In the present study, the influence of the quenching temperature and partitioning conditions (temperature and time) have been investigated on a 0.6%C-1.2%Mn-1.6%Si-1.75%Cr alloy. Maps of hardness, impact toughness and amount of retained austenite have been developed for three quenching temperatures as a function of partitioning temperature and partitioning time. Results demonstrate that, in this material, the carbon depletion of the martensite and the stabilization of austenite can be achieved significantly faster at high partitioning temperatures, promoting higher retained austenite fractions, lower hardness, and maximizing the energy absorbed in a Charpy V‑Notch test. In addition, the effect of the partitioning time was also analysed, presenting different behaviour at high and low partitioning temperatures. Whereas an increment of time at high partitioning temperatures (>400 ºC) leads to an austenite consumption, at low partitioning temperatures it is effective to retain a higher amount of austenite.  Furthermore, tensile properties are shown to be better than in conventional alloys utilized in industry. Whilst, for example, the AISI 52100 alloy achieves 2 GPa of tensile strength and 1‑2% of fracture deformation, in the present study the notable combination of 2.5 GPa of tensile strength and 5.7 % of fracture deformation was achieved in samples quenched until room temperature. Untempered martensite transformed during final cooling in samples quenched until higher temperatures was shown to be detrimental for tensile properties. A comparison between the Q&P process and the austempering process on this alloy has been carried out. Results reveal that the quenching and partitioning heat treatment is presented as a promising alternative to reach higher hardness (>700 HV) and similar specific wear rates in dry conditions performing a shorter heat treatment.    Finally, a complementary study about the effect of micro-segregation on the Q&P process and an optimization method to minimize the inhomogeneity of the structure by a correct selection of the quenching temperature were established.

In the oxidative refining of metallurgical grade silicon the loss of Si to the slag in the form of SiO2 is an economical concern. The purpose of this report is to investigate the possibility of using SiO2 and mechanical stirring to remove Ca and Al as a substitute to the oxidative refining. In the experiments graphite crucibles were used in a vertical resistance furnace and controlled argon atmosphere. The removal rate of Ca and Al are measured by X-ray fluorescence and the slag is examined in a scanning electron microscope. The slag formation kinetics are examined and a calculation of the activities of Ca, Al and their respective oxides in the slag phase is conducted. The driving forces of creating CaO and Al2O3 in this system is calculated to better understand the behavior of the Ca and Al removal. The results show that removal of dissolved Ca and Al by mechanical stirring is possible and in this setup a stirring time of 20 minutes is sufficient since no more refining can be obtained by increasing it.

An investigation of austenite grain growth of two bearing steel grades; 100Cr6 and100CrMnMoSi8-4-6 is performed. Austenitization treatments were performed between 860°C and 1200 °C for 5 minutes to 5 hours and the grain size was determined for each sample.Grain boundary etching was carried out using a water based, picric-acid etchant. Generally,100CrMnMoSi8-4-6 was harder to etch than 100Cr6. Therefore, a precipitation heattreatment was performed in order to facilitate etching of prior austenite grain boundaries in100CrMnMoSi8-4-6. The precipitation treatment was found to be effective. However, theprecipitation heat treatment was not suitable for 100Cr6 as the grain size increased duringthe precipitation heat treatment.Light optical microscope equipped with a camera was utilized to take micrographs for grainsize evaluation. Jeffries' standard procedure according to ASTM E112-96 was used tomeasure the grain size. The results shows that the austenite grain size increases withtemperature and time as expected. The experimental data was fitted to a well-known graingrowth model. The model only worked for the temperatures investigated and could not bemade to fit different temperatures.Local grain size variation was studied and its influence on fatigue properties was evaluated.The result showed that variation in local grain size can significantly alter the fatigueproperties. The findings are only theoretical and have not been tested practically.Two different spheroidization heat treatments and one homogenization heat treatmentwere performed. Both spheroidization heat treatments investigated exhibited similar grainsize. The homogenization heat treatment reduced the local grain size variation.Homogenization treatment prior to the spheroidization treatments did not increase ordecrease the grain size. The long heating, holding and cooling times in the secondspheroidization heat treatment is probably the reason for the lack of grain refinementcompared to the first spheroidization heat treatment. The grains had time to grow to theinitial austenite grain size during each cycle.

Powder metallurgy (PM) is a technology used to manufacture near net shape components for an increasing number of applications like automobile components, aircraft components, cutting tools, refractory, household appliances, etc. The general PM process comprises of Powder manufacturing/powder tailoring, Compacting, and Sintering. Based on product’s final requirements, optional secondary operations are performed. PM components for automotive application are experiencing a growth coupled with new challenges.  PM´s capability for producing complex net shaped components with desired properties has enabled it to be an alternative to other traditional manufacturing processes. Average U.S. made vehicle in 2010 contained an estimated 41.6 pounds of PM parts and in Europe, the average per vehicle PM parts in 2010 is estimated 18.5 pounds [3].  New design goals set by OEMs (original equipment manufacturers) demands for complex shaped components with high mechanical properties. Stupendous developments are done in the field of PM component manufacturing and PM raw material manufacturing, endeavoring to cater the technical and economic needs set by OEMs. Based on the application, unique powder characteristics are demanded which are in turn associated with the quality of powders produced.  Powder production for conventional PM application encompasses reduction or atomization followed by annealing. Reduced powders are called sponge iron powders, used for low density (density of PM component) application and atomized powders are used for relatively high density application. Atomization can be further classified into water atomization and gas atomization. Coarse, irregular shapes are the common features of water atomized powders and fine, spherical shapes are the common features of gas atomized powders. Water atomization is one of the prominent methods used in production of powders for conventional PM application. Oxygen content of the powders produced by water atomization plays an important role in determining it’s as sintered properties. In this work, oxide formation during various stages of water atomization and annealing were studied for iron, carbon and manganese alloy system and iron, carbon, chromium, molybdenum and manganese alloy system. Manganese content was varied (0.0%, 0.5%, 1.0%) in the above said two alloy system maintaining the same amount of other alloying constituents for comparison. Total oxygen content and oxide composition formed during processing were studied. Both alloy system showed that total oxygen content increases with increasing manganese content. The composition of oxides includes manganese, chromium and iron for Fe+C+Cr+Mo+Mn alloy system and manganese and iron for Fe+C+Mn alloy system. Key words: Powder metallurgy, Water atomization, Gas atomization, Reduced powders,  Oxygen content, Oxide composition, Annealing, Sintered properties, Iron, Chromium, Molybdenum, Manganese.

The aim of the present work is to study the formation of the cubic carbide phase (gamma phase) free gradient zone and the gamma cone structure at the edges of gradient sintered cemented carbides. Four types of cemented carbides; WCTi(C,N)-Co, WC-Ti(C,N)-Ni, WC-Ti(C,N)-Fe, WC-(Ti,Ta,NB)(C,N)-Co were gradient sintered and the thicknesses of the gradients were measured. Formation of the gradients is simulated and the simulations results are compared with experimental data. For all of the one-dimensional simulations, the DICTRA [1] software is used. The two-dimensional simulations are carried out by using a new simulation tool which is called “YAPFI”. The YAPFI software is a tool for simulation of diffffusion in multiphase systems along one, two, or three spatial coordinates. Various numerical parameters have been studied by running less computationally demanding one-dimensional simulations. The optimized parameters are used to setup the two-dimensional simulations. Two different kinetic databases were used in the simulations. The effect of different so-called labyrinth factors were studied systematically. The simulation results are in close agreement with the experimental observations, although some anomalies are present in the results. Results of the two-dimensional simulations show the formation of the gamma cone at the edges of the insert.

hree-­‐dimensional characterization of fully equiaxed Ti-­‐6Al-­‐4V has been performed using the recently developed TriBeam system. To date, no general model for full prediction of Ti-­‐6Al-­‐4V tensile properties as a function of empirical microstructural parameters exist. To develop such a model would require knowledge about the relevant deformation mechanisms and also detailed information about the microstructure of the material. As a thrust to develop such a model a large three-­‐dimensional dataset was collected, reconstructed and analyzed, in order to extract statistical information about microstructural parameters. It was found that the material contained heavily textured regions with α grain boundaries that have misorientation of 1° to 2° or less. The low grain misorientation angle required segmentation parameter optimization, which included the integration of a grain size filter and a thorough exploration of the segmentation parameter space. The α grains are shown to be volumetrically smaller in textured regions compared to bulk, while β grains showed an even grain volume distribution throughout the structure. The TriBeam system collected the dataset faster than any other available serial sectioning methods and is described in detail with its subsystems and operating conditions. The extracted statistical information is presented in detail numerically and visually in this report.

This report describe the wear of the protruding areas on the sides of the grate plates in the grate-kiln process in the hematite pellet production in LKAB, Kiruna. The steel plates are exposed to a hostile environment with heat cycles and corrosive atmosphere. An evaluation of the plates was made in co-operation with LKAB Metlab in Luleå and LKAB mechanical workshop in Kiruna. Instruments used are stereomicroscope, LOM, SEM, Spectroscope, Vickers Hardness and a surface nish meter. Results show the protruding areas of the plates are exposed to a tribochemical wear, where tops of the rough areas are torn down. A coating test is carried out at Tribolab, LTU in Luleå, using an SRV. Samples with a wear and corrosion resistant coating called Diamalloy 4276 abrade against eachother at high temperature and pressure. The coating do help to resist wear, but the environment of the test is to unrealistic to say by certain that it will help in the grate. A FEM-model in COMSOL Multiphysics 4.4 is made to calculate thermal stresses between coating and metal, the result show stresses up to 1 GPa will occur, this can be explain by the big dierence in thermal expansion coefficients of the materials. It will probably create cracks in the coating surface. Two solutions are presented, a coating is not recommended. The tribochemical wear is decreased by using a better surface nish. Therefore one can either machine the areas by drilling or milling, or one can change the casting method. Today sand casting is used, by using shell casting or precision casting, for example Shaw process, the surface nish is better over the whole plate, which also is better for corrosion resistance since less initiation points exist. / Denna rapport presenterar en undersökning av slitaget på sidorna av grateplattor som används i gratekilnprocessen i hematitpelletstillverkningen på LKAB i Kiruna, även lösningar presenteras. Plattorna benner sig i en svår miljö med termiska cykler och korrosiva substanser. Utvärderingen av slitaget gjordes i samarbete med LKAB Metlab i Luleå och LKAB mekaniska verkstad i Kiruna. Utrustning som användes var Stereomikroskop, LOM, SEM, Spektroskop, Vickers hårdhetsmätare och ytnhetsmätare. Resultatet visar att sidorna av plattorna utsetts för ett tribokemiskt slitage där toppar av den grova utan slits ner. Ett ytbeläggningstest utfördes på Tribolab, LTU i Luleå, med en SRV. Prover med en beläggning har gnidits mot varandra under tryck och hög temperatur och jämförts med prover utan beläggning som utsattes för samma test. Ytbeläggningen som används står främst emot korrosion, men även slitage, den kallas Diamalloy 4276. Resultatet visar att beläggningen skyddar bra mot slitage, men miljön under testet var för orealistiskt för att med säkerhet kunna säga att det kommer hjälpa i graten. En FEM-modell gjordes med hjälp av COMSOL Multiphysics 4.4 för att beräkna de termiska spänningarna som uppstår mellan ytbeläggningen och metallen. Resultatet visar att spänningar på upp till 1 GPa kommer uppstå, detta kan förklaras med den stora skillnaden i termisk utvidgningskoecient mellan de två materialen. De höga spänningarna kan skapa sprickor i ytan. Två lösningar presenteras, en ytbeläggning rekommenderas inte i dagsläget. Det tribokemiska slitaget kan motverkas genom att förbättra ytnheten. Detta kan antingen utföras genom att bearbeta ytan, med fräsning eller slipning, eller att man byter gjutningsmetod. Idag används manuell formtillverkning, om man istället skulle använda skalformsgjutning eller precisionsgjutning, till exempel Shawprocessen, skulle man få en bättre ytnhet över hela plattan. Detta leder även till bättre korrosionsbeständighet då färre initieringspunkter nns.

Fluid flow accompanied by heat transfer, solidification and interrelated chemical reactions play a key role during Continuous Casting (CC) of steel. Generation of defects and production issues are a result of the interaction between mould flux, steel grade and casting conditions. These issues are detrimental to both productivity and quality. Thus, the development of reliable numerical models capable of simulating fluid flow coupled to heat transfer and solidification are in high demand to assure product quality and avoid defects. The present work investigates the influence of steel grade, mould powder and casting conditions on process stability by including heat and mass transfer through liquid steel, slag film layers and solidifying shell. The thesis addresses the application of a numerical model capable of coupling the fluid flow, heat transfer and solidification developed by Swerea MEFOS; based on the commercial CFD code FLUENT v12. The Volume of Fluid (VOF) method, which is an interface tracking technique, is coupled to the flow model for distinction of the interface between steel and slag. The current methodology not only allows the model to describe the behaviour of molten steel during solidification and casting but also makes the assessment of mould powders performance possible.  Direct prediction of lubrication efficiency, which is demonstrated by solid-liquid slag film thickness and powder consumption, is one of the most significant advantages of this model. This prediction is a direct result of the interaction between metal/slag flow, solidification and heat transfer under the influence of mould oscillation and transient conditions.  This study describes the implementation of the model to analyse several steel and mould powder combinations. This led to detection of a combination suffering from quality problems (High Carbon Steel + High Break Temperature Powder) and one, which provides the most stable casting conditions (Low Carbon Steel + Low Break Temperature Powder).  Results indicate the importance of steel pouring temperature, mould powder break temperature and also solidification range on the lubrication efficiency and shell formation. Simulations illustrate that Low Carbon Steel + Low Break Temperature Powder delivers the best lubrication efficiency and thickest formed shell. In contrast, High Carbon Steel + High Break Temperature Powder conveys the minimum lubrication efficiency. Therefore, it was concluded that due to absence of proper powder consumption and solidification rate the latter combination is susceptible to production defects such as stickers and breakouts during the casting sequence.

The aim of this report was to investigate new methods for measuring the condition of the scrap in the electric arc furnace. This was done by evaluating three different methods theoretically and chooses two of them for test in the electric arc furnace in Avesta. Due to lack of time and equipment only Total harmonic distortion (THD) measurements was used. The results show that THD reaches low values during refining. This suggests that all the scrap is melted and the arcs are stable.

No description available.