Sanicro 25 is a newly developed austenitic stainless steel, designed for the next generation of Ultrasupercritical coal-fired boilers in electrical power plants. This material is applicable in reheater and superheater tubes, where the material temperature is up to 700 °C. One of the main strengthening mechanisms in high temperature materials is solid solution strengthening. A combination of this mechanism and precipitation hardening, promotes creep strength of heat resistance materials. The aim of this work was to characterize the effects of solid solution strengthening on creep strength of Sanicro 25.Previous works has been done for effects of phosphorous in copper and also for influence of laves phase on the creep properties of CrMo alloys. The results of these two works are used and the model is adapted to austenitic stainless steel. First a Zero starting state was defined which was Alloy 316H and then the calculation was made for Sanicro 25. Thermodynamic calculations were made using DICTRA and Thermo-Calc. Elastic misfit parameter was determined using ab initio calculations. The results from the simulation in this work indicate that solutes with larger size misfit compare to the parent atoms have better solid solution strengthening effect. A decrease in the creep strength by increasing temperature has been observed which could be attributed to growth of laves phase.

The research presented in this thesis investigated the mechanisms by which cavitation erosion damage develops in lamellar graphite iron (LGI) and austempered ductile irons (ADIs). This has been achieved by image sequences of surface erosion on test samples in tandem with weight change measurements. Cavitation erosion is caused by the appearance and collapse of bubbles in a liquid which undergoes rapid pressure oscillations. Imploding bubbles release heat, shockwaves and high-speed microjets which may strike nearby solid walls and damage them. The heavy-duty automotive industry encounters this problem in the engine cooling system. The combustion chamber requires precise temperature control for optimal operation and excess heat must be removed by a liquid coolant. In trucks, the coolant liquid achieves this by circulating around the cylinder liner, a hollow cylindrical part that encloses the combustion chamber and prevents its gases from escaping. However, the engine’s intense vibrations create repeated pressure variations in the coolant, and bubbling ensues. With prolonged operation, the cylinder liner’s wet outer wall may be severely worn, resulting in surface roughening, eroded patches and pits. Cavitation is responsible for great losses due to vehicle downtime and maintenance costs. The present work aims, therefore, at analyzing the behavior under cavitation exposure of cast irons that are currently used, or being considered for use, in the cooling system. Cylinder liners are currently made of lamellar graphite iron with a matrix structure consisting of pearlite and a network of steadite, and the analysis for this material has been presented in Paper 1. Austempered ductile irons are candidate materials for pumps and other components of the cooling system due to their very good mechanical properties; three ADIs of increasing hardness, obtained from different heat treatments of a spheroidal graphite iron, have been analyzed in Paper 2. Experiments consisted of an ultrasonic vibratory probe to which material samples were attached and subsequently immersed in a beaker containing engine coolant. The samples were weighed and photographed in an SEM after several predetermined time intervals. This produced a detailed sequence of images which, in combination with mass loss data, can explain the mechanisms by which cavitation damage initiates and develops in these materials. The text of this thesis summarizes the findings presented in the appended articles and compares the behavior of LGI and ADI. / Forskningen som presenteras i denna avhandling undersöker kavitationsmekanismerna och uppkomsten av kavitationsskador i gjutjärn med fjällgrafit (LGI) och i ausferritiskt segjärn (ADI). Detta har gjorts med sekventiell fotografering av yterosionen på prover samtidigt som viktsförlusten har registre- rats. Kavitationserosion uppstår genom bildning och kollaps av bubblor i en vätska som utsätts för snabba tryckoscillationer. Imploderande bubblor frigör värme, chockvågor och höghastighets- mikrojetstrålar som kan träffa närliggande fasta ytor och skada dessa. Den tunga fordonsindustrin stöter på detta problem bland annat i motorernas kylsystem. Förbränningsrummet fordrar noggrann temperaturkontroll för optimal förbränning och måste kylas av en kylvätska. I lastbilar cirkuleras kylmedlet runt cylinderfodret, en ihålig, cylindrisk komponent som omsluter förbränningskammaren och som hindrar gaser från att lämna systemet. På grund av motorns intensiva vibrationer bildas återkommande tryckvariationer i kylvätskan med uppkomst av bubblor. Efter lång tid i drift kan cylinderfodrets våta utsida bli allvarligt eroderad med ökad ytråhet och med bildande av erosionmönster och erosionsgropar. Kavitation är förknippad med stora förluster pga stillestånd och underhållskostnader. Målet med detta arbete är därför att analysera hur nuvarande, och kandiderande gjutjärn för kylsystem, beter sig under kavitationsexponering. Cylinderfoder görs för närvarande av lamellärt gjutjärn med en matrisstruktur av perlit och ett nätverk av steadit, och en analys av detta material presenteras i artikel 1. Ausferritiska segjärn är kandidatmaterial för pumpar och andra komponenter i kylsystemet pga sina goda mekaniska egenskaper. Tre ausferritiska segjärn med sfärisk grafit och successivt ökande hårdhet, från tre olika värmebehandlingar av samma segjärnsbatch analyseras i artikel 2. Experimenten bestod av ett ultraljudshorn till vilket prover fästes och därefter sänktes ner i en bägare med kylvätska. Proven vägdes och fotograferades i SEM enligt förutbestämda tidsintervall. Detta resulterade i en detaljerad sekvens med bilder som, i kombination med viktsförlusten, kan förklara mekanismerna för initiering och utveckling av kavitationsskador i nämnda material. Avhandlingen summerar fynden som presenteras i de bifogade artiklarna och jämför beteendena mellan LGI och ADI. / <p>QC 20211108</p>

No description available.

The necessity to improve the durability of the machinery used in the milling industry has lead to several types of research. One study is focused on the plates that are located in the stationary and moving jaws of crushers to diminish particles sizes of Gneiss and Diabase rocks. Thus, one type of approach to increase its durability is by reducing the material loss of the plates. Amongst all the parameters to reduce the wear ratio that includes inputs from geometry to load, just the hardness input of the material can be in constant development. Consequently, there are two well-known types of heat treatment that can produce this change in hardness and are named Carbide Free Bainite (CFB) and Quenching and Partitioning (QP). In this master thesis the topic is to perform the QP heat treatments for two compositions A and B to obtain the microstructure of the steels that consist in a mix of austenite, bainite and martensite which considerably increase the hardness while the toughness is not drastically reduced due to the austenite soft phase. Five samples have been studied at four different partitioning temperatures: QP250 A, QP180 B, QP210 B, QP240 B and Mn Steel as it is the composition most used nowadays in the industry. In order to characterise both mechanical properties and microstructural features, different analysis had been performed with Micro-indentations, Charpy-V, Gouging Abrasion Tests, Optical Microscopy, Scanning Electron Microscopy and X-Ray Diffraction. These analysis had been done in the samples before and after wear as a result in change of the microstructure. As the abrasive-impact of the rocks collide with the sample, austenite transforms to martensite by induced plasticity called TRIP effect. Thus, the surface of the alloy is harder than the bulk material as no austenite is found and the wear ratio is seen to be improved. The results have shown several behaviours. Austenite transforms in its majority to fresh martensite which is an unstable martensitic phase but harder than tempered martensite that is the stable martensitic phase. Moreover, the difference in hardness between the bulk and the surface produce an affected depth layer as a consequence of the abrasive-impact penetration of rocks in which the microstructure has fully transformed to martensite on the surface and the austenite phase increases as it goes further inside the steel. The thinner this layer is, the better wear ratio presents the alloy. From all the samples, the best combination of hardness and toughness is for QP210 B.

No description available.

The increased copper price during the first world war forced the Swedish master founder OttoMeyer to invent a new alloy in order to continue casting artworks at a reasonable cost. The recipe of the alloy was a secret that Meyer kept to himself even unto death. The name of the alloy became Fritzi, but the number of objects cast in this alloy was never published.However, among the art pieces is G. Lindberg’s statuette “Vågen”. In this project, the composition of Fritzi was determined using SEM and EDS analysis on a sample from “Vågen”, and some thermodynamic, physical, and casting properties were evaluated usingsimulations and calculations. In addition to this, a 3D-replica of “Vågen” was created. / Det ökade kopparpriset under första världskriget tvingade gjutmästaren Otto Meyer attuppfinna en ny legering för att kunna fortsätta driva sitt konstgjuteri. Legeringen fick namnet Fritzi och blev tillverkad i ett okänt antal föremål. Receptet skrevs aldrig ned och fick följa med sin skapare ned i graven. Bland konstverken som göts i Fritzi finns G. Lindbergs statyett “Vågen”, från vilken prover har tagits i analyssyfte. Som en del av projektet har sammansättningen av Fritzi bestämts med SEM- och EDS-analys och några termodynamiska, fysikaliska och gjuttekniska egenskaper har bestämts genom simuleringar och beräkningar.Utöver detta har en 3D-replik av “Vågen” tillverkats.

This project that has been executed in collaboration with Saab aerostructures deals with how three materials, aluminum, titanium and corrosion resistant steel react when they are affected by different energy levels. These energy levels serve the purpose of representing damages that can happen in storage and handling to components used in production. A literature study was made to gather information regarding the treated materials as well as some methods that can be used to test a materials property. The goal of the project is to create a tool for Saab to use in their production in order to first estimate the energy levels that created a mark on a material and secondly evaluate if a crack can be suspected, by consequence evaluate if a NDT (non-destructive test) is required. The experiment was executed as such that all of the materials were put through drop-tests simulating different energy levels, with two different strikers, blunt and sharp, and then the materials were examined. Non-destructive testing was made on all of the marks made on the different materials using penetrant- or eddy current-method to see if there were any cracks formed in the material after impact. The experiment did not show signs of any cracks from the tested energy levels. However, it showed that crack propagation is highly dependent on the shape of the striker. To make the experiment more reliable and give a better result more energy levels would have needed to be tested. Also, a large number of different strikers and more non-destructive testing methods would have to be used. / Detta projekt som har utförts i samarbete med Saab aerostructures behandlar hur tre material, aluminium, titan och rostfritt stål reagerar när de blir utsatta för olika energinivåer. Dessa energinivåer ska simulera skador som kan uppkomma under hantering och förvaring av komponenter i Saabs produktion. En litteraturstudie har utförts för att samla information om materialen samt om några testmetoder som kan användas för att utvärdera ett materials egenskaper. Målet med projektet är att få fram ett tillvägagångssätt för Saab att i första hand uppskatta energinivåerna bakom ett slagmärke i ett material, därefter bedöma ifall en sprickinitiering kan misstänkas och därmed avgöra huruvida komponenter som utsatts för energinivåer behöver undergå oförstörande provning eller om de kan fortsätta användas i produktionen utan någon form av testning. Ett experiment utfördes genom att utsätta samtliga av materialen för dropp-tester med olika energinivåer med två olika slagdon, trubbigt och spetsigt, för att sedan kunna undersöka om sprickor hade propagerats. Oförstörande provning gjordes på alla simulerade skador antingen via penetrantmetoden eller virvelströmsprovning, för att se om det bildats sprickor i de olika materialen efter slaget. Experimentet visade inte på några sprickor vid de testade energinivåerna. Däremot såg man att sprickinitiering beror bland annat på slagdonets utformning, där en skarpare form ökade risken för sprickor. För att experimentet ska bli mer pålitligt och ge ett bättre resultat hade fler energinivåer behövt testas, en större variation av slagdon hade behövt användas samt att man hade behövt använda fler typer av oförstörande provning.

During the time we live in, climate change is more important than ever. HYBRIT, formed bySSAB, LKAB, and Vattenfall, is an initiative set out to make the steel production fossil free, by developing a novel process that produce direct reduced iron (DRI) using hydrogen as reagent. Electric arc furnaces (EAF) will then be employed to melt the DRI. For SSAB, it is important to obtain a satisfied dephosphorisation in the EAFs for the production of high strength steel. The composition of the DRI, has a big impact on the dephosphorisation and it is important that the slag has an optimal basicity and FeO content. To better understand the impact that FeO has on dephosphorisation, experimental data has to be collected and the FeO activity calculated in different slag systems. Activity measurements of FeO is rather complex. In this thesis, three methods were looked at: experimental determination, electrochemical methods and equilibrating the slag. Equilibrating the slag turned out to be the best suitable method forcalculating the FeO activity and is recommended to be evaluated further. / I den tid vi lever i nu är frågan om klimatförändringarna viktigare än någonsin. HYBRIT, bildatav SSAB, LKAB och Vattenfall, är ett initiativ som syftar till att göra stålproduktionen fossilfri genom att utveckla en ny process som producerar direkt reducerat järn (DRI) med väte som reagens. Elektriska bågugnar (EAF) kommer sedan att användas för att smälta DRI. För SSAB är det viktigt att få en bra fosforrening i EAF:erna för produktion av höghållfast stål. DRI:s sammansättning har stor inverkan på fosforreningen och det är viktigt att slaggen har en optimal basicitet och FeO-innehåll. För att bättre förstå vilken inverkan FeO har på fosforreningen måste experimentella data samlas in och FeO-aktiviteten beräknas i olika slaggsystem. Aktivitetsmätningar av FeO är ganska komplicerade. I denna avhandling undersöktes tre metoder: experimentell bestämning, elektrokemiska metoder och jämvikt av slaggen. Jämvikt av slaggen visade sig vara den mest lämpliga metoden för beräkning av FeO-aktiviteten och rekommenderas att utvärderas ytterligare.

Abstract Hot ductility during continuous casting of duplex stainless steels In the continuous casting of the duplex stainless steel, longitudinal corner cracks in the first casted bloom of SAF 2507 have been discovered by Sandvik. SAF 2205 contains the same alloying substances as SAF 2507, but with some difference in the concentration of the elements. Despite this similarity, the occurrence of corner cracks in SAF 2205 is minimal and thus is not considered to be a significant problem. The reason for the appearance of hot cracks in SAF 2507 may be due to reduced ductility and due to stress variations in the material that occurs during casting. An earlier research for mapping longitudinal corner cracks in SAF 2507 and SAF 2205 proved to occur due to thermal stresses created by shrinkage of the shell in the mold. A reduced ductility can be obtained by embrittlement of grain boundaries that may arise with a brittle phase. The high amount of alloy elements in duplex stainless steels can result in precipitation of intermetallic phase, which is a brittle phase. Through a mapping of microstructure of continuous casted SAF 2507 and SAF 2205, intermetallic phase was observed in samples from SAF 2507.In order to gain an understanding of the appearance of hot cracks in SAF 2507, in situ hot tensile tests were performed. The hot tensile tests were performed in order to compare and analyze the ductile behavior of SAF 2507 with SAF 2205. The purpose of the tensile tests was to simulate continuous casting process at Sandvik.The results from the tensile tests show that SAF 2507 and SAF 2205 are not sensitive to hot cracking at temperatures near solidus. However, intermetallic phases were found in SAF 2507 during hot tensile testing at 800 ° C. But no intermetallic phase could be found in SAF 2205. Temperature measurements and calculations by CFD during continuously casting of SAF 2507 showed that intermetallic phases could possibly precipitate in the mold. In a previous research done by Sandvik Materials Technology, shows how thermal stresses can occur on the corners of a cast inside the mold, during continuous casting of SAF 2205 and SAF 2507.The conclusion of this work is that longitudinal corner crackers in SAF 2507 can be initiated in the mold, because of a combination of thermal stresses and intermetallic phases. Keywords ∙ Duplex rostfritt stål ∙ Varmsprickkänslighet ∙ SAF 2507 ∙ SAF 2205 ∙ Stränggjutning ∙ Duktilitet ∙ Sigma ∙ Kromnitrider ∙

The fundamental aspects of rising argon bubbles in molten metal flow were investigated by numerical simulations. The process of a bubble rising in the molten metal includes two steps, one is the bubble rising inside the liquid, and the other one is the bubble rising across the liquid surface. The bubbling dynamics inside the liquid phase was studied in terms of the bubble’s trajectory, shape and terminal velocity over a wide range of bubble diameters. The flow was assumed to be laminar. The results show that 3~10 mm bubbles rise in a spiral way with strong instabilities which cause them to change their instantaneous shapes. In addition, 10~20 mm bubbles rise rectilinearly and their shapes are kept almost steady. All these bubbles’ terminal velocities are around 0.3 m/s, which are in accordance with literature data. For a bubble with a specific size, small metal droplets can be formed due to the bubble bursting which takes place at the free surface. In a situation when the top surface of the bubble is ruptured, the remains of the bubble will collapse and jet droplets may be formed. Therefore, the simulations of jet droplets were qualitatively analyzed. The results show that when the surface tension is 1.4 N/m, the critical bubble size is 9.3 mm. Also, the ejection is found to increase with an increased surface tension value, unless a critical bubble size is reached. The bubble formation during gas injection into liquids was studied by using a water model and a three-dimensional numerical model. In the experiment, a high-speed camera was used to record the bubble formation processes. Nozzle diameters of 0.5 mm, 1 mm and 2 mm were investigated under both wetting and non-wetting conditions. The bubble sizes and formation frequencies as well as the bubbling regimes were identified for each nozzle size and for different wettabilities. The results show that the upper limits of the bubbling regime were 7.35 L/h, 12.05 L/h and 15.22 L/h under wetting conditions for the 0.5 mm, 1 mm and 2 mm nozzle diameters, respectively. Meanwhile, the limits were 12.66 L/h, 13.64 L/h and 15.33 L/h for the non-wetting conditions. In the numerical model, the Volume-of-Fluid (VOF) method was used to track the interface between the gas and liquid. The simulation results were compared with the experimental observations in the air-water system. The comparisons show a satisfactory good agreement between the two methods. The mathematical model was then applied to simulate the argon-steel system. Simulation results show that the effect of nozzle size is insignificant for the current studied metallurgical conditions. The upper limits of the bubbling regime were approximate 60 L/h and 80 L/h for a 2 mm nozzle and for wetting and non-wetting conditions, respectively. In addition, a poor wettability leads to a bigger bubble size and a lower frequency compared to a good wettability, for the same gas flow rate. / <p>QC 20150504</p>