This study has been conducted with the aim to examine the extent of the heat affected zone in order to use laser cutting when making samples for tensile testing. When cutting with a laser the material absorbs heat energy from the laser beams which causes changes in the microstructure. The heat affected zone affects the properties of the materials, lowering the accuracy of the tensile test. Therefore, it is desired to know the extent of the heat affected zone in order to remove it before tensile testing. In this study two materials were used, the high strength steel Docol 1000DP and the duplex stainless steel LDX 2101. The materials were cut in the shape of dog bones for tensile testing using two different laser powers, 2500 W and 3500 W. The samples were cut with different cutting speeds, starting at lower cutting speed, increasing until the laser was unable to cut through. Thereafter, the heat affected zone, and the surface quality was examined. The results from this study showed that the heat affected zone decreases with increased cutting speed. When cutting with high cutting speeds in Docol 1000DP it is enough to turn away 0.30 mm in order to remove the heat affected zone with margin. Negligible difference in heat affected zone was observed between the samples cut with 2500 W and 3500 W. The heat affected zone in LDX 2101 was very small, in order of 50 μm, making it hard to measure. This resulted in no exact measurements being made. However, the heat affected zone was in the order of 50 μm for all samples, concluding that turning away 0.15 mm is sufficient to remove the heat affected zone with margin. No difference could be observed between the samples cut with a laser power of 2500 W or 3500 W. Common to both materials is that the amount of dross decreases with increased cutting speed. / Denna studie har utförts i syfte att undersöka utsträckningen av den värmepåverkade zonen för att kunna använda laserskärning för att skära prover till dragprovning. Ett problem med laserskärning är att metaller absorberar värmeenergin, vilket orsakar förändringar i mikrostrukturen. Denna värmepåverkade zon bör minimeras och avlägsnas från metallen, då det minskar kvalitén på proverna samt på dragprovningen. I denna studie har två material undersökts, det höghållfasta stålet Docol 1000DP och det duplexa rostfria stålet LDX 2101. Stålen skars ut i form av hundben för dragprovning med två olika effekter på lasern 2500 W och 3500 W. Proverna skars ut med olika skärhastigheter, började med lägre hastigheter och ökade sedan tills lasern inte längre kunde skära igenom materialet. Därefter undersöktes både den värmepåverkade zonen och kvaliteten på skärytan. Resultaten från denna studie visade att den värmepåverkade zonen minskar med ökad skärhastighet. Vid skärning i Docol 1000DP med höga skärhastigheter räcker det att avlägsna 0,30 mm för att ta bort den värmepåverkade zonen med marginal. Ingen skillnad i värmepåverkad zon observerades mellan proverna skurna med 2500 W och 3500 W vid skärning med högsta skärhastigheten för varje lasereffekt. Den värmepåverkade zonen i LDX 2101 var mycket liten, i storleksordningen 50 μm, vilket gjorde den svårt att mäta. Slutsatsen gav att det är tillräckligt att avlägsna 0,15 mm för att avlägsna den värmepåverkade zonen med marginal. Ingen skillnad kunde observeras mellan proverna skurna med en lasereffekt på 2500 W eller 3500 W. Gemensamt för båda materialen var att gradbildningen minskade med ökad skärhastighet.

Due to coming emission legislations, the temperature is expected to increase in heavy-duty diesel engines, specifically in the hot-end of the exhaust system affecting components, such as exhaust- and turbo manifolds. Since the current material in the turbo manifold, a ductile cast iron named SiMo51, is operating close to its limits there is a need for material development in order to maintain a high durability of these components. When designing for increased life, many material properties need to be considered, for example, creep-, corrosion- and fatigue resistance. Among these, the present work focuses on the latter two up to 800°C improving the current material by additions of Cr, for corrosion resistance, and Ni, for mechanical properties. The results show improved high-temperature corrosion resistance in air from 0.5 and 1wt% Cr additions resulting in improved barrier layer at the oxide/metal interface. However, during oxidation in exhaust-gases, which is a much more demanding environment compared to air, such improvement could not be observed. Addition of 1wt% Ni was found to increase the fatigue life up to 250°C, resulting from solution strengthening of the ferritic matrix. However, Ni was also found to increase the oxidation rates, as no continuous SiO2-barrier layers were formed in the presence of Ni. Since none of the tested alloys showed improved material properties in exhaust gases at high temperature, it is suggested that the way of improving performance of exhaust manifolds is to move towards austenitic ductile cast irons or cast stainless steels. One alloy showing good high-temperature oxidation properties in exhaust atmospheres is an austenitic cast stainless steel named HK30. This alloy formed adherent oxide scales during oxidation at 900°C in gas mixtures of 5%O2-10%H2O-85%N2 and 5%CO2-10%H2O-85%N2 and in air. In the two latter atmospheres, compact scales of (Cr, Mn)-spinel and Cr2O3 were formed whereas in the atmosphere containing 5%O2 and 10%H2O, the scales were more porous due to increased Fe-oxide formation. Despite the formation of a protective, i.e. compact and adherent, oxide scale on HK30, exposure to exhaust-gas condensate showed a detrimental effect in form of oxide spallation and metal release. Thus, proving the importance of taking exhaust-gas condensation, which may occur during cold-start or upon cooling of the engine, into account when selecting a new material for exhaust manifolds. / <p>QC 20130508</p>

Hardening distortions are unwanted changes in shape and dimension that arise during hardening of steel components. Uncontrolled distortions induce random errors to the manufacturing process, and have a strong negative impact on manufacturing costs. The distortions are not only caused by the hardening process, several factors from previous manufacturing steps including the component geometry itself contribute to varying extent. The aim of the current work is to investigate the main influencing factors on hardening distortions for serial produced gears. The investigations were done on two different types of gears for heavy-duty transmissions, crown wheels for the rear axle central gear and main shaft gears for the gearbox. The steel was produced using either continuous casting or ingot casting. For rectangular continuously cast steel, the effect of disabling magnetic stirring of the steel melt during casting was investigated, finding a strong reduction of gear runout for crown wheels. Segregations in crown wheels produced from the top and bottom of ingots were shown to go in opposite directions, producing opposite back-face tilts. For crown wheels quenched one at a time, influences of stacking level on the hardening tray were found, indicating an impact from small variations in the carburizing process, despite identical quenching conditions. For main shaft gears, horizontal loading gave considerably less roundness and runout errors but increased flatness errors compared to vertical loading. This thesis shows the complexity of the distortion phenomenon and how several factors interact and contribute to the final result. It is shown that factors with significant impact on hardening distortions for one component may be less important for another component. With this in mind, each type of component to be hardened should be produced by a manufacturing chain where each process step is carefully chosen with respect to minimizing distortions. / <p>QC 20170516</p>

The muffle furnace main purpose is to anneal the rough sponge iron powder transported through it, which is done by burning natural gas. Heat is absorbed by the muffle and is transferred to the bed of sponge iron powder. In order to reduce the consumptions of fossil fuel, some companies of the industry aims to exchange the natural gas in their muffle furnace’s burners to syngas, produced from biomass. This will however affect the performance of the furnace in the heating aspect. For this work, it is assumed that the effect will be negative. Thus the aim of this study is to investigate how to compensate the loss of effect from the burners, by examining which other parameters have influence on the furnace heating performance of the sponge iron powder transported through the furnace. The investigation is executed by simulating a 1 meter of the furnace in COMSOL multiphysics for 10 min, not including the combustion chambers. The investigated parameters are the packing degree of the powder, surface emissivity of the muffle, process gas velocity, conveyor belt velocity and the heat transfer rate coefficient to muffle from the combustion chambers. Alas, the process gas velocity and conveyor belt velocity only have minor influence on the final result, according to this simulation. However, the simulation exhibited that the surface emissivity of the muffle and the packing degree of the powder has great impact on the heating of the powder and could compensate some of the lost effect from the burners. This could be obtained by using an unpolished and oxidized muffle surface, and use densely packed powder sample.

The strand similarity and inclusion removal capability are two critical parameters to measure the performance of multi-strand tundish in clean steel production. In this work, the effect of two flow regulators, i.e., Flow Control Devices (FCD) and Electromagnetic Stirring (EMS) on eight-strand tundish performance have been investigated by establishing a water model and conducting numerical simulations of water model. The water model was focused on revealing the effect of stirring while the simulation was employed to investigate the effect of two FCDs, namely baffle wall and turbo-stopper. The analysis of strand similarity and inclusion removal were conducted by analyzing flow characteristics derived from Combined Model of Residence Time Distribution (RTD) curve and observing the flow movement in the tundish model. In addition, the tundish capability to remove inclusions was also studied by injecting inclusion particles using Discrete Phase Model (DPM) in ANSYS Fluent. Experiment results cause the Combined Model needs to be modified. This modification was employed when analyzing tundish configuration involving stirring. By using the modified Combined Model, the stirring can significantly increase the well-mix volume to almost 100% as it annihilates dead zone. The stirring also increases the similarity between strands and makes the RTD curve more similar to ideal mixing curve.  However, the problem of short-circuiting flow need to be solved and care should be taken into consideration regarding the selection of stirring direction as well as bath surface condition when implementing EMS in reality. The simulation results show that the addition of baffle wall and turbo-stopper are beneficial to improve mixing as well as to avoid the short-circuiting flow. Furthermore, compared to individual FCD, the combination of baffle wall and turbo-stopper results in the best performance to remove inclusions by providing surface-directed flow and generating a higher plug flow.

This Thesis is about the aging of FECRAL surface coatings. In this thesis various substrates have been investigated such as 16 Mo3, 304, 347, Sanicro 31, 800HT, Nikrothal 80 and Kanthal APMT. These substrates have been coated with different FeCrAl alloys, using two different coating methods spraying with (High Velocity Air Force) and welding with (Metal Inert Gas). The purpose of coating is to achieve specific properties of the layer without affecting the original properties of the substrate. Therefore, it is important to investigate the boundary layer between these two different materials to observe how the interdiffusion of different substances such as Cr, Al, Fe and C is affected, which is the purpose of this project. The method used to investigate this purpose was to expose these combinations in different temperatures and in different environments for different time intervals. Then, using LOM, SEM and EDS analysis, the change that the boundary layers have undergone is examined. Some calculations in DICTRA have also been performed to see if it was possible to find any connection between experimental data and simulation results. The result showed carburization of FeCrAl-coatings on 16Mo3 substrates which can lead to deterioration of mechanical properties in the substrates but also decreased corrosion resistance for the coated layers. The result has also shown that it is difficult to perform spraying for small cylindrical products. The reason for this may be the high powder dispersion and the expansion of certain products when spraying, which causes the layer to loosen due to the shrinkage followed by cooling. APMT sprayed with Nikrothal 80 has shown high porosity in the substrates and high interdiffusion of Fe and Ni. High Ni diffusion in low Al alloys such as K 198 may be a reason why the coated layer cannot optimally form the protective oxide. / Detta projekt handlar om åldring av FECRAL ytbeläggningar. I den här avhandlingen så har olika substrat blivit undersökta såsom 16Mo3, 304, 347, Sanicro 31, 800HT, Nikrothal 80 och Kanthal APMT. Dessa substrat har blivit belagda med olika FeCrAl legeringar, med hjälp av två olika beläggningsmetoder, påsprutning (High Velocity Air Force) och påsvetsning (Metal Inert Gas). Syftet med att materialet beläggs är att uppnå specifika egenskaper utan att påverka substratens ursprungliga egenskaper. Det är därför viktigt att undersöka gränsskiktet mellan dessa två olika material för att se hur interdiffusionen av olika element såsom Cr, Al, Fe och C påverkas av värmebehandling. Metoden som användes för att undersöka detta var att exponera dessa kombinationer i olika temperaturer och i olika miljöer för olika tidsintervall. Därefter med hjälp av LOM, SEM och EDS analys undersöktes förändringen som gränsskikten har genomgått. Några beräkningar i DICTRA har även utförts för att se om det var möjligt att hitta någon koppling mellan experimentella data och simuleringsresultatet. Resultaten visade att 16Mo3 kombinationer fått en tydlig hög uppkolning i skiktet vilket kan påverka mekaniska egenskaperna och korrosionbeständigheten under användning vid höga temperaturer. Resultatet har även visat att det är svårt att utföra påsprutning för små cylindriska produkter. Anledningen till detta kan vara hög pulverspridningen samt den termiska expansionen av vissa produkter vid påsprutning som leder till att skiktet kan lossna på grund av krympningen vid svalning. APMT påsprutad med Nikrothal 80 har visat hög porositet i substraten och hög interdiffusion av Fe, Al och Ni under exponering vid 1200°C. Hög uppblandning och diffusion av nickel för det FECRAL belagda skiktet med relativt låg halt av aluminium K 198 kan vara en anledning till att belagda skiktet inte kan forma en skyddande oxid på ett optimalt sätt.

Söderberg electrodes take part in the production of ferroalloys, copper, nickel, platinum, and calcium carbide. They are involved in a continuous and with low costs operation. The study of such electrodes is essential, since research and new findings will provide us with vital information regarding the operation of such furnaces leading to a more efficient production. Therefore, the study of Söderberg electrodes materials characteristics is of great importance. The current work refers to the thermal properties of Söderberg electrode paste by focusing on the thermal conductivity coefficient from room temperature up to 800 °C with the Transient Plane Source (TPS) method applied to an electrode paste material with softening point at 65°C. Another electrode paste with higher softening point at 90 °C and an already baked material are studied to some extent. The study gives significant results for the thermal conductivity coefficient for all the investigated cases. Results indicate variation of coefficients regarding the phase evolved during heating at different temperatures. In principle, thermal conductivity of the green paste with low softening point decreases until 400°C and increases after the baking point which is found in between 400-500°C. A few measurements for the green paste with higher softening point indicate the same trend. For the case of the fully baked electrode, thermal conductivity seems to keep an increasing trend according to temperature increase. On the two last mentioned materials, more experimental work will be conducted in future. / Söderberg-elektroder används till produktionen av ferrolegeringar, koppar, nickel, platina och kalciumkarbider. De är involverade i kontinuerliga och lågkostnadsoperationer. Studien av sådana elektroder är väsentlig eftersom forskning och nya fynd kommer att ge oss viktig information om driften av sådana ugnar vilket leder till en effektivare produktion. Därför är studien av Söderberg-elektrodens materialegenskaper av stor betydelse. Det nuvarande arbetet refererar till de termiska egenskaperna hos Söderberg-elektrodpastan genom att fokusera på den termiska konduktivitetskoefficienten från rumstemperatur upp till 800°C med den TPS-metoden (Transient Plane Source) tillämpad på ett elektrodpasta-material med en mjukningspunkt vid 65°C. En annan elektrodpasta med en högre mjukningspunkt vid 90°C samt ett redan bakat material studeras även till viss del. Studien ger signifikanta resultat för värmeledningsförmågan för alla undersökta fall. Resultaten indikerar på variationer av koefficienterna gällande fasen som utvecklas under uppvärmning vid olika temperaturer. I stort sett minskar värmeledningsförmågan hos den gröna pastan med låg mjukningspunkt upp till 400°C och ökar efter bakningspunkten som finns mellan 400-500°C. Några mätningar för den gröna pastan med en högre mjukningspunkt visar samma trend. När det gäller den helt bakade elektroden verkar värmdeledningsförmågan hålla en ökande trend beroende på temeperaturökningen. På de två sistnämnda materialen kommer mer experimentellt arbete att genomföras i framtiden.

High-pressure die casting of semi-solid aluminium-silicon alloys is used in the automotive industry to manufacture components, like housings, brackets, and bars. It is commonly known that during high-pressure die casting, defect bands may be created that follow the contour of the component surface. These bands consist mainly of a eutectic phase. This phenomenon is also observed in semi-solid metal slurry high-pressure die casting. These bands could lead to premature failure of the component in service. The origin of these bands is not fully understood and so this research focuses on investigating these bands and their origins further. A series of casting trials were conducted with varying plunger velocity. Subsequent investigation using optical and scanning electron microscopy showed that a change of the plunger velocity alters the number of bands present in the samples. Energy dispersive X-ray spectroscopy revealed that a measurable difference in aluminium quantity across the band was noticed and it was postulated that aluminium migrates towards the component centre. Therefore, different mechanisms responsible for particle migrations found in literature were investigated and assessed quantitatively using experimental data and information from published literature. It was found that the Saffman lift force and the Mukai-Lin-Laplace effect were the mechanisms that were most likely to cause such a migration of aluminium. Further experimental investigation is recommended to identify which of the two mechanisms is ultimately responsible for the migration and to optimise the high-pressure die casting procedure to minimise defect band formation. / Produktion av högtrycksgjutning av halvfasta aluminium-kisellegeringar används i fordonsindustrin för att tillverka komponenter, som exempel till kåpor, konsoler och stag. Det är allmänt känt att defektband kan formas under högtrycksgjutning som följer konturen av komponentytan. Dessa band består huvudsakligen av eutektisk fas. Detta fenomen har också observerats vid högtrycksgjutning produktion av halvfast slurry. Potentiellt kan dessa band leda till en försämring av komponentens mekaniska egenskaper och resultera i ett förtida brott. Ursprunget av dessa band är inte helt kartlagda och det är därför viktigt att fokusera ytterligare på denna forskning och att undersöka dessa band och deras ursprung. En serie med gjutningsförsök genomfördes med varierande kolvhastighet. Efterföljande undersökning med optisk- och svepelektronmikroskopi visade att en förändring av kolvhastigheten förändrar antalet band som finns i proverna. Energidispersiv röntgenspektroskopi avslöjade en mätbar skillnad i aluminiumkvantitet över bandet, och det antogs att aluminium migrerar mot centrum av komponenten. Därför undersöktes och utvärderades olika mekanismer som ansvarar för partikelmigrationer som finns att finna i litteratur med hjälp av experimentella data och information från publicerad litteratur. Det visade sig att Saffman lyftkraft och Mukai-Lin-Laplace effekten var de mekanismer som mest troligen orsakade migration av aluminium. Ytterligare experimentella försök rekommenderas för att identifiera vilken av dessa två mekanismerna som i slutändan är ansvarig för migrationen. Detta för att optimera gjutningsprocessen och därmed minimera uppkomsten av defektband.

Precipitation of second phase particles is a key factor dominating the mechanical properties of high temperature alloys. In order to control and optimize the precipitation effect it is of great importance to study the role of alloying elements in the formation and stability of precipitates. As a favored family of corrosion and creep resistant austenitic stainless steels the 20Cr-25Ni alloy was modified by addition of copper, molybdenum, nitrogen, niobium and vanadium. A set of alloys with similar matrix but varying contents of niobium, vanadium and nitrogen were prepared. Sample preparation process included melting, hot forging, solution annealing and finally aging for 500 h at 700, 800 and 850 ºC.Light optical and scanning electron microscopy revealed micron-scale precipitates on grain and twin boundaries as well as sub-micron intragranular precipitates in all samples. Characterization of precipitates was carried out by means of energy dispersive X-ray spectroscopy (EDS). Among micron-scale precipitates M23C6 carbide was the dominant phase at 700 ºC aging temperature; whereas silicon-rich eta phase (M5SiC) was the main precipitate in samples aged at 800 and 850 ºC. A few sigma phase particles were found in one of the niobium containing samples aged at 700 and 800 ºC. Sub-micron intragranular precipitates were analyzed using low voltage EDS. The spatial resolution of EDS microanalysis at 5 kV accelerating voltage was estimated as almost 100 nm which was at least eight times better than that using the ordinary 20 kV voltage. Also, low voltage EDS revealed the presence of light elements (carbon, nitrogen and boron) in the composition of sub-micron particles thanks to the less matrix effect in absorption of low energy X-rays of light elements. In samples aged at 700 ºC niobium-rich and vanadium-rich carbonitrides were found as the dominant precipitates; whereas they contained much less carbon in samples aged at 800 ºC and mostly became carbon-free nitrides with well-defined cuboidal shapes at 850 ºC aging temperature. This showed that niobium/vanadium-rich nitride phases are stable precipitates at aging temperatures above 700 ºC.The drawbacks of low voltage EDS were indicated as high detection limit (no detection of low- content elements), poor accuracy of quantitative analysis and high sensitivity to surface contamination. Some possible ways to improve the accuracy of low voltage EDS, e.g. longer acquisition time were examined and some other suggestions are proposed for future works.

The third-generation advanced high strength steels, AHSS, represent an opportunity for today’s steel development, where lighter materials with maintained strength and toughness are in demand. The unique properties of these materials often stem from a tailored microstructure. In the continued development of these steels, without relying on expensive alloying methods, process design in the form of precise heat treatments plays an increasingly important role. This work focuses on Medium Mn AHSS with the aim of investigating one of these heat treatments, intercritical annealing, which is essential for achieving the desired material properties. Experimental testing of annealing effects is acknowledged to be a challenging process, and this study aims to present a novel approach for these types of tests. During experimental testing of intercritical annealing, the thermomechanical testing system Gleeble 3800 is a recognized tool. The mounting technique employed in the Gleeble results in an inhomogeneous heat distribution in the samples, generating a thermal gradient. This report aims to utilize this gradient as an opportunity to test the effect of several intercritical annealing temperatures on one sample, thereby increasing the efficiency of experimental work. The method is based on data retrieved from thermocouples attached to the specimen during Gleeble trials with the intent to identify the thermal gradient. This data is combined with x-ray diffraction measurements where the retained austenite fraction is measured. Thermodynamic calculations of expected retained austenite fraction following intercritical annealing are performed parallel to experimental work. The results of this work show that it is possible to utilize the thermal gradient to retrieve extensive data regarding the effect of intercritical annealing using only one sample. The results show a distinct thermal gradient and a corresponding gradient of retained austenite fraction along the specimen. The results for retained austenite fraction at room temperature can be rationalized on the basis of computational predictions. These variations potentially arise due to the material not reaching equilibrium within the annealing timeframe. This conclusion is supported by other computational results concerning austenite composition. In summary, the present work illustrates a new approach streamlining experimental work that, with some refinements, has the potential to benefit the broader scienitific community, in addition to providing a powerful new tool for rapid technological advancement in the steel industry / Tredje generationens avancerade höghållfasta stål representerar en möjlighet för dagens stålutveckling där lättare material med bibehållen styrka och seghet efterfrågas. De unika egenskaperna hos dessa material härrör ofta frän en skräddarsydd mikrostruktur. Vid fortsatt utveckling av dessa stål är det önskvärt att minimera användningen av legeringsämnen, vilket betyder att processdesign i form av korrekta värmebehandlingar blir  av  stor  betydelse.  Detta  arbete  fokuserar  på  Medium  Mn  avancerade höghållfasta stål med syftet att undersöka en av dessa värmebehandlingar, interkritisk glödgning,  vilken  har  en  avgörande  betydelse  för  att  uppnå önskad  prestanda. Experimentell  testning  av  glödgningseffekter  anses  vara  en  utmanande  process och avsikten med denna studie är att presentera ett nytt tillvägagångssätt för denna typ av test. Under experimentell utvärdering av glödgningseffekter används ofta det termomekaniska testsystemet  Gleeble  3800.  Provmonteringen  i  Gleeblen  resulterar i en  inhomogen värmefördelning i proverna vilket medför en temperaturgradient. Denna rapport syftar till att använda gradienten som en möjlighet att testa effekten av flera  glödgningstemperaturer  på  ett  enda  prov  och  därigenom  öka  effektiviteten i det  experimentella  arbetet.  Metoden  grundas  på  data  från  termoelement  fästa  på provet under Gleebleförsök, med avsikt att identifiera den termiska gradienten. Denna data kombineras sedan med XRD-mätningar där austenitfraktion efter värmebehandling utvärderas.  Termodynamiska  beräkningar  av  förväntad  austenitfraktion  efter interkritisk glödgning genomförs parallellt med experimentellt arbete. Resultaten  från  detta  arbete  påvisar  att  den  presenterade  metoden  är  genomförbar då omfattande data gällande interkritisk glödgningseffekt grundat på endast ett prov erhålls. Resultaten visar en tydlig termisk gradient och en motsvarande gradient av austenitfraktion längs provet, vilka är i överensstämmelse med tidigare experimentella resultat för samma material. Resultaten för austenitfraktion vid rumstemperatur uppvisar  betydande  likheter  med  de  termodymiska  beräkningarna, med  några  undantag. Orsaken till dessa variationer ¨ar troligen en otillräcklig glödgningstid, vilket gör att  materialet  inte  når  jämvikt.  Denna  hypotes  stöds  av andra  beräkningsresultat gällande austenitens sammansättning. Sammanfattningsvis presenterar denna rapport ett nytt tillvägagångssätt för att effektivisera experimentellt arbete, som med vissa förbättringar har potential att gynna det bredare forskarsamhället.