Luossavaara-Kiirunavaara AB (LKAB) rullar järnmalmslig till råkulor, som sedan bränns till pellets. Råkulorna bildas i rullkretsar som består av rulltrummor och rullsiktar. Under 2017 färdigställdes en pilotskaleanläggning för kulrullning i LKAB:s Agglomeringslaboratorium i Malmberget. Syftet med anläggningen är att prediktera dynamiken i en storskalig rullkrets, under olika betingelser. Detta examensarbete är ett första försök att i forskningssyfte studera gensvaret i LKAB:s pilotrullkrets. Syftet var att undersöka om pilotrullkretsen kan prediktera dynamiken och råkulekvalitet i rullning i storskaliga rullkretsar och målet var att fastställa ett effektivt körsätt. Kulrullning är inom LKAB:s kärnkompetens och därför har reagensursprung och karaktär samt dimensionering av rullkretsen lagts med sekretess. Kodnamn används både för sliger och reagens. Arbetet inleddes med att skapa ett körschema med målet att så många olika blandningar som möjligt kunde köras i pilotrullkretsen under en normal arbetsdag. Fem olika blandningar kunde köras. Fyra olika tillsatser testades: bentonit, ett flotationsreagens (FLOT), ett organiskt bindemedel (OB) och en ny utvecklingsprodukt (UTV). Första körningen i pilotrullkretsen var med varierande doseringar av bentonit eftersom dess inverkan i kulrullning är välkänt hos LKAB. Försök två och tre, med FLOT respektive OB, kunde jämföras mot tidigare erfarenhet från storskaliga försök. Det fjärde och sista försöket var ett test hur pilotrullkretsen predikterade utvecklingsprodukten UTV. Varje typ av försök utfördes två gånger. Pilotrullkretsen predikterade väl både dynamik och råkulekvalitet i alla de tre försöken där erfarenhet från storskaliga körningar var tillgängligt. Den nya, okända, UTV-produkten visade en förbättrad råkulekvalitet, utan att dynamiken i kretsen påverkades negativt. UTV kan därför vara ett intressant alternativ för ett framtida storskaligt försök hos LKAB. Det framtagna körschemat fungerade mycket väl. Ett ”grundanalyspaket” har skapats för att underlätta planering och genomförande för framtida pilotrullkretsförsök hos LKAB. Antalet personer som behövs vid rullkretskörningar beror på antalet blandningar och analyser. Vid enklare körningar behövs minst fem personer, utöver försöksledaren. Mer komplexa körningar kan kräva sju personer. / Luossavaara-Kiirunavaara AB (LKAB) produce pellets from magnetite iron ore. Pellets are formed by balling moist iron ore concentrate to green pellets, which are then burned to pellets. The green pellets are formed in balling circuits consisting of balling drums and roller decks for screening. In 2017 a pilot scale balling circuit with a drum was completed in LKAB's agglomeration laboratory in Malmberget. The purpose of the pilot balling circuit is to predict the dynamics in a full scale balling circuit under different conditions. This master degree project is an initial attempt to study the response in LKAB's pilot circuit in terms of green pellet quality and dynamics in the circuit. The goal was to determine an effective way to run experiments and to investigate whether the pilot circuit can predict the dynamics of balling in large-scale circuits. Pelletizing production is within LKAB's core competence, and therefore the origin and character of the reagents, as well as the design of the pilot balling drum circuit, are confidential. Code names are used for both iron ore concentrates and reagents. The work began by creating a test procedure with the aim of running as many different mixtures as possible in the pilot balling circuit during a normal working day. Five different mixtures could be run. Four different additives were tested: bentonite, a flotation reagent (FLOT), an organic binder (OB) and a new development product (UTV). The first experiment in the pilot balling circuit was run with varying doses of bentonite because its impact in balling is well known at LKAB. Experiment two and three, with FLOT and OB, could be compared to previous experience from large scale test runs. The fourth and last experiment was a test of how the pilot circuit predicted the behavior of a new development product UTV. Each type of experiment was performed twice. The pilot balling circle predicted well both dynamics and green pellet quality in all three experiments where experience from large-scale runs was available. The new, unknown, UTV product showed improved green pellet quality, without affecting adversely on the dynamics of the circuit. UTV can therefore be an interesting option for a future large scale run at LKAB. The developed working schedule worked very well. A "basic analysis package" has been created to facilitate planning of future experiments in the pilot balling circuit. The number of persons needed to run the circuit depends on the number of mixtures and analyzes. For smaller experiments, at least five people is required, in addition to the leader of the experiments. More advanced experiments will demand seven people.

This thesis study employs textural classification techniques applied to four different data groups: (1) visible light photography, (2) high-resolution drill core line scan imaging (3) scanning electron microscopy backscattered electron (SEM-BSE) images, and (4) 3D data from X-ray microtomography (μXCT). Eleven textural classes from Aitik ores were identified and characterized. The distinguishing characteristics of each class were determined such as modal mineralogy, sulphide occurrence and Bond work indices (BWI). The textural classes served as a basis for machine learning classification using Random Forest classifier and different feature extraction schemes. Trainable Weka Segmentation was utilized to produce mineral maps for the different image datasets. Quantified textural information for each mineral phase such as modal mineralogy, mineral association index and grain size was extracted from each mineral map.  Efficient line local binary patterns provide the best discriminating features for textural classification of mineral texture images in terms of classification accuracy. Gray Level Co-occurrence Matrix (GLCM) statistics from discrete approximation of Meyer wavelets decomposition with basic image statistical features[PK1]  (e.g. mean, standard deviation, entropy and histogram derived values) give the best classification result in terms of accuracy and feature extraction time. Differences in the extracted modal mineralogy were observed between the drill core photographs and SEM images which can be attributed to different sample size[PK2] . Comparison of SEM images and 2D μXCT image slice shows minimal difference giving confidence to the segmentation process. However, chalcopyrite is highly underestimated in 2D μXCT image slice, with the volume percentage amounting to only half of the calculated value for the whole 3D sample. This is accounted as stereological error. Textural classification and mineral map production from basic drill core photographs has a huge potential to be used as an inexpensive ore characterization tool. However, it should be noted that this technique requires experienced operators to generate an accurate training data especially for mineral identification and thus, detailed mineralogical studies beforehand is required. / Primary Resource Efficiency by Enhanced Prediction (PREP) / Center for Advanced Mining and Metallurgy (CAMM)

In a particle based geometallurgical model, the behavior of the particles can be used for forecast the products and quantify the performance of the different ore types within a deposit. The particle tracking is an algorithm developed by Lamberg and Vianna 2007 whose aim is to balance the liberation data in a mineral processing circuit composed by several processing units. Currently, this tool is being developed for the HSC Chemistry software by Outotec.The objective of this study is to understand and evaluate the particle tracking algorithm in a geometallurgical test for iron ore. To achieve this objective, the liberation data is balanced in a Davis tube test circuit. A total of 13 samples from Leveäniemi iron ore were process in a Davis tube circuit.The magnetite is the main mineral in the Leveäniemi iron ore samples. Its high recovery in the Davis tube circuit along with the V, Ti and Mn suggest that these elements are present in the magnetite lattice. These penalty elements in the iron concentrates cannot be avoided at the stage of mineral concentrations.The washing effect of the Davis tubes controlled by the rotational and longitudinal agitation of the tube perturb the particles agglomeration between the pole tips of the electromagnet. A higher agitation frequency and amplitude will wash away most of the gangue minerals and also fine grained magnetite.In this work, the particle tracking is depicted and implemented in a magnetic separation circuit for high liberated material. The liberation data was balanced in a way that the particle classes can be followed through circuit and their recoveries can be calculated. Nevertheless, the algorithm requires further validation and analysis of its limitations in terms of resolution and reproducibility.

The development of alternative binder systems for tungsten carbide (WC) based cemented carbides has again become of relevance due to possible changes in EU regulations regarding the use of Cobalt (Co). A framework for the ICME (Integrated Computational Materials Engineering) based Materials Design is presented to accelerate the development of alternative binder systems. Part one of this work deals with the design of the cemented carbide composite hardness. It has been shown that the intrinsic binder hardness is comparable to a bulk metal alloy and that based on the binder solubilities a solid solution strengthening model developed in this work can be employed. Using a method presented in this work the non-equilibrium, frozen-in binder solubilities can be obtained. Both the design of the binder phase and composite hardness is presented based on a general Materials Design approach. Part two deals with a multiscale approach to model the surface gradient formation. The experimentally missing data on liquid binder diffusion has been calculated using AIMD (Ab initio Molecular Dynamics). The diffusion through the liquid cemented carbide binder has to be reduced to an effective diffusion value due to the solid carbides acting as obstacles that increase the diffusion path. The geometrical reduction of the diffusion has been investigated experimentally using the SIMS (secondary ion mass spectroscopy) technique in WC-Nickel-58Nickel diffusion couples. The geometrical contribution of the so-called labyrinth factor has been proven by the combination of the experiments and in conjunction with DICTRA simulations using the precise liquid AIMD diffusivities. Unfortunately, despite the improved kinetic database and the geometrical diffusion reduction, the surface gradient formation cannot be explained satisfactory in complex cemented carbide grades. Additional, but so far unidentified, contributions have to be considered to predict the surface gradient thickness. / <p>QC 20170919</p>

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. / InDeGrainS I

This thesis focuses on the different degradation mechanisms of the stainless steel in a travelling grate in a Grate-Kiln iron ore pellet indurator. The travelling grate is a conveyor belt that transports green-body pellets to a rotary kiln while the pellets are being dried and pre-heated to a temperature of 900-1100 °C by recycled hot air. After unloading of the pellets to the rotary-kiln for further sintering, the travelling grate is cooled in room temperature while returning to the loading zone of the wet pellets. The steel was tested during thermal cycling in a test-rig, in order to simulate the influence of thermo mechanical fatigue and oxide spallation. The influence of erosion-deposition was investigated in a modified horizontal industrial combustion kiln at 800 °C, with slag and coal from production used as erosive media and combustion fuel, respectively. The influence of minor alloying additions of Mn, Si and Ti on the microstructure was explored by eight different casted alloy compositions. Isothermal heat treatments were performed at 800 °C during 200 hours on steel immersed in deposits recovered from a travelling grate in production. The three main degradation mechanisms found in this work are thermal spallation, erosion-deposition and deposit induced accelerated corrosion (DIAC). Thermal spallation of the oxide layer is caused by the thermal expansion difference between the oxide and the metal during heating and cooling. It has been found that Ti improves the spallation resistance while Si reduces it. Spallation of deposits is another cause believed to increase the degradation. Erosion-deposition appears due to simultaneous erosion and deposition of particles on the travelling grate that causes erosion or deposition depending on the amount of alkali metals in the environment. The velocity of the particles also influences erosion and deposition in the way that higher velocities increase erosion. DIAC is proposed to form on the travelling grate due to the concentration of chloride- and sulphate containing alkali metals in the deposits.  Other than these major degrading mechanisms, minor degradation mechanisms such as internal oxidation, sigma formation, carburization and sensitization towards inter-granular attack have been found inside the steel during heating. Thermo mechanical fatigue (TMF) causes intergranular cracks in the material of the travelling grate. Casting issues such as micro-segregation have also been addressed in this thesis. A few different ways to improve degradation resistance have been proposed, such as homogenization heat treatments, optimization of process parameters and inhibitor solutions.

The thesis focuses on exploring the sub-grain structure in stainless steel 316L prepared by additive manufacturing (AM). Two powder-bed based AM methods are involved: selective laser melting (SLM) and electron beam melting (EBM). It is already known that AM 316L has heterogeneous property and hierarchy structure: micro-sized melt pools, micro-sized grains, nano-sized sub-grain structure and nano-sized inclusions. Yet, the relation among these structures and their influence on mechanical properties have not been clearly revealed so far. Melt pool boundaries having lower amount of sub-grain segregated network structures (Cellular structure) are weaker compared to the base material. Compared with cell boundaries, grain boundaries have less influence on strength but are still important for ductility. Cell boundaries strengthen the material without losing ductility as revealed by mechanical tests. Cellular structure can be continuous across the melt pool boundaries, low angle sub-grain boundaries, but not grain boundaries. Based on the above understanding, AM process parameters were adjusted to achieve customized mechanical properties. Comprehensive characterization were carried out to investigate the density, composition, microstructure, phase, magnetic permeability, tensile property, Charpy impact property, and fatigue property of both SLM and EBM SS316L at room temperature and at elevated temperatures (250°C and 400°C). In general, SLM SS316L has better strength while EBM SS316L has better ductility due to the different process conditions. Improved cell connection between melt pools were achieved by rotating 45° scanning direction between each layer compared to rotating 90°. Superior mechanical properties (yield strength 552 MPa and elongation 83%) were achieved in SLM SS316L fabricated with 20 µm layer thickness and tested in the building direction. Y2O3 added oxide dispersed strengthening steel (ODSS) were also prepared by SLM to further improve its performance at elevated temperatures. Slightly improved strength and ductility (yield strength 574 MPa and elongation 90%) were obtained on 0.3%Y2O3-ODSS with evenly dispersed nanoparticles (20 nm). The strength drops slightly  but ductility drops dramatically at elevated temperatures. Fractographic analysis results revealed that the coalescence of nano-voids is hindered at room temperature but not at elevated temperatures. The achieved promising properties in large AM specimens assure its potential application in nuclear fusion. For the first time, ITER first wall panel parts with complex inner pipe structure were successfully fabricated by both SLM and EBM which gives great confidence to application of AM in nuclear industry. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Manuscript. Paper 5: Manuscript.</p>

Automotive industry products portfolio includes a wide variety of complex‐shaped cast iron products, such as truck engine components, that need to withstand a constant trend of higher demands, especially urged by stricter environmental regulations on emissions. Combined with this continued demand on properties improvement, cast iron industry faces a process problem related to the lack of understanding of solidification and mechanisms behind defect formation. Casting products are highly affected by the product design and the manufacturing method itself, which governs the final microstructure and hence the final mechanical properties. Wall thickness of the moulding material strongly influences the solidification time, varying the microstructural coarseness, resulting in a component with different properties depending on the local shape of the casting. The main objective of this work is the characterization of the primary austenite microstructure and its coarsening process, which has been poorly documented in cast iron literature, to allow the prediction and control of these microstructural features present in the casting. The microstructural evolution of the primary austenite in hypoeutectic lamellar graphite iron (LGI) is studied under isothermal coarsening conditions. The dendritic microstructure suffered major morphological changes that included dendrite fragmentation, globularization, and coalescence. Empirical relations based on morphological parameters are introduced to predict the microstructural evolution of primary austenite. A novel technique for colour‐etching and semi‐automatic image analysis for the characterization of quenched dendritic microstructures in cast iron is presented. A new experimental technique for production of graphitic iron with varying nodularity is presented as a solution to control the production of compacted (CGI) and spheroidal graphite iron (SGI) under laboratory conditions. The nodularity evolution is controlled as a function of the holding time and the residual Mg, allowing the study of the primary solidification and primary microstructures of hypoeutectic CGI and SGI in future investigations.

There are great energy savings to be made by recycling aluminium; as little as 5% of the energy needed for primary aluminium production may be required. Striving to produce high quality aluminium castings requires knowledge of microstructural imperfections, which is extra important when casting recycled aluminium that generally contains higher levels of imperfections compared to primary aluminium. Imperfections include amongst others Si, Fe, and Mn as well as oxides. Si is needed for castability, but it may also initiate fracture. There are different types of Fe-rich intermetallics influencing properties of castings, generally in a negative direction. Oxides constitute cracks and they are elusive because they are difficult to quantify. This thesis aims to increase knowledge about imperfections in recycled aluminium castings originating from alloying elements and the melt. Experiments were performed in advanced laboratory equipment, including X-radiographic imaging during solidification and in-situ tensile testing in a scanning electron microscope. Experiments were also performed at industrial foundry facilities. The experiments showed that the nucleation temperature of primary α-Fe intermetallics increased with higher Fe, Mn, and Cr contents. Primary α-Fe are strongly suggested to nucleate on oxides and to grow in four basic morphologies. Lower nucleation frequency of α-Fe promoted faster growth and hopper crystals while higher nucleation frequency promoted slower growth rates and massive crystals. Results also showed that a decrease in the size of the eutectic Si and plate-like β-Fe intermetallics improved tensile properties, foremost the elongation to fracture. In β-Fe containing alloys the transversely oriented intermetallics initiated macrocracks that are potential fracture initiation sites. In alloys with primary α-Fe foremost clusters of intermetallics promoted macrocracks. In fatigue testing, a transition from β-Fe to α-Fe shifted the initiation sites from oxides and pores to the α-Fe, resulting in a decrease of fatigue strength. Oxides in Al-Si alloys continue to be elusive; no correlations between efforts to quantify the oxides and tensile properties could be observed. / Genom att återvinna aluminium kan stora energibesparingar göras eftersom återvinning kan förbruka så lite som 5% av den energi som behövs för produktion av primär aluminium. Vid gjutning av högkvalitativa aluminiumprodukter krävs förståelse för defekter i mikrostrukturen och denna kunskap är extra viktig vid användning av återvunnen aluminium, som i regel innehåller mer defekter än primär aluminium. Defekterna består bland annat av Si, Fe och Mn samt oxider. Si behövs för gjutbarhet men kan också initiera brott. Järnrika intermetaller kan ha olika morfologier som generellt påverkar gjutna komponenter negativt. Oxider, som kan utgöra sprickor, är gäckande då de är svåra att kvantifiera. Denna avhandlings syfte är att öka kunskapen om defekter i gjutna komponenter av återvunnen aluminium. Experiment utfördes med avancerad laborationsutrustning så som röntgenfotografering av prover under stelning och dragprovning i svepelektronmikroskop. Experiment utfördes också i industrimiljö. Experimenten visade att kärnbildningstemperaturen steg för primära α-Fe intermetaller med ökade andelar av Fe, Mn och Cr. Resultaten tyder starkt på att primär α-Fe kärnbildas på oxider och att de växer i fyra olika morfologier. Lägre kärnbildningstäthet av α-Fe främjade snabbare tillväxt av kristaller med håligheter men högre kärnbildningstäthet främjade långsammare tillväxt av massiva kristaller. Resultaten visade också att minskad storlek av eutektiskt Si och β-Fe intermetaller ledde till förbättring av dragprovsresultaten, främst brottförlängningen. I legeringar med β-Fe ledde transversellt orienterade intermetaller till makrosprickor vilka kan initiera brott. I legeringar med primär α-Fe var det främst kluster av intermetaller som orsakade makrosprickor. I utmattningsprovning orsakade modifiering av β-Fe till α-Fe förflyttning av sprickinitieringen från oxider och porer till α-Fe, vilket resulterade i en reducerad utmattningshållfasthet. Oxiderna i Al-Si-legeringar fortsätter att gäcka; ingen korrelation mellan försök att kvantifiera oxiderna och draghållfasthet kunde påvisas.

Fe-Cr based steels, i.e. stainless steels, possessing a combination of excellent corrosion resistance and good mechanical properties, have indispensable applications ranging from low-end cooking utensils, to sophisticated components for nuclear power plants. However, the bcc/bct phase containing stainless steels which have a miscibility gap (MG) suffer from the so-called “475 oC embrittlement” leading to hardness increase and toughness deterioration. It occurs due to demixing of Fe and Cr leading to the formation of Fe-rich (α) and Cr-rich (α′) regions in bcc/bct phases. The demixing is referred to as phase separation (PS). The goal of this work was to study PS in ferrite containing stainless steels mainly by small-angle neutron scattering (SANS). Firstly, the application of different experimental techniques for the study of phase separation in Fe-Cr based steels was reviewed and supplemented by new measurements. SANS was shown to be very sensitive to the nanostructure change caused by PS and capable of characterizing the early stages of PS in Fe-Cr alloys. However, atom probe tomography and transmission electron microscopy are complementary to SANS. Therefore, in order to have a more complete view of the microstructure, the combination of these techniques should be pursued. Secondly, the factors affecting the initial microstructure prior to aging treatment and the effect of the resulted initial microstructure on PS were systematically investigated using binary Fe-Cr model alloys. The critical temperature of the MG was determined to be located between 560 and 580 oC in binary Fe-Cr. The results indicate that the solution treatment temperature above the MG and the cooling rate after solution treatment have significant effects on the initial microstructure and thus on PS during subsequent aging. The mechanisms responsible for the changed aging behavior are Cr clustering, quenched-in vacancy and decomposition during cooling. Therefore, computational simulations should take into account these factors and the initial microstructure to make predictions that are more accurate. Thirdly, the study was extended to PS in commercial duplex stainless steels (DSSs) which are of practical importance in various industries, e.g., nuclear power. It is found that alloying elements have an important effect on PS in DSSs. The grade 2507 (25 %Cr, 7 %Ni) experiences stronger PS than grade 2205 (22 %Cr, 5 % Ni) for the same heat treatment. Moreover, the fracture mechanisms as well as the mechanical properties depend on the extent of PS.  Finally, the fundamental aspects regarding the neutron scattering behavior for Fe-Cr alloys were examined. The results show that the nuclear and magnetic scattering of neutrons depend on the evolution of the nanoscale compositional fluctuation in Fe-Cr alloys. The ratio of the magnitude of nuclear scattering versus magnetic scattering varies with the extent of PS. / Stål baserade på Fe-Cr systemet, det vill säga rostfria stål, som har en kombination av utmärkta korrosionsegenskaper och bra mekaniska egenskaper, har många tillämpningar; allt från köksredskap, till sofistikerade komponenter för kärnkraftverk. Rostfria stål som innehåller Bcc / bct-fasen och som således har en blandningslucka, är känsliga för den så kallade "475 °C försprödningen" som leder till en hårdhetsökning men kraftigt försämrad slagseghet. Detta uppstår på grund av en uppdelning av Fe och Cr som leder till bildandet av Fe-rika (a) och Cr-rika (a’) regioner i bcc / bct-fasen. Denna uppdelning brukar kallas fasseparation. Målet med detta arbete var att studera fasseparationen i ferrit-innehållande rostfria stål främst genom lågvinkel-spridning av neutroner (SANS). Till att börja med studerades och jämfördes olika experimentella tekniker för undersökning av fasseparation i Fe-Cr-baserade stål med nya SANS- mätningar. SANS visade sig vara mycket känslig för förändringar på nano-skala orsakad av fasseparation och tekniken visade sig även kapabel att karakterisera de tidiga stadierna av fasseparation i Fe-Cr-legeringar. För att få en mer fullständig bild av mikrostrukturen efter fasseparation, bör emellertid en kombination av SANS och komplementära tekniker, såsom atomsond och transmissions-elektronmikroskopi, användas. Vidare undersöktes de faktorer som påverkar den ursprungliga mikrostrukturen före åldringsbehandling, och effekten av den initiala mikrostrukturen på fasseparation studerades systematiskt med användning av binära modell-legeringar av Fe-Cr. Den kritiska temperaturen för blandningsluckan i Fe-Cr bestämdes vara belägen mellan 560 och 580 °C. Resultaten indikerar att temperaturen för upplösningsbehandling ovanför blandningsluckan och kylhastigheten har en signifikant inverkan på den initiala mikrostrukturen och därmed på fasseparationen under efterföljande åldring. Mekanismerna som är ansvariga för det förändrade åldringsbeteendet är: Cr-klustring, insläckta vakanser och fasseparation under kylning. Simuleringar av fasseparationen bör därför ta hänsyn till dessa faktorer och den ursprungliga mikrostrukturen för att göra mer exakta förutsägelser av hur mikrostrukturen utvecklar sig med åldringstiden. Fasseparationen i kommersiella duplexa rostfria stål (DSS), som är av stor praktisk betydelse i olika branscher, t ex kärnkraft, studerades också med SANS. Det visade sig att mängden av olika legeringselement har en viktig effekt på graden av fasseparation i DSS. Legeringen 2507 uppvisade en tydligare fasseparation jämfört med legering 2205 för samma värmebehandling. Brottmekanismerna såväl som de mekaniska egenskaperna visade sig bero på omfattningen av fasseparationen. Slutligen undersöktes de grundläggande aspekterna hos neutronspridnings-beteendet för binära Fe-Cr-legeringar. Resultaten visade att kärn- och magnetisk spridning av neutroner beror på utvecklingen av sammansättningsfluktuationerna på en nanoskala i Fe-Cr-legeringar. Förhållandet mellan magnetisk- och kärnspridning varierar med omfattningen av fasseparationen. / <p>QC 20171117</p>