The introduction of gas-driven Otto engine and the corresponding usage of bio-fuels in heavy-duty engines will render the exhaust atmosphere more corrosive and bring a higher working temperature to exhaust manifolds. The current service material, a ferritic ductile cast iron called SiMo51, will soon meet its upper temperature limit set by the ferrite-austenite transformation at 860ºC. Three alternative materials, as well as SiMo51 serving as reference, are investigated in the present thesis emphasizing on high-temperature corrosion fatigue.  The first aim of this study is to obtain material data and give a quantitative ranking of the materials’ performance. Low-cycle fatigue (LCF) tests at 800ºC in a synthetic exhaust gas (5%O2-10%CO2-5%H2O-1ppmSO2-N2 bal.) are conducted to evaluate the materials’ performance in simulated real working scenarios, where high-temperature, corrosive atmosphere and fatigue conditions during testings are similar to the conditions experienced by the exhaust manifolds. To evaluate the individual effect from high-temperature fatigue and isolate the impact from corrosion, the materials are tested under the same settings but in an argon atmosphere. To evaluate the individual effect from high-temperature corrosion and isolate the impact from mechanical deformation, oxidation tests are carried out at 800ºC in the same synthetic exhaust gas. The second aim is to identify and understand different oxidation behavior and failure mechanisms in the materials, realized by considerable characterizations of the tested specimens. From the fatigue tests, it is found that the austenitic stainless steel HK30 has the highest fatigue resistance, followed by the austenitic cast iron Ni-resist D5S, and the ferritic ductile cast irons SiMo1000 and SiMo51, a ranking valid in both atmospheres. In the exhaust atmosphere, for instance, the improvement in fatigue strength at 15,000 cycles relative to SiMo51 are 260%, 194% and 26%, respectively. Different crack initiation and propagation mechanisms are found for the various combinations of materials and atmospheres. In the exhaust atmosphere, for instance, crack initiation is assisted by oxide intrusion in SiMo51 and crack propagation is affected by crack branching in HK30, mechanisms not observed in argon. By comparing the S-N fatigue curves in the two atmospheres, the influence of oxidation on fatigue life is evaluated. The fatigue life of the cast irons are surprisingly found to be higher in the exhaust atmosphere. Several explanations are suggested for this, considering their very different oxidation behaviors.  This study provides accurate test data that can be used to help industry avoid over-dimensioned design. The investigation of the failure mechanisms promotes better understanding of the correlation between microstructure and mechanical properties. Moreover, the combination of fatigue tests in argon, fatigue tests in exhaust and oxidation tests in exhaust, shows how corrosion and fatigue individually and synergistically affect the materials’ performance at high temperature. / <p>QC 20180917</p>

Fatigue and ductility properties in various tool steels, produced by powder metallurgy, spray forming or conventionally ingot casting, have been analysed experimentally and successfully compared to developed models. The models are able to predict the fatigue limit and cause for fatigue fracture, and strain- and stress-development until fracture during the ductile fracture process respectively. Total fracture in a tool steel component, both in fatigue and ductility testing, is caused by a propagating crack initiated by particles, i.e. carbides or non-metallic inclusions. The models are based on experimentally observed size distributions. The axial fatigue strength at two million cycles was determined for various tool steels. The fracture surface of each test bar broken was examined in SEM to determine the cause for fatigue failure, i.e. a single carbide or inclusion particle or a cluster of carbides, and the size of the particle. The particles act as stress concentrators where a crack is easily initiated when the material is subjected to alternating stresses. The developed models calculate the probability that at least one particle will be present in the material which is larger than the threshold level for crack initiation at a certain stress range. The ductility testing was performed on various tool steels by four-point bending under static load. The load and displacement until total fracture were recorded and the maximum strain and stress acting in the material were calculated. The fracture surface of each broken test bar was examined in SEM, though the crack initiating area appears different compared to a fatigue failure. Ductile fracture is caused by a crack emanating from voids nucleated around many particles in a joint process and then linked together. By finite element modelling of void initiation and propagation in 2D of an experimentally observed carbide microstructure for each tool steel, successful comparisons with experiments were performed. Carbides were modelled as cracked when larger than a certain size, based on fracture surface observations, and the matrix cracked above a pre-defined plastic deformation level. The stresses and strains at total failure were in good agreement between model and experiments when evaluated. The use of these developed models could be a powerful tool for optimisation of fatigue and ductility properties for tool steels. With good fatigue and ductility properties normal failures appearing during operation of a tool steel product could be minimised. By theoretical tests in the developed models of various carbide microstructures the optimum mechanical properties could be achieved with a minimum of experiments performed. / QC 20101119

During the production of steel in the LD converter the refractory lining is exposed to high temperature emulsion of steel, slag and gas. It protects the steel body of the vessel to come in contact with the molten steel.The main purpose of this work was to observe the temperature distribution profile in converter refractory lining which is very important to understand the life of the refractory lining of the LD converter.In this study, a three dimensional (3D) heat transfer model for the refractory lining of converter was developed. The lining of the refractory material was considered as magnesite brick for inner lining, dolomite for intermediate lining and steel shell as outer part. In order to do the numerical modeling, the CFD software Ansys Fluent 13.0 was used. After considering the proper dimensions, meshing, properties of the lining material and boundary conditions, the modeling in Ansys was performed in two stages. In the first stage, the modeling was performed by assuming that the converter is already heated and the inside temperature of the furnace is 1923K and the outside temperature of the steel body is 300K. In the second stage, the temperature change of the molten steel, slag and the gas was considered as function of blowing time and slag height based on theories from different references. Firstly, the three dimensional (3D) heat transfer model was used for the refractory lining of the converter to show transient heat flow through the lining at different times. Secondly, 3D modeling results from fluent 13.0 was used to develop temperature distribution profile through the lining at different height for different time steps and at different positions with time and also along the converter height from the bottom to top. It has been noticed that refractories in the lining in contact with steel and slag must be of good quality for the reduction of wear cost and downtime and therefore the reduction of refractory cost per ton of steel production.

Stainless steel, an alloy of iron and chromium, is renowned for its corrosion resistance, strength, ductility and durability. Phosphorus in stainless steel production is considered an impurity due to its detrimental impact on the material's properties, for example, increased brittleness and decreased corrosion resistance. Due to this reason, the amount of phosphorus in the stainless steel must be controlled. Currently, dephosphorization is not applied in stainless steel production using the EAF and AOD pathway, since chromium is oxidized simultaneously along with phosphorus. This thesis explores whether phosphorus refinement is theoretically possible for stainless steel production and evaluates its feasibility from both economic and environmental perspectives. The aim is to offer valuable insights and potentially enhance stainless steel manufacturing processes. The goal of this thesis is achieved through conducting a literature study, a theoretical study using the software Thermo-Calc, interviewing various steel industries and a study visit to Outokumpu in Avesta where an empirical experiment is carried out. The results of this thesis show that dephosphorization is theoretically possible for stainless steel production when varying the temperature, CaO content, gas quantity, and argon quantity. However, regardless of the dephosphorization degree, high amounts of chromium oxidize to the slag. The chromium losses increase production costs and environmental impacts. Therefore, it is not feasible from an economic and environmental standpoint. / Rostfritt stål, en legering av järn och krom, är känt för sin korrosionsbeständighet, styrka och duktilitet. Fosfor i rostfritt stål tillverkning betraktas som en förorening på grund av dess negativa inverkan på materialets egenskaper. Fosfor bidrar till exempel med ökad sprödhet och minskad korrosionsbeständighet. På grund av detta måste mängden fosfor kontrolleras under tillverkningen. I dagsläget utför man inte fosforraffinering vid tillverkning av rostfritt stål i ljusbågsugn och AOD konverter eftersom krom oxideras samtidigt med fosfor, som är ett dyrt och värdefullt material.Detta projekt syftar till att undersöka om fosforraffinering är teoretiskt möjligt för tillverkning av rostfritt stål, samt undersöka dess genomförbarhet ur både ett ekonomiskt och miljömässigt perspektiv. Målen med detta projekt uppnås genom att genomföra en litteraturstudie, termodynamiska beräkningar med programvaran Thermo-Calc, intervjuer med olika stålindustrier och ett studiebesök till Outokumpu i Avesta där även ett empirisk experiment utförs. Resultatet visar att fosforraffinering är teoretiskt möjligt vid tillverkning av rostfritt stål när varierande temperaturer, kalk mängder, gas mängder och argon mängder testas i Thermo-Calc. Höga halter krom oxideras till slaggen oavsett graden av fosforraffinering. Dessa kromförluster ökar produktionskostnaderna och medför en negativ miljöpåverkan. Sammanfattningsvis så är fosforraffinering inte genomförbart ur ett ekonomiskt och miljömässigt perspektiv.

Monitoring the non-metallic inclusions formed in steels is of the utmost importance. In fact, inclusions, depending on their type, can affect both the properties of the steel and its processing. Once the most problematic inclusions have been detected, solutions can be found and applied to counter the arising issues. One such solution is the addition of calcium during ladle treatment to modify the inclusions shapes and avoid the precipitation of problematic inclusions. The focus was put on the detection, analysis and calcium addition countermeasure of inclusions. No clear conclusion could be drawn as to the effects of calcium addition on the inclusions, due to the very high zirconium content of the inclusions. A high zirconium content has a significant impact on the thermodynamics governing inclusion formation and prevents reliable analysis of the results. After discussion with the company, it has been found that the zirconium is not present in the steel grade but instead originates from the samplers that were used. / Övervakning av icke-metalliska inneslutningar som bildas i stål är av yttersta vikt. Faktum är att inneslutningar, beroende på typ, kan påverka både stålets egenskaper och dess bearbetning. När de mest problematiska inneslutningarna har upptäckts kan lösningar hittas och tillämpas för att motverka de uppkomna problemen. En sådan lösning är att tillsätta kalcium under skänkbehandlingen för att ändra inneslutningarnas form och undvika utfällning av problematiska inneslutningar. Fokus låg på detektering, analys och kalciumtillsats som motåtgärd för inneslutningar. Ingen tydlig slutsats kunde dras om effekterna av kalciumtillsats på inneslutningarna, på grund av inneslutningarnas mycket höga zirkoniuminnehåll. En hög zirkoniumhalt har en betydande inverkan på den termodynamik som styr bildandet av inneslutningar och förhindrar en tillförlitlig analys av resultaten. Efter diskussion med företaget har det visat sig att zirkoniumet inte finns i stålsorten utan istället härrör från de provtagare som användes.

The current thesis focuses on the deformation behaviour and strain distribution in the microstructure of ductile iron during tensile loading. Utilizing Digital Image Correlation (DIC) and in-situ tensile test under optical microscope, a method was developed to measure high resolution strain in microstructural constitutes. In this method, a pit etching procedure was applied to generate a random speckle pattern for DIC measurement. The method was validated by benchmarking the measured properties with the material’s standard properties. Using DIC, strain maps in the microstructure of the ductile iron were measured, which showed a high level of heterogeneity even during elastic deformation. The early micro-cracks were initiated around graphite particles, where the highest amount of local strain was detected. Local strain at the onset of the micro-cracks were measured. It was observed that the micro-cracks were initiated above a threshold strain level, but with a large variation in the overall strain. A continuum Finite Element (FE) model containing a physical length scale was developed to predict strain on the microstructure of ductile iron. The materials parameters for this model were calculated by optimization, utilizing Ramberg-Osgood equation. For benchmarking, the predicted strain maps were compared to the strain maps measured by DIC, both qualitatively and quantitatively. The DIC and simulation strain maps conformed to a large extent resulting in the validation of the model in micro-scale level. Furthermore, the results obtained from the in-situ tensile test were compared to a FE-model which compromised cohesive elements to enable cracking. The stress-strain curve prediction of the FE simulation showed a good agreement with the stress-strain curve that was measured from the experiment. The cohesive model was able to accurately capture the main trends of microscale deformation such as localized elastic and plastic deformation and micro-crack initiation and propagation.

Face à l'augmentation générale de la consommation d'énergie, l'exploitation du Gaz Naturel Liquéfié (GNL) connaît un intérêt croissant, d'où un marché en forte expansion avec de nombreux projets d'installation de terminaux méthaniers. Les installations de gaz naturel liquéfié ont la particularité de fonctionner à très basses températures (~ -160°C), ce qui exige l'utilisation de matériaux particuliers présentant des caractéristiques adaptées aux températures extrêmes. Cette étude nous a permis d'évaluer le comportement structural de l'acier 9% Ni métal de base, consistant en une phase ferrique d'un grain martensitique en présence d'austénite, utilisé dans la construction du réservoir interne de stockage du GNL.Ce métal présente des domaines inhomogènes au niveau mésoscopique principalement formés par la phase austénitique riche en Ni mis en évidence par la diffusion des neutrons aux petits angles. Suite à une déformation mécanique, une augmentation du pourcentage de la phase austénitique est observée au niveau de la zone de déformation plastique. Ce phénomène est probablement dû à la diffusion préférentielle du Ni le long des dislocations au cours du traitement mécanique et son accumulation au niveau de cette zone. Au cours du processus de soudage, une diffusion intergranulaire du Ni au sein de la zone affectée thermiquement (ZAT) est observée. Ce phénomène permet de stabiliser la phase austénitique au niveau de la ZAT et d'améliorer les propriétés mécaniques au sein de cette zone. La déformation mécanique appliquée à basse température sur l'acier 9% Ni, ne détériore pas les propriétés structurales de ce matériau. / Due to the overall increase in energy consumption, the use of the Liquefied Natural Gas (LNG) is experiencing an increasing interest, resulting in a rapidly growing market with many LNG terminals installation projects. LNG installations have the particularity of operating at extremely low temperatures (~ -160°C), which requires materials with specific characteristics suitable to extreme temperatures. This study allowed us to evaluate the structural behavior of the base metal 9% Ni steel, consisting of a ferritic phase with a martensitic grain in the presence of residual austenite, used in the construction of the inner wall of LNG storage tank. This metal presents, at the mesoscopic level, non-homogeneous domains formed primarily by the Ni rich austenitic phase revealed by small angle neutron scattering. Due to a mechanical deformation, an increase in the percentage of the austenitic phase is observed at the plastic deformation zone. This phenomenon is probably due to the preferential diffusion of Ni along dislocations during the mechanical treatment and its accumulation at this area. During the welding process, a grain boundary diffusion of Ni in the Heat Affected Zone (HAZ) is observed. This phenomenon allows the stabilization of the austenitic phase at the HAZ and the improvement of the mechanical properties within this area. Mechanical deformation applied at low temperatures on the 9% Ni steel, does not deteriorate the structural properties of the material.

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

A liga de alumínio designada AA4006 é muito utilizada na indústria. É uma liga do sistema Al-Fe-Si, com teores (% em massa) de Si na faixa de 0,8 a 1,2% e Fe entre 0,5 e 0,8%. Apesar de ser bastante utilizada, ela foi pouco estudada. Neste trabalho foi realizado um estudo comparativo da microestrutura e da textura cristalográfica entre chapas da liga AA4006 produzidas por dois processos industriais de lingotamento: contínuo (Twin roll caster TRC) e semicontínuo (Direct chill DC). Para a caracterização microestrutural, foram utilizadas as técnicas de microscopia óptica com luz polarizada, microscopia eletrônica de varredura com microanálise química, medidas de condutividade elétrica e ensaios de dureza Brinell. A textura cristalográfica foi determinada por difração de raios X. Foram detectadas e discutidas diferenças significativas nas morfologias e distribuições de grãos e de partículas de fases intermetálicas. O estudo da textura cristalográfica foi realizado ao longo da espessura das tiras e os resultados mostraram variações significativas da textura entre as chapas ao longo da espessura. A chapa produzida por lingotamento contínuo apresentou uma típica textura de cisalhamento nas proximidades de sua superfície, enquanto nas regiões mais internas a fibra foi observada. O estudo da recristalização de chapas metálicas laminadas a frio é muito útil para a obtenção da temperatura de amolecimento do material submetido a um tratamento térmico. Tratamentos térmicos isócronos no intervalo de uma hora foram feitos em amostras das duas chapas e a chapa produzida pelo processo TRC apresentou a temperatura para 50% de recristalização em torno de 290 ºC e a amostra da chapa produzida pelo processo DC em torno de 270 ºC. A textura cristalográfica pode mudar com a recristalização e com a laminação do metal. Utilizando estas etapas de processamento do material, a orientação dos grãos de uma tira metálica pode ser otimizada, a fim de, por exemplo, melhorar a estampabilidade de chapas na obtenção de um dado produto com valor agregado. Neste trabalho as curvas de amolecimento para duas chapas produzidas por lingotamento contínuo e lingotamento semicontínuo da liga de alumínio AA4006 também foram determinadas e comparadas. Embora as diferenças detectadas entre as curvas de amolecimento tenham sido pequenas, foi possível verificar que a recristalização da chapa produzida por twin roll caster TRC ocorre em temperaturas mais elevadas do que na chapa produzida pelo processo direct chill DC. Resultados da textura cristalográfica em amostras destas chapas (laminadas e recozidas) foram obtidos utilizando difração de raios X e difração de elétrons retroespalhados EBSD. Estes resultados indicaram a presença da textura de cisalhamento na superfície e a fibra no centro da amostra laminada a frio (70% de redução) da chapa obtida por lingotamento contínuo. Na amostra da chapa obtida por lingotamento semicontínuo, a componente cubo e a fibra foram vistas na superfície e no centro. Uma textura fraca com grãos orientados ao acaso foi vista nas duas amostras (TRC e DC) recristalizadas das duas chapas, possivelmente, devido à nucleação estimulada por partículas. A fibra desapareceu nas amostras (TRC e DC) recristalizadas. / AA4006 Aluminum alloy is extensively used in industry. It belongs to the Al-Fe-Si system, with Si between 0,8 and 1,2 % mass, and Fe between 0,5 and 0,8 % mass. This alloy is less studied despite its extensive use. A comparative microstructural study has been performed in as-received AA4006 alloy strip produced by two industrial casting processes: twin roll caster (TRC) and direct chill (DC). Polarized optical microscopy, scanning electron microscopy with microanalysis, electrical conductivity measurements and Brinnel hardness tests have been used for microstructural characterization. Significant differences in the grain and intermetallic particle sizes, morphologies and distributions were detected and are discussed. Thermal treatments effects on the silicon content in solid solution were also studied. Crystallographic textures have been also determined. Textures across thickness of both sheets have been analyzed and compared. Results showed significant texture changes across thickness of the specimens. Texture analysis was carried out using X-ray diffraction technique. Twin roll caster (TRC) sheet presented the typical shear texture near the surface, while, in internal regions, the -fibre was observed. A recrystallization study of cold rolled metallic sheets is very important to obtain softening temperature for the material during annealing. After cold rolling with 70% of reduction in thickness, followed by isochronous heat treatments, the samples of the two sheets produced by TRC and DC presented a 50% recrystallization temperature around 290 ºC and 270 ºC, respectively. Crystallographic texture can change during the metal rolling and recrystallization. These processing steps can optimize the grain orientation distribution in a metal strip to improve, for instance, the stamping process, in order to obtain an aggregated value product. Softening curves were also compared and determined for the two sheets (rolled and annealed) of the AA4006 aluminum alloy produced by twin roll caster TRC and direct chill DC processes. It was detected that the recrystallization of the strip produced by TRC process occurs at a higher temperature than that for the DC process, despite the little differences in their softening curves. Crystallographic texture results, for the sheet samples, were obtained by using X-ray diffraction and electron back scatter diffraction EBSD techniques. These results indicated the shear texture presence on the surface and fiber at the center of the cold rolled (70% area reduction) sample for the sheet produced by TRC process. In the sheet sample produced by the DC process, under the same conditions, the cube component and fiber texture (at the surface and at the center) were observed. A texture with random oriented grains was detected in two deformed and recrystallized samples of the two sheets (TRC and DC). It is suggested that this texture occurs due to the particle stimulated nucleation. There was fiber absence in the recrystallized samples (TRC and DC).

Additive manufacturing has developed radical through the years. Sandvik has invested in the area by building a center specific for additive manufacturing. Due to problems with the material- and product properties and high production costs no products have been used with additive manufacturing method. These aspects have improved over the years and therefore the master thesis was made with an objective: to compare two different produced blades with focus on the aspects of material- and product properties and production costs. One of the blades was produced through additive manufacturing (AM) and the other blade was produced in today’s production at Sandvik Coromant in Gimo. If the blade can be produced through AM there is a possibility to lower the production costs and improve the degree of design freedom. The material that will be used is SS2230 (50CrV4) which are used in conventionally produced blades and 1.2709 which are used in AM produced blades.   The investigation consisted of five different tests (flow rate, pressure force, vibration, fatigue and keyhole wear) and a study on production aspects with focus on value stream mapping, investments and production costs. The main objective in the result was to compare each test between the two different produced blades, not to investigate the optimal value. Therefore, was the test designed to have continuity with as small deviation as possible between the tests. This resulted in choosing values which were not optimal for the blades but focused on continuity and deviation.   The coolant channels flow rate improved with 35% on the AM produced blades but pressure force, fatigue and keyhole wear resistance did not deviate much from conventionally produced blades. Fatigue tests were made twice with two different inserts because the result from the first test differentiated too much from the expected results on both blades. Production costs will be higher with AM but on a long-term may an investment improve the degree of design freedom on a product and a possibility to produce towards costumer (just in time). This will need an expensive investment with a bigger perspective on the timeframe. The value of the product may increase but the production costs will increase too.