CaO)x-Al2O3-S slag layers, which are formed on the rake face of the cutting tool during machining. Moreover, the transfer of work material to the rake face crater is characteristic in hard part turning of clean steels. It can be because of the lack of sulfides that protect the cutting edge when turning machinability treated steels. This corresponds to the more pronounced crater wear caused by the low‑sulfur steels than that of the steels with higher sulfur contents. It was also concluded that the composition of the non‑metallic inclusions in the Ca‑treated steel is a more important factor than the inclusion number and size, in hard part turning using a PCBN cutting tool. Also, a 3D analysis after electrolytic extraction was found to give a more precise characterisation of non‑metallic inclusions than the conventional 2D analysis by SEM‑EDS. In turn, better correlations to machinability and mechanical properties can be obtained. Hence, the use of this technique is beneficial for future material development. Finally, the challenge for future metallurgy is to manufacture high‑performance steels with improved combined properties of mechanical strength and machinability.

QC 20150422

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23

Brisenmark, Emil, and Valencik Jane Jönsson. "Evaluation of the Effect of Non-Metallic Inclusions on the Corrosion Resistance of Stainless Steels and Nickel-based Alloys." Thesis, KTH, Materialvetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-277900.

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Non-metallic inclusions (NMI) are small impurities that can always be found in steel and other materials. NMIs are of great importance because they may negatively impact various properties of the steel, depending on their composition, morphology and numbers. In the oil and gas industry, one of the most concerning property that can be affected by the NMIs is corrosion resistance. In this report, certain aspects of NMIs were investigated, such as size or composition and effect which they have on the corrosion resistance. To accomplish this, two different steel alloy samples from pipelines were analyzed using electrolytic extraction,a scanning electron microscope (SEM) and a software called ImageJ. The results showed that only Niobium-Titanium carbides (NbTi-C) which were found on one of the samples had the potential to be dangerous, due to them causing pits ranging from 1 to 12.5 times their inclusion size. It was also found out that the size of the inclusions did not affect the size of the pitting that they caused.
Icke metalliska inneslutningar (NMI) är små föroreningar som alltid finns i stål och andramaterial. NMI:er är mycket viktiga eftersom de kan negativt påverka olika egenskaper hos stål, beroende på deras komposition, morfologi och antal. I olje -och gasindustrin är en särskilt oroande egenskap som kan påverkas av NMI:er deras korrosionsmotstånd. I denna rapport undersöktes hur olika aspekter hos NMI:er, som storlek eller komposition, påverkade korrosionsmotståndet i rostfritt stål. För att utföra detta analyserades två olika stållegeringsprovbitar från pipelines med elektrolytisk extraktion, ett svepelektronmikroskop (SEM) och ett program som kallas ImageJ. Från resultatet framkom det att baraNiob-Titankarbider (NbTi-C) som fanns på en av provbitarna hade potentialen att vara farlig, då den orsakar gropar som är 1 till 12.5 gånger större än sin egen storlek. Det framkom också att storleken på inneslutningarna inte påverkade storleken på deras gropar.

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Gutman, Lucie. "Selection of high-temperature abrasion resistant steels for the mining and processing industry." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-80967.

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High-temperature abrasion is an expensive issue in industrial fields such as glass and cement production or mining and processing industry. Yet its effects on steel are not well documented. This study investigates and analyses the behaviour of six different steel grades placed in hot abrasive conditions similar conditions encountered in the industry to enables better material selection. Abrasion tests in a slurry pot were done at room temperature and at 500 °C. Impact and tensile tests were also performed at different temperatures. To complete the mechanical properties evaluation, hardness measurements were executed before and after tempering at 500 °C. Wear rates assessed at room temperature or at 500 °C, are independent of the mechanical properties of the material. At high temperature, it was shown that wear rates and performance of the steels were influenced by tempering and leading to a unique microstructures for all steel grades investigated and equalize their performances. To conclude, high temperature wear of the investigated grades does not depend on their mechanical properties, however, it can be influenced by their tempering resistance. As the temperature increase, steel tempers, its mechanical properties decrease and homogenise with other steel grades' performances, but some grades keep their properties longer at high temperature.

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25

Facchini, Eugenia. "Analisi del surriscaldamento indotto nel corpo umano dalle onde a radiofrequenza durante la risonanza magnetica anche in presenza di stent e cavi metallici." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2021.

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Gli esami di risonanza magnetica sono una delle tecniche di imaging diagnostico più frequentemente utilizzate. Essi portano con sé un rischio di surriscaldamento nei tessuti del corpo umano dovuto alle onde a radiofrequenza, questo rischio si acuisce in presenza di dispositivi medici dotati di componenti metallici, quali in particolare stent e cavi metallici, impiantati nell’individuo sottoposto all’esame. Questo elaborato vuole analizzare i principi fisici alla base di questo fenomeno e lo stato dell’arte per quanto riguarda queste tematiche.

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Gram, Tove, and Amanda Vickerfält. "Characterization of non-metallic inclusions according to morphology and composition : A comparison of two different steels before and after turning." Thesis, KTH, Materialvetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-170024.

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Investigation of non metallic inclusions in two different steels from Sandvik was made before and after turning. After dissolving the non-metallic inclusions by electrolytic extraction the particles were analysed manually or by INCA feature. This was referred to as 3D analysis. INCA feature analysis without extraction of particles was also performed, this was referred to as 2D analysis. The aim of the report was to a make a characterization of non-metallic inclusions with respect to chemical composition, aspect ratio, size and shape. The aim was also to compare different investigation methods. Samples were prepared and investigated. It was obtained that inclusions with sulphur content was elongated and crushed during the turning process. Broken sulphides were detected in one of the steels, and broken oxysulphides in the other steel in the electrolytically extracted chips created by turning. The first steel, steel 1, mainly contained sulphide and oxysulphide inclusions, and steel 2 mainly contained oxysulphides. The aspect ratio obtained by 2D analysis of the sulphide inclusions in steel 1 before turning showed similar results to the electrolytic extracted inclusions measured by hand. The aspect ratio increased with the length of the inclusion. However the deviation of data obtained by the 2D analysis was larger than deviation from the extracted particles measured by hand. The reason for this was assumed to be that the 2D method was not able to analyse the true shape of the inclusions e.g. if inclusions were partly concealed by metal matrix. In analysis of steel 2 the average aspect ratio decreased for oxides and increased for oxysulphides after turning. The chemical composition of inclusions did not change after the turning process for neither of the steels. Copper was detected in the electrolytic extracted inclusions, however not in the 2D investigation by SEM. This is an interesting topic for future research.

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Hedberg, Petra. "Method to assess machinability of engineering steels using coated carbide tools." Thesis, Uppsala universitet, Tillämpad materialvetenskap, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-442898.

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In this master thesis, performed at Ovako Group R&D (Hofors) a new machining test method for ranking heats of calcium-treated steels, M-Steels, has been proposed. A total of six different heats of 42CrMo4-M steel in the quenched-and-tempered (Q+T) condition were tested. The proposed method uses dry turning with coated cemented carbide tools at a cutting speed of 225 m/min, 2 mm depth of cut, and a feed rate of 0.35 rev/min. The machining test is tuned so that M-Steels within medium-sized bar diameters and a small hardness interval can be differentiated by monitoring the flank wear progression of the cutting tool. This method is easily taught to a CNC-operator, it mimics real workshop conditions and can be repeated with relative robustness and ease of execution. It is possible to get a ranking where both the M-Steel treatment and hardness are included. The major differentiator of tool wear performance was found to be a combination of wear of the outermost Al2O3 coating and the build-up and renewal of protective slag deposits on the tool rake. The rake face wear was found similar between the M-Steels samples, so it is thought that the effect of the slag deposits, as thermal barriers, affect the plastic deformation and wear of the flank face. Given the slag deposits sub-micron thickness, this indirect method of recording the flank wear is highly recommended to showcase the positive effects of the M-Steel in machining The inclusion content was evaluated according to ASTM E45 and with a scanning electron microscope (SEM) automated inclusion assessment. The link between the machinability performance of the M-Steels and their inclusion characteristics could not be clarified in this work. Teknisk-naturvetenskapliga fakulteten

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Ekengren, Jens. "Large and rare : An extreme values approach to estimating the distribution of large defects in high-performance steels." Doctoral thesis, Karlstads universitet, Avdelningen för maskin- och materialteknik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-8226.

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The presence of different types of defects is an important reality for manufacturers and users of engineering materials. Generally, the defects are either considered to be the unwanted products of impurities in the raw materials or to have been introduced during the manufacturing process. In high-quality steel materials, such as tool steel, the defects are usually non-metallic inclusions such as oxides or sulfides. Traditional methods for purity control during standard manufacturing practice are usually based on the light optical microscopy scanning of polished surfaces and some statistical evaluation of the results. Yet, as the steel manufacturing process has improved, large defects have become increasingly rare. A major disadvantage of the traditional quality control methods is that the accuracy decreases proportionally to the increased rarity of the largest defects unless large areas are examined. However, the use of very high cycle fatigue to 109 cycles has been shown to be a powerful method to locate the largest defects in steel samples. The distribution of the located defects may then be modelled using extreme value statistics. This work presents new methods for determining the volume distribution of large defects in high-quality steels, based on ultrasonic fatigue and the Generalized Extreme Value (GEV) distribution. The methods have been developed and verified by extensive experimental testing, including over 400 fatigue test specimens. Further, a method for reducing the distributions into one single ranking variable has been proposed, as well as a way to estimate an ideal endurance strength at different life lengths using the observed defects and endurance limits. The methods can not only be used to discriminate between different materials made by different process routes, but also to differentiate between different batches of the same material. It is also shown that all modes of the GEV are to be found in different steel materials, thereby challenging a common assumption that the Gumbel distribution, a special case of the GEV, is the appropriate distribution choice when determining the distribution of defects. The new methods have been compared to traditional quality control methods used in common practice (surface scanning using LOM/SEM and ultrasound C-scan), and suggest a greater number of large defects present in the steel than could otherwise be detected.

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Åström, August, and Morgan Sten. "Macro segregation in continuous cast HSLA steels : With correlation to impact toughness." Thesis, KTH, Materialvetenskap, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-254348.

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The report reviews macro segregations in continuous cast steels and possible correlations to impact toughness. The purpose of the thesis is to investigate centreline segregates and V-segregates to see which of them that affect impact toughness the most. Apart from a literature study, Charpy-V data was collected with permission from SSAB for two steel types, grade A and grade B, each with respective dominant segregation type. The collected data was yielded in three individual Charpy-V tests at different spots on the metal sheet, derived within a close area. The average value of these tests were used in statistical analysis to observe the spread of values in different heats of the two steels. Additionally, the specimens were etched and captured in cross-section. Results indicated that for the data of grade A, where centreline segregates were dominant, the spread of values was higher than for the data of grade B. The conclusion is that centreline segregations are worse in relation to impact toughness, since higher deviations translates to less predictable properties from a customers perspective.
Denna rapport granskar makrosegringar i stränggjutet stål och eventuella kopplingar till slagseghet. Centrumsegringar och V-segringar undersöks för att undersöka vilken segringstyp som har störst effekt på slagseghet, vilket är syftet med denna avhandling. Förutom en litteraturstudie, hämtades Charpy-V data med SSAB’s medgivande från två olika stålsorter, kvalitet A och kvalitet B, med respektive dominant segringstyp. Datan som inhämtades erhölls från tre stycken Charpy-V tester för varje plåt, från ett närliggande område. Medelvärdet för dessa datapunkter användes i statistisk analysför att obeservera spridningen av datapunkter i olika charger av de två stålen. Dessutom, erhölls segringsbilder för respektive slab från SSAB. Resultaten visade att datapunkterna för kvalitet A, som hade centrumsegring som domiant segringstyp, var mer spridd än datan för kvalitet B. Således, är slutsatsen att centrumsegring är värre i relation till slagseghet eftersom en högre avvikelse leder till mindre förutsägbara egenskaper från en kunds perspektiv.

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Laarich, Abdellatif. "Designing a Heat Treatment to Achieve Ductile Advanced High Strength Steels." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-79754.

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Heat treatment is a way to significantly change materials properties. When presented with materials that lack certain mechanical properties, it is possible to change its chemical properties and microstructures by applying heat. This can help achieve better yield strength, ductility and toughness. This project discusses the effects of multiple distinct heat treatment methods for several materials in order to improve ductility and elongation without diminishing strength. The materials in question are High Aluminum Steel and Strenx 700MC steel, the first being under development and the second being a commercially available steel. These steels show promise to be used as high ductility, high strength, and 3rd generation steels. The heat treatments can change the mechanical proprieties of the base materials in order to optimize these steels for applications in vertical access solutions. The heat treatments in this project were Quenching and Partitioning (QP), Quenching and Tempering (QT), Austempering (AUST), Intercritical Heat Treatment (IHT) and other usual heat treatments such as Double normalizing (D-Norm). First, the most beneficial type of the above mentioned heat treatments was selected for each steel and series of heat treatments were performed in order to identify and optimize the best method for each steel. Then, heat treated samples underwent a series of tests to numerically quantify their properties and compare them to the existing steels in Alimak’s applications. The results show that Quenching and Partitioning is the most promising heat treatment for optimizing strength and ductility in High Aluminum Steel, with elongation values up to 19% together with yield strengths of 700 MPa. For Strenx 700MC a combination of temperature and time was found that gave an elongation of above 25% with a yield strength of 450 MPa. The explanation for the good properties was partly grain refinement and phase transformations during heat treatments.

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Ameen, Ahamed. "Optimization of annealing parameters for SANDVIK 13C26 and 20C strip steels : By MODDE analysis and modified JMAK method." Thesis, KTH, Materialvetenskap, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-259336.

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The process optimization of continuous annealing furnace, RHF 125, for recrystallization annealing of two steel grades, Sandvik 13C26 and Sandvik 20C has been carried out. To recreate the continuous annealing process carried out in the roller hearth furnace in the industry, samples with different cold reduction rates were chosen from ongoing production lines. An experimental heat treatment model was chosen by the ‘Design of Experiments’ approach from MODDE (from U-Metrics). The annealing temperature was chosen below the austenitization temperature for both steel grades and soaking time of 30 seconds to 240 seconds were chosen. Microscopic estimation of fraction recrystallized was performed with the help of Electron Back Scattered Diffraction, accompanied by mechanical testing methods to measure the hardness and yield strength of the steel strips. The experimental output was used to create a model to correlate between the different cold reduction rates and annealing parameters to achieve a higher degree of recrystallization along with desirable mechanical properties. Also, a modified Johnson-Mehl-Avrami-Kolomogrov model, based on hardness values, to determine the transformation kinetics by tracking the progress of recrystallization was developed. The model was verified with EBSD measurements for Sandvik 13C26 strip steels. For 20C, inhomogeneous recrystallization was observed, thus limiting the model’s adaptability to steels which exhibit homogeneous recrystallization behavior and negligible change in precipitation and/or coarsening of secondary phases.
Processoptimering av en kontinuerlig glödgningsugn, RHF 125, för rekristallisationsglödgning av två Sandvik-stål, Sandvik 13C26 och Sandvik 20C, har genomförts. För att återskapa den kontinuerliga glödgningsprocessen som utförs den verkilga processen i valdes prover och olika kallreduktionshastigheter från pågående produktionslinjer. En experimentell värmebehandlingsmodell valdes med metoden 'Design of Experiments' med MODDE (från U-Metrics). Glödgningstemperaturen valdes till en temperatur under austeniseringstemperaturen för båda stålen och hålltider varierade från 30 s till 240 s. Mikroskopisk uppskattning av fraktionen rekristalliserat material utfördes med hjälp av Electron Back Scatter Diffraktion (EBSD), åtföljd av mekaniska testmetoder för att mäta hårdheten och sträckgränsen för stålproverna. De experimentella resultaten användes för att skapa en modell för att korrelera mellan de olika reduktionshastigheterna och glödgningsparametrarna för att uppnå högre grad av rekristallisation tillsammans med önskvärda mekaniska egenskaper. Dessutom utvecklades en modifierad Johnson-Mehl-Avrami-Kolomogrov-modell, baserad på hårdhetsvärden, för att bestämma transformationskinetiken genom att spåra evolutionen för rekristallisation. Modellen verifierades genom jämförelse med EBSD-mätningarna för Sandvik 13C26 bandstål. För 20 °C observerades inhomogen rekristallisation, vilket begränsade modellens användbarhet till stål som uppvisade homogent rekristallisationsbeteende och försumbar förändring i utskiljning och/eller förgrovning av sekundära faser.

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Noftz, Maria Raili [Verfasser]. "Spätkomplikationen nach Implantation von selbstexpandierenden Metall-Stents bei Patienten mit maligner Ösophagusstenose : Möglichkeiten der Reintervention und Einfluss auf die Überlebenszeit / Maria Raili Noftz." Lübeck : Zentrale Hochschulbibliothek Lübeck, 2011. http://d-nb.info/1014186684/34.

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Jubica, Jubica. "Characterization of Secondary Carbides in Low-Alloyed Martensitic Model Alloy Tool Steels." Thesis, KTH, Materialvetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-284449.

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The development of tool steels for making and shaping other materials requires a better understanding of the material's properties during manufacture. These high-quality steels include many alloying elements, which give increased hardness during tempering. For producing hardened microstructures, austenite generation is essential. The martensite formed by rapid quenching of austenite followed by tempering helps develop high strength steels. Studying carbide precipitation is a challenge as they are very small in size, present only in small volume fractions and high number densities. The carbide reactions are complicated due to so-called metastable carbides, which are only present as part of the precipitation process. This work focuses on model alloys with two main elements in addition to iron and carbon, molybdenum, and vanadium, to clarify and simplify the carbide characterization. This is done to determine the effect of molybdenum and vanadium carbides on the overall hardness. In this work, two model alloys, A and B, are tempered at 550°C and 600°C with the same vanadium content but different molybdenum contents. The hardness of the materials is evaluated and compared at these temperatures. A more detailed characterization work is done for material A with Scanning Transmission Electron Microscopy-Energy Dispersive Spectroscopy (STEM-EDS) to understand the microstructure and analyze the precipitates. Simulations are performed with Thermo-Calc Prisma (TC-Prisma) to support the experimental work, which includes the simulation of the secondary carbide precipitation, mainly molybdenum carbides in material A tempered for 24h at 600°C, and predicts the carbide precipitation behavior in this steel. The results from STEM-EDS and TC-Prisma for material A, show that the small secondary carbides in the martensite contribute to the increased strength of material A. Due to the overaging of the carbides at 600°C, the hardness at 550°C is higher than at 600°C for material A. The given thesis work is an attempt to interpret the development of secondary carbides of Mo and V in the martensitic matrix and their role in the overall hardness.
Den ständiga utvecklingen av högpresterande stål för transport, konstruktion och energisektorn kräver bättre förståelse för materialets egenskaper vid tillverkning. Dessa martensitiska stål inkluderar många legeringselement vilket ger ökad hårdhet vid härdning och anlöpning. Att studera utskiljning av karbider är en utmaning eftersom de är närvarande endast i liten volymsfraktion. Karbidreaktionerna är komplexa till följd av så kallade metastabila karbider vilka endast är närvarande vid en del av utskiljningsförloppet. För att tydliggöra och förenkla karbidkarakteriseringen fokuserar detta arbete på modellegeringar med två huvudelement utöver järn och kol, molybden och vanadin. Detta görs för att fastställa effekten av molybden och vanadinkarbider på den totala hårdheten. I detta arbete studeras två modellegeringar, A och B, härdade och anlöpta vid 550 °C och 600 °C med samma vanadininnehåll men olika molybdeninnehåll. Materialens hårdhet utvärderas och jämförs vid dessa temperaturer. Ett mer detaljerat karaktäriseringsarbete görs för material A med hjälp av STEM-EDS för att förstå mikrostrukturen och analysera utskiljningarna. Simuleringar görs med TC-PRISMA för att stödja det experimentella arbetet, vilket inkluderar simulering av den sekundära karbidutskiljningen och predikterar karbidstrukturen i dessa stål. Resultaten visar att de små sekundärkarbiderna i martensiten bidrar till den ökade styrkan hos material A. Hårdheten vid 550 °C är högre än vid 600 °C för material A eftersom både utskiljningen av karbider är sker långsammare och även dislokationsåterhämtning.

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Hall, Emily. "Modelling the influence of porosity on fatigue strength of sintered steels." Thesis, Uppsala universitet, Strukturkemi, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-398977.

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The pores in pressed and sintered components constitute weak points in the material since the stress concentration is larger than the nominal stress there. Therefore, fatigue cracks initiate at the pores. Specifically, it can be assumed that the fatigue cracks initiate at the largest pore in the stressed volume. Studies have previously looked at finding ways to model the fatigue strength of the material based on the largest pore. This thesis looks at a model previously derived for hardened pressed and sintered materials that is based on linear elastic fracture mechanics and investigates if said model can be modified to include non-hardened pressed and sintered materials that do not necessarily behave linear elastically. A model describing the influence of the size of the largest pore on the fatigue limit using empirical coefficients is suggested. Furthermore, the area of the largest pore is modelled using extreme value statistics. The model proved successful in modelling the density effect of the porosity on the fatigue strength for two materials with different microstructures: one with a homogeneous microstructure and one with a heterogeneous microstructure. For the material with the homogenoeous microstructure the model also accounted well for the notch effect when tested on samples with a different geometry. However, for the heterogeneous material the model did not account for the notch effect. Deformation hardening due to local plastic deformation in the softer phases was suggested as a possible explanation and was supported by tensile tests.

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Alonso, Frank Micael [Verfasser], Sannakaisa [Gutachter] Virtanen, and Aldo R. [Gutachter] Boccaccini. "Functionalization of Steels and other Metallic Materials with Hydrophobic Layers - Influence on Wetting and Corrosion Resistance / Micael Alonso Frank ; Gutachter: Sannakaisa Virtanen, Aldo R. Boccaccini." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2017. http://d-nb.info/1150964286/34.

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Burrows, Christopher John. "The irradiation resistance of oxide dispersion strengthened steels." Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:e464cc9c-5ac0-43cb-acd2-c09706176d9a.

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Reduced activation oxide dispersion strengthened (ODS) steels are candidate alloys for use in fusion reactor systems and are fabricated by mechanically alloying yttrium oxide to a reduced activation ferritic steel powder. The product is consolidated at high temperature by hot isostatic pressing (HIP), producing a dispersion of nanometre sized oxide particles throughout the ferritic microstructure. These particles have been shown to both improve the high temperature mechanical properties of the alloy and provide trapping sites for helium gas. The use of these particles to sequester helium is of particular significance in the development of a structural ODS steel for fusion reactor systems. A fusion power reactor, based on the ITER design, is expected to produce over 2000 appm transmutant helium in any steel components exposed to the core neutron flux. At these gas concentrations, conventional steels undergo severe swelling and embrittlement, motivating the development of materials capable of managing helium accumulation. This thesis investigates the use of the oxide particle dispersion in sequestering helium introduced by ion implantation. An initial characterisation of a model Fe-14Cr-0.25Y₂O₃ (wt%) system was completed using high resolution transmission electron microscopy (HRTEM) and atom probe tomography (APT). This demonstrated the efficacy of the production methods and the gas trapping capabilities of the oxide particles via argon gas, introduced during the mechanical alloying process. The subsequent consolidation of a full set of Fe-14Cr-3W-0.2Ti-0.25Y₂O₃ (wt%) ODS alloys at 1150°C, 1050 °C and 950 °C produced a systematic variation in the density of the particle dispersion. The characterisation of these materials using APT provided an insight into the consistent Y₂Ti₃O₅ particle chemistry found in each consolidation, and identified a stoichiometric shift from Y₂Ti₃O₅ to YTiO2 following short term annealing periods at 1000°C. Though further work is required, this shift is thought to be consistent with a thermodynamically mediated transition of the metastable clusters to stable oxide particles. Following implantation with 2000 appm helium and examination under TEM, the helium bubble and particle densities were found to be closely correlated thus providing evidence for an association between the particles and the gas bubbles. Controlling the helium bubble density via the particle dispersion demonstrates the potential use of processing temperature in controlling how helium accumulates in an implanted ODS microstructure. The effects of both bubble and particle densities on mechanical properties were investigated further using nanoindentation methods. Significant local variation in the hardness of the ODS steels was found to result from the bimodal grain size distribution of the material. By using only those measurements taken from large grained regions of the ODS, the grain refinement and particle hardening effects could be deconvolved and used to quantify particle hardening using a dispersed barrier model. The significant hardening effects with helium addition observed in the reference alloys were found to be almost entirely absent from the ODS systems, though anomalous softening in the 950°C consolidation indicated a potentially unexpected interaction between the bubble and particle populations. A possible explanation for this anomaly and a proposal for further work to establish its origin is discussed.

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Lin, Sen. "Deformation-Induced Martensitic Transformation and Mechanical Properties of Duplex and Austenitic Stainless Steels : A Synchrotron X-Ray Diffraction Study." Thesis, KTH, Metallografi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-233334.

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Metastable austenitic and duplex stainless steels are widely used materials in industrial anddomestic applications, owing to their attractive characteristics such as good corrosion resistanceand favorable mechanical properties. Both types of steel experience enhanced mechanicalproperties during plastic deformation due to the formation of the martensite phase from theparent austenite phase, this is called deformation-induced martensitic transformation (DIMT).It is therefore of technical interest to study the transformation mechanism and its impact onmechanical properties for a better understanding and ultimately for developing new materialswith improved performance in certain applications. In the present thesis, two austenitic stainless steels (201Cu, HyTens® 301) and two duplexstainless steels (FDX25®, FDX27®) were investigated. Samples were tensile tested during insitusynchrotron radiation experiments performed at the Cornell High Energy SynchrotronSource (CHESS), Ithaca, USA. Tests were performed at both room temperature and at elevatedtemperatures. The collected diffraction data were then processed by software such as Fit2D andMATLAB. Quantitative phase fraction analysis based on the direct comparison method wasperformed successfully. Microstructural analysis of samples before deformation and after thefull tensile testing was also performed using electron microscopy. The deformation induced martensitic transformation took place in HyTens 301, FDX25 andFDX27, but in 201Cu the austenite was stable during the tensile tests conducted here. The a’-martensite formed in a significantly higher fraction than the ε-martensite in all alloys. At roomtemperature, the critical stress levels for martensitic transformation were 490 MPa, 700 MPaand 700MPa for HyTens 301, FDX25 and FDX27, respectively.

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Christopher, Petersson. "Erosion-Corrosion experiments on Steels in liquid lead and Development of Slow Strain Rate testing rig." Thesis, KTH, Kärnenergiteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-261611.

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Lai, Libang. "Low temperature embrittlement of duplex stainless steels : A study of alloying elements’ effect." Thesis, KTH, Materialvetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-289565.

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Duplex stainless steels (DSSs), consisting of an equal amount of ferrite and austenite phases, have wide applications in e.g. vehicles, chemical engineering as well as nuclear plant because of the combination of excellent mechanical properties and corrosion resistance. However, low temperature embrittlement has existed for a few decades restricting the application of DSSs over about 250 ºC. When the service temperature ranges from around 250 to 500 °C, DSSs would become brittle because of the phase separation in the ferrite phase. The phase separation is the main reason for the low temperature embrittlement, and the kinetic of this phase separation achieves the fastest rate at about 475°C, so it is also termed as ‘475°C embrittlement’. Plenty of research has been performed in this field, but the problem remains. The mechanism of phase separation is due to the existence of a miscibility gap in the iron chromium binary system, and previous research has reported some alloying elements can have the potency to delay the phase separation and the goal of my thesis is to investigate the influence of different alloying elements and select one which could be a plausible one to retard phase separation, and subsequently try to mitigate the low temperature embrittlement problem of DSSs. This work includes the literature survey of different alloying elements which could influence the microstructure and mechanical properties of DSSs in general. Subsequently the thermodynamic calculation was performed to identify the effect of the selected alloying elements addition on phase formation during heat treatment. Vanadium was selected to be a potentially suitable alloying element to be added into DSSs and experimental investigations were performed on the heat treatment process and the effect of V alloying. The main conclusions of the proposed thesis can be drawn as follow: The elemental addition of Al, Si, V, Nb and Ti are calculated by Thermo-Calc, they are all ferrite stabilisers and V addition seems most likely to be effective due its combination with the interstitial elements C and N. In the experimental part, vanadium additions combined with intermediate temperature solution treatment could be effective to retard the age hardening effect and the impact toughness test has a consistent tendency. Also, according to Thermo-Calc calculations and experimental results, the more interstitial elements that combine with V and precipitate from the ferrite phase the better was the performance of the duplex stainless steels.
Duplexa rostfria stål (DSS), bestående av lika stor mängd ferrit- och austenit, har bredtillämpning inom t.ex. fordon, kemiteknik samt kraftverk på grund av kombinationen av utmärkta mekaniska egenskaper och korrosionsbeständighet. Försprödning vid låg temperatur begränsar emellertid tillämpningen av DSS över 250 °C. När driftstemperaturen varierar från cirka 250 till 500 ° C så kan DSS bli spröda på grund av fasseparation i ferritfasen. Fasseparationen är den främsta orsaken till lågtemperaturförstöring, och kinetiken för denna fasseparation uppnår den snabbaste hastigheten vid cirka 475 °C, så den kallas också '475 °C-försprödning'. Mycket forskning har utförts inom detta område, men problemet kvarstår. Mekanismen för fasseparation beror på förekomsten av ett blandningslucka i det binära järn-krom-systemet, och tidigare forskning har rapporterat att vissa legeringselement kan ha förmågan att fördröja fasseparationen. Målet med mitt examensarbete är att undersöka påverkan av olika legeringselement och välja ett som kan användas för att fördröja fasseparationen och därav mildra problemet med lågtemperaturförsprödning hos DSS. Detta arbete inkluderar litteraturundersökning av olika legeringselement som kan påverka mikrostrukturen och mekaniska egenskaper hos DSS i allmänhet. Därefter termodynamiska beräkningar för att identifiera effekten av de valda legeringselementen på fasjämvikt under värmebehandlingen. Vanadin valdes som ett potentiellt lämpligt legeringselement som kan tillsättas i DSS. Experimentella undersökningar utfördes på värmebehandlingsprocessen och effekten av V-legering. De huvudsakliga slutsatserna av examensarbetetär: tillsatsen av Al, Si, V, Nb och Ti beräknades av Thermo-Calc, de är alla ferritstabiliserande och V-tillsats verkar kunna vara effektiv på grund av dess kombination med de interstitiella elementen C och N. I den experimentella delen studerades vanadintillsatser i kombination med värmebehandling för att fördröja den hårdnandet och försprödningen. Enligt Thermo- Calc-beräkningar och experimentella resultat så kan prestanda förbättras desto merinterstitiella element som kombineras med V.

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Arvidsson, Sofia, Lena Fransson, and Carin Lundgren. "Communication of Values : A Qualitative Study at Stena Metall." Thesis, Jönköping University, JIBS, EMM (Entrepreneurship, Marketing, Management), 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-12368.

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Purpose: The purpose of this thesis is to investigate Stena Metall’s values and how they are communicated within the organization.

Background: In the Fall of 2008, the world was shocked by the worst financial crisis in decades. The crisis had deep effects on the Swedish economy, and many companies suffered heavily. The recycling and environmental service company Stena Metall experienced their first negative result in 30 years, and 900 employees had to leave the company. An action program, including an altered culture was established with the purpose to adapt the operations to the new business environmental conditions. Values, which are a part of the organizational culture, were decided to be an important part of the change. To implement these in the entire organization a well-structured communication process is needed. Within these subjects; values and communication, a qualitative study at Stena Metall has been conducted.

Method: To fulfill the purpose, a qualitative method has been used. Thirteen interviews were conducted to collect data from different levels of the organization. The interviews were designed differently based on the employee’s level of responsibility in the organization. The theoretical framework used when analyzing the empirical material includes earlier research in the areas of culture, with emphasis on values, and communication.

Conclusion: Two set of values have been identified, core values and aspiration values. The findings indicate a gap in the communicational process at Stena Metall. Part of the new information communicated about Stena Metall´s values is lost on its way from the management to the lower levels in the organization. The perception of what the values mean, both core and aspiration values, differs depending on level in the organization.

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Valgimigli, Marco <1972&gt. "Correlazione tra i livelli circolanti di cellule staminali CD34+ e sviluppo di ristesosi binaria in pazienti sottoposti ad angioplastica coronarica con impianto di stent metallico tradizionale: studio prospettico osservazionale." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/146/.

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Boulnat, Xavier. "FAST high-temperature consolidation of Oxide-Dispersion Strengthened (ODS) steels : Process, microstructure, precipitation, properties." Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0139/document.

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Ce travail vise à améliorer la compréhension de la microstructure d’aciers ferritiques appelés aciers ODS. Ils sont fabriqués par métallurgie des poudres, ce qui inclut le cobroyage d’une poudre ferritique avec une fine poudre d’oxydes, suivi d'une consolidation à haute température. La consolidation permet de former un matériau dense renforcé par des particules nanométriques qui sont responsables des bonnes propriétés mécaniques à haute température. Cependant, les procédés conventionnels, notamment la Compaction Isostatique à Chaud, provoquent des microstructures hétérogènes qui étaient jusqu’à ce jour mal comprises. Ainsi, la technique rapide de consolidation assistée par courant électrique appelée "Spark Plasma Sintering" (SPS), a été testée afin d’étudier la microstructure. Pour la première fois, on montre que d’excellentes propriétés mécaniques peuvent être obtenues par SPS, comparables à celles des matériaux ODS obtenus classiquement par Compaction Isostatique à Chaud, mais avec un temps de procédé largement réduit. Cependant, la consolidation par SPS échoue quand il s’agit d’obtenir une micro-structure ferritique homogène. En effet, malgré la cinétique rapide de consolidation, on obtient des grains dits ultrafins (D < 500 nm) entourée de grains plus grossiers (D >10 μm). Une caractérisation microstructurale poussée a permis de comprendre l’évolution du matériau durant la consolidation. Un modèle d’évolution microstructurale a été proposé. Le calcul des pressions gouvernant la mobilité des interfaces souligne l’importance de la déformation plastique hétérogène issue du cobroyage des poudres. Par ailleurs, il est montré que la précipitation des particules d’oxydes ancre les joints de grains et stabilise la microstructure hétérogène, même à très haute température. On montre aussi qu’augmenter la teneur en renforts n’empêche pas la croissance anormale mais permet de contrôler la fraction et la taille de grains ultrafins, et donc les propriétés mécaniques des ODS. Parce que les particules jouent un rôle primordial dans la croissance des grains, une caractérisation fine de l’état de précipitation a été réalisée sur les matériaux consolidés par SPS. L’étude par Microscopie Electronique en Transmission, Diffusion des Neutrons et Sonde Atomique révèle une grande densité d’oxydes qui varient en taille et en composition chimique. Un modèle thermodynamique de type germination/croissance/coalescence a été développé pour simuler les cinétiques de précipitation des phases Y2O3 et Y2Ti2O7 durant les étapes de consolidation non isothermes. Tant les résultats expérimentaux que numériques démontrent la précipitation rapide des nano-particules qui sont ensuite extrêmement stables durant les recuits. Ce modèle permet de mieux comprendre la spécificité des microstructures et de la précipitation dans les ODS, de la formation rapide de particules nanométriques à la précipitation grossière d’oxydes de titane aux interfaces
This work aims to lighten the understanding of the behavior of a class of metallic materials called Oxide-Dispersion Strengthened (ODS) ferritic steels. ODS steels are produced by powder metallurgy with various steps including atomization, mechanical alloying and high-temperature consolidation. The consolidation involves the formation of nanoparticles in the steel and various evolutions of the microstructure of the material that are not fully understood. In this thesis, a novel consolidation technique assisted by electric field called "Spark Plasma Sintering" (SPS) or "Field-Assisted Sintering Technique" (FAST) was assessed. Excellent mechanical properties were obtained by SPS, comparable to those of conventional hot isostatic pressed (HIP) materials but with much shorter processing time. Also, a broad range of microstructures and thus of tensile strength and ductility were obtained by performing SPS on either milled or atomized powder at different temperatures. However, SPS consolidation failed to avoid heterogeneous microstructure composed of ultrafine-grained regions surrounded by micronic grains despite of the rapid consolidation kinetics. A multiscale characterization allowed to understand and model the evolution of this complex microstructure. An analytical evaluation of the contributing mechanisms can explain the appearance of the complex grain structure and its thermal stability during further heat treatments. Inhomogeneous distribution of plastic deformation in the powder is argued to be the major cause of heterogeneous recrystallization and further grain growth during hot consolidation. Even if increasing the solute content of yttrium, titanium and oxygen does not impede abnormal growth, it permits to control the fraction and the size of the retained ultrafine grains, which is a key-factor to tailor the mechanical properties. Since precipitation through grain boundary pinning plays a significant role on grain growth, a careful characterization of the precipitation state was performed on consolidated ODS steels. The experimental data obtained by transmission electron microscopy, small angle neutron scattering and atom-probe tomography evidenced the presence of dense and nanosized particles in SPS ODS steels, similarly to what is observed in conventional ODS steels. This is of great importance since it proves that the precipitation is very rapid and mainly occurs during the heating stage of the consolidation process. Using a thermodynamic model, the precipitation kinetics of Y2O3 and Y2Ti2O7 were successfully reproduced at various consolidation temperatures. Both experimental and numerical findings agree with the rapid precipitation of nanoparticles that are then extremely stable, even at high temperature. Consequently, this model can be an efficient tool to design ODS steelsby the optimization of the precipitation state

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Lundberg, Daniel, Filip Wilson, Hjalmar Gunnarsson, Leo Sjörén, Robin Xu, and Erik Djurberg. "Long term aging and creep exposure for advanced heat resistant alloys : A phase analysis." Thesis, Uppsala universitet, Institutionen för materialvetenskap, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-446407.

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This project was ordered by Sandvik Materials Technology and was performed by a group of students at Uppsala university. The purpose of the project was to study precipitation behavior and structure stability in six advanced heat resistant alloys. Each sample were subjected to a creep rupture test in 600 or 700°C depending on the alloy type. Two parts of each alloy where examined; one part which had been affected by creep and another part which was unaffected by creep. A literature study was performed first to gain knowledge of the scientific theory utilized in this project, namely creep, precipitation hardening, and about the different materials which were analyzed. Preliminary results for the phase composition of the materials were obtained from a Thermo-Calc (TC) simulation. The SEM-images showed nothing noteworthy for any sample due to the roughness of the sample surfaces. The EDS-analysis showed chromium depletion in the centers of the aged samples of HT9 and Sanicro® 75X. Other minority phases such as Cr23C6 in Sanicro®70, P-phase and a titanium nitride phase in sanicro® 60X, VB in Esshete 1250 and Sigma-phase in 4C54 were identified using EDSmapping. It was found that when using XRD to analyze the phase compositions of small samples it is impractical to have the samples cast in bakelite beforehand. The XRD-results obtained in this project showed that more than 90% of the XRD diffractogram for every sample was graphite, which made the identification of minority phases impossible. The quality of the LOM-images varied greatly between samples, for 4C54 grain sizes were measured in all images, for Esshete 1250 grain sizes were measured for the crept sample, and for Sanicro® 60X measurements could only be taken from one image. Most of the sample preparation was insufficient to achieve the test results necessary for complete microstructural analysis and phase analysis of the samples. The mistakes in the practical steps of the project were noted and improvements for these mistakes are presented in the conclusion.

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Beltrami, Júlia. "Estudo de viabilidade de produção de um vergalhão de aço dual-phase com alto teor de silício via termodinâmica computacional." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2016. http://hdl.handle.net/10183/163461.

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Com o envelhecimento das estruturas de concreto armado, ficou evidente sua deterioração num período de tempo muito menor do que o previsto, pois sempre foram consideradas construções de elevada vida útil. Entre os fenômenos de maior gravidade para a sua estabilidade estrutural está a corrosão das armaduras de aço. Visando melhorar o desempenho das construções, aumentando a vida útil e diminuindo custos com manutenção, esta dissertação propõe o desenvolvimento de um vergalhão com melhor resistência à corrosão, de microestrutura dual-phase. O objetivo principal foi propor uma rota de produção viável, agregando o mínimo de custo possível, de forma a se obter um produto competitivo. A simulação da produção do vergalhão, desde o refino na aciaria, passando por tratamento térmico e propriedades mecânicas, foi realizada com auxílio da termodinâmica computacional, através do software FactSage. A simulação consistiu de três etapas: 1) determinação das temperaturas A1 e A3 e janelas de tratamento térmico; 2) cálculo das propriedades mecânicas a partir de modelos empíricos; 3) comportamento das inclusões durante o refino, durante a solidificação e durante a laminação. O estudo das inclusões é importante porque os aços simulados possuem alto teor de silício (de 1% a 2,5% em massa), podendo precipitar óxidos sólidos nos moldes de lingotamento contínuo. O estudo termodinâmico apontou que a produção de vergalhões com aços dual-phase com alto teor de silício é possível e sugere-se a fabricação pela seguinte rota: aciaria elétrica convencional, com ajuste final do teor de silício após a desoxidação e adição de alumínio controlada para obter inclusões com 15% a 25% de Al2O3, ajuste da escória, rica em CaO, de maneira a obter inclusões favoráveis ao lingotamento contínuo e laminação, e após o último passe de laminação, têmpera por resfriamento em água online (Thermex/Tempcore).
With the aging of reinforced concrete structures, their premature wearing became evident. Among the phenomena of greater severity to the structural stability of buildings is the corrosion of the steel rebar. To improve the performance of these structures, increase their service life and reduce maintenance costs, this work proposes the development of a rebar with better corrosion resistance, with a dual-phase microstructure. The main objective was to propose a viable production route, which adds the least possible cost, so as to obtain a competitive product. The thermodynamic simulation of the rebar manufacturing, from steelmaking to heat treatment and mechanical properties was carried out with the aid of computational thermodynamics using the FactSage software. The simulation consisted of three steps: 1) determining the temperatures A1 and A3 and the heat treatment windows; 2) calculating the mechanical properties from empirical models; 3) analyzing the behavior of inclusions during refining, solidification and hot-rolling. The study of the inclusion system is important because the simulated steels have high silicon content (from 1% to 2.5% by weight) and solid oxides may precipitate in the continuous casting molds. As a result of the study, it was found that the production of rebars with dual-phase microstructure and high silicon content is possible and the manufacturing route proposed is as follows: conventional electric steelmaking, with final adjustment of the silicon content after deoxidation and controlled addition of aluminum to obtain inclusions with 15% to 25% of Al2O3, refining slag rich in CaO, in order to obtain inclusions favorable to continuous casting and hot-rolling, and direct water quenching after the final rolling step (Thermex / Tempcore processes).

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Ahlgren, Peters Adam. "A SIMULATION WITH FINITE ELEMENTS TO MODEL STEEL SHEET SLITTING : A Master Thesis in Engineering Physics." Thesis, Uppsala universitet, Tillämpad mekanik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-385495.

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A steel slitting process is simulated using FEM (Finite Element Method) in order to see potential defects along the edge in a steel sheet after it has been cut. The model's results were compared to microscope images of the steel sheet in order to verify accuracy. The purpose is conceptual and to find a model that successfully simulates a steel cutting process and (hopefully) how the edge depends on different parameters. The model developed seems to achieve this task, and a more thorough calibration of the model could result in (more) optimal parameters for the machine to use.

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Rothpfeffer, Caroline. "From wood to waste and waste to wood : aspects on recycling waste products from the pulp mill to the forest soil /." Uppsala : Dept. of Forest Soils, Swedish University of Agricultural Sciences, 2007. http://epsilon.slu.se/200783.pdf.

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Barguet, Laurianne. "Contrôle acoustique et vibratoire de la mécano-synthèse des matériaux composites à matrice métallique nanostructurés." Thesis, Le Mans, 2015. http://www.theses.fr/2015LEMA1027/document.

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Lors de la synthèse des aciers ODS, la première étape consiste à réaliser un broyage actif, appelé mécano-synthèse, entre les matériaux de départ qui sont la poudre métallique et les renforts d’oxyde. Ce procédé peut se réaliser au moyen d’un broyeur à boulets, constitué d’une cuve cylindrique à l’intérieur de laquelle des billes en acier sont introduites. Le broyage résulte des combinaisons de chocs entre billes, poudre et paroi de la cuve, ce qui conduit à une évolution de la de la taille, de leur forme et de leur polydispersité. La première partie de cette thèse s’est attachée à élaborer un moyen de caractérisation de la poudre par des mesures ultrasonores. Une méthode qui consiste à sonder un échantillon de poudre métallique pour la mesure des paramètres acoustiques s’est avérée être adaptée pour la qualification de la poudre métallique en cours de broyage. Une dépendance des paramètres acoustiques avec les caractéristiques morphologiques du milieu a également été mise en évidence pour des échantillons granulaires. Dans une deuxième partie, l’optimisation du procédé par l’identification de la vitesse optimale de rotation de la cuve est recherchée dans un premier temps. Une mise en parallèle des signaux acoustiques et vibratoires en fonction de la vitesse de rotation de la cuve avec le mouvement des billes, montre que les énergies acoustique et vibratoire sont des indicateurs pouvant conduire à la vitesse de rotation optimale. Puis, il est montré comment des mesures acoustiques et vibratoires durant un broyage permettent de caractériser l’évolution de la nature des poudres et d’identifier la présence de colmatage de la poudre sur les parois de la cuve
During the ODS steel (Oxide Dispersion Strengthened) synthesis, the first stage consists in an active milling between original materials, which are metallic powder and oxide to obtain reinforced micro/nanoscale dispersions. This process, known as mechanical alloying, could be realized by balls milling composed by a cylindrical tank rotating around its main axis, within which steel beads are introduced. The grinding results from different combinations of collisions between beads and powders on the tank walls, that lead to morphological grain powder evolution (grain size and shape). The first part of this thesis proposes an ultrasonic method to characterize the metallic powder. An experimental method, which consists in acoustic probing for measuring linear acoustic parameters (longitudinal wave velocity and elastic modulus) of a slab of powder sample, appears to be suitable to follow different mechanical alloying stages. A dependence of the acoustic parameters on the morphological characteristics of metallic powder (grain shape and grain size distribution) is shown with the same sample preparation and the same confining pressure. In the second part, optimization process by identification of ball milling optimal rotation speed is researched in a first step. Correlation between acoustic or vibration signals and bead motion versus rotation speed, shows that acoustic and vibration energy are good indicators that can be used to find the optimal rotation speed. In a second step, acoustic and vibration measures are used to follow grain material properties evolution during a grinding (for a period of 176hrs) and to identify powder clogging mechanism on a milling tank

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Röttinger, Michael Heinrich [Verfasser]. "Metall-Stent-Implantation bei Tracheomalazie : Früh- und Langzeitergebnisse / Michael Heinrich Röttinger." 2001. http://d-nb.info/963428403/34.

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Gulapura, Hanumantharaju Arun Kumar. "Thermodynamic modelling ofmartensite start temperature in commercial steels." Thesis, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-221719.

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Firstly, an existing thermodynamic model for the predicting of martensite start temperature of commercial steels has been improved to include more elements such as N, Si, V, Mo, Nb, W, Ti, Al, Cu, Co, B, P and S and their corresponding composition ranges for Martensitic transformation. The predicting ability of the existing model is improved considerably by critical assessment of different binary and ternary systems i.e. CALPHAD approach which is by wise selection of experimental data for optimization of the interaction parameters. Understanding the degree of variation in multi-component commercial alloys, various ternary systems such as Fe-Ni-X and Fe-Cr-X are optimized using both binary and ternary interaction parameters. The large variations between calculated and the experimental values are determined and reported for improvements in thermodynamics descriptions.Secondly, model for the prediction of Epsilon martensite start temperature of some commercial steels and shape memory alloys is newly introduced by optimizing Fe-Mn, Fe-Mn-Si and other Fe-Mn-X systems considering the commercial aspects in the recent development of light weight steels alloyed with Al and Si.Thirdly, the effect of prior Austenite grain size (pAGS) on martensite start temperature is introduced into the model in the form of non-chemical contribution which will greatly influence the Gibbs energy barrier for transformation. A serious attempt has been made to describe the dependency of transition between lenticular and thin-plate martensite morphologies on the refinement of prior Austenite grain size.Finally, the model is validated using a data-set of 1500 commercial and novel alloys. Including the newly modified thermodynamic descriptions for the Fe-based TCFE9 database by Thermo-Calc software AB, the model has the efficiency to predict the martensite start temperature of Multi-component alloys with an accuracy of (±) 35 K. The model predictability can be further improved by critical assessment of thermodynamic factors such as stacking faults and magnetism in Fe-Mn-Si-Ni-Cr systems.

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Van, der Merwe Ryno. "Corrosion characteristics of steels and metallic alloys used as construction materials in plants exposed to fluorine containing acids." Thesis, 2018. https://hdl.handle.net/10539/26652.

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A dissertation submitted in fulfilment of the requirement for the degree of Master of Science in Engineering, to the Faculty of Engineering and the Built Environment, School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Johannesburg, 2018
The two hydrofluoric acid (HF) storage tanks used for holding 70% technical grade HF product at the HF plant at Necsa started leaking in March 2012. An evaluation of the failure was conducted in the form of a corrosion failure analysis. It was confirmed that a higher than usual nitric acid (HNO3) content in the technical grade HF stream changed the corrosion mechanisms typically experienced within the HF storage vessels, which then caused the tanks to fail. Immersion type corrosion experiments were done to safely simulate the corrosive environment experienced by the mild steel, stainless steel and nickel alloys used on site, and to predict the change in corrosion rates and characteristics associated with the HNO3 contamination in the HF production plant circuit. Since the corrosion resistance of mild steel in HF is heavily dependent on the thickness of the protective scale on the steel, a series of planned interval corrosion tests (PICTs) was done to reproduce and then examine the oxidefluoride barrier on mild steel coupons in pure 70% HF prior to corrosion tests. These shorter PICTs were also done on the stainless steel and nickel alloys and showed that the prepassivation step had a surface cleaning effect when exposed for only 24 h. Eleven day corrosion tests were conducted to establish the effect of HNO3 concentration and temperature on mild steel corrosion in 70% HF, and to determine the change in corrosion rates and mechanisms associated with HNO3 contamination (0.1-1% HNO3) of the downstream HF products. The corrosion was characterized by analysing the corroded coupons for mass loss, apparent corrosion rates, acid consumptions, visual observations of scale formation and pits, as well as depth profiles from scanning electron microscopy and energy dispersive spectroscopy analyses. Linear relationships were frequently observed when analysing mass losses for the coupons over time, making it possible to define corrosion rates in terms of first order reaction kinetics. The harshest corrosive condition for mild steel in HF was determined to be 1% HNO3 in 70% HF at a constant temperature of 25ºC. The corrosion characteristics of alloys used in the HF plant, as affected by HNO3 impurities (in the range 50–10000 ppm) in the final HF acid product (70% Technical grade) were successfully established. Normalized SA516 Grade 70 mild steel and Monel 400 were found not adequate for use as construction materials in a plant where HNO3 contamination was >100 ppm. However, the corrosion resistance of SS 904 L was suitable under these conditions and was recommended for applications in HF solutions where the presence of an oxygen-containing acid (e.g. HNO3) is consistent. It was recommended that Alloy 31, Alloy 33 or Nirosta 4565S, with higher chromium content (>20 wt% Cr), should be considered for construction material of the HF plant when HNO3 contamination becomes unavoidable. However, if the continued use of mild steel at the plant cannot be avoided, other inhibition strategies tailored to the selective consumption of HNO3 in the HF product stream need to be investigated.
XL2019

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