A good understanding of the solidification process of a cast material is essential to understand how the combination of alloy composition and the casting process variables combines into the solid cast component and its performance. The wrong combination may result in poor performance or casting defects. Spheroidal graphite has been well researched in ductile irons (SGI) where it is predominant. Spheroidal graphite is also present in smaller amounts in compacted graphite irons (CGI), but its nature and role in this material is less understood. Recent associations of spheroidal graphite in CGI with shrinkage porosity problems highlights the need for better understanding in this area. The importance of the dendritic austenite structure to the properties and solidification behaviour of cast irons has been highlighted in recent research. However, progress is to a degree limited by lack of practical means to characterize the structure. In the present work, the transition of a cast iron from SGI to CGI though remelting was studied. As the fraction of SG dropped, the tips of the compacted graphite tended to lose contact with the melt at a later stage. After this occurred, solidification appeared to be dominated by spheroidal graphite. Compacted and spheroidal graphite was found to solidify mostly segregated, and the increased recallescence induced by a higher fraction of compacted graphite displayed small influence on the size distribution of spheroidal graphite apart from the total number and fraction. The partitioning of Si, Mn and Cu in SGI and CGI was found to agree well with each other, as well as with theoretical predictions under the assumptions of zero diffusion of the elements in the solid. This shows that the proportions of spheroidal and compacted graphite has small or no influence on the evolution of these elements in the melt during solidification. A method for characterization of the dendritic austenite in quenched cast irons was introduced and evaluated. The method includes a technique for producing a visual contrast between the ledeburite matrix and the dendritic austenite, and a scheme for producing binary images from the resulting micrographs which are suitable for automatic image analysis. Measurements of the volume fraction and surface area per unit volume of the dendritic austenite structure using the introduced method was found to agree reasonably with traditional point counting and line intercept techniques. The difficulty in finding the exact boundary was proposed to be the major source of systematic disagreement. / En god förståelse för stelningsprocessen av ett gjutet material är väsentligt för att förstå hur kombinationen av legeringens kemiska sammansättning och gjutprocessens variabler resulterar i den stelnade komponenten och dess prestanda. Fel kombination kan resultera i sänkt prestanda eller gjutdefekter. Sfärisk grafit är väl studerad i segjärn (SGI) där grafitmorfologin är dominant. Mindre mängder sfärisk grafit är dock närvarande även i kompaktgrafit, där dess karaktär och roll är mindre känd. Samband mellan sfärisk grafit i kompaktgrafitjärn och krympporositet understryker behovet av bättre förståelse inom detta område. Dessutom har betydelsen av den tidiga dendritiska austenitstrukturen för senare delen av stelningen uppmärksammats. Utveckling inom detta område är dessvärre till en grad begränsad av bristen på kunskap om praktiska metoder för att karaktärisera dess struktur. I detta arbete studerades övergången från segjärn till kompaktgrafit genom omsmältning. Vid sänkt fraktion sfärisk grafit visade sig kompaktgrafiten tappa kontakten med smältan vid senare stadie av stelningen. Efter detta inträffade, dominerades stelningen till synes av tillväxt av sfärisk grafit. Kompaktgrafit och sfärisk grafit bildades i huvudsak segregerade. Ökad rekallesens till följd av ökad fraktion kompaktgrafit visade sig ha låg inverkan på storleksfördelningen av eutektisk sfärisk grafit bortsett från dess totala antal och fraktion. Omfördelningen av Si, Mn och Cu mellan stelnad matris och smälta i segjärn och kompaktgrafitjärn fanns stämma bra överens med varandra, samt med teoretiska värden med antagande om försumbar diffusion i stelnad matris. Detta visar att proportionerna av sfärisk och kompaktgrafit har liten eller ingen inverkan på halten av dessa ämnen i smältan under stelningen. En metod för karaktärisering av den dendritiska austenitstrukturen i släckt gjutjärn introducerades och utvärderades. Metoden inkluderar en teknik för att åstadkomma kontrast mellan ledeburitmatrisen och den dendritiska austeniten, och en teknik för att producera binära bilder från resulterande mikroskopbilder som är lämpliga för automatisk bildanalys. Mätningar av volymfraktion och yta per volymenhet av dendritstrukturen genom tillämpning av den introducerade metoden visade rimlig överensstämmelse med traditionella punktfraktion‐ och linjetekniker. Svårigheten att hitta den exakta gränslinjen mellan dendritisk struktur och ledeburit föreslogs vara den huvudsakliga källan till systematisk oöverensstämmelse.

Wear and friction are among the major problems faced in several industries such as mining industry. This creates challenges to select better materials with good wear behavior in order to improve the service life of the components. In the present project, three steel wire grades OH 70, OH 75 and OH 101 have been heat treated by quenching and partitioning heat treatment and tested using three wear testing methods. The wear tests performed were a pin-on-disc test, dry-pot test and slurry pot-test, and the results were compared with the conventional quenched and tempered steel. Tensile tests, hardness, impact Charpy tests, scanning electron microscope, optical microscope, X-ray diffraction and magnetic measurements were applied to characterize mechanical properties and microstructure of the steels before wear tests. The results showed that the quenched and partitioned steels with considerable amount of retained austenite had higher ductility and good impact toughness than the quenched and tempered steels. After the pin on disc tests, OH 75 grade showed the highest wear resistance, while the lowest wear resistance was obtained by OH 70 grade. The damage mechanisms identified after pin-on-disc were abrasion and oxidative wear. During erosive wear, almost no measurable wear was recorded under the dry pot conditions, while the slurry pot test owned significant wear mass loss. The main modes of the worn surfaces after erosive tests were ploughing and cutting. In addition, cracks were also observed.

Products manufactured by aluminium casting have become very popular and already replaced many parts that were once produced by iron and steel casting. This trends upwards especially in the automotive industry as it has become extremely important to reduce vehicle weight due to environmental requirements and economical aspects. This popularity of aluminium alloys could be ascribed to their light weights and many other advantages including excellent castability, good corrosion resistance, good thermal and electrical conductivity, good machinability, low melting temperatures and minimal gas solubility with the exception of hydrogen. The most important alloy group among casting alloys is Aluminium Silicon (Al - Si).   Al-Si alloys must undergo a specific melt treatment procedure prior to casting. This treatment consists of several steps including degassing of hydrogen, grain refinement and eutectic modification. The aim of this study is to make an assessment of the metal treatment process of an (Al-Si) casting alloy at Unnaryd Modell AB for the purpose of improving the melt conditions and thus the quality of the final product. A rotary degasser provided by Foseco is also tested instead of the traditional tablet degassing method to see if this technique would result in any significant improvement of the melt quality. The results show that Unnaryd modell AB follows a proper treatment routine. It shows moreover that the rotary degassing is superior to the tablet degassing in many aspects including the level of degassing achieved, time efficiency, environmental consideration and personnel security.

No description available.

Primary aluminum production brings about severe environmental burden due to its energy intensive process.  Secondary aluminum production contributes to cutting off high energy demand around 90-95% and greenhouse gas emission by remelting scraps. However, previous research indicates melting furnace’s energy efficiency in secondary plant is still very low, which is around 26-29% and more than 70% heat is lost in different way. The objective of this project is to investigate energy consumption and greenhouse gas (GHG) emission in secondary aluminum cast house through process analysis. The result offers a comprehensive overview to aid decision-maker to compare energy consumption and environmental impacts caused by different product or process. This project has been done in collaboration with SAPA Heat Transfer. This project consists of two tasks. First task is aimed to give an overview of annual energy distribution and carbon footprint of per ton aluminum slab in SAPA cast house. In order to analyze energy distribution, mass and energy conservation has been applied for calculation. Meanwhile, International standard method, life cycle assessment, has been used to evaluate greenhouse gas contribution of the whole production process. The second task intends to investigate two effects (melting furnace type, raw material type) on products’ energy consumption and carbon footprint.  Melting furnace’s effect is compared by selecting electric induction furnace and oxy-fuel furnace. On the other hand, raw material’s effect is studied by comparison of four different cast house products which have different raw material recipe. Calculation and analysis results indicates that per ton Sapa cast house aluminum slab consumes energy 3826MJ and contributes to 306kgCO2eq. green house gas. Meanwhile, comparison results show that oxy-fuel melting furnace has higher energy efficiency than electric induction furnace, however, it contributes much more GHG due to consumption of propane fuel. In addition, primary ingot has been concluded as distinct carbon footprint contribution than others contributors (i.e. fuel) for Sapa cast house’s slab.

Destructive testing of creep exposed components is a powerful tool for evaluation of remaining lifetime of high temperature pipe systems. The most common destructive evaluation method used today is uniaxial creep testing. Uniaxial creep tests can produce accurate creep curves but the test method has some drawbacks such as costliness and long testing times. It also demands large sample material outtake which often involve weld repair. Impression creep (IC) testing is a relatively new alternative test method for evaluating primary and secondary creep rates. The scope of this work is to evaluate the benefits and drawbacks of IC testing over uniaxial creep testing in order to determine its usefulness as a test method. A literature survey was carried out over the area creep testing of high temperature pipe systems, with particular focus on impression creep testing. The result of the literature survey clearly showed several benefits with impression creep testing. An IC test series was performed in order to determine the secondary creep rate of a service exposed 10CrMo9-10 high temperature pipe steel. The IC tests were performed by VTT in Finland, using the same test parameter and sample material as in previous projects where the creep properties of the test material were determined by uniaxial creep testing. The result of the predicted secondary creep rate obtained from the IC tests was compared with the secondary creep rates measured during the uniaxial tests. The IC tests results did not align satisfactory with the results from the uniaxial creep tests, which would have been expected. The reason for this may be due to sources of error during impression creep testing, since very small displacements due to creep have to be measured with high precision during the tests. Further testing of the impression creep test method is recommended as a result of this work, in order to evaluate the method.

Destructive testing of creep exposed components is a powerful tool for evaluation of remaining lifetime of high temperature pipe systems. The most common destructive evaluation method used today is uniaxial creep testing. Uniaxial creep tests can produce accurate creep curves but the test method has some drawbacks such as costliness and long testing times. It also demands large sample material outtake which often involve weld repair. Impression creep (IC) testing is a relatively new alternative test method for evaluating primary and secondary creep rates. The scope of this work is to evaluate the benefits and drawbacks of IC testing over uniaxial creep testing in order to determine its usefulness as a test method. A literature survey was carried out over the area creep testing of high temperature pipe systems, with particular focus on impression creep testing. The result of the literature survey clearly showed several benefits with impression creep testing. An IC test series was performed in order to determine the secondary creep rate of a service exposed 10CrMo9-10 high temperature pipe steel. The IC tests were performed by VTT in Finland, using the same test parameter and sample material as in previous projects where the creep properties of the test material were determined by uniaxial creep testing. The result of the predicted secondary creep rate obtained from the IC tests was compared with the secondary creep rates measured during the uniaxial tests. The IC tests results did not align satisfactory with the results from the uniaxial creep tests, which would have been expected. The reason for this may be due to sources of error during impression creep testing, since very small displacements due to creep have to be measured with high precision during the tests. Further testing of the impression creep test method is recommended as a result of this work, in order to evaluate the method. / Förstörande provning av krypexponerade komponenter är ett kraftfullt redskap för utvärdering av återstående livslängd hos rörsystem med höga drifttemperaturer. Den vanligaste formen av förstörande provning i dessa fall är idag enaxlig krypprovning. Enaxliga krypprovningar producerar fullständiga krypkurvor men provningsmetoden har vissa nackdelar såsom att den är relativt dyr och tar förhållandevislång tid. Impression creep eller (IC) –provning är en relativt ny, alternativ, testmetod för att utvärdera primär och sekundärkryp. Det här arbetet ämnar utreda för- och nackdelar med IC-provning gentemot enaxlig krypprovning, samt undersöka dugligheten av IC-provning som testmetod. En litteraturstudie över området provning av krypegenskaper hos rörsystem med höga drifttemperaturer, med extra fokus på IC-provning har genomförts. Resultatet av litteraturstudien pekade tydligt på fördelarna med IC provning. En serie IC-tester utfördes också i syfte att bestämma den sekundära kryphastigheten hos ett driftpåkänt 10CrMo9-10 låglegerat tryckkärlsstål avsett för höga drifttemperaturer. IC-provningen gjordes av VTT Finland. Samma testparametrar och samma provmaterial som hade använts i tidigare projekt där krypegenskaperna hos provmaterialet har utvärderats bl.a. genom enaxlig krypprovning. Resultaten från IC-provningen jämfördes med de sekundära krypningshastigheterna som hade observerats vid den enaxliga krypprovningen. Resultaten från IC-provningen visade sig avvika från resultateten från den enaxliga krypprovningen. Orsaken till det kunde inte förklaras. Mätningar av mycket små förskjutningar samt små temperaturavvikelser föreslogs eventuellt kunna leda till felkällor. Som ett resultat av det här arbetet förslås fortsatt utvärdering och provning med IC-metoden behövs innan provningsmetoden kan tas i bruk.

This study examined the micro- and surface structures of objects manufactured by selective laser melting (SLM). The results show that the surface roughness in additively manufactured objects is strongly dependent on the geometry of the built part whereas the microstructure is largely unaffected. As additive manufacturing techniques improve, the application range increases and new parameters become the limiting factor in high performance applications. Among the most demanding applications are turbine components in the aerospace and energy industries. These components are subjected to high mechanical, thermal and chemical stresses and alloys customized to endure these environments are required, these are often called superalloys. Even though the alloys themselves meet the requirements, imperfections can arise during manufacturing that weaken the component. Pores and rough surfaces serve as initiation points to cracks and other defects and are therefore important to consider. This study used scanning electron-, optical- and focus variation microscopes to evaluate the microstructures as well as parameters of surface roughness in SLM manufactured nickel based superalloys, Inconel 939 and Hastelloy X. How the orientation of the built part affected the surface and microstructure was also examined. The results show that pores, melt pools and grains where not dependent on build geometry whereas the surface roughness was greatly affected. Both the Rz andRa values of individual measurements were almost doubled between different sides of the built samples. This means that surface roughness definitely is a factor to be considered when using SLM manufacturing.

This thesis focuses on experimental characterization, understanding and modelling of nickel-based alloy 718, for a large range of loading conditions. Alloy 718 is the most widely used nickel-based superalloy, due to its high strength, high corrosion resistance and excellent mechanical properties at high temperatures. In this work, the mechanical behavior and microstructure evolution of this alloy during high strain rate deformation is investigated. Compression tests using a Split-Hopkinson pressure bar (SHPB) device were performed and the microstructure of the deformed sample was observed using optical microscope (OM) and scanning-electron microscope (SEM) coupled with electron back-scattered diffraction (EBSD) technique. The microstructural evolution according to the deformation conditions was characterized. For high deformation temperatures (1000 C and above), recrystallisation is identifed as the main deformation mechanism. A physics-based model was employed to simulate the deformation behavior of alloy 718. This type of models accounts for the microstructural mechanisms taking place during deformation. Knowledge about the deformation mechanisms of alloy 718, acquired experimentally and from literature, enables to formulate mathematically the microstructural phenomena governing the deformation behavior of the alloy. The proposed model includes the effects of strain hardening, grain boundary strengthening (Hall-Petch), solid solution strengthening, phonon and electron drag and recovery by dislocation glide and cross-slip. It is calibrated and validated using data obtained from mechanical tests, as well as values captured by the microstructural analysis. / H2020-MSCA-ITN-2017 grant agreement Nº764979 - ENABLE project

Understanding the precipitation reaction is very important since precipitation hardening is one of the most effective strengthening mechanisms in metallic alloys. In martensitic steels, a tempering heat treatment is often performed. During tempering various new phases are precipitated and the spatial and temporal evolution of these precipitates strongly influences the properties of the steel, such as strength/ductility, creep, fatigue and hot corrosion resistance. Therefore, the possibility of quantitative modelling of the precipitation process will provide many opportunities for advanced materials and process design and optimization as well as service life assessments. The Fe-C-Cr system forms the basis for tool steels and is consequently used in many applications such as e.g. metal forming operations. They are characterized by a high hardness and good toughness, even at elevated temperatures.In the present work, the as-quenched martensitic microstructures of four Fe-C-Cr alloys with varying Cr and C contents were characterized by Light Optical Microscopy (LOM) and Electron Microscopy. The effects of Cr and C on the morphology of martensite were investigated. It was found that Cr addition had a similar effect as C on the martensitic morphology and on the ratio of high-angle grain boundary (HAGB) to low-angle grain boundary (LAGB). However, the micro-hardness was unaffected by the Cr addition whilst it was strongly influenced by the C addition.In addition, a quantitative experimental characterization of the precipitates formed during tempering of the martensite was performed. The Langer-Schwartz theory combined with the Kampmann-Wagner-Numerical (KWN) method, as implemented in the software TC-PRISMA, was used to predict the precipitation of carbides after tempering in one of the model alloys: Fe-0.15C-4.0Cr (mass%). The microstructure characterization of the as-quenched material provided vital input parameters for the modelling work and a comparison was made between the modelling predictions and the experimental results. The effect of parameters such as dislocation density, grain size and interfacial energy on the precipitation of carbides was discussed. / <p>QC 20151105</p>