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Kasimagwa, Ismail. "A study of slag corrosion of oxides and oxide-carbon refractories during steel refining." Licentiate thesis, KTH, Tillämpad processmetallurgi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-25221.
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The use of ceramic material as refractories in the manufacturing industry is a common practice worldwide. During usage, for example in the production of steel, these materials do experience severe working conditions including high temperatures, low pressures and corrosive environments. This results in lowered service lives and high consumptions of these materials. This, in turn, affects the productivity of the whole steel plant and thereby the cost. In order to investigate how the service life can be improved, studies have been carried out for refractories used in the inner lining of the steel ladles. More specifically, from the slag zone, where the corrosion is most severe. By combining thermodynamic simulations, plant trails and post-mortem studies of the refractories after service, vital information about the behaviour of the slagline refractories during steel refining and the causes of the accelerated wear in this ladle area has been achieved. The results from these studies show that the wear of the slagline refractories of the ladle is initiated at the preheating station, through reduction-oxidation reactions. The degree of the decarburization process is mostly dependent on the preheating fuel or the environment. For refractories without antioxidants, refractory decarburization is slower when coal gas is used in ladle preheating than when a mixture of oil and air is used. In addition, ladle preheating of the refractories without antioxidants leads to direct wear of the slagline refractories. This is due to the total loss of the matrix strength, which results in a sand-like product. Thermal chemical changes that take place in the slagline refractories are due to the MgO-C reaction as well as the formation of liquid phases from impurity oxides. In addition, the decrease in the system pressure during steel refining makes the MgO-C reaction take place at the steel refining temperatures. This reduces the refractory’s resistance to corrosion. This is a serious problem for both the magnesia-carbon and dolomite-carbon refractories. The studies of the reactions between the slagline refractories and the different slag compositions showed that slags rich in iron oxide lead mostly to the oxidation of carbon/graphite in the carbon-containing refractories. This leads to an increased porosity and wettability and therefore an enhanced penetration of slag into the refractory structure. If the slag contains high contents of alumina and or silica (such as the steel refining slag), reactions between the slag components and the dolomite-carbon refractory are promoted. This leads to the formation of low-temperature melting phases such as calcium-aluminates and silicates. The state of these reaction products during steel refining leads to an accelerated wear of the dolomite-carbon refractory. The main products of the reactions between the magnesia-carbon refractory and the steel refining slag are MgAl2O4 spinels, and calcium-aluminates, and silicates. Due to the good refractory properties of MgAl2O4 spinels, the slag corrosion resistance of the magnesiacarbon refractory is promoted.QC 20101013
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Abuluwefa, Husein. "Characterization of oxides (scale) growth of low carbon steel during reheating." Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=40307.
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This study involved characterizing the oxidation behaviour of low carbon steel in various gas mixtures of O$ rm sb2, CO sb2, H sb2O$ and N$ sb2,$ at different oxidation temperatures. Rate measurements for the oxidation of the low carbon steel during reheating in a walking-beam steel reheat furnace were also carried out. Scaling rates during reheating were predicted from oxidation rates obtained in the laboratory.In-situ characterization of the phase compositions of the iron oxides, "scale", that form on low carbon steels during their oxidation at elevated temperatures was carried out using a neutron diffraction technique. Growths in the intensities of the diffraction peaks associated with characteristic crystal planes of the various oxides (Fe$ rm sb{x}$O, Fe$ rm sb3O sb4$ and Fe$ rm sb2O sb3)$ were monitored on-line. The volume fractions of the oxides in the developing scale were calculated on the basis of ideal structure factors and measured relative intensities of diffraction peaks.
Oxidation in binary gas mixtures of oxygen and nitrogen in the temperature range from 1000 to 1250$ sp circ$C was carried out. Sample weight gain versus time data were analyzed, along with measurements and calculations of sample heating rates due to exothermic reactions at the sample surface. It was found that initial rates of oxidation depended on oxygen content in the gas mixture and that these rates were linear up to oxide thicknesses between 0.4 and 0.5 mm. The linear rates of oxidation were found to be controlled by the mass transport of oxygen from the gas phase, to the reaction surface, through a gas boundary layer. Subsequent oxidation rates followed a parabolic oxidation mechanism.
Oxidation experiments were also carried out in binary, ternary and quaternary gas mixtures of O$ rm sb2, CO sb2, H sb2O$ and N$ sb2$ at various temperatures. Reaction rates during oxidation in binary gas mixtures of CO$ sb2$-N$ sb2$ and H$ sb2$O-N$ sb2$ followed a linear rate law and were found to be proportional to the partial pressures of CO$ sb2$ and H$ sb2$O in the gas mixtures. The oxidation rates showed a strong dependency on temperature. Oxidation in oxygen containing atmospheres showed that the main oxidizing agent was free O$ sb2.$ Additions of CO$ sb2$ and H$ sb2$O had little effect on the magnitude of oxidation rates. Oxidation in these atmospheres exhibited an initial linear rate law which gradually transformed to a parabolic rate law.
During reheating in a walking-beam steel reheat furnace, it was observed that scaling rates can be reduced by lowering input air/fuel ratios to the furnace, which resulted in lowering concentrations of free oxygen in the combustion products from about 3% to about 1.5%. The predicted scaling rates during reheating using isothermal oxidation rate constants suggested that rates of oxidation during reheating in the industrial reheat furnace followed a combination of linear and parabolic rate laws, with the components of the linear oxidation rates being predominant. The observed reduction in scaling rates was a result of the decrease in the free oxygen within the furnace atmosphere.
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Hillan, Marguerita Charlotte. "Investigations into steel substrate surface composition and the assessment of Cr. (VI) electrodeposit characteristics." Thesis, University of the West of Scotland, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365054.
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Cerully, Laura B. "The fabrication of thin-walled steel alloys through the gas carburization of reduced metal oxide extrusions." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34809.
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Investigations of the production of thin-walled steel alloys through the reduction and subsequent gas carburization of structures made from metal oxide powders were performed. Batch compositions, as well as the heat treatment parameters necessary for the formation of structures were determined through the use of thermogravimetric analysis, dilatometric measurements, and microstructural investigation. Parameters for the high temperature carburization of thin-walled 4140 structures were determined. The research has shown that the amount of carbon in the walls of the structures can be controlled and uniform carbon contents across the cross-sections can be achieved in less than 30 minutes. Heat treatments for carburized samples were performed and subsequent microhardness testing resulted in values similar to conventionally produced 4140 steel. Studies on the decarburization behavior of similar alloys under various conditions were also performed in order to aid in the prediction of the microstructural behavior of samples during carburization and subsequent heat treatment. Low temperature gas carburization of structures with 316 steel composition has also been performed. Hardness variations present through the cross-section of the part after carburization suggest some transfer of carbon, though contents are not as high as anticipated. Suggestions for future work in this area are presented. The results of these investigations yield a novel method for the production of steel parts from metal oxide powders. The speed and low cost of the process, coupled with the proven ability of the process to yield parts with similar microstructural and mechanical characteristics as conventionally made alloys, allows for the techniques presented in this study to be used for the development of alloys which could not be previously done economically.
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Sohi, A. M. "Metal oxide films on glass and steel substrates." Thesis, Teesside University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391529.
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Palm, Martin. "Reliable Carburization of AISI H13 Steel : The Impact of Preoxidation." Thesis, KTH, Materialvetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-279103.
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Case hardened Uddeholm Orvar® Superior (Orvar) has the potential to replace currently used materials in shafts inside transmissions, which would lower the overall weight and thus result in lower fuel consumption while maintaining the necessary mechanical properties. However, previous studies have failed to reliably carburize the steel during the case hardening process. The case contains tempered martensite, which has high wear resistance, hardness, and good fatigue properties, and will be affected by the absence of the additional carbon. The presence of passive oxide layers such as chromia and silica is believed to inhibit the carburization, this by their impact of the adsorption and diffusion. One suggested solution is a preoxidation step before the carburization, to promote the formation of iron oxides which are preferential for carburization due to higher diffusion. To evaluate the impact of preoxidation different times, temperatures, and cooling methods were used and analyzed by LOM, XRD, SEM, and hardness measurements. The results indicate that reliable carburization can be obtained by preoxidation performed at 600 °C for 24 hours followed by immediate case hardening.Sätthärdat Uddeholm Orvar® Superior (Orvar) har potential att ersätta nuvarande material i drivaxlari växellådor, detta skulle minska vikten och därmed sänka bränslekonsumtionen medan de nödvändiga mekaniska egenskaperna behålls. Tidigare studier har emellertid misslyckats med att tillförlitligt uppkola stålytan under sätthärdningen. Ytan består utav tempererad martensit som har hög slitstyrka, hårdhet, och bra utmattningsegenskaper, och påverkas utav avsaknaden av tillfört kol. Närvaron av passiva oxidskikt som kiseldioxid och kromoxid tros hindra uppkolningen, detta på grund utav deras påverkan på adsorption och diffusion. En föreslagen lösning är ett föroxideringssteg innan sätthärdningen, för att gynna bildandet utav järnoxider vilka är fördelaktiga för uppkolningen på grund utav högre diffusion. För att utvärdera påverkan av föroxideringen användes olika tider, temperaturer, och kylningsmetoder som blev analyserade utav LOM, XRD, SEM, och hårdhetsmätningar. Resultaten indikerar att tillförlitlig uppkolning kan uppnås med föroxideringutförd vid 600 °C i 24 timmar följt utav omedelbar sätthärdning.
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Siafakas, Dimitrios. "On deoxidation practice and grain size of austenitic manganese steel." Licentiate thesis, Tekniska Högskolan, Högskolan i Jönköping, JTH. Forskningsmiljö Material och tillverkning – Gjutning, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-37788.
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The exceptional wear resistance and work hardenability, place Hadfield steel as one of themost important materials for manufacturing cast components used in the mining, crashing,drilling, and excavation industries. In all metallic alloys used for component casting, themechanical properties are highly influenced by the microstructure of the material. Castcomponents with finer microstructural characteristics are known to present bettermechanical properties and reduced risk of defects when compared with components witha coarser microstructure. A reduced grain size in Hadfield steel can increase the strengthof the material up to 30% and reduce the risk of porosity formation during solidification.The practice of adding selected compounds or alloying elements in a metal melt to modifyand refine the microstructure is called inoculation. It is currently one of the trendingmethods utilized in light-metal alloys and cast-iron components production but has not,yet, gained adequate acceptance in the steel casting industry because researchers have notbeen able to find proper inoculants.The main objective of this work is to investigate the qualitative and quantitativecharacteristics of the by-products of deoxidation of Hadfield steel that remain in thematerial after solidification and their positive or negative effect on the coarseness of thefinal as-cast microstructure. This type of research can help to identify the type of particlesor alloying elements that are most effective for refining the microstructure of austeniticsteels and pave the way for developing new or improving conventional deoxidation andinoculation processes that will, in turn, result in the improvement of the properties of thecomponent.The precipitation of particles and the as-cast grain size are studied in aluminum andtitanium deoxidized Hadfield steel samples acquired under pilot scale experimentalconditions. In the first part of this work, the qualitative and quantitative characteristics ofparticles such as type, morphology, composition amount and size are identified. Thesequence of precipitation is established. A model for predicting particle size and growth isdeveloped. The experimental results are compared against thermodynamic equilibriumcalculations and the precipitation mechanisms for each type of particles are described. Inthe second part, the as-cast grain size of samples with varying deoxidation treatments ismeasured. Then, the grain-size is correlated with certain particle characteristic and theparticles are ranked according to their ability to refine the microstructure. The particledisregistry with austenite is calculated and compared to the experimentally acquiredranking.Hadfieldstålen exceptionella slitstyrkan och deformationshårdnande har gjort dessa till ettav de viktigaste materialen för tillverkning av gjutna komponenter som används inomgruv-, kross-, borr-och gruvindustrin. I alla metallegeringar som används för tillverkningav gjutna komponenter styrs de mekaniska egenskaperna av materialets mikrostruktur.Gjutna komponenter med fin mikrostruktur presentera bättre mekaniska egenskaper ochminskad risk för defekter jämfört med komponenter med grov mikrostruktur. En minskadkornstorlek i Hadfieldstål kan öka materialets hållfasthet upp till 30% och minska riskenför porositetsbildning vid stelning.Tillsatsning av spårämnen eller legeringselement i en metallsmälta för att modifiera ochförbättra mikrostrukturen kallas ympning. Denna metod används i lättmetaller och vidtillverkning av gjutjärnskomponenter, men har ännu inte fått acceptans i stålindustrineftersom forskningen inte har funnit effektiva kärnbildare att användas som ympmedel.Huvudsyftet med detta arbete är att undersöka kvalitativa och kvantitativa egenskaper hosde desoxideringsprodukter som skapas under tillverkningen av Hadfield stål och hur deunder och efter stelning påverkar mikrostrukturens grovlek. Arbetet syftar till att identifierapartikeltyper och legeringselement som är effektiva för att förfina den austenitiskamikrostrukturen och bana väg för utveckling nya och förbättra desoxiderings- ochympningsprocesser som i sin tur kommer att resultera i en förbättring av den gjutnakomponentens egenskaper.Partiklarnas utskiljning och materialet resulterande kornstorlek studerades i aluminiumochtitan-desoxidiserade Hadfieldstål, tillverkade i pilotskala. Den första delen av dettaarbete var att identifiera kvalitativa och kvantitativa egenskaper hosdesoxidationspartiklar, som typ, morfologi, sammansättning och storlek.Utskiljningssekvensen fastställdes. En modell för att förutsäga partikelstorlek och derastillväxt utvecklades. De experimentella resultaten jämfördes med termodynamiskajämviktberäkningar och utskiljningen för varje typ av partikel beskrevs. I den andra delenstuderades kornstorleken och hur denna varierade desoxideringsbehandlingen. Därefterkorrelerades kornstorleken med partikeltyp och dess karaktäristika och rangordnades efterderas förmåga att förfina mikrostrukturen. Partiklarnas kristallografiska missanpassningmot austenitens kristallstruktur beräknades och jämfördes med experimentellt fastställdarangordningen.
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Watkins, Mark Edward. "Calcium modification of surface oxides formed on levitated iron and steel alloy droplets and related surface tension phenomena /." The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487330761217245.
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JIANG, ZHUOYING. "A Study of the Fate and Effect of Steel Sheet Surface Oxides on Galvanizing Bath Management." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1395924244.
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Harris, Michael D. "Mechanisms of Formation and Effects of Transition Metal Oxides in Silicon Nitride on Steel Dry Sliding Contacts." Thesis, University of North Texas, 2018. https://digital.library.unt.edu/ark:/67531/metadc1404592/.
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Silicon nitride on steel sliding contacts may provide advantageous tribological properties over traditional self-mated pairs, however the friction and wear behavior at high sliding speeds (>1 m/s) is not well understood. Previous studies at low sliding speeds (< 1 m/s) have found that the wear mechanisms change as a function of the operating parameters, e.g. atmosphere, sliding speed, load, and temperature, due to the formation of transition metal oxides such as Fe2O3 and Fe3O4. This study detected transient effects of the dry silicon nitride on steel contact over a range of sliding speeds to understand their relation to tribochemical reactions and the resulting tribological behavior. Two sets of dry silicon nitride on steel experiments were conducted at 1.45 GPa maximum Hertzian pressure. The first set were low sliding speed reciprocating experiments, conducted at an average of 0.06 m/s, conducted at variable operating temperature, ranging from 23 °C to 1000 °C. In the low sliding speed experiments, transitions of the wear mechanism from adhesive wear, to abrasive wear, then to oxidative wear was observed when the operating temperature increased. The second set were high sliding speed experiments, conducted at variable sliding speeds, ranging from 1 m/s to 16 m/s. In the high sliding speed experiments, a transition from adhesive wear to oxidative wear was observed when the sliding speed surpassed 4.5 m/s. The high sliding speed experiments were accompanied by in-situ instrumentation which detected the presence of a tribofilm which correlated to a reduction in friction, and its formation was linked to tribochemical reactions induced by high flash temperatures. Both sets of experiments had a maximum estimated contact temperature of 1000 °C where oxidative wear was prevalent. Although, the low sliding speed experiments underwent severe bulk oxidation and thermal softening effects, while the high sliding speed experiments experienced localized flash heating events with temperatures sufficient to form a semi-coherent tribofilm that was lubricious and significantly improved wear resistance. Therefore, the effects of transition metal oxides in sliding contacts are determined to be significantly influenced on their mechanisms of formation and interrelated to the operating parameters as found for dry sliding silicon nitride on steel contacts.
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Bergman, Ola. "Studies of oxide reduction and nitrogen uptake in sintering of chromium-alloyed steel powder." Licentiate thesis, KTH, Materials Science and Engineering, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9555.
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The powder metallurgy (PM) process route is very competitive for mass production of structural steel components with complex shape, due to efficient material utilisation, low energy consumption, and short overall production time. The most commonly used alloying elements are the processing friendly metals Cu, Ni and Mo. However, the prices for these metals are today high and volatile, which threatens to make the PM process less competitive compared to conventional metal forming processes. Consequently, there is a strong desire in the PM industry to increase the use of less costly alloying elements. Cr is an attractive alternative since it, besides low cost, provides high hardenability and also recyclable components. The drawback is that Cr has high affinity for oxygen, which makes oxidation and oxide reduction in PM processing of Cr-alloyed materials a challenging issue. Furthermore, the interaction between nitrogen and Cr-alloyed powder during processing is important to consider, since Cr also has high nitrogen affinity and is prone to form nitrides.
The aim of the research work presented in this thesis was to study oxide reduction and nitrogen uptake in sintering of Cr-alloyed steel powder. Water-atomized powder grades pre-alloyed with 1.5-3% Cr were used as test materials. Sintering experiments were performed in N2/H2 (90/10) atmospheres with test bars pressed to density 7.0-7.2 g/cm3. The oxygen content of the sintering atmosphere was varied and different sintering temperatures and cooling rates were applied. The experimental study has been complemented with thermodynamic calculations using the software Thermo-Calc.
The oxygen partial pressure should be below 4 x 10-18 atm in order to have reducing conditions during sintering at 1120°C of steel powder pre-alloyed with 3% Cr. With graphite added to the powder, conditions are reducing at higher oxygen partial pressures (up to 10-16 atm) due to favourable conditions locally in the material. Sintering at 1120°C for 30 minutes leads to incomplete reduction of Cr-oxides in the Cr-alloyed PM grades, but remaining oxides are not detrimental for mechanical properties of the PM components. Increased sintering temperature is beneficial for the oxide reduction kinetics and practically all oxides are reduced after sintering for 30 minutes above 1200°C. Nitrogen uptake by Cr-alloyed steel powder from N2-based sintering atmospheres is strongly dependent on the cooling rate applied after sintering. No nitrides appear in the sintered material and mechanical properties are not affected when normal cooling rates (0.5-1°C/s) are applied. Very low cooling rates (such as 0.05°C/s) may lead to grain boundary precipitation of Cr-nitrides in the sintered material.
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Westin, Elin M. "Welds in the lean duplex stainless steel LDX 2101 : effect of microstructure and weld oxides on corrosion properties." Licentiate thesis, Stockholm : Industriell teknik och management, Kungliga Tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9299.
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Riyahimalayeri, Kamrooz. "Slag, Steel, Ladle and Non-metallic Inclusions Equilibria in an ASEA-SKF Ladle Furnace." Doctoral thesis, KTH, Termodynamisk modellering, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-102149.
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This study explores the possibility of prediction and modification of some of the physicochemical properties of non-metallic inclusions by considering top slag-steel-ladle equilibria in an ASEA-SKF ladle furnace. To test the reliability of an available computational thermodynamic computer program, the first sub project was done. It was concluded that LiMeS, an interface for Thermo-Calc, is a useful tool for slag-steel equilibrium calculations. The second sub project was set out to find some model/s that could calculate the most accurate oxygen activity of molten steel compared to the measured one. This study concluded that both Wagner’s and Turkdogan's equations are useful. It was further seen that increasing the Al contents in the molten steel, increasing the CaO/Al2O3 ratio in the top slag, and reducing the temperature, resulted in reduction of the oxygen activity of the molten steel. In the third sub project a comparison was made between measured CaO and Al2O3 (normalised to CaO-Al2O3) in top slag, calcium aluminate inclusions, and the results of theoretical calculations. The average contents of CaO and Al2O3 in all inclusions were close to the composition of the phase Ca12Al14O33 and the contents of CaO and Al2O3 in the slags were close to the composition of the phase Ca3Al2O6 in the binary phase diagram of CaO-Al2O3. The forth sub project set out to study the effect of vacuum degassing time on non-metallic inclusions. It was concluded that during the vacuum degassing process the share of calcium aluminates compared to spinels, Ca content of the oxides, and the average equivalent circle diameters of the oxides were increasing, and oxides tended to form spherical shapes. Finally, based on the preceding four sub projects, the fifth sub project aimed to optimize the steel treatment in an ASEA-SKF ladle furnace. The final results showed that by adding 200 kg fluorite to the top slag of 1200 kg, it was possible to achieve a sulphur content of less than 10 ppm in the steel and a sulphur ratio between slag and steel of 1570, and at the same time reduce the oxygen activity of the molten steel and the degassing time.QC 20120917
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Li, Peigang. "Cold lap formation in Gas Metal Arc Welding of steel : An experimental study of micro-lack of fusion defects." Doctoral thesis, Högskolan Väst, Avd för maskinteknik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-5596.
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Cold laps are defined as micro-lack of fusion defects at the weld toe more or less parallel to the surface of the parent plate. These defects are known to negatively influence the fatigue properties of weldments. Previous studies suggest that cold lap formation can not be avoided completely in Gas Metal Arc Welding (GMAW). Therefore, a better understanding of formation mechanisms is imperative to be able to minimize the number and size of these defects. The main objective of this work has been to provide a more comprehensive understanding of cold laps, including categorising, characterisation and defining the most significant factors for formation. GMAW was used to produce welds that were investigated by metallographic methods using light optical microscopy, scanning electron microscopy and energy dispersive spectrometry. A novel classification of cold laps was introduced and three types of cold laps were identified: spatter cold laps, overlap cold laps and spatter-overlap cold laps. It was shown that cold laps are partially or fully filled by oxides. The most common oxides are manganese silicon oxides which were concluded to be formed primarily by oxidation of droplets. The presence of oxides was found to significantly increase the tendency to form spatter cold laps as well as overlap cold laps. Particularly for overlap cold laps, it was found that the depth (in transverse direction of weld) is reduced when welding in a non-oxidising environment. Welding on blasted surfaces increased the cold lap formation by entrapment of gas. The droplet and base metal temperatures were also found to be significant factors in cold lap formation. For overlap cold laps the occurrence frequency decreased with increased preheating temperature of the base metal. Mechanisms of overflowing resulting in overlap cold laps were discussed based on an extensive literature review. Several phenomena are believed to contribute to overflow including Rayleigh instability, the balance of forces, transfer of lateral momentum by droplets and an outward Marangoni fluid flow of the weld pool. The present studies suggest that cold lap formation can be suppressed by ensuring that the welding process (arc) is as stable as possible and by welding on a preheated work piece in a non-oxidising environment.
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Doostmohammadi, Hamid. "A Study of Slag/Metal Equilibrium and Inclusion Characteristics during Ladle Treatment and after Ingot Casting." Doctoral thesis, KTH, Materialvetenskap, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-11596.
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Today, there is a high demand on clean steel for high performance materialproperties. Thus, steel producers try to deliver a steel product with the highestquality and cleanliness to the market. The number of parameters that affect thesteel cleanliness may vary depending on the required material properties of thefinal product. However, the non-metallic inclusion characteristics represent one ofthe most important parameters. More specifically, the composition, size, numberand morphology affect steel cleanliness. In this work, selected parameters affectingthe inclusion characteristics were studied using the following methods: i)thermodynamic calculations (including computational thermodynamiccalculations), ii) inclusion determinations using a cross sectional (CS) method (2Dinvestigations) and iii) inclusion determinations using an electrolytic extraction(EE) method (3D investigations). The computational thermodynamic calculations of the slag-steel and inclusion-steelequilibriums were carried out using the Thermo-Calc software. With the help ofthese calculations, the influence of the slag carryover on the top slag, aluminumcontent in steel and sulfur distribution ratio as well as predictions of stable phasesof inclusions were studied. In addition, inclusion determinations of tool steel gradesamples collected during various stages of the ladle treatment in a scrap-based steelplant were carried out using both 2D and 3D methods. Furthermore, inclusiondeterminations of bearing steel grade samples from a runner system after ingotcasting were performed using a 2D metallographic method (CS-method). Also, theINCAFeature software was used, when using cross sectional method, in order tocollect more statistics of the inclusion characteristics. It was found that slag carryover has a large influence on the composition of theactual top slag as well as the aluminum content in the steel as well as the sulfurdistribution ratio. In addition, steel and slag were found to be in “near”-equilibriumconditions, after the completion of the vacuum degassing operation. Furthermore,the composition of small-size inclusions in samples taken from tool steel was foundto be very scattered. Moreover, the composition of the large-size inclusions wasfound to be less scattered. Furthermore, closer to the top slag composition insamples collected after vacuum degassing. Finally, the accuracy of the inclusioncomposition determinations of tool steel samples using the electrolytic extractionmethod was found to be better than for the cross sectional method. The worseaccuracy of the CS-method is due to a considerable effect of matrix elements oninclusion composition.QC 20100709
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Haluza, Vít. "Predikce vlivu povrchové vrstvy oxidů na intenzitu vodního chlazení." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-232176.
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This diploma thesis is dealing with the impact of oxide scales on heat conduction. One of the main tools that were used are numerical simulations. Heat conduction is modelled by solving partial differential equations. Regression models and artificial neural networks are used for the prediction of the influence of oxides on cooling intensity. Determination of the conditions when the cooling was intensified and comparison of individual methods of prediction are the main results of the thesis.
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Westin, Elin M. "Welds in the lean duplex stainless steel LDX 2101 : effect of microstructure and weld oxide on corrosion properties." Licentiate thesis, KTH, Materials Science and Engineering, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9299.
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Duplex stainless steels are a very attractive alternative to austenitic grades due to their higher strength and good corrosion performance. The austenitic grades can often be welded autogenously, while the duplex grades normally require addition of filler metal. This is to counteract segregation of important alloying elements and to give sufficient austenite formation to prevent precipitation of chromium nitrides that could have a negative effect on impact toughness and pitting resistance. The corrosion performance of the recently-developed lean duplex stainless steel LDX 2101 is higher than that of 304 and can reach the level of 316. This thesis summarises pitting resistance tests performed on laser and gas tungsten arc (GTA) welded LDX 2101. It is shown here that this material can be autogenously welded, but additions of filler metal, nitrogen in the shielding gas and use of hybrid methods increases the austenite formation and the pitting resistance by further suppressing formation of chromium nitride precipitates in the weld metal. If the weld metal austenite formation is sufficient, the chromium nitride precipitates in the heat-affected zone (HAZ) could cause local pitting, however, this was not seen in this work. Instead, pitting occurred 1–3 mm from the fusion line, in the parent metal rather than in the high temperature HAZ (HTHAZ). This is suggested here to be controlled by the heat tint, and the effect of residual weld oxides on the pitting resistance is studied. The composition and the thickness of weld oxide formed on LDX 2101 and 2304 were determined using X-ray photoelectron spectroscopy (XPS). The heat tint on these lean duplex grades proved to contain significantly more manganese than what has been reported for standard austenitic stainless steels in the 300 series. A new approach on heat tint formation is consequently presented. Evaporation of material from the weld metal and subsequent deposition on the weld oxide are suggested to contribute to weld oxide formation. This is supported by element loss in LDX 2101 weld metal, and nitrogen additions to the GTA shielding gas further increase the evaporation.
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Janis, Jesper. "Inclusions and/or Particles Engineering for Grain Refining Purposes in Ferritic Fe-20mass%Cr alloys." Doctoral thesis, KTH, Tillämpad processmetallurgi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-13012.
Full textAbstract:
Compared to more common used austenitic stainless steels, ferritic stainless steels contain very low amounts of the expensive alloying element Ni. In addition, they have good corrosion properties, but are sometimes suffering from poor weldability and bad mechanical properties. This is mainly due to the presence of large grains after casting and large grain growth during heat treatment or welding. Processes for reducing the grain size (grain refining) of metal alloys are widely known and proven before to be suitable for many alloys. A successful grain refining process can increase the strength of an alloy without decreasing the ductility. This can be achieved by different methods, such as rolling or cooling. In this work, the focus has been on studying the aspect from a metallurgist point of view, to analyse the possibilities to create small particles in the liquid stage to enhance the solidification. The focus has been on oxide and nitride formation for nucleation of smaller grains during solidification. This study was made by forming particles, develop the analysis methods and thereafter to study the effect of particles on the structure of a ferritic stainless steel. The particles were formed by additions of Ti, Ce and Zr in to a liquid Fe-20mass% Cr alloy containing different amounts of oxygen and nitrogen. The electrolytic extraction technique was used to achieve a good understanding of the reaction processes and the particles size, number, composition and morphology. The grain sizes and the particles were then studied in as-cast samples as well as in specimens heat treated for 60 minutes at 1200, 1300 and 1400°C in a Confocal Scanning Laser Microscope (CSLM). Also, based on Scanning Electron Microscope (SEM) determinations and Thermo-Calc calculations, the precipitated particles were divided as primary and secondary particles. Thereafter, the grain refining potential was studied for each of these types. In this work, particles engineering by using small particles have been proven suitable for the Fe-20mass% Cr ferritic stainless steel alloys. Although the work has been based on small-scale samples and experiments, the results show good tendencies with respect to grain refining as well as a clear relationship between the particles in the steels and the microstructures. It was found that Ti-Ce additions in Fe-20mass% Cr alloys resulted in complex oxides including Ti, Ce and Cr. These oxides were observed to have high agglomeration tendencies and therefore to form larger particles or clusters. The grain refining potential on the solidification structure was insignificant, despite a relatively large amount of particles. However, Ti-Zr additions in Fe- 20mass% Cr alloys on the other hand resulted in primary precipitated particles such as ZrO2 and ZrO2+ZrN. Furthermore, ZrN nucleated ferrite during solidification, which lead to a clearly observed grain refining effect. This effect was also increased with an increased number of particles. The amount of particles (primary and secondary) was also found to increase with an increased amount of nitrogen. Secondary particles (mostly TiN) were precipitated near grain boundaries, which lead to a location based pinning effect of the grain growth during heat treatment at 1200 °C. This pinning effect was increased by an increased nitrogen content and thereby an increased number of particles. Finally, the pinning effect was clearly reduced during heat treatment at 1400 °C.QC20100524
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Owusu-Mensah, Martin. "Understanding the first formation stages of (Y,Ti) nano-oxides in Oxide Dispersion Strengthened (ODS) steels." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS310.
Full textAbstract:
Les aciers appelés ODS (pour Oxide Dispersion Strengthened), renforcés par une dispersion homogène de nano-oxydes, sont des matériaux de structure avancés pour les futurs réacteurs nucléaires de fusion et de fission. En effet ces nano-oxydes, à base d’Y et Ti, servent comme centres de recombinaison de défauts ponctuels et d'obstacles aux mouvements des dislocations, améliorant de ce fait leur résistance aux radiations et aux températures élevées. La fabrication conventionnelle des aciers ODS est réalisée par broyage mécanique suivi de traitements thermo-mécaniques, et ne permet pas facilement de comprendre les mécanismes physiques conduisant à la précipitation des nano-oxydes, ce qui serait potentiellement utile pour optimiser leur production. La cinétique de formation de ces nano-oxydes peut être étudiée en utilisant une technique alternative, à savoir la synthèse par faisceaux d’ions, qui présente de nombreux avantages, notamment le contrôle précis des paramètres expérimentaux et la possibilité de décorréler divers facteurs contribuant à la cinétique de précipitation. Au cours de cette thèse, cette technique a été utilisée pour étudier la coprécipitation d'ions métalliques (Y et/ou Ti) et d'oxygène implantés dans un alliage modèle Fe-Cr de composition proche de celle typique des aciers ODS commerciaux. Des ions de Y, Ti et O à basse énergie ont été implantés dans des échantillons d'alliage Fe10wt%Cr de haute pureté à température ambiante. Les échantillons implantés ont ensuite été recuits à diverses températures entre 600 à 1100°C pour favoriser la précipitation de nano-oxydes, conformément au principe de cette technique. La microscopie électronique à transmission a été utilisée pour caractériser la structure cristallographique et la composition chimique des nano-oxydes formés lors de trois séries d'expériences. Tout d'abord, l'implantation séquentielle d'ions Ti et O a été mise en œuvre. Un recuit ultérieur a révélé qu’il n’y avait pas de précipitation d'oxyde de titane jusqu’à des températures inférieures à 1000°C, mais la présence de nano-oxydes riches en chrome avec une structure hexagonale de type corundum, qui contiennent une certaine quantité de Ti à des températures suffisamment élevées. Ce n’est qu’après le recuit à 1100°C que des nano-oxydes d’un autre type à cœur enrichi en Ti et coquille enrichie en Cr ont également été observés. Deuxièmement, l'implantation séquentielle d’ions Y et O a entraîné la formation à 800°C de nano-oxydes probablement riches en yttrium. Le recuit à 1100°C a favorisé la croissance des particules identifiées comme étant des nano-oxydes d’yttrium avec une coquille enrichie en Cr. Enfin, une implantation ionique séquentielle de deux ions métalliques (Y et Ti) a été réalisée, suivie d'une implantation d’O. L'ordre d'implantation des ions métalliques s'est révélé crucial pour la précipitation de nano-oxydes lors du recuit ultérieur. Lors de la séquence avec une implantation de Ti en premier, une précipitation d'oxyde riche en chrome de structure corundum hexagonale a été observée, très similaire au cas de l'implantation d’ions Ti et O. En revanche, la séquence avec une implantation d’ions Y en premier a produit des nano-oxydes d'yttrium-titane qui possèdent une structure non identifiable. En résumé, l’étude a démontré la faisabilité de la formation de nano-oxydes de Y, Ti et (Y, Ti) par implantation ionique. La thèse présente la caractérisation détaillée de ces nano-oxydes, ainsi que certaines de leurs caractéristiques spécifiques, telles que la présence de relations d'orientation entre les nano-oxydes et la matrice FeCr, qui ont été observées même dans le cas de nano-oxydes de type corundum riches en Cr. Enfin, les résultats obtenus, combinées avec les données de la littérature, sont discutées pour une meilleure compréhension des mécanismes impliqués dans la formation des nano-oxydes dans les aciers ODSOxide Dispersion Strengthened (ODS) steels, that is steels reinforced with a homogeneous distribution of (Y,Ti) oxide nano-particles, are advanced structural materials for nuclear applications. The oxide particles serve as point defect recombination centres and obstacles to dislocation motion thereby improving radiation resistance and high-temperature strength of these steels making them perfect candidate materials for future fusion and fission nuclear reactors. The conventional fabrication of ODS steels is achieved by mechanical alloying followed by thermomechanical heat treatments. This way of ODS steel production seems complicated to understand the physical mechanisms leading to the precipitation of nano-oxide particles. The kinetics of nanoparticle formation can be much better studied using an alternative technique of nanoparticle growth, namely Ion Beam Synthesis (IBS). This approach has many advantages including the precise control of experimental parameters and the ability to de-correlate various factors contributing to precipitation kinetics. A better knowledge gained in this way would be potentially helpful for optimization of ODS steel production routines. In the course of this PhD study, the IBS approach was applied to investigate the co-precipitation of metal (Y and/or Ti) and oxygen ions implanted into a model Fe-Cr alloy with the composition close to those typical for commercial ODS steels. Following the standard IBS schedule, consisting of ion implantation followed by high-temperature heat treatment, ions of Y, Ti and O at low energies were implanted into high-purity Fe10wt%Cr alloy samples at room temperature. The implanted samples were then annealed at various temperatures ranging from 600 to 1100°C to promote the precipitation of nano-oxide particles. A range of Transmission Electron Microscopy techniques were used to characterize the crystallographic structure and chemical composition of the nanoparticles. The study has been performed following three sets of experiments. First of all, the sequential implantation of Ti and O ions was implemented. Subsequent annealing at temperatures below 1000°C revealed that precipitation of titanium oxide was suppressed. Instead, chromium-rich nano-oxide particles with corundum hexagonal structure were found to precipitate. At sufficiently high temperatures these corundum particles were found to contain certain amount of Ti. Only after annealing at the highest temperature of 1100°C, particles of another type with Ti enriched core and Cr enriched shell were additionally fixed. Secondly, sequential Y and O ion implantation resulted in the formation of probable yttrium-rich oxides at 800°C. Annealing at 1100°C promoted their growth to larger sized yttria (Y₂O₃) particles with a Cr enriched shell. Finally, sequential ion implantation of both metal ions (Y and Ti) was performed, followed by O implantation. The order of metal ion implantation has been found to be crucial for subsequent oxide precipitation at the annealing stage. With the Ti implantation first in the sequence, the precipitation of corundum hexagonal chromium-rich oxide was observed, very similar to the case of Ti and O implantation. In contrast, implantation starting with Y produced yttrium-titanium oxide particles with unidentifiable structure. Summing up, the study has demonstrated the feasibility of the formation of Y, Ti and (Y,Ti) oxides by ion implantation. The thesis presents the detailed characterization of the nanoparticles, as well as the discovered specific features of precipitated particles, such as the presence of orientation relationships between the particles and the FeCr matrix, which was observed even for the case of Cr-rich corundum particles. Finally, the implications of the obtained results, in conjunction with the already known data from the existing literature, for the better understanding of the mechanisms involved in the formation of nano-oxide particles in ODS steels are discussed
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Nagel, Adam Richard. "Closed cell steel foams from oxide reduction." Thesis, Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/19569.
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Mahmood, K. "Influence of strain rate on oxide fracture." Thesis, Cranfield University, 1988. http://dspace.lib.cranfield.ac.uk/handle/1826/11358.
Full textAbstract:
The ability of metals and alloys to form and retain protective oxide
scales is crucial to their stability at elevated temperatures for
extended times. Hence the identification of factors that promote or
limit the integrity of oxides on high temperature materials has been the
subject of intensive investigations.
In the present study the mechanical properties of this chromiwm.-rkh
scale on 304 stainless steel foil has been investigated in relation to
the deformation rates in the substrate. It was shown that heavy cold
working (up to 90%) delays the onset of breakaway oxidation and results
in a very adherent scale.
The cracking behaviour of the scale was found to be strain rate and
temperature dependent under slow strain rate conditions when the
substrate deforms by creep. No strain rate dependence was observed over
the temperature range 700-900°C when faster strain rates (> 10-
S
sec -1)
were applied. The transition between these two responses was found to
vary only slightly with temperature between S.Ox10-
S
sec-
1
and 7.Sx10-
S
sec
-1
,increasing as the temperature is raised.
A new method has been described for determining the fracture behaviour
of oxide scale by estimating the composite defect size. From a
knowledge of the onset of scale cracking, determined in Sl(U usi ng (h~
acoustic emission technique, it was possible to correlate the measured
intercrack spacing with the fracture toughness from which the tensile
properties of the scale can be evaluated.
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Clarke, Richard. "Coatings on stainless steel for solid oxide fuel cell interconnects." Thesis, University of St Andrews, 2012. http://hdl.handle.net/10023/3639.
Full textAbstract:
Enabling inexpensive and ubiquitous steels for use as solid oxide fuel cell interconnects has two major hurdles to overcome. Firstly, corrosion must be limited such that the interconnect can have longevity. Secondly, the evaporation of chromium from the corrosion layer must also be limited such that the fuel cell can have longevity. The evaporation of chromium from chromia, titanium doped chromia, and chromium cobalt spinels was studied and characterized. Spinels lost the least amount of mass during evaporation experiments, and changed the least after experimental conditions were imposed on them that. Chromium titanate samples retained a significant amount of chrome that would have evaporated had the sample been chromium oxide alone. This was due to local changes at the surface with titanium becoming enriched and blocking loss of further chromium. Various methods of depositing titanium doped chromia on the surface of SS430 were investigated. Sol-gel was attempted, but proved problematic. Evaporation of elemental titanium onto SS430 followed by conversion to rutile by heating followed by the evaporation of chromium into the rutile layer was investigated at length. These layers are nanoscale when evaporated and about 10 times thicker after oxidation. Characterization of the resulting Ti layers showed that at low temperatures a thick dense layer of rutile could be observed. At higher oxidation temperatures, the titanium was difficult to find. Evaporation of cobalt onto SS430 created thin films when oxidized. The films were shown to control the evaporation of chromium by production of spinels. These layers were characterized with X-Ray Diffraction and scanning electron microscopy and impedance spectroscopy. They were shown to be quite conductive compared to the titanium coatings.
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Bird, Mathew J. "Oxide evolution in ODS steel resulting from friction stir welding." Thesis, Monterey, California: Naval Postgraduate School, 2014. http://hdl.handle.net/10945/42582.
Full textAbstract:
Approved for public release; distribution is unlimitedThis thesis investigated the evolution of oxide particles caused by friction stir welding of oxide dispersion strengthened steel, MA956. Eight welding conditions were used of different rotation and traverse rates, resulting in a range of heat inputs affecting weld quality. Raman spectroscopy was used to identify and map the distribution of yttrium-aluminum oxide particles in cross sections of the welds. Electron microscopy and energy dispersive X-ray spectroscopy provided additional information on the size and spatial distribution of these oxides as a function of welding condition. As the heat input increased, the oxide particles grew in size and incorporated aluminum and oxygen from the matrix. This compositional change resulted in the formation of aluminum-rich oxides such as yttrium aluminum perovskite and yttrium aluminum garnet. The tool rotation rate was the largest contributor to oxide evolution, while traverse rate had less impact on oxide evolution. Higher heat input welding conditions also lowered the hardness of MA956 due to oxide evolution and grain growth.
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Boegelein, Thomas. "Selective laser melting of a ferritic oxide dispersion strengthened steel." Thesis, University of Liverpool, 2014. http://livrepository.liverpool.ac.uk/2010620/.
Full textAbstract:
Oxide dispersion strengthened (ODS) steels contain a fine dispersion of nano-sized, typically Y based, oxide particles which result in the material displaying significantly better creep, irradiation and oxidation resistance when compared to conventional alloys. Thus, such materials are considered as candidate structural materials for a number of applications in the fossil and nuclear energy sectors and in other high-temperature applications. ODS steels are currently produced by powder metallurgy which includes mechanical alloying (MA) of master alloys or elemental powder, hot extrusion or hot isostatic pressing (HIP) followed by a final heat treatment. Recent studies revealed that Y added during MA in the form of yttria (Y2O3) breaks down and the elements go into supersaturated solution in the Fe matrix; and Y based dispersoids form during fabrication of the alloy. In this work, an additive manufacturing method, selective laser melting (SLM), was applied to as-MA ODS-PM2000 (Fe-19.0wt.%Cr-5.5Al-0.5Ti-0.5Y2O3) powder. SLM produces almost fully dense solid freeform components by successively melting thin layers of metal powder. In order to investigate the feasibility of SLM in an ODS alloy environment, a number of builds were fabricated. These included a complex thin walled structure, coatings on Inconel IN939 (Ni-22.5wt.%Cr-19.0Co-3.7Ti-2W-1.9Al-1.0Nb-1.4Ta-0.15C), a nickel based superalloy, and optimised wall and solid builds. A wide range of microstructural and mechanical characterisation techniques were carried out on these builds with the focus to study the fundamentals of SLM in ODS environment. The most important finding of this work was that a fine homogeneous dispersion of globular shaped nanoscopic particulates could be retained in the SLM build configurations investigated. Indications were found that there is a very low number of dispersoids in the deposited layer after it was put down. Repeated heating cycles during SLM deposition of further slices resulted in coarsening and growth of existing precipitates, but probably also in nucleation and growth of new dispersoids in the α-Fe matrix. Such heating cycles and post-build annealing trials resulted in modification of initially multiphased dispersoid compounds including originally a number of elements, such as O, Al, Si, Ti, Cr, Fe and Y, into structures having significantly increased concentrations of Al and Y. After post-build annealing, the particles were most frequently of the compound type yttrium aluminium monoclinic, Y4Al2O9. SLM processing parameters were developed leading to a relative density of >99.5 % for wall builds having different thicknesses and of >98.5 % for solid builds. Electron backscatter diffraction (EBSD) was conducted and revealed a strong [001] fibre texture along the growth direction of a wall build. For annealed walls, values of the 0.2% offset yield strength YS0.2 up to those of recrystallized conventional produced PM2000 could be achieved. Fracture behaviour and the individual key parameters determined, YS0.2 and Young's modulus were anisotropic due to this texture. In coatings, Y-rich dispersoids could be retained. When oxidised isothermally in laboratory air at 1100°, the SLM deposit PM2000 formed a mainly α-Al2O3 (alumina) scale, which was similar to conventionally fabricated PM2000. Oxidation at 870°C, however, resulted in different scale morphologies between both variants. Those were Al-rich equiaxed structures and nodules and Ti-rich needles for conventional PM2000. On the other hand, the SLM material exhibited Al-rich platelet structures and Al-rich equiaxed crystals in pores. The observations of this work confirmed the feasibility of SLM in ODS alloy environment, which may motivate further studies in this field.
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London, Andrew James. "Irradiation damage of oxide dispersion strengthened steels." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:4860651a-e919-449c-9e1c-8c6843adddd2.
Full textAbstract:
Advanced fission and fusion power offer long-term energy production from fundamentally carbon-free fuel sources, with high-energy densities and high reliability. However, for these power sources to be realised, many materials challenges need to be addressed. Oxide dispersion strengthened (ODS) ferritic alloys are recognized as potential fission fuel cladding and fusion structural materials because of their high-temperature stability and swelling-resistance imparted by the nano-scale oxide clusters they contain. This work presents the study of a set of model ODS alloys with a systematic variation in alloy chemistry in order to investigate the influence of chemical additions on the oxide cluster nature and the irradiation resistance. To investigate these properties, the high-resolution characterisation techniques of atom probe tomography and transmission electron microscopy were applied in combination with nanoindentation to assess mechanical properties and X-ray diffraction to study the crystallinity. The quantification of the character of the oxide particles in these ODS alloys by atom probe tomography presented a number of challenges and I extend the conventional analysis techniques in order to overcome these difficulties. By comparison of the addition of Ti, and then Cr, to a Fe-Y2O3 alloy, the influence of alloy chemistry on the oxide particles was evaluated. The main aims were to investigate the microstructure, the oxide cluster composition and to set a baseline to which the irradiated samples were compared. The irradiation damage of the oxide clusters was investigated using ion irradiation as an analogue for neutron damage. Irradiation experiments were performed at a range of temperatures and the stability of the clusters was assessed based on their size, number density and chemistry. Subtle changes in cluster chemistry at elevated temperatures and the dramatic changes which occurred after irradiation at low temperatures lead to conclusions about the competition of thermal diffusion and irradiation damage.
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Harrington, M. T. "Oxide growth on ferritic stainless steels exposed to high temperature steam." Thesis, University of Manchester, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233277.
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Ha, Yoosung. "Recrystallization Behavior of Oxide Dispersion Strengthened Ferritic Steels." Kyoto University, 2014. http://hdl.handle.net/2433/192210.
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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.
Full textAbstract:
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.
29
Liu, Chuangwei. "Electrodepostion of Iron Oxide on Steel Fiber for Improved Pullout Strength in Concrete." Thesis, University of North Texas, 2014. https://digital.library.unt.edu/ark:/67531/metadc700033/.
Full textAbstract:
Fiber-reinforced concrete (FRC) is nowadays extensively used in civil engineering throughout the world due to the composites of FRC can improve the toughness, flexural strength, tensile strength, and impact strength as well as the failure mode of the concrete. It is an easy crazed material compared to others materials in civil engineering. Concrete, like glass, is brittle, and hence has a low tensile strength and shear capacity. At present, there are different materials that have been employed to reinforce concrete. In our experiment, nanostructures iron oxide was prepared by electrodepostion in an electrolyte containing 0.2 mol/L sodium acetate (CH3COONa), 0.01 mol/L sodium sulfate (Na2SO4) and 0.01 mol/L ammonium ferrous sulfate (NH4)2Fe(SO4)2.6H2O under magnetic stirring. The resulted showed that pristine Fe2O3 particles, Fe2O3 nanorods and nanosheets were synthesized under current intensity of 1, 3, 5 mA, respectively. And the pull-out tests were performed by Autograph AGS-X Series. It is discovering that the load force potential of nanostructure fibers is almost 2 times as strong as the control sample.
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Lieu, T. D. "Creep and creep fracture of MA 957 oxide dispersion-strengthened ferritic steel." Thesis, Swansea University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637910.
Full textAbstract:
The creep and creep fatigue properties of a 14% Cr ferritic steel (MA 957) strengthened with a dispersion of Y2O3 particles have been determined using high precision constant stress creep machines. Creep testing was carried out under tension over a stress range of 250 to 420 MPa at 873 to 973K. In addition, compression creep tests were also performed over a stress range of 250 to 320 MPa at 948K. Normal creep curves were observed under all tensile conditions, i.e. after the initial strain on loading, the strain rate decreased to an apparently steady state before the onset of a tertiary stage leading to fracture. Curve shapes varied with testing conditions. At low temperatures, all creep curves were primary dominated. At higher temperatures, the creep curve shapes were primary dominated at low stresses but tertiary dominated at higher stresses. Like all oxide dispersion-strengthened alloys (ODS), the stress exponent (n) and the activation energy (Qc) values of MA 957 were found to be anomalously large; n varied from 25 to 52, whilst Qc varied from 498 to 856 KJmol-1 over the stress and temperature ranges studied. Despite much research on ODS alloys, power law creep behaviour of ODS alloys is still not well understood. Thus, the creep properties of MA 957 were analysed using the θ methodology. It was shown that entire creep curves can be constructed accurately when using the θ Projection Concept, allowing minimum creep rates and times to failure to be calculated for any stress and temperature. Moreover, this study indicated that the complex behaviour patterns observed when power law equations are used to describe the creep properties of MA 957 can be rationalised convincingly using the θ methodology.
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Shahryari, Arash. "Enhancement of biocompatibility of 316LVM stainless steel by electrochemical cyclic potentiodynamic passivation." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=107543.
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Note:as hip and knee prosthesis, orthopaedic fixations and coronary stents. The definition of a material's biocompatibility necessitates meeting a number of criteria, including high corrosion resistance and desirable interactions of the material's surface with biological species, such as cells, platelets, and serum proteins. SSs offer acceptable resistance to uniform (general) corrosion when used as materials of construction in sorne industrial applications, which is due to the formation of a thin passive oxide film on their surface. [...]
Les aciers inoxydables (AI) 316-L sont fréquemment utilisés dans le domaine biomédical. Par exemple, nous les retrouvons dans les prothèses de hanche et de genou, dans les fixatures orthopédiques et dans les prothèse vasculaires. Pour qu'un matériel soit biocompatible, il doit avoir une résistence élevée à la corrosion. De plus, la surface du matériel doit avoir des intéractions favorables avec les différentes espèces biologiques c'est-à-dire les cellules.[...]
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Clowe, Samantha Jane. "Oxide scale failure on AISI430 ferritic stainless steel under simulated roll-break conditions." Thesis, University of Sheffield, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.440919.
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Song, Peng. "Effect of oxide former elements on ion-irradiation response of oxide dispersion strengthened ferritic steels." Kyoto University, 2018. http://hdl.handle.net/2433/236000.
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Metaferia, Ineku Amhayesus. "Characterization of Steel Corrosion Products in Reinforced Concrete." Thesis, Université d'Ottawa / University of Ottawa, 2021. http://hdl.handle.net/10393/42128.
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Steel corrosion is one of the major distress mechanisms that causes the deterioration of reinforced concrete structures around the world. It is an electrochemical reaction between the reinforcing steel and the surrounding concrete that produces a mass loss of the metal. Through the process of corrosion in reinforced concrete, iron ions get oxidized to form corrosion products (CP). Although multiple experiments and studies have been developed to understand the rheological behavior of corrosion products, this topic stays inconclusive. This work aims to characterize corrosion products at micro-scale in order to trace the progress of the formation of rust, to determine its nature and to analyse its rheological behavior in reinforced concrete. An experimental procedure to produce CP in the laboratory is also presented in this research. In addition, material characterization methods have been used to identify the iron oxide phases present in CP, determine their viscosity and rheological behavior and to study how CP flows in a porous media. In order to identify the different stages in the corrosion process, the CP was analysed at 2, 4, 6 and 8 weeks. The experiments identified four phases of iron oxide for each period. Furthermore, it was found that CP behaves as a shear-thinning slurry and as a result, its viscosity decreases with the applied shear rate. In addition, the damage caused by CP on concrete depends on the w/c ratio of the concrete mix and the exposure time to a corroding environment. The rebar mass loss results show that CP is formed in layers around the rebar, and the flow of each CP layer can differ.
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Gorley, Michael. "Powder processing of oxide dispersion strengthened steels for nuclear applications." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:6a3f2843-d87d-45b8-8c41-676220412813.
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Ferritic ODS steels show improved high temperature strength and irradiation tolerance compared with conventional ferritic steels, and are one of the key potential materials for fusion blanket structural applications. The processing of ODS steels is critical to their subsequent performance; however knowledge of the optimum processing approaches for these alloys is not complete. The microstructural evolution of ODS steels containing Y2O3 and other additions during manufacture has been investigated and the processing conditions optimised based on microstructural and mechanical investigations. Ferritic powders with Y2O3 and other additions were investigated, primarily using analysis on the micro- and nano-scale, with an emphasis on identifying the requirements for homogenization of the Y within the steel matrix. The Y2O3 dispersion and subsequent development of the nano-precipitates during thermal treatment was investigated using in-situ neutron diffraction. The nano-precipitates were resolved at approximately 900◦C after 1hr, with coarsening and/or re-precipitation progressively increasing at higher temperatures. A significantly increased number density of nano-precipitates (∼2x1023m−3 to ∼7x1023m−3) was established by hot isostatically pressing an Fe-14Cr-3W-0.2Ti0.25Y2O3 alloy at 950◦C compared with more traditional temperatures at 1150◦C, attributed to the increased coarsening and/or re-precipitation of the nano-precipitates at the higher temperatures. The influence of the mechanical alloy (MA)ing conditions on bulk mechanical properties was investigated using four point bend. The highest fracture toughness of ∼55MN/m3/2 and ultimate strength of ∼1450MPa was achieved under conditions that minimised the mechanical alloying time and increased the average final size of the powders. An Fe-14Cr-3W-0.2Ti-0.25Y2O3 (wt%) ODS alloy manufactured under optimised conditions showed a bi-modal grain structure size distribution and had a comparatively high yield strength of >1200MPa at 20◦C and >330MPa at 700◦C. The grain structure and high yield strength were attributed to the random distribution of 25nm radius of gyration (Rg) Y, Ti and O rich nano-precipitates randomly dispersed throughout the alloy. Long term thermal ageing (750hr at 1000◦C) reduced the room temperature yield strength and increased the proportion of larger grains in the bi-modal distribution, but high temperature yield strength was remarkably stable.
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Jones, Christopher A. "A micromechanical investigation of proton irradiated oxide dispersion strengthened steels." Thesis, University of Oxford, 2016. http://ora.ox.ac.uk/objects/uuid:fadd9abf-b5d0-4ea1-9d86-50628ec0476a.
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This thesis was most concerned with the mechanical response to irradiation of two in-house produced oxide dispersion strengthened (ODS) steels and two non-ODS coun- terparts. The steels, manufactured by Dr. M. J. Gorley (University of Oxford), were me- chanically alloyed from gas-atomised Fe-14Cr-3W-0.2Ti, with the addition of 0.25Y2O3 powder in the case of the ODS variants. The powders were hot isostatic pressed at consolidation temperatures of 950 °C and 1150 °C. The four steels were designated 14WT 950 (non-ODS), 14YWT 950 (ODS), 14WT 1150 (non-ODS) and 14YWT 1150 (ODS), and were used in the as-produced condition. Initially, the macroscale elastic modulus and yield stress were determined using a four-point flexure test, employing digital image correlation (DIC) as a strain gauge. The microcantilever size eects were then characterised, and it was determined that the yield stress signicantly diverged from macroscale values at microcantilever beam depths of < 4.5 μm. Using knowledge of this, the in-house produced alloys were irradiated with 2 MeV protons at the Surrey Ion Beam Centre (University of Surrey, UK) to a displacement damage of ∼ 0.02 dpa and 0.2 dpa (Bragg peak). This was to produce a deep irradiated layer for the fabrication of large microcantilevers with reduced size effects. The cross-sectional surface of the irradiated layer was then exposed and inclined linear arrays of 250 nm deep indents were placed across the damage prole. 14WT 1150 (non-ODS) revealed a clear proton damage prole in plots of hardness against irradiation depth, 14WT 950 (non-ODS) also showed modest hardening in the region of the Bragg peak. No appreciable hardening was observed in either 14YWT specimens, attributed to the fine dispersion of nanoscale oxides providing a high number density of defect sink sites. However, a large bimodal variation in hardness was measured in both ODS variants. This was investigated using EBSD and EDX, and was determined to be caused by a pronounced heterogeneity of the microstructure. While Hall-Petch strengthening and changes in the local chemistry had some effect on the measured hardness, the most likely cause of the large variation in local hardness was heterogeneity in the nanoscale oxide population. Microcantilevers were fabricated out of the irradiated layer cross-section in 14WT 1150 and 14YWT 1150. Larger microcantilevers, with ∼ 5 μm beam depth, were placed with their beam centre at ∼ 0.026 dpa. Smaller microcantilevers, with ∼ 1.5 μm beam depth, were placed with their beam centre at the Bragg peak, 0.2 dpa. Both the large and the small microcantilevers fabricated in 14WT 1150 (non-ODS) displayed significant irradiation hardening. In the ODS variant, 14YWT 1150, irradiation hardening appeared to be reduced. The work in this thesis successfully showed that it was possible to extract a close approximation of the macroscale yield stress from shallow irradiated layers, providing that the irradiation condition is carefully chosen in response to known size dependent behaviour. This thesis also investigated the size dependent behaviour of microcantilevers using a lengthscale dependent crystal plasticity UMAT, developed by Dunne et al. and implemented within ABAQUS 6.14-2 commercially available nite element software. The simulation of the GND density evolution with increasing plastic strain allowed their contribution to the microcantilever size effect, through mobile dislocation pinning, to be determined. This novel approach to modelling size effects in three dimensional finite element microcantilever models demonstrated that while it was possible to simulate a lengthscale-dependent response in finite element microcantilever models, the constitutive equation for the plastic velocity gradient needs to be more physically based in order the match the experimentally derived results; for example, a lengthscale-dependent term relating to the dislocation source density of the material. Although the apparent reduction of irradiation hardening in ODS in-house produced alloys showed great promise, these alloys also displayed a large amount of scatter in measured hardness and yield stress, attributed to the pronounced heterogeneity in the microstructure. Alloys with such signicant microstructural heterogeneity are not suitable for engineering or commercial use.
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Grieveson, Eleanor M. "Irradiation effects on the deformation of oxide dispersion strengthened steels." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:6234be04-02f3-44bd-9b11-cc915b2ecbee.
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This study concerns four high performance structural alloys designed to withstand the extreme temperature and irradiation environment inside fusion and fission fast breeder reactors: two Reduced Activation Ferritic Martensitic (RAFM) steels (Fe-14wt%Cr and a European standard alloy EUROFER97) and two equivalent Oxide Dispersion Strengthened (ODS) steels (Fe-14wt%Cr ODS (CEA ODS) and EUROFER ODS). Neutron irradiation of the samples was impractical due to timescale and specific handling requirements for radioactive samples. Instead, ion implantation was used to simulate the helium and damage of neutron irradiation. Samples of each alloy were subjected to a range of ion implantations: 75appm He, 2000appm He, 2000appm He + 4.5dpa Fe and 2000appm Ne. The matrix of four materials and five implantation conditions was analysed using the following experimental techniques: nanohardness indentation, Vickers hardness testing, micropillar compression, microcantilever bending, transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX). These techniques were used to compare the properties of the unimplanted materials and their response to implantation. Yield stress (σy) was comparable across hardness testing and microcantilever bending, and consistently showed σy Fe-14wt%Cr < EUROFER < EUROFER ODS < CEA ODS. When subject to helium implantation, 75appm He caused insignificant changes in σy while 2000appm He increased σy in all materials. This increase was most significant in Fe-14wt%Cr due to its low grain boundary density and lack of oxide/carbide particles. The particle dispersions in the other materials act as helium traps, preventing the formation of TEM visible bubbles and reducing the hardening effects of the helium. Across all results it becomes clear that, although not to the degree of the ODS materials, EUROFER is more radiation resistant than Fe-14wt%Cr. It therefore appears that it is the presence of a complex microstructure including small grains and a distribution of oxide or carbide particles, rather than the specific inclusion of oxide nanoparticles, that provides RAFM steels with superior irradiation resistance properties.
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Birosca, Soran. "The microstructural development of oxide scales on low carbon steels." Thesis, Loughborough University, 2006. https://dspace.lboro.ac.uk/2134/5852.
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RincoÌn, Omar GarciÌa. "Oxide scale failure during multi-stage deformation in the hot rolling of mild steel." Thesis, University of Sheffield, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.434624.
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Bergman, Ola. "Studies of oxide reduction and nitrogen uptake in sintering of chromium-alloyed steel power /." Stockholm : Materialvetenskap, Kungliga Tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9555.
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Je, Hwanil. "Stress Corrosion Cracking Behavior of Oxide Dispersion Strengthened Ferritic Steel in Supercritical Pressurized Water." Master's thesis, Kyoto University, 2013. http://hdl.handle.net/2433/180448.
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Myrsell, Johan. "Effect of shot blasting on processoxidised stainless steel – morphology,chemistry and pickling performance." Thesis, KTH, Materialvetenskap, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-161877.
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The oxide scale created during manufacturing of stainless steel is often removed by a chemical pickling with mixed acid. Various pre-treatments to pickling are also applied to increase the efficiency of the oxide scale removal. Shot blasting is one such pre-treatment, which operates to remove a certain amount of oxide and also to generate cracks and openings for the subsequent pickling. In this work, three materials, AISI 2205, 430 and 304 have been blasted and later exposed to mixed acid. This was conducted to quantify the effect shot blasting has on the subsequent pickling of stainless steel. Three shot products and two blasting parameters were investigated and varied. Shot blasting significantly reduced the oxide scale but was unable to remove the chromium oxide layer closest to the steel surface. No significant difference was observed when comparing the result from the three shot products after blasting. Increasing the particle velocity or the coverage rate further enhanced the pickling but reduced the amount of oxide removed during blasting. These effects are however relative small, so in practise relatively mild conditions seems preferable for economic reasons. Oxide scale containing hematite was difficult to remove by both shot blasting and pickling.
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Bothma, Jan Andries. "Heat transfer through mould flux with titanium oxide additions." Diss., Pretoria : [s.n.], 2006. http://upetd.up.ac.za/thesis/available/etd-10182007-161313/.
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Lazauskas, Tomas. "Simulating radiation effects in iron with embedded oxide nanoparticles." Thesis, Loughborough University, 2014. https://dspace.lboro.ac.uk/2134/15411.
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Alloys used in fission and in future fusion reactors are subjected to extreme conditions including high temperatures, corrosive and intense radiation environments. Understanding the processes occurring at the microscopic level during radiation events is essential for the further development of them. As a prospective candidate material for new reactors, oxide dispersion strengthened (ODS) steels have shown good radiation resistance and the ability to trap He into fine scale bubbles, thus preventing swelling and preserving high-temperature strength. This thesis represents the findings obtained by performing computational studies of radiation effects in pure iron, Y-Ti-O systems and a simplified model of ODS using Molecular Dynamics (MD) and on-the-fly Kinetic Monte Carlo (otf-KMC) techniques. MD studies of radiation damage were carried out in a perfect body-centred cubic (bcc) iron matrix (alpha-Fe) in which yttria nanoparticles are embedded as a simplified model of an ODS steel. The results have shown how the nanoparticles interact with nearby initiated collision cascades, through cascade blocking and energy absorption. Fe defects accumulate at the interface both directly from the ballistic collisions and also by attraction of defects generated close by. The nanoparticles generally remain intact during a radiation event and release absorbed energy over times longer than the ballistic phase of the collision cascade. Also the nanoparticles have shown ability to attract He atoms as a product of fission and fusion reactions. Moreover, studies showed that He clusters containing up to 4 He atoms are very mobile and clusters containing 5 He or more become stable by pushing an Fe atom out of its lattice position. The radiation damage study in the Y-Ti-O materials showed two types of residual damage behaviour: when the damage is localized in a region, usually close to the initial primary knock-on atom (PKA) position and when PKA is directed in the channelling direction and creates less defects compared to the localised damage case, but with a wider spread. The Y2TiO5 and Y2Ti2O7 systems showed increased recombination of defects with increased temperature, suggesting that the Y-Ti-O systems could have a higher radiation resistance at higher temperatures. The otf-KMC technique was used to estimate the influence of the prefactor in the Arrhenius equation for the long time scale motion of defects in alpha-Fe. It is shown that calculated prefactors vary widely between different defect types and it is thus important to determine these accurately when implementing KMC simulations. The technique was also used to study the recombination and clustering processes of post-cascade defects that occur on the longer time scales.
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Williams, Ceri Ann. "Atomic scale characterisation of oxide dispersion strengthened steels for fusion applications." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:4f03864f-4fe1-4005-ac28-6d9e8244989b.
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Reduced-activation ferritic steels are considered as the primary candidate materials for structural applications within nuclear fusion power plants. It is known that by mechanically alloying ferritic steel powder with Y (usually in the form of Y₂O₃) then consolidating the material by hot isostatic pressing, a nanoscale dispersion of oxygen rich nanoclusters as small as ~2nm is introduced into the microstructure. This vastly improves high temperature strength and creep resistance, and the nanoclusters also act as trapping sites for helium and point defects produced under irradiation. In this thesis, the evolution of the oxide nanoclusters in a Fe-14Cr-2W-0.3Ti & 0.3Y₂O₃ ODS alloy was investigated primarily using atom probe tomography. The microstructure was characterised at various points during processing to give an insight into the factors influencing the formation of the nanoclusters. It was found that the nanoclusters nucleated during the mechanical alloying stage, then followed near classical nucleation and growth mechanisms keeping the same composition of ~8%Y, ~12%Ti,~25%O and ~45%Cr throughout. The formation and evolution of 5-15nm grain boundary oxides was also observed, and these were shown to form first as Cr₂O₃ particles that subsequently transform into a Y-Ti-O based oxide on further processing. The influence of mechanical alloying with 0.5wt.%Fe₂Y rather than 0.3wt.%Y₂O₃ was also investigated, and this showed that there was no difference in the final microstructure produced provided the level of Ti in the starting powder was tightly controlled. Without sufficient Ti, the nanoclusters were Y-O based and ~6nm diameter. Both the Y-O and Y-Ti-O nanoclusters were moderately stable on annealing at 1200°C for up to 100 hours, with only minimal coarsening observed. Ti was found not to influence the coarsening rate of the nanoclusters significantly. The stability of the oxide nanoclusters under irradiation was investigated by using Fe²⁺ ion irradiation to simulate displacement cascade damage in the ODS-Eurofer material (the official European candidate material for testing in the ITER fusion test reactor). Doses up to ~6 dpa at 400°C were used, and there was no significant change to the nanocluster distribution. However segregation of Mn to dislocations was observed after irradiation. These results indicate that ODS steels are good candidate structural materials, as the microstructure is stable at high temperature and under irradiation. The starting powders, and processing parameters need to be tightly controlled in order to produce the optimal material for use in service.
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Noh, Sanghoon. "Welding and Joining Technology Development of Oxide Dispersion Strengthened Ferritic Steels." Kyoto University, 2010. http://hdl.handle.net/2433/126766.
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CHEN, DONGSHENG. "Iron/Chromium Phase Decomposition Behavior in Oxide Dispersion Strengthened Ferritic Steels." Kyoto University, 2015. http://hdl.handle.net/2433/199417.
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Åkerlind, Kristina, and Zenja Jefimova. "Possible reasons for flaking appearance during cold rolling on an austenitic stainless steel." Thesis, KTH, Materialvetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-213835.
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The research describes possible reasons why the flaking tendency during cold rolling can vary between different austenitic stainless steels. The flaking phenomenon was observed after a rolling process in Granlund Tools AB’s roll reducing mill “KOR-8”. A literature review was conducted with the purpose of finding a connection between rolling process, austenitic stainless steels and flaking. The laboratory work aimed at revealing possible differences between the flaked material and materials that is known to be cold rolled with high surface finish in the particular machine. In order to come to a conclusion regarding the flaking appearance, scanning electron microscopy (SEM), Vickers hardness test and light optical microscopy (LOM) were performed. The literature review along with the laboratory results made it possible to determine the two major factors affecting the flaking behavior. Two independent analyses revealed what came to be the most important discovery in this study. LOM showed the appearance of a thick oxide scale on the surface of the flaked steel which was further confirmed by SEM-Energy-Dispersive X-ray Spectroscopy that indicated the existence of oxides on the steel’s surface. These observations along with the knowledge that oxide scales grow only during high-temperature processing led to the conclusion that the steel is not appropriate for the cold rolling process due to the earlier steel manufacturing.
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Ma, Zhongting. "Control of nonmetallic inclusions in continuously cast steels : applications of oxide metallurgy /." Freiberg : TU Bergakad, 2002. https://fridolin.tu-freiberg.de/archiv/html/WerkstofftechnologieMaZhongting41933.html.
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Mu, Wangzhong. "Microstructure and Inclusion Characteristics in Steels with Ti-oxide and TiN Additions." Doctoral thesis, KTH, Tillämpad processmetallurgi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-162284.
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Non-metallic inclusions in steels are generally considered to be detrimental for mechanical properties. However, it has been recognized that certain inclusions, such as Ti-oxide and TiN, can serve as potent nucleation sites for the formation of intragranular ferrite (IGF) in low-alloy steels. The formation of IGF could improve the toughness of the coarse grained heat affected zone (CGHAZ) of weld metals. Thus, the present thesis mainly focuses on the effect of size of nucleation sites on the IGF formation. Quantitative studies on the composition, size distribution and nucleation probability for each size of the inclusions as well as the area fraction, starting temperature and morphology of an IGF have been carried out. In the present work, the Ti-oxide and TiN powders were mixed with metallic powders. The mixed powders were heated up to the liquid state and cooled with a slow cooling rate of 3.6 ºC/min. These as-cast steels with Ti-oxide and TiN additions were used to simulate the IGF formation in the CGHAZ of weld metals. Specifically, the inclusion and microstructure characteristics in as-cast steels have been investigated. The results show that the nucleant inclusion was identified as a TiOx+MnS phase in steels with Ti2O3 additions and as a TiN+Mn-Al-Si-Ti-O+MnS phase in steels with TiN additions. In addition, the TiOx and TiN phases are detected to be the effective nucleation sites for IGF formation. It is clearly shown that an increased inclusion size leads to an increased probability of IGF nucleation. This probability of IGF nucleation for each inclusion size of the TiOx+MnS inclusions is clearly higher than that of the complex TiN+Mn-Al-Si-Ti-O+MnS inclusions. In addition, the area fraction of IGF in the steels with Ti2O3 additions is larger than that of the steels with TiN additions. This result agrees with the predicted tendency of the probability of IGF nucleation for each inclusion size in the steels with Ti2O3 and TiN additions. In order to predict the effective inclusion size for IGF formation, the critical diameters of the TiO, TiN and VN inclusions, which acted as the nucleation sites of IGF formation, were also calculated based on the classical nucleation theory. The critical diameters of TiO, TiN and VN inclusions for IGF formation were found to be 0.192, 0.355 and 0.810 μm in the present steels. The calculation results were found to be in agreement with the experiment data of an effective inclusion size. Moreover, the effects of the S, Mn and C contents on the critical diameters of inclusions were also calculated. It was found that the critical diameter of the TiO, TiN and VN inclusions increases with an increased content of Mn or C. However, the S content doesn’t have a direct effect on the critical diameter of the inclusions for IGF formation. The probability of IGF nucleation for each inclusion size slightly decreases in the steel containing a higher S content. This fact is due to that an increased amount of MnS precipitation covers the nucleant inclusion surface. In the as-cast experiment, it was noted that an IGF can be formed in steels with Ti2O3 and TiN additions with a cooling rate of 3.6 ºC/min. In order to control the microstructure characteristics, such as the area fraction and the morphology of an IGF, and to investigate the starting temperature of IGF and grain boundary ferrite (GBF) formation, the dynamic transformation behavior of IGF and GBF was studied in-situ by a high temperature confocal laser scanning microscope (CLSM). Furthermore, the chemical compositions of the inclusions and the morphology of IGF after the in-situ observations were investigated by using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and electron probe microanalysis (EPMA) which equipped wavelength dispersive spectrometer (WDS). The results show that the area fraction of IGF is larger in the steels with Ti2O3 additions compared to the steels with TiN additions, after the same thermal cycle has been imposed. This is due to that the TiOx phase provides more potent nucleation sites for IGF than the TiN phase does. Also, the area fraction of IGF in the steels is highest after at an intermediate cooling rate of 70 ºC/min, since the competing phase transformations are avoided. This fact has been detected by using a hybrid methodology in combination with CLSM and differential scanning calorimetry (DSC). In addition, it is noted that the morphology of an IGF is refined with an increased cooling rate.QC 20150325