This master thesis studies the behaviour of two aluminium alloys in ultrasonic cleaning at two different intensities, as well as the effect of a cleaning solution, Formula 815 GD-NF on the same surface have been studied with respect to surface roughness and material composition. Methods like Light Optical Microscopy (LOM), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and 3D topography using white light interferometry (VSI) was used to study the surface and material composition. It was found that both the ultrasonic cleaning, as well as the solution itself both increase surface roughness of the samples. When crossing a threshold in ultrasonic intensity micro jet cavitation dislodge precipitates, or areas weakened by precipitate to form a large pit. And the following heat from the jet causes the surface to oxidise, becoming more brittle, and be broken up by other cavitation phenomena to cause rapid acceleration of surface roughness in an area originating from the pit.

Classical fatigue models teach that there is an intrinsic fatigue limit for steels, representing a level of stress that is too low for regular crack growth where every cyclic load propagates a fatigue crack through the material. Modern application with extreme lifetimes has shown that fatigue will still take place in steels with stress levels well below the expected fatigue limit. This relatively new area of study has been named Very High Cycle Fatigue, or VHCF, and describes fatigue failures with a number of load cycles exceeding 107. Fractography of steels that has suffered VHCF tends to reveal an especially rough crack surface adjacent to where the fatigue crack originates, which is typically some form of defect in the bulk of the steel. This area is believed to be critical for VHCF and has been referred to in a number of ways by different studies, but will herein be called Fine Granular Area, or FGA. The aim of this study is to try and get a better understanding of VHCF. This was done by fractography analysis of test specimens of high strength tool steel that suffered fatigue failure at lifetimes ranging from about 106 cycles to 1,9x109 cycles. The lower lifetimes were achieved using hydraulic testing equipment, while the specimens in the VHCF range suffered fatigue failure in ultrasonic testing equipment allowing the application of a cyclic stress at a rate of 20 000 Hz. The resulting fracture surfaces were then investigated using a scanning electron microscope, or SEM, taking special note of the fatigue initiating defects and, in the case of VHCF, the rough area found adjacent to it. In combination with the SEM an elemental analysis of the fatigue initiating defects as well as the bulk of the material was done using energy-dispersive X-ray spectroscopy, or EDS. This was done to find out what the defects consisted of; confirming that they were slags and checking that the composition of the material of the bulk of the specimen matches what was expected. Using light optical microscopy in combination with acid etching of the surface of samples cut out of the test specimens the structure of the steel was investigated. Calculating the local stresses at the location of the fatigue initiating defect was done using FEM in combination with displacement amplitude gathered from the ultrasonic testing equipment. The data gathered was then measured and compared to that of previous studies, using models of prediction and seeing how they match the experimental results. The results suggest that the stress intensity factor at the internal slags is critical for VHCF and that with lower stress intensity factors one can expect longer lifetimes. Another observation is a relatively consistent stress intensity factor at the edge of the FGA combined with the original defect, likely signifying the transition from the creation of FGA to traditional crack propagation. There also seems to be a connection between the size of the FGA and the number of cycles to failure, with larger FGA with increasing lifetimes. The most glaring shortcoming of this study is the amount satisfactory tests conducted, and thus amount of data points, is very low due to the majority of specimens suffered failure at the threading used to connect them to the ultrasonic testing equipment at lifetimes far too low to be relevant. / Klassiska utmattningsmodeller lär ut att det finns en utmattningsgräns för stål, vilket representerar en spänningsnivå som är för låg för regelbunden sprickväxt där varje cyklisk belastning sprider en utmattningsspricka genom materialet. Moderna applikation med extrema livstider har visat att utmattning fortfarande äger rum i stål med spänningsnivåer långt under den förväntade utmattningsgränsen. Detta relativt nya studieområde har fått namnet Very High Cycle Fatigue, eller VHCF, och beskriver utmattningsfall med ett antal belastningscykler som överstiger 107. Fraktografi av stål som har drabbats av VHCF tenderar att ha en särskilt gropig sprickyta som ligger intill där utmattningssprickan har sitt ursprung, vilket typiskt är någon form av defekt i stålets bulk. Detta område tros vara kritiskt för VHCF och har hänvisats till på ett antal sätt av olika studier, men kommer här att kallas Fine Granular Area eller FGA. Syftet med denna studie är att försöka få en bättre förståelse för VHCF. Detta gjordes genom fraktografianalys av testprover av verktygsstål med hög hållfasthet som drabbades av utmattningsbrott vid livstider från cirka 106 cykler till 1,9x109 cykler. De lägre livslängderna uppnåddes med hjälp av hydraulisk testutrustning, medan proverna i VHCF-området drabbades av utmattningsbrott i ultraljudstestutrustning som klarar att applicera en cyklisk stress med en frekvens på 20 kHz. De resulterande sprickytorna undersöktes sedan med hjälp av ett svepelektronmikroskop, eller SEM, med särskild fokus på utmattningsinitierande defekter och, i fallet med VHCF, det grova området som hittades intill det, FGA. I kombination med SEM utfördes en elementanalys av utmattningsinitierande defekter liksom huvuddelen av materialet med energidispersiv röntgenspektroskopi, eller EDS. Detta gjordes för att ta reda på vad inneslutningarna bestod av för att bekräfta att de var slagg samt kontrollera att sammansättningen av materialet i huvuddelen av provet matchar det som förväntades. Med användning av optisk ljusmikroskopi i kombination med syraetsning av ytan på prover som skars ut ur testproverna undersöktes stålets struktur. Beräkning av de lokala spänningarna på platsen för den utmattningsinitierande defekten gjordes med hjälp av FEM i kombination med förskjutningsamplituden som samlats från ultraljudsutrustningen. De insamlade uppgifterna mättes sedan och jämfördes med tidigare studier genom att använda diverse modeller och se hur de matchar de experimentella resultaten. Resultaten antyder att stressintensitetsfaktorn vid inneslutningarna är kritisk för VHCF och att man med lägre stressintensitetsfaktorer kan förvänta sig längre livstid. En annan observation är en relativt konsekvent stressintensitetsfaktor vid kanten av FGA, vilket sannolikt markerar övergången från skapandet eller utbredning av FGA till traditionell sprickutbredning. Det verkar också finnas en koppling mellan storleken på FGA och antalet cykler till fel, med större FGA med ökande livslängd. Den mest uppenbara bristen i denna studie är mängden tillfredsställande tester som genomförts. Därmed är mängden datapunkter mycket låg, detta på grund av att majoriteten av proverna misslyckades vid gängningen som användes för att ansluta dem till ultraljudstestutrustningen vid livstider alltför låga för att vara relevanta.

Lead (Pb) is frequently used as an alloying element in brass to enhance machinability and castability. However, this element poses a significant risk to human health and the environment. The 2021 revision of the Drinking Water Directive imposed stricter limits on Pb content in brass, encouraging the development of lead-free brass. Several studies have identified tin (Sn) as a potential substitute for Pb in brass. This master’s thesis examines the thermodynamic description of the Cu-Zn-Sn ternary system, using the Swerim Cu database. The investigation involved casting five alloys in the Cu-rich corner, followed by heat treatment at 550 oC until homogenized, and quenching, after which the samples were analyzed to determine the bcc and fcc phase composition. The results were used to confirm the thermodynamic description, and the ternary parameters of the fcc and bcc phases were optimized to match the experimental results. After the optimization, a significant enhancement is achieved in the description of the Cu-Zn-Sn ternary system, which better fits the experimental data. / Bly  (Pb)  används  ofta  som  ett  legeringselement  i  mässing  för  att  förbättra bearbetbarheten och  gjutbarheten.    Detta  element  utgör  dock  en  betydande  risk för människors  hälsa  och miljön.   2021 års översyn  av  dricksvattendirektivet införde strängare  gränser  för  Pb-halten  i mässing,  vilket  uppmuntrade utvecklingen av blyfri mässing.    Flera  studier  har  identifierat tenn  (Sn)  som  ett potentiellt substitut  för  Pb i mässing.   Denna  masteruppsats  undersöker den termodynamiska beskrivningen  av det ternära  Cu-Zn-Sn-systemet  med  hjälp  av Swerim Cu-databasen.   Undersökningen innefattade  gjutning  av  fem  legeringar  i det  Cu-rika hörnet, följt av värmebehandling vid 550 oC tills de homogeniserades, och härdning, varefter proverna analyserades  för  att bestämma  bcc-  och  fcc-fassammansättningen.   Resultaten  användes  för att  bekräfta den  termodynamiska  beskrivningen,  och  de  ternära  parametrarna  för  faserna  fcc och bcc  optimerades  för  att  matcha  experiment resultaten.  Efter  optimeringen  uppnås  en betydande  förbättring  av  beskrivningen  av  det  ternära  Cu-Zn-Sn-systemet,  vilket bättre  passar experimentdata.

The ladle furnace process is an important process in the steel manufacturing industry. The purpose of this process is to optimize the composition of the elements in the melt as well as to homogenize the temperature in the liquid. It is common practice to model this process using smaller water models. In order to accurately scale these models a variety of criteria and scaling factors are needed. The central phenomenon which all else is derived from is the two-phase gas plume dominating the fluid flows. The plume, and its dependant parameters are difficult to define. Which ones ought to be used and how to use them has not been standardized. Concerns have been raised whether the most common method of scaling is even applicable in ladle metallurgy. This report gives an account for studies concerning these variables and their effect on the subject. The objective of this report is to highlight ways to improve these simulations with respect to debated parameters. The conclusion of this study points out the reasons for why these variables may be of importance for the modeling of the ladle furnace process. It also specifically mentions future work that should be conducted in order to provide deeper knowledge of thedifferent parameters affecting the method of modeling. / Skänkmetallurgin är en viktigt process inom stålindustrin. Syftet med denna process är att optimera den kemiska sammansättningen i smältan och att homogenisera temperaturen i vätskan. Det är vanligt att modelera denna process med hjälp av vattenmodeller. För att träffsäkert skala dessa modeller krävs en mängd kriterier och skal-faktorer. Det mest centrala fenomenet, utifrån vilket allt annat kan härledas, är två-fas gasplymen som dominerar flödena i skänken. Plymen och dess beroende parametrar är svåra att definera. Vilka som bör användas och hur de används har inte standardiserats. Oro har väckts över om den vanligaste skalningsmetoden ens går att använda i skänkmetallurgi. Denna rapport redogör för studier rörande dessa variabler och deras påverkan på ämnet. Syftet med denna rapport är att belysa olika tillvägagångssätt till att förbättra dessa simulationer med hänsyn till debaterade parametrar. Slutsatsen för denna studie lyfter fram anledningarna till varför dessa variabler är av vikt för modellering för skänkmetallurgin. Även framtida arbete som bör utföras föratt ge djupare förståelse för de olika parametrarna belyses.

This study has been conducted with the aim to examine the extent of the heat affected zone in order to use laser cutting when making samples for tensile testing. When cutting with a laser the material absorbs heat energy from the laser beams which causes changes in the microstructure. The heat affected zone affects the properties of the materials, lowering the accuracy of the tensile test. Therefore, it is desired to know the extent of the heat affected zone in order to remove it before tensile testing. In this study two materials were used, the high strength steel Docol 1000DP and the duplex stainless steel LDX 2101. The materials were cut in the shape of dog bones for tensile testing using two different laser powers, 2500 W and 3500 W. The samples were cut with different cutting speeds, starting at lower cutting speed, increasing until the laser was unable to cut through. Thereafter, the heat affected zone, and the surface quality was examined. The results from this study showed that the heat affected zone decreases with increased cutting speed. When cutting with high cutting speeds in Docol 1000DP it is enough to turn away 0.30 mm in order to remove the heat affected zone with margin. Negligible difference in heat affected zone was observed between the samples cut with 2500 W and 3500 W. The heat affected zone in LDX 2101 was very small, in order of 50 μm, making it hard to measure. This resulted in no exact measurements being made. However, the heat affected zone was in the order of 50 μm for all samples, concluding that turning away 0.15 mm is sufficient to remove the heat affected zone with margin. No difference could be observed between the samples cut with a laser power of 2500 W or 3500 W. Common to both materials is that the amount of dross decreases with increased cutting speed. / Denna studie har utförts i syfte att undersöka utsträckningen av den värmepåverkade zonen för att kunna använda laserskärning för att skära prover till dragprovning. Ett problem med laserskärning är att metaller absorberar värmeenergin, vilket orsakar förändringar i mikrostrukturen. Denna värmepåverkade zon bör minimeras och avlägsnas från metallen, då det minskar kvalitén på proverna samt på dragprovningen. I denna studie har två material undersökts, det höghållfasta stålet Docol 1000DP och det duplexa rostfria stålet LDX 2101. Stålen skars ut i form av hundben för dragprovning med två olika effekter på lasern 2500 W och 3500 W. Proverna skars ut med olika skärhastigheter, började med lägre hastigheter och ökade sedan tills lasern inte längre kunde skära igenom materialet. Därefter undersöktes både den värmepåverkade zonen och kvaliteten på skärytan. Resultaten från denna studie visade att den värmepåverkade zonen minskar med ökad skärhastighet. Vid skärning i Docol 1000DP med höga skärhastigheter räcker det att avlägsna 0,30 mm för att ta bort den värmepåverkade zonen med marginal. Ingen skillnad i värmepåverkad zon observerades mellan proverna skurna med 2500 W och 3500 W vid skärning med högsta skärhastigheten för varje lasereffekt. Den värmepåverkade zonen i LDX 2101 var mycket liten, i storleksordningen 50 μm, vilket gjorde den svårt att mäta. Slutsatsen gav att det är tillräckligt att avlägsna 0,15 mm för att avlägsna den värmepåverkade zonen med marginal. Ingen skillnad kunde observeras mellan proverna skurna med en lasereffekt på 2500 W eller 3500 W. Gemensamt för båda materialen var att gradbildningen minskade med ökad skärhastighet.

Due to coming emission legislations, the temperature is expected to increase in heavy-duty diesel engines, specifically in the hot-end of the exhaust system affecting components, such as exhaust- and turbo manifolds. Since the current material in the turbo manifold, a ductile cast iron named SiMo51, is operating close to its limits there is a need for material development in order to maintain a high durability of these components. When designing for increased life, many material properties need to be considered, for example, creep-, corrosion- and fatigue resistance. Among these, the present work focuses on the latter two up to 800°C improving the current material by additions of Cr, for corrosion resistance, and Ni, for mechanical properties. The results show improved high-temperature corrosion resistance in air from 0.5 and 1wt% Cr additions resulting in improved barrier layer at the oxide/metal interface. However, during oxidation in exhaust-gases, which is a much more demanding environment compared to air, such improvement could not be observed. Addition of 1wt% Ni was found to increase the fatigue life up to 250°C, resulting from solution strengthening of the ferritic matrix. However, Ni was also found to increase the oxidation rates, as no continuous SiO2-barrier layers were formed in the presence of Ni. Since none of the tested alloys showed improved material properties in exhaust gases at high temperature, it is suggested that the way of improving performance of exhaust manifolds is to move towards austenitic ductile cast irons or cast stainless steels. One alloy showing good high-temperature oxidation properties in exhaust atmospheres is an austenitic cast stainless steel named HK30. This alloy formed adherent oxide scales during oxidation at 900°C in gas mixtures of 5%O2-10%H2O-85%N2 and 5%CO2-10%H2O-85%N2 and in air. In the two latter atmospheres, compact scales of (Cr, Mn)-spinel and Cr2O3 were formed whereas in the atmosphere containing 5%O2 and 10%H2O, the scales were more porous due to increased Fe-oxide formation. Despite the formation of a protective, i.e. compact and adherent, oxide scale on HK30, exposure to exhaust-gas condensate showed a detrimental effect in form of oxide spallation and metal release. Thus, proving the importance of taking exhaust-gas condensation, which may occur during cold-start or upon cooling of the engine, into account when selecting a new material for exhaust manifolds. / <p>QC 20130508</p>

Hardening distortions are unwanted changes in shape and dimension that arise during hardening of steel components. Uncontrolled distortions induce random errors to the manufacturing process, and have a strong negative impact on manufacturing costs. The distortions are not only caused by the hardening process, several factors from previous manufacturing steps including the component geometry itself contribute to varying extent. The aim of the current work is to investigate the main influencing factors on hardening distortions for serial produced gears. The investigations were done on two different types of gears for heavy-duty transmissions, crown wheels for the rear axle central gear and main shaft gears for the gearbox. The steel was produced using either continuous casting or ingot casting. For rectangular continuously cast steel, the effect of disabling magnetic stirring of the steel melt during casting was investigated, finding a strong reduction of gear runout for crown wheels. Segregations in crown wheels produced from the top and bottom of ingots were shown to go in opposite directions, producing opposite back-face tilts. For crown wheels quenched one at a time, influences of stacking level on the hardening tray were found, indicating an impact from small variations in the carburizing process, despite identical quenching conditions. For main shaft gears, horizontal loading gave considerably less roundness and runout errors but increased flatness errors compared to vertical loading. This thesis shows the complexity of the distortion phenomenon and how several factors interact and contribute to the final result. It is shown that factors with significant impact on hardening distortions for one component may be less important for another component. With this in mind, each type of component to be hardened should be produced by a manufacturing chain where each process step is carefully chosen with respect to minimizing distortions. / <p>QC 20170516</p>

The muffle furnace main purpose is to anneal the rough sponge iron powder transported through it, which is done by burning natural gas. Heat is absorbed by the muffle and is transferred to the bed of sponge iron powder. In order to reduce the consumptions of fossil fuel, some companies of the industry aims to exchange the natural gas in their muffle furnace’s burners to syngas, produced from biomass. This will however affect the performance of the furnace in the heating aspect. For this work, it is assumed that the effect will be negative. Thus the aim of this study is to investigate how to compensate the loss of effect from the burners, by examining which other parameters have influence on the furnace heating performance of the sponge iron powder transported through the furnace. The investigation is executed by simulating a 1 meter of the furnace in COMSOL multiphysics for 10 min, not including the combustion chambers. The investigated parameters are the packing degree of the powder, surface emissivity of the muffle, process gas velocity, conveyor belt velocity and the heat transfer rate coefficient to muffle from the combustion chambers. Alas, the process gas velocity and conveyor belt velocity only have minor influence on the final result, according to this simulation. However, the simulation exhibited that the surface emissivity of the muffle and the packing degree of the powder has great impact on the heating of the powder and could compensate some of the lost effect from the burners. This could be obtained by using an unpolished and oxidized muffle surface, and use densely packed powder sample.

The strand similarity and inclusion removal capability are two critical parameters to measure the performance of multi-strand tundish in clean steel production. In this work, the effect of two flow regulators, i.e., Flow Control Devices (FCD) and Electromagnetic Stirring (EMS) on eight-strand tundish performance have been investigated by establishing a water model and conducting numerical simulations of water model. The water model was focused on revealing the effect of stirring while the simulation was employed to investigate the effect of two FCDs, namely baffle wall and turbo-stopper. The analysis of strand similarity and inclusion removal were conducted by analyzing flow characteristics derived from Combined Model of Residence Time Distribution (RTD) curve and observing the flow movement in the tundish model. In addition, the tundish capability to remove inclusions was also studied by injecting inclusion particles using Discrete Phase Model (DPM) in ANSYS Fluent. Experiment results cause the Combined Model needs to be modified. This modification was employed when analyzing tundish configuration involving stirring. By using the modified Combined Model, the stirring can significantly increase the well-mix volume to almost 100% as it annihilates dead zone. The stirring also increases the similarity between strands and makes the RTD curve more similar to ideal mixing curve.  However, the problem of short-circuiting flow need to be solved and care should be taken into consideration regarding the selection of stirring direction as well as bath surface condition when implementing EMS in reality. The simulation results show that the addition of baffle wall and turbo-stopper are beneficial to improve mixing as well as to avoid the short-circuiting flow. Furthermore, compared to individual FCD, the combination of baffle wall and turbo-stopper results in the best performance to remove inclusions by providing surface-directed flow and generating a higher plug flow.

The microstructures of a metal determine the physical, electrical and chemical properties of the metal, and analysis of microstructures is therefore an important part of materials science. Modern microscopes are capable of generating a lot of high-quality micrographs in a short period of time. Analysis of metallic micrographs has traditionally been done by human experts but with the drastic increase in imaging capabilities, it becomes incredible labor intensive for humans to manually analyze the images. A way of dealing with this is to utilize computers for automatic analysis of the micrographs. An important part of the microstructural analysis of a metal is being able to segment various microstructures from each other. This thesis looks into two different metallic microstructural segmentation problems: (1) being able to automatically infer grain size by finding grain boundaries in metallic micrographs by utilizing 2D convolutions and optimization, and (2) instance segmentation of 3D dendrite structures from volumetric images using a 3D CNN. The results from the first problem indicate that the proposed method works well for synthetic images, but not for real micrographs. The results from the second problem indicate that there is a lack of data for utilizing a CNN. / Mikrostrukturerna i en metal bestämmer fysiska, elektriska samt kemiska egenskaper hos metallen och analys av mikrostrukturer är därför en viktig del av materialvetenskapen. Moderna mikroskop är kapabla att generera många högupplösta mikroskopbilder på kort tid. Analys av metalliska mikrostrukturer har traditionellt sett utförts av mänskliga experter, men med den drastiska ökningen av förmågan att generera bilder blir det en otrolig arbetsbörda för människor att manuellt analysera bilderna. Ett sätt att hantera detta är att utnyttja datorer för att automatiskt analysera mikroskopbilderna. En viktig del av mikrostruktur-analysen är att kunna segmentera olika mikrostrukturer från varandra. Denna avhandling tittar närmare på två olika problem inom segmentering av metalliska mikrostrukturer: (1) att automatisk kunna bestämma kornstorlek genom att hitta korngränser i mikroskopbilder av metaller med hjälp av 2D faltning och optimering, samt (2) instans-segmentering av 3D dendritstrukturer utifrån volymetriska bilder med hjälp av en 3D CNN. Resultaten från första problemet indikerar att den föreslagna metoden fungerar väl för syntetiska bilder, men inte för riktiga mikroskopbilder. Resultaten från andra problemet indikirerar att det finns en brist på data för att utnyttja en CNN.