This paper deals with the effects of three low-carbon steel filler metals consisting of ferritic and austenitic phases on the weld joints of the tungsten inert gas (TIG) welding of Hardox 500 steel. The correlation between the microstructure and mechanical properties of the weld joints was investigated. For this purpose, macro and microstructure were examined, and then microhardness, tensile, impact, and fracture toughness tests were carried out to analyze the mechanical properties of joints. The results of optical microscopy (OM) images showed that the weld zones (WZ) of all three welds were composed of different ferritic morphologies, including allotriomorphic ferrite, Widmanstätten ferrite, and acicular ferrite, whereas the morphology of the heat-affected zone (HAZ) showed the various microstructures containing mostly ferrite and pearlite phases. Further, based on mechanical tests, the second filler with ferritic microstructure represented better elongation, yield strength, ultimate tensile strength, impact toughness, and fracture toughness due to having a higher amount of acicular ferrite phase compared to the weld joints concerning the other fillers consisting of austenitic and ferritic-austenitic. However, scanning electron microscopy (SEM) images on the fracture surfaces of the tensile test showed a ductile-type fracture with a large number of deep and shallow voids while on the fracture surfaces resulting from the Charpy impact tests and both ductile and cleavage modes of fracture took place, indicating the initiation and propagation of cracks, respectively. The presence of acicular ferrite as a soft phase that impedes the dislocation pile-up brings about the ductile mode of fracture while inclusions may cause stress concentration, thus producing cleavage surfaces.

Half of today's global energy consumption is in the form of heating and cooling. Solar collectors are the most promising sustainable alternative to fossil fuels in this sector. The most important component in a solar collector is the receiver, which by use of a selective surface absorbs and converts solar irradiance to thermal energy. Herein, a novel selective surface for low-to mid-temperature solar collectors is developed, studied and presented. The surface is produced by electroplating a cobalt-chromium coating on a stainless steel substrate using an electrolyte based on a deep eutectic solvent. Our method makes use of trivalent instead of traditionally used hexavalent chromium, which significantly reduces health-related issues and makes it more environmentally benign. We obtain a coating of chromium doped cobalt where the surface exhibits an absorptance and emittance of 0.96 and 0.14, respectively, giving it a solar-to-thermal efficiency of 0.95. An observed loss in optical efficiency, is shown to correlate to an oxidation of the metallic cobalt to Co₃O₄ at elevated temperatures. We further show that this oxidation can be mitigated by dip-coating a protective silica top coating, which concurrently improves the optical selectivity of the surface. The present selective surface is efficient, cheap, scalable, and easy to produce sustainably, making it competitive to industry standards. We foresee that our method will have impact on the advancement of improved low-to mid-temperature solar collectors, assisting a faster transition towards a sustainable society.

An embedded sensor, designed for rapid and accurate response times and using wireless data transmission, has been developed for the on-site measurement of temperatures in industrial continuous casting moulds. The sensor has been used to measure the temperature at several points in the mould during production in a Southwire copper casting process. The measured data has been used to calculate the temperature gradient in the mould to estimate the heat flux through it; this is then used as a boundary condition for numerical simulations of solidification. For these, we employ a method that tracks the solidification front explicitly; this has an advantage over fixed-grid methods in simulations for materials having a short solidification interval, since the release of latent heat at the solidification front can be resolved without resorting to a very fine mesh. The special considerations required for setting the initial condition for the numerical scheme and the time taken for the superheated melt to form a solid shell are also discussed.

To study the production of pure copper and copper alloys in the Southwire process the temperature in the mould has been measured on-site in the production process in a number of positions. To increase the accuracy and robustness of measurements a new type of thermocouple based temperature sensor has been developed and tested. The test system includes wireless transmission of measured data from the moving mould. The results from the measurements are then used to calculate the energy transfer rate from the solidifying shell as a function of time. An initial in-situ measurement campaign has been performed and the results are very promising.

The South-Wire process, a development of the Properzi process, to continuously cast copper has been studied both experimentally and by finite element computer simulation. The experimental work has been performed on site to get temperature data as a function of time at several locations within the mould. These experimental data have been used to evaluate boundary conditions for the heat transfer from the strand-mould interface and through the mould. A simulation model of the casting process has been developed in the program FEMLAB. In this program temperature varying material data and time varying boundary conditions have been used. The simulation model has been verified by comparing with an analytical solution, and then applied to the real physical process.

The materials genome initiative was announced by US President Obama 2011. Its actual meaning was initially rather unclear and it seemed as it could contain everything. Nevertheless, in their Scripta paper 2014 Kaufman and angstrom gren argued that the materials genome, analogously with biological genomes, should be defined as a set of information (databases) allowing prediction of materials structure as well as its response to processing and usage conditions. It thus seemed natural that CALPHAD thermodynamics and kinetics should play an essential role.In the present paper the role of CALPHAD as a way of processing different kind of materials data will be emphasized. The extension from thermochemistry to other properties, industrial applications and extrapolation far from equilibrium will be reviewed.

As emphasized by Stokes (1997), the common assumption of a linear progression from basic research (science), via applied research, to technological innovations (engineering) should be questioned. In fact, society would gain much by supporting long-term research that stems from practical problems and has usefulness as a key word. Such research may be fundamental, and often, it cannot be distinguished from "basic" research if it were not for its different motivation. The development of the Calphad method and the more recent development of accompanying kinetic approaches for diffusion serve as excellent examples and are the themes of this symposium. The drivers are, e.g., the development of new materials, processes, and lifetime predictions. Many challenges of the utmost practical importance require long-term fundamental research. This presentation will address some of them, e.g., the effect of various ordering phenomena on activation barriers, and the strength and practical importance of correlation effects.

The basics of thermodynamics are reviewed with special attention to phase transformations. The distinction between internal and external variables is emphasized and the general equilibrium conditions are derived from the combined first and second law. The concepts of entropy production and driving force as well as stability are discussed. The calculation of thermodynamic properties and phase equilibria is considered and the Calphad method is briefly reviewed, including modeling of substitutional and interstitial disorder. The thermodynamic bases of phase diagrams are examined, and finally, the effect of interfaces, fluctuations and thermodynamics of nucleation are reviewed.

With the use of today's computer softwares, phase diagrams can readily be plotted with a wide choice of variables on the axes. Hillert defined a true phase diagram as a diagram where each point uniquely defines the stable phases. He also showed that not all choices of axis variables give true phase diagrams. In this note we will demonstrate that although the rules stated by Hillert are necessary they are not sufficient to have true phase diagrams.

Magnesium is the lightest metal currently processed by powder bed fusion - laser beam (PBF-LB). Its low density implies very different powder characteristics compared to materials more established within AM. To gain a greater understanding of the characteristics of magnesium powder and its implications for AM, a gas-atomized WE43 powder was characterized and processed by PBF-LB. The spreadability of the powder was evaluated using TQC Sheen Automatic Film Applicator, while in parallel, the powder was processed in PBF-LB. The flowability was evaluated using Hall and Gustafsson flowmeters. Apparent density was measured and general behaviour during handling was evaluated. The results were compared with powders commonly used in PBF-LB. The spreadability of the powder was greater than expected: the powder flowed in both the Hall and Gustavsson flowmeters, although the flow time was extremely long. Parts were successfully built in an EOS M290 printer using the powder with the as-atomized particle size distribution. 

Magnesium (Mg) has gained a lot of attention for its biodegradable properties. Additive manufacturing of Mg would further provide an opportunity to manufacture optimized structures for implants. However, much work remains to ensure stable processes and to understand the correlation between processing parameters, microstructure and related properties. The aim of this study was to process gas-atomized WE43 powder by Powder Bed Fusion-Laser Beam (PBF-LB) in a commercially available machine (EOS M290). The built material was characterized in terms of microstructure and composition and compared with the virgin powder. Thermodynamic computations based on the Calphad-method were for the first time employed to an additively manufactured Mg-alloy to predict phases present. Samples with above 99% density were successfully manufactured. The phases predicted using computational thermodynamics partly overlapped with phases observed experimentally. The study confirms the feasibility of using commercial PBF-LB systems for processing Mg-alloys, and the applicability of thermodynamic modelling to this system. 

Additive manufacturing techniques for production of cemented carbides have been investigated through experiments and through studies of published literature. The experimental part consisted of trials with the technique Binder Jet 3D-Printing, used for 3D-printing of cemented carbide green parts. In this diploma work, green parts of WC-12%Co powder were successfully produced with the ExOneInnovent+. Furthermore, properties such as phases and grain sizes of sintered cemented carbides produced through Binder Jet 3D-Printing was investigated.

Sc(Al_xNi_1-x)₂ is a pseudobinary C14 Laves phase and a potential interstitial hydrogen storage material or anode in a Ni-MH battery. A previous study showed that Sc₁Al₁Ni₁ can store hydrogen reversibly; both interstitially and trough decomposition into ScH2 and AlNi. It is also known that the exact composition is very important for the hydrogen storage properties of pseudobinary Laves phases. This thesis work is aimed at synthesising Sc(Al_xNi_1-x)₂ and study the effect of the Ni/Al ratio on the hydrogen absorption/desorption process as well as the interstitial storage capacity. Compositions with high nickel content had the highest capacity (at least 0.67wt% for ScAl_0.66Ni_1.34) and ones with high aluminium content had the lowest total storage capacity (0wt% for ScAl_1.28Ni_0.62). The former composition was also shown to absorb and desorb hydrogen during multiple cycles. Desorption of interstitial hydrogen from ScAl_0.66Ni_1.34 requires 4.6kJ/mol in activation energy.

Metal hydrides have existing and potential uses in many applications such as in batteries, for hydrogen storage and for heat storage. New metal hydrides and a better understanding of the behaviour of known metal hydrides may prove crucial in the realisation or further development of these applications. The aims of the work described in this thesis have been to characterise new metal hydrides, investigate how the properties of known metal hydrides can be improved and understand how their structure influences these properties. Metal hydrides, in most cases synthesised via high-temperature techniques, were structurally characterised using X-ray powder diffraction, X-ray single crystal diffraction and neutron powder diffraction and their thermodynamic and kinetic properties by in-situ X-ray powder diffraction, thermal desorption spectroscopy and pressure-composition-temperature measurements.

The investigations showed that: the storage capacity of the hexagonal Laves phase Sc(Al_1-xNi_x)₂ decreases with increasing Al content. There is a significant decrease in the stability of the hydrides and faster reaction kinetics when Zr content is increased in the cubic Laves phase Sc_1-xZr_x(Co_1-xNi_x)₂. Nb₄M_0.9Si_1.1 (M=Co, Ni) form very stable interstitial hydrides which have very slow sorption kinetics. MgH₂ mixed with 10 mol% ScH₂ reaches full activation after only one cycle at 673 K while it takes at least four cycles at 593 K. LnGa (Ln=Nd, Gd) absorb hydrogen in two steps, it is very likely that the first step is interstitial solution of hydride ions into Ln₄ tetrahedra and the second step places hydrogen atoms in Ln₃Ga tetrahedra. The nature of the Ga-H bond is still unclear.

This thesis covers some aspects of hard part turning of carburised steels using a poly‑crystalline cubic boron nitride (PCBN) cutting tool during fine machining. The emphasis is on the influence of the steel cleanliness and the characteristics of non‑metallic inclusions in the workpiece on the active wear mechanisms of the cutting tool. Four carburising steel grades suitable for automotive applications were included, including one that was Ca‑treated.

A superior tool life was obtained when turning the Ca-treated steel. The superior machinability is associated with the deposition of lubricating (Mn,Ca)S and (CaO)_x-Al₂O₃-S slag layers, which are formed on the rake face of the cutting tool during machining. Moreover, the transfer of work material to the rake face crater is characteristic in hard part turning of clean steels. It can be because of the lack of sulfides that protect the cutting edge when turning machinability treated steels. This corresponds to the more pronounced crater wear caused by the low‑sulfur steels than that of the steels with higher sulfur contents. It was also concluded that the composition of the non‑metallic inclusions in the Ca‑treated steel is a more important factor than the inclusion number and size, in hard part turning using a PCBN cutting tool. Also, a 3D analysis after electrolytic extraction was found to give a more precise characterisation of non‑metallic inclusions than the conventional 2D analysis by SEM‑EDS. In turn, better correlations to machinability and mechanical properties can be obtained. Hence, the use of this technique is beneficial for future material development.

Finally, the challenge for future metallurgy is to manufacture high‑performance steels with improved combined properties of mechanical strength and machinability.

This study focused on the evaluation of the machinability of different carburising steel grades by using a cemented carbide cutting tool during semi finishing of steel. The effect of the steel composition, microstructure and inclusion characteristics on the cutting tool wear in the soft part turning was evaluated for a reference steel R (0.028% S, 0.0009% O), a clean C steel (0.003% S, 0.0005% O), and an UC ultra clean steel (0.002% S, 0.0004% O). An improved cutting tool life of about 10-25% was obtained when machining the reference steel R. The favorable machining performance of this steel was attributed to its higher content of non-metallic inclusions, larger grain size and lower micro hardness than that of the clean steels.

This study describes the influence of the steel characteristics of Ca-treated carburising steel grades during hard part turning of synchronising rings in gearbox production. The main focus was on the chemical composition of the non-metallic inclusions in the evaluated workpieces and their effect on the PCBN tool wear. In addition, a Ca-treated carburising steel grade was compared to a standard steel grade.

Machining tests were performed at the transmission machining site at Scania in order to evaluate the PCBN cutting tool life as defined by the generated surface roughness during actual production. The progression of flank and crater wear was evaluated by using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS) and a secondary electron (SE) detector.

The Ca-treated steel showed a more than doubled tool life than that of the standard steel grade. The superior machinability was linked to the formation of a Ca-enriched slag barrier composed of (Mn,Ca)S and (Ca,Al)(O,S). It is believed that the stability of the protective deposits is essential to minimise diffusion-induced chemical wear of the PCBN tool. Furthermore, the improved machinability corresponds to a reduced tooling cost of 50% during an industrial production of transmission components at the site of Scania. Therefore, to implement the M-steel on a wider range of components would lead to a significantly reduced manufacturing cost per produced component. However, the capability of Ca-treated steels through the complete production route must be further investigated in order to allow for a large scale introduction of Ca-treated steels in the production.

In modern steelmaking, carburizing steels are often used for production of automotive components with elevated levels of toughness and fatigue strength. This study is focused on the link between the characteristics of non-metallic inclusions in the steel and the machinability of the given steel grades. For this purpose, inclusion characteristics (such as composition, number, size, morphology etc.) in steel samples were determined by common two-dimensional (2D) observations of inclusions on polished metal surface of samples as well as by three-dimensional (3D) investigations of inclusions after electrolytic extraction from steel samples. The inclusion characteristics were investigated in the three types of 20NiCrMo carburizing steel grades: Steel A ‑ reference steel (410ppm S) having a common level of mechanical properties and machinability, Steel B ‑ steel grade (having 340ppm S) with an improved machinability due to the Ca-treatment and modification of MnS inclusions and Steel C ‑ clean steel grade (40ppm S) having a small amount of inclusions and a higher fatigue strength. It was found that the number of inclusions in Steel B is smaller than that in Steel A and that the inclusion composition is different. At the same time, the estimated machinability (tool life) of the Ca‑treated steel was superior to that of the reference steel. However, the significant decrease of the number of inclusions in the clean steel (Steel C) resulted in a lower machinability in comparison to the reference steel grade.

Considerable research has been conducted over recent decades on the role of non-metallic inclusions and their link to the machinability of different steels. The present work reviews the mechanisms of steel fractures during different mechanical machining operations and the behavior of various non-metallic inclusions in a cutting zone. More specifically, the effects of composition, size, number and morphology of inclusions on machinability factors (such as cutting tool wear, power consumption, etc.) are discussed and summarized. Finally, some methods for modification of non-metallic inclusions in the liquid steel are considered to obtain a desired balance between mechanical properties and machinability of various steel grades.

Additive manufacturing (AM) is an attractive manufacturing technology in tooling applications. It provides unique opportunities to manufacture tools with complex shapes, containing inner channels for conformal cooling. In this investigation, H13, a widely used tool steel, was manufactured using a laser powder bed fusion method. Microstructure, tensile mechanical properties, hardness, and porosity of the AM H13 after stress relieve (SR), standard hardening and tempering (SR + HT), and hot isostatic pressing (SR + HIP + HT) were investigated. It was found that the microstructure of directly solidified colonies of prior austenite, which is typical for AM, disappeared after austenitizing at the hardening heat treatment. In specimens SR + HT and SR + HIP + HT, a microstructure similar to the conventional but finer was observed. Electron microscopy showed that SR and SR + HT specimens contained lack of fusion, and spherical gas porosity, which resulted in remarkable scatter in the observed elongation to break values. Application of HIP resulted in the highest strength values, higher than those observed for conventional H13 heat treated in the same way. The conclusion is that HIP promotes reduction of porosity and lack of fusion defects and can be efficiently used to improve the mechanical properties of AM H13 tool steel.

A high-alloy (Cr-Mo-V) cold-work tool steel was manufactured by laser powder-bed fusion (PBF-LB) without preheating and by electron-beam powder-bed fusion (PBF-EB) with the build temperature set at 850 degrees C. The solidification rates, cooling, and thermal cycles that the material was subjected to during manufacturing were different in the laser powder-bed fusion than electron-beam powder-bed fusion, which resulted in very different microstructures and properties. During the solidification of the PBF-LB steel, a cellular-dendritic structure was formed. The primary cell size was 0.28-0.32 mu m, corresponding to a solidification rate of 2.0-2.5 x 106 degrees C/s. No coarse primary carbides were observed in the microstructure. Further rapid cooling resulted in the formation of a martensitic microstructure with high amounts of retained austenite. The high-retained austenite explained the low hardness of 597 +/- 38 HV. Upon solidification of the PBF-EB tool steel, dendrites with well-developed secondary arms and a carbide network in the interdendritic space were formed. Secondary dendrite arm spacing was in the range of 1.49-3.10 mu m, which corresponds to solidification rates of 0.5-3.8 x 104 degrees C/s. Cooling after manufacturing resulted in the formation of a bainite needle-like microstructure within the dendrites with a final hardness of 701 +/- 17 HV. These findings provide a background for the selection of a manufacturing method and the development of the post-treatment of a steel to obtain a desirable final microstructure, which ensures that the final tool's performance is up to specification.

Denna rapport är ett examensarbete utfört på Ovako Bar AB i Smedjebacken, vilket är det avslutade momentet i utbildningen ”Materialteknik med inriktning metallurgi” på Bergsskolan i Filipstad.

Grunden till detta arbete ligger hos ”frysningar” (att stålet slutar rinna från gjutlådan) som företrädesvis sker på yttersträngarna. Igensättning av denna typ orsakas generellt av två faktorer, för låg övertemperatur i förhållande till likvidustemperatur eller otillräcklig förvärmning av gjutlåda samt gjutrör.

Syftet med detta arbete har varit att fokusera på förvärmningen, där målet var att utvärdera hur förvärmningstider ser ut i förhållande till de föreskrivna. Samt utvärdera prestandan hos värmningsutrustningen. Och utvärdera hur temperaturfördelningen ser ut i gjutlådan under gjutning.

Arbetet utfördes med hjälp av termoelement som monterades in i gjutlådan vid 1: a sträng och 3:e sträng för att kunna se hur temperaturfördelning är i gjutlådan. Mätningarna visade tydligt att temperaturen skiljde sig mellan yttersträng (1: a) och centrumsträng (3:e) vilket kan var en orsak till att frysningar sker företrädesvis på yttersträng där temperaturen visat sig vara lägre än centrumsträng.

Vid utvärdering av prestandan på värmningsutrustningen så användes en handpyrometer som möjliggjorde mätning av gjutrören för att ta fram en trendkurva, som visar när temperaturökningen avtar och upphör. Vilket visade brister i tid och prestanda i nuläget.

Med en fullt fungerande förvärmning skulle igensättningsgraden kunna minskas.

Advanced planning and automation are increasingly important in modern mines. Sophisticated methods for long-term mine planning are often used, and the advent of autonomous machines makes the actual operation more predictable. However, the interface between these two timescales, i.e. the scheduling of the mobile production fleet, often limits the ability to operate mines at maximum profitability. We show how scheduling the production fleet in an underground mine can be modelled as a flow shop. A flow shop is a general abstract process formulation that captures the key properties of a scheduling problem without going into specific details. Thus, the flow shop enables mine scheduling to reap the benefits of scheduling research from other industries. We review recent results from the mining community and the flow shop community, and introduce scheduling methods used in these two fields. This work aims at providing value to researchers from the mining community who want to leverage their skill set, as well as to theoretical researchers by presenting the mining process as a potential application area. Lastly, we discuss the results, and outline some future challenges and opportunities facing the industry.

The report reviews macro segregations in continuous cast steels and possible correlations to impact toughness. The purpose of the thesis is to investigate centreline segregates and V-segregates to see which of them that affect impact toughness the most. Apart from a literature study, Charpy-V data was collected with permission from SSAB for two steel types, grade A and grade B, each with respective dominant segregation type. The collected data was yielded in three individual Charpy-V tests at different spots on the metal sheet, derived within a close area. The average value of these tests were used in statistical analysis to observe the spread of values in different heats of the two steels. Additionally, the specimens were etched and captured in cross-section. Results indicated that for the data of grade A, where centreline segregates were dominant, the spread of values was higher than for the data of grade B. The conclusion is that centreline segregations are worse in relation to impact toughness, since higher deviations translates to less predictable properties from a customers perspective.

The solubility of vanadium oxide in the SiO2–CaO–VOX system was investigated as a function of basicity (CaO/SiO2) at a fixed temperature of 1600°C and oxygen partial pressure of 10−10 atm. Formed phases and microstructures of saturated samples were identified with SEM–EDS analysis and XRD. Maximum solubility of vanadium oxide was between 15 and 20% independent of basicity. Pure karelianite (V2O3) was formed in all samples at saturation of vanadium oxide. The morphology of karelianite changed with the change in basicity in the slag, where needles or threads were formed for slags with basicity B2 = 0.54 and B2 = 0.67 and stars or dendritic patterns were formed with basicity B2 = 1.0 and B2 = 1.22. Wollastonite (CaSiO3) was also formed in the slags with star or dendritic patterns.

Cyclic deformations of two ferritic, ductile cast irons, SiMo51 and SiMo1000, were studied in air and Ar using a new method, SRTC (stress relaxation with thermal cycling). Locked specimens were thermally cycled up to 800 °C with isothermal holds, varying temperature interval, heating/cooling rates and hold times. A description of the mechanical response to thermal cycling of a locked specimen is given.

The ferritic ductile cast iron, SiMo51, with graphite nodules and grain boundary carbides, was tested at 700°C with respect to creep, uniaxial strain and oxidation, investigating the internal damage evolution. Creep curves, with total lives of 65–339 days, show a short primary creep followed by predominantly tertiary creep displaying two stages. The first was associated with cavitation around carbides and nodules with a short initial effect from oxidation. The second was associated with the formation of cracks through linking of elongated voids. Misorientation maps demonstrate local dislocation activity during creep and tensile testing. Oxidation tests, between 15 min and 2 weeks, show that three oxide layers are formed and that an innermost precipitation zone of SiO2 is present in the initial stage. Elemental line scans, compared with thermodynamic calculations, suggest the layers are FeO with precipitates of SiO2 and/or Fe2SiO4, FeO without precipitates, and Fe2O3.

LKAB beslöt 2004 att starta en grundläggande studie som underlag för framtida expansion av anläggningarna i Malmberget. En del processer och produktionslinjer riskerade att bli flaskhalsar i framtiden. I den här rapporterade studien är det sovringsverket som undersökts och resultatet visade att flera enhetsoperationer kommer att vara begränsande med nuvarande maskinpark. Därför var ett syfte med studien att undersöka hur byte av maskiner skulle påverka kapacitet och drift samt om de framtida produktionsplanerna kunde innehållas. Sovringsprocessen har genomgående simulerats med ModsimTM för ett antal olika fall, som har skilt sig åt i järnhalt och partikelstorleksfördelningar hos ingående malm. Modelleringsparametrarna har hämtats, till en del från existerande undersökningar i pilotskala, men i största möjliga utsträckning från mätningar i existerande kretsar. Simuleringarna visade att installation av nya siktar skulle ge en väsentligt förbättrad drift, men också att nya krossar skulle vara en förbättring eftersom de skulle kunna köras fullmatade med snävare ansättning, vilket skulle ge process-tekniska fördelar. Under 2007 har de flesta av de föreslagna åtgärderna genomförts och resultatet visar att flaskhalsarna är borta och att halter och massbalanser är till och med bättre än vad som förutsågs i simuleringarna.

The demand for new and improved materials for the energy sector is rising as more efficient power plants needs to be built to meet the challenges of tomorrow. However, at the moment more expensive Ni-based alloys will be used to meet the requirements for the next generation of power plants, Advanced Ultra-Supercritical (A-USC). Therefore, a more economical Heat Resistant Material(HRM) candidate has to be developed, which will fulfill the requirements of exhibiting a minimum creep rupture strength of 100MPa at 700°C for 100 000h. One such candidate is austenitic stainless steels.

In this study, the microstructural stability of long-term aged and creep tested austenitic stainless steels is investigated. Nine austenitic stainless steels with different chemical compositions have been creep tested until failure at temperatures ranging from 600°C to 800°C for a duration of up to 30 years. Microstructural characterization of undeformed (aged) and deformed (crept) regions of the creep tested specimens was carried out using Light Optical Microscopy (LOM) and Field Emission Scanning Electron Microscope (FEG- SEM) equipped with Energy Dispersive X-ray Spectroscopy (EDS) and Electron Backscatter Diffraction (EBSD) techniques. In addition, prediction and quantification of stable phases were simulated with Thermo-Calc and TC-PRISMA.

The experimental observations were focused on the influence of several parameters such as alloying elements, temperature and deformation on the microstructural developments in aged and crept regions. The results clearly showed that the high Ni containing alloys are very stable at high temperatures. However, low Ni alloys can undergo a martensitic transformation at high temperature due to an unstable austenitic structure caused by Cr depletion.

In addition, a clear correlation between the test temperature and the Cr2N precipitation has been noted. Above 700°C, Cr2N is the dominant precipitate and below 700°C, sigma phase is the most prominently observed phase. It is also noted that the precipitation of phases and the volume fraction of these phases increase with deformation, as new sites for nucleation form.

Moreover, dynamic recrystallization (DRX) have also been observed in some crept specimens. The comparison between experimental results from EBSD phase mapping and thermodynam- ical simulations, reveals that the Thermo-Calc gives sufficient indication on the precipitation of possible stable phases at equilibrium. However, phases such as Cr2N and G-phase/η- nitrides(M6C) are not predicted. Furthermore, estimations of the volume fractions are not correctly predicted, as these are either over- or underestimated.

This study explores the possibility of utilizing a recirculated autogenous H-DRI slag for dephosphorization, to evaluate a possibly more sustainable slag practice. For a recirculated slag to be usable, the phosphorus content must be low to ensure a proper dephosphorization. Therefore, the possibility relies on removing enough phosphorus from the slag. Correspondingly, the phosphorus partition (L_p ) between slag and metal was evaluated experimentally at different fixed oxygen partial pressures. Slag and metal, with a 1:1 mass ratio, were equilibrated for different durations, between 4 to 24 hours, in magnesia crucibles at 1873 K. The oxygen partial pressure was fixed between 3.05·10^-15 and 3.12·10^-13 atm using the 𝐶(𝐹𝑒)+1/2O_{2 (𝑔)} → 𝐶𝑂_(𝑔)  equilibrium, by adding carbon to the metal and utilizing a CO atmosphere. The resulting 𝐿_𝑃 values varied between 0.24 and 0.90. The possibility of slag recirculation is discussed based on the experimental results and mass balance calculations. The present results suggest that a future upgrading process could make a recirculation practice possible. Furthermore, the feasibility of such a practice is discussed.

Based on 100% pellets operation at BF No. 3 at SSAB Tunnplåt in Luleå a new pellet with CaO/SiO2=1 was developed during early nineties. The pellet showed good results in metallurgical laboratory test but caused slag formation problems in the bosh. A high basicity slag was formed during interaction with basic fluxes and its melting point was increased when the slag was finally reduced. By injection of basic fluxes, the slag formation problems in the bosh can be avoided. Without a sinter plant, dusts have to be recycled in a cold bonded briquette. Injection of some of BF flue dust would improve the properties of the briquette and may be beneficial for the BF process. Based on top charging or tuyere-injection of basic fluxes and the injection of BF flue dust studies have been done. The studies carried out will clarify some phenomena of slag formation and the effect of co- injection on coal combustion in the blast furnace, including the effect of: 1) basic fluxes on slag formation in the blast furnace, if they are top- charged; 2) basic fluxes on slag formation in the blast furnace, if they are tuyere injected; 3) chemical composition and metallurgical properties of pellet and fluxes on slag formation; 4) reduction conditions on (reduction temperature, reducing gas composition) on bosh slag formation; 5 co- injection of BOF slag or BF flue dust on coal combustion efficiency and BF performance. From the results, it can be concluded that the interaction between pellets and fluxes starts when softening and melting starts in the cohesive layer. By choosing fluxes of a high melting point the dissolution of them in the bosh slag can be delayed and the excessive basicity of the bosh slag can be limited. A basic flux with a low melting point will easily dissolve into the bosh slag causing its basicity to increase, which is beneficial to S refining when acid pellets are used. The formation of a bosh slag of excessive basicity (which causes BF operation disturbances, because its high melting point, increases further during reduction) can be avoided by tuyere injection of basic fluxes with the coal. The positive effect is greatest when a fluxed pellet of basicity B21 and with a high Fe content is used as ferrous burden. In this case, the slag amount can be significantly decreased. BOF slag has suitable high-temperature properties for use as a basic flux in combination with e.g., olivine pellets. It has a low softening and melting temperature, does not shrink, is slowly reduced in the BF shaft and its properties are almost unaffected by the partial reduction occurring in the shaft of the BF. BOF slag absorbs a low content of alkalies, which causes volume increase at elevated temperatures, when the basicity is still high. The results indicate that co-injection of BOF slag or BF flue dust with PC has positive effects on the BF operation. The injection of BOF slag decreases the Si content in HM by an increased basicity of the slag formed during combustion leading to a decreased activity of SiO2 in the slag and by an increased FeO content in the tuyere slag that will be reduced by SiFe in the metal at the tuyere level, if the SiFe is initially high. The consumption of reducing agents can be reduced because of a decreased Si content in HM and a decreased slag amount. The permeability is improved by prohibiting the formation of a shell at the raceway end because of improved melting properties of tuyere slag caused by an increased basicity and FeO content, consumption of coal and coke fines by FeO and improved radial transport of tuyere slag. The injection of BOF slag improves the bosh slag because an excessive basicity caused by top-charged fluxes added for neutralisation of coal and coke ashes and non-uniform slag formation caused by uneven distribution of top-charged fluxes are avoided. The productivity increases because of the possibility to decrease the slag amount. The injection of BOF slag can be done without negative effects on combustion efficiency by using very finely ground BOF slag and because of improved total consumption of coal and coke fines by direct reduction in the coke bed. The injection of BF flue dust decreases the Si content in HM by an increased FeO content of the tuyere slag that will be reduced by SiFe in the metal at the tuyere level, if the SiFe is initially high. The consumption of coal and coke is decreased because of a high of C content in BF flue dust and the decreased Si content in HM. The permeability is improved by prohibiting the formation of a shell at the raceway end because of consumption of coal and coke fines by FeO and improved melting properties of tuyere slag promoting the radial transport of the tuyere slag. The injection of BF flue dust can be done without negative effects on the total consumption of coal and coke fines by direct reduction in the coke bed. Injected BF flue dust supplies oxygen for combustion, but because of endothermic reactions as reduction of hematite and calcination of limestone occurring in the BF flue dust at the same temperatures as release and disintegration of VM, it will have a negative effect on the combustion of HV coal. SSAB Luleå and SSAB Oxelösund have started up projects aiming to make tuyere- injection of BF flue dust part of the standard BF operation.

Slag formation in the bosh and raceway is an important issue in the blast furnace process. SSAB works in Lulea operate with 100 % olivine pellets. A small amount of basic fluxes is added from the top, slag and limestone are used. To improve the control of slag formation, a concept with injection of BOF slag was evaluated and tested in the LKAB etxperimental blast furnace (EBF). In this paper, the behaviour of BOF slag as a slag former, when it is top-charged or tuyere-injected, is evaluated based on the results from a laboratory study including reduction tests, softening and melting tests, XRD analyses and SEM analyses. Samples taken from the EBF during excavation, and with a burden probe during operation, are examined. The evaluations show that the melting point of BOF slag is quite low and will not be increased, because of the partial reduction that occurs in the BF shaft. When carbon is present at high temperatures, reduction proceeds and a high basicity slag with a high melting point, consisting of di- and tricalcium silicates, is formed. When pellets with a basicity of B2 - 1 are used, a slag with similar properties can be formed as a result of interaction with the BOF slag. BOF slag in combination with olivine pellets with a low basicity generates a slag with intermediate basicity and the reduction of iron oxides in the slag has a small effect on the melting temperature. The BOF slag decreases the melting point of coal and coke ashes.

This work is based on experiences from industrial blast furnaces. Process irregularities when testing self-fluxed pellets Process disturbances when charging increased proportions of coarse pellets Laboratory tests to evaluate the effect of basic fluxes on the slag formation in the bosh and in the raceway have been carried out. Pilot scale tests have been performed to verify the effect of coarse pellets. The effect of reduction degree and the reduction behaviour on the slag formation and blast furnace performance have been evaluated It was found that decreased degree of reduction of pellets or lowly reduced core of coarse pellets decrease the melting temperature and increase the softening and melting temperature interval. Basic fluxes have a negative effect on the melting properties of the self-fluxed pellets and a positive effect on the melting properties of the olivine pellets. Basic fluxes have a positive effect on the melting properties of tuyere slags.

Injection into a BF of BOF slag to improve the slag formation and of BF flue dust to improve the recycling of in-plant fines has previously been tested. The effects on the PC combustion efficiency at different conditions, when these materials are co-injected with coal, have so far not been tested. Combustion efficiencies at varied temperature, O2 enrichment, amount of PC, amount of added BOF slag or BF flue dust and particle size of the added material are measured in a fixed bed and a blowpipe model. The established facts that an increased temperature and O2 enrichment or a decreased amount of coal increase the combustion efficiency are valid also when BOF slag or BF flue dust are added to the coal. By adjusting the combustion conditions, a decreased combustion efficiency can be counteracted, when a second material is co-injected with coal. The effect of BOF slag addition on coal combustion efficiency measured in the blowpipe model is in-significant, if a fine fraction is used. The combustion efficiency is higher in the fixed bed compared with that in the blowpipe model. The addition of BF flue dust increases the combustion efficiency in the fixed bed

22Cr-5Ni duplex stainless steel (DSS) was aged at 748 K (475 A degrees C) and the microstructure development correlated to changes in mechanical properties and fracture behavior. Tensile testing of aged microstructures confirmed the occurrence of 748 K (475 A degrees C) embrittlement, which was accompanied by an increase of strength and hardness and loss of toughness. Aging caused spinodal decomposition of the ferrite phase, consisting of Cr-enriched alpha aEuro(3) and Fe-rich alpha' and the formation of a large number of R-phase precipitates, with sizes between 50 and 400 nm. Fracture surface analyses revealed a gradual change of the fracture mode from ductile to brittle delamination fracture, associated with slip incompatibility between ferrite and austenite. Ferrite became highly brittle after 255 hours of aging, mainly due to the presence of precipitates, while austenite was ductile and accommodated most plastic strain. The fracture mechanism as a function of 748 K (475 A degrees C) embrittlement is discussed in light of microstructure development.

The effect of 475 degrees C embrittlement on microstructure development of grade 2205 duplex stainless steel was investigated. Spinodal decomposition products and associated precipitates in ferrite, austenite, and at interphase boundaries were characterized using analytical transmission electron microscopy (TEM) and scanning electron microscopy (SEM) techniques. Microanalyses confirmed the presence of Cr-enriched alpha'' and Cr-depleted alpha' spinodal structures in the ferrite after 5 h of aging at 475 degrees C. Long-term aging for 255 h resulted in heavily-faulted R-phase precipitates with sizes of similar to 50-400 nm, chi-phase, and epsilon-Cu in the ferrite, TiN and Cr2N precipitates in the austenite, and a continuous network of M23C6-carbides at interphase boundaries. A significant hardness increase was observed after 255 h of aging, which was accompanied by a reduction of ferrite fraction. X-ray diffraction (XRD) stress measurements showed a general reduction of residual stresses in both ferrite and austenite with aging. Electron backscatter diffraction (EBSD) showed increased local misorientations, primarily close to precipitate interfaces within the ferrite, indicating the development of strain heterogeneities in the microstructure. The data presented provided a better understanding of 475 degrees C embrittlement in duplex stainless steel, suggesting that not only the ferrite alone is responsible for embrittlement. A comprehensive microstructure characterization study has been provided and the explanation for 475 degrees C embrittlement of duplex stainless steel has been discussed.

We report the evolution of metastable precursor structures during hydrogen infusion in the near-surface region of a super duplex stainless steel. Grazing-incidence x-ray diffraction was employed to monitor, operando, the lattice degradation of the austenite and ferrite phases. Electrochemical hydrogen charging resulted in the splitting of the diffraction peaks of the austenite phase, suggesting the evolution of a metastable precursor structure. This may be explained by the formation of quasi-hydrides, which convert back into the austenite parent structure during hydrogen effusion. The ferrite showed less lattice deformation than the austenite and no phase transformation.

Grazing-incidence x-ray diffraction was employed to measure, operando, during electrochemical hydrogen charging, the lattice strain development of the near-surface in super duplex stainless steel under applied tensile load. Hydrogen absorption led to the formation of tensile strains in both the austenite (gamma) and ferrite (delta) phases perpendicular to the loading axis, whereas compressive strains were formed in the ferrite phase parallel to the loading direction, despite the acting tensile load. The earliest stages of degradation are discussed in light of understanding hydrogen embrittlement. 

Corrosion rates of strained grade UNS S32202 (2202) and UNS S32205 (2205) duplex stainless steel wires have been measured, in situ, using time-lapse X-ray computed tomography. Exposures to chloride-containing (MgCl2) atmospheric environments at 50 degrees C (12-15 M Cl(-)and pH similar to 5) with different mechanical elastic and elastic/plastic loads were carried out over a period of 21 months. The corrosion rates for grade 2202 increased over time, showing selective dissolution with shallow corrosion sites, coalescing along the surface of the wire. Corrosion rates of grade 2205 decreased over time, showing both selective and pitting corrosion with more localised attack, growing preferentially in depth. The nucleation of stress corrosion cracking was observed in both wires. Stainless steel: Comprehending corrosion The corrosion of two grades of stainless steel has been studied, in situ, under atmospheric exposure conditions. Grade '2205' duplex stainless steel (DSS) has been suggested as a possible container material for the storage of intermediate-level radioactive nuclear waste in the UK because of its high resistance to corrosion and stress corrosion cracking (SCC). Now a team led by D. Engelberg from The University of Manchester, United Kingdom, have used time-lapse X-ray computed tomography to determine the corrosion rates of strained grade '2202' and '2205' DSS wires-over the course of 21 months-that had been exposed to a chloride-containing thin-film electrolyte. They saw that although the corrosion rate of grade 2202 DSS wires increased with time, the corrosion rate for grade 2205 decreased, confirming its superior corrosion resistance. They also observed the nucleation of SCC cracks in both grades of wire and demonstrated that duplex stainless steels can suffer from low-temperature SCC.

The characterisation of passive oxide films on heterogeneous microstructures is needed to assess local degradation (corrosion, cracking) in aggressive environments. The Volta potential is a surface-sensitive parameter which can be used to assess the surface nobility and hence passive films. In this work, it is shown that the Volta potential, measured on super duplex stainless steel by scanning Kelvin probe force microscopy, correlates with the electrochemical properties of the passive film, measured by electrochemical impedance spectroscopy and potentiodynamic polarisation. Natural oxidation by ageing in ambient air as well as artificial oxidation by immersion in concentrated nitric acid improved the nobility, both reflected by increased Volta potentials and electrochemical parameters. Passivation was associated with vanishing of the inherent Volta potential difference between the ferrite and austenite, thereby reducing the galvanic coupling and hence improving the corrosion resistance of the material. Hydrogen-passive film interactions, triggered by cathodic polarisation, however, largely increased the Volta potential difference between the phases, resulting in loss of electrochemical nobility, with the ferrite being more affected than the austenite. A correlative approach of using the Volta potential in conjunction with electrochemical data has been introduced to characterise the nobility of passive films in global and local scale.

Various mechanisms have been proposed for hydrogen embrittlement of duplex stainless steel, but the causation of hydrogen-induced material degradation has remained unclear. This work shows that phase instability (decomposition) of the austenite phase and ductile-to-brittle transition of the ferrite phase precedes hydrogen embrittlement. In-situ diffraction measurements revealed that Ni-rich sites of the austenite phase decompose into metastable hydrides. Hydride formation is possible by increasing the hydrogen chemical potential during electrochemical charging and low defect formation energy of hydrogen interstitials. Our findings demonstrate that hydrogen embrittlement can only be understood if measured in situ and in real-time during the embrittlement process.

The effects of austenite spacing, hydrogen charging, and applied tensile strain on the local Volta potential evolution and micro-deformation behaviour of grade 2507 (UNS 532750) super duplex stainless steel were studied. A novel in-situ methodological approach using Digital Image Correlation (DIC) and Scanning Kelvin Probe Force Microscopy (SKPFM) was employed. The microstructure with small austenite spacing showed load partitioning of tensile micro-strains to the austenite during elastic loading, with the ferrite then taking up most tensile strain at large plastic deformation. The opposite trend was seen when the microstructure was pre-charged with hydrogen, with more intense strain localisation formed due to local hydrogen hardening. The hydrogen-charged microstructure with large austenite spacing showed a contrasting micro-mechanical response, resulting in heterogeneous strain localisation with high strain intensities in both phases in the elastic regime. The austenite was hydrogen-hardened, whereas the ferrite became more strain-hardened. SKPFM measured Volta potentials revealed the development of local cathodic sites in the ferrite associated with hydrogen damage (blister), with anodic sites related to trapped hydrogen and/or micro voids in the microstructure with small austenite spacing. Discrete cathodic sites with large Volta potential variations across the ferrite were seen in the coarse-grained microstructure, indicating enhanced susceptibility to micro-galvanic activity. Microstructures with large austenite spacing were more susceptible to hydrogen embrittlement, related to the development of tensile strains in the ferrite.

The RheoMetal process, previously also called the Rapid Slurry Forming process (“Rapid S”) or RSF process, is a novel method to produce high quality, cost effective, semi-solid magnesium slurries for component casting. The RheoMetal process uses an Enthalpy Exchange Material (EEM) as internal cooling to produce the slurry. Typical critical process parameters in the RheoMetal process are alloy content, stirring speed, superheat and EEM to melt ratio. In this study the effects of EEM to melt ratio and superheat on the slurry characteristics was examined for binary Mg-Al alloys in the range 5.8 - 11.2 wt % Al. Samples were quenched after slurry preparation and the microstructure was studied with respect to solid fraction and a-Al grain diameter. The solid fraction increased with an increasing EEM to melt ratio for all Al-contents investigated. Further, it was found that the solid fraction as well as the grain diameter decreased with increasing aluminium content (at constant EEM to weight ratio).

Background: In the microscopic observation of deforming metals, it is well known that crystallite defects that accommodate strain can occasionally become visible, namely, they introduce image contrast to their locality. For microscopic digital image correlation (DIC) applications, this is typically known as a disturbance. Objective: Here, we explore a potential upside of these image-intensity offsets, to present a new mode of differential imaging that exclusively displays the underlying plasticity agents. Methods: For this, the intensity-offset signal is isolated with residual intensity, essentially the differential between reference- and deformed-configuration intensity of each material point. The premise is showcased over an autocatalytic twin band in Magnesium AZ31, with an advanced DIC instrument that utilizes bright-field optical microscopy. With robust area-scanning that utilizes in-situ corrective measures, a material field of around 5000 grains (13 μm average size) is sampled with a maximal intragranular resolution (~250 data points per grain) for this technique. For added robustness against the intensity alterations, a DIC algorithm (Augmented Lagrangian DIC) that enforces global kinematic compatibility constraints is utilized. Results: The calculated residual intensity map yields a detailed image of the twin networks that show a strong positional alignment with the strain localizations. At the band boundary, the twins (and their accompanying strain localization) protrude into the dormant material in a comb-like pattern. Conclusions: With a combination of high-resolution optics and defects that alter the surface topography, residual intensity presents a new in-situ microscopy mode that is tied to the DIC analysis. This principle also offers potential micro-deformation imaging capabilities for various other material-microscopy combinations.