O tratamento de inclusões com cálcio é uma ferramenta poderosa para a produção de aços mais limpos e com melhores propriedades mecânicas. A simulação em laboratório do processo industrial tem sua importância na possibilidade de estudar as reações e interações químicas do tratamento de inclusões no aço líquido. Esse tipo de estudo é possível através do uso de experimentos associados entre fornos a cálculos termodinâmicos. Dessa forma, os objetivos deste trabalho foram: 1) Avaliar - em escala laboratorial - a evolução de inclusões modificadas com a adição de cálcio no banho do aço SAE 8620; 2) Comparar os resultados obtidos com simulações via termodinâmica computacional; 3) Consolidar uma metodologia para estudo de inclusões em escala laboratorial. Para isso, foram executadas corridas em um forno elétrico resistivo de escala de laboratório. As matérias-primas utilizadas foram: ferro com alta pureza e as ferroligas usadas na indústria. Houve injeção de alumínio e cálcio no aço líquido. Na análise química do aço foram considerados os elementos de liga de rotina de produção inclusive os teores de cálcio e oxigênio total. Nas análises de inclusões foram avaliados, via MEV/EDS: composição química, morfologia, distribuição de fases e tamanho.Para calcular o equilíbrio termodinâmico entre aço líquido e inclusões não-metálicas - via termodinâmica computacional - foram utilizados os bancos de dados do software FactSage. Observou-se a modificação química das inclusões com a adição de cálcio, formando diferentes tipos de cálcio-aluminatos, como previsto. Devido à presença de enxofre, verificou-se a formação de sulfetos de cálcio e manganês associados aos cálcio-aluminatos. Também obteve-se uma boa correlação entre os resultados calculados via termodinâmica computacional e a literatura consultada. / The inclusion treatment with calcium is a powerful tool for the production of cleaner steels with improved mechanical properties. The simulation in laboratory of the industrial process has its importance in the possibility of studying the reactions and chemical interactions of the inclusions treatment in the liquid steel. This kind of study is just possible through the use of experiments associated with furnaces and thermodynamics simulations. This way, the aims of this work were: 1) to evaluate - in laboratorial scale - the evolution of inclusions modified with the calcium addition in the SAE 8620 steel bath; 2) to compare the results obtained with computational thermodynamics simulation; 3) to consolidate a methodology for study inclusions in laboratorial scale. Trials in a electrical resistive furnace in laboratory scale were carried out. The raw materials used were: high purity iron and ferroalloys used in the industry. It had also injection of aluminium and calcium in the liquid steel. In the chemical analysis of the steel it was considered the common alloying elements of steel including calcium and total oxygen. In the inclusions analysis were evaluated by SEM/EDS: chemical composition, morphology, phases distribution and size. To calculate the thermodynamic balance between liquid steel and nonmetallic inclusions - by computational thermodynamics simulation - the FactSage data bases software were used. The chemical modification of the inclusions with calcium addition was observed, forming different types of calcium-aluminates, as predicted. Due to sulphur presence it was verified the formation of calcium and manganese sulphides associates with calciumaluminates. Also it was obtained a good correlation between these results, calculated by computational thermodynamics and literature.

The control of non-metallic inclusions is very important for the improvement of performance during the application of tool steel. This present study was performed to see the effect of changing of some process parameters during the vacuum degassing of the melt and how these changing parameters affects the characteristics of inclusions in tool steel. The main parameters that were changed during the vacuum degassing were the change of induction stirring, argon flow rate from both the plug 1 and 2 and different ladle ages for different heat. Electrolytic extraction method was used to observe the morphology and characteristics of inclusions as a 3 dimensional view in tool steel. Four lollipop samples from four different heats were used for the experiment and all the samples were after vacuum (AV) degassing. In this study four different types of inclusions were found and they are classified as type 1, 2, 3 and 4. Of them type 1 inclusion was the major one with mostly spherical shaped. This study shows that among the three parameters, induction stirring has the biggest effect for the total number of inclusions per volume in the sample than the other two parameters Heat 4A showed the lowest number of inclusions per volume comparing with the other heats. The main reason behind this can be said that the induction stirring was the lowest comparing with the other heats with moderate argon flow and ladle age of 12. Extreme value analysis was used in this study to predict the probability of getting largest size inclusions in a certain volume of the metal. For the prediction of the largest inclusion size, both the electrolytic extraction (3D) and cross-sectional (2D) method was used. Later in this study comparison was done to determine the accuracy of both the methods and it is concluded that for the type 1 inclusions electrolytic extraction method shows almost similar trend with cross-sectional method and electrolytic extraction method shows better accuracy for the prediction of largest size inclusions than the cross-sectional method. Electrolytic Extraction method is also applicable for the prediction of largest size inclusions for multiple types of inclusions.

Целью работы является изучение влияния донной продувки в промежуточном ковше на содержание неметаллических включений в транспортном металле и пути повышения качества данных марок стали. В качестве решения проблемы рассмотрена гипотеза о зависимости содержания неметаллических включений в стали от состава шлака на установке «печь-ковш»; создана физическая модель МНЛЗ; предложена схема расположения аргонных блоков в промежуточном ковше, что позволит создать оптимальные потоки металла для флотации неметаллических включений. / The aim of the work is to study the effect of bottom blowing in the intermediate bucket on the content of non-metallic inclusions in the transport metal and ways to improve the quality of these steel grades. As a solution to the problem, the hypothesis of the dependence of the content of non-metallic inclusions in steel on the composition of the slag at the furnace-ladle installation is considered; a physical model of the CCM is created; a scheme for the arrangement of argon blocks in the intermediate ladle is proposed, which will create optimal metal flows for flotation of non-metallic inclusions.

Reoxidation is a phenomenon that occurs in steel products during the initial stage of the formation of liquid steel, mainly during casting. This leads to the formation of inclusions which is a common problem that affects the properties, such as strength and ductility of the steel, and thus decreases its quality. To investigate these inclusions an electrolytic extraction and a scanning electron microscope(SEM) were performed on four carbon steel samples taken before and throughout continuous casting. To get a better understanding of the inclusions, the chemical composition, morphology, and sizes were analyzed, these were measured with the software ImageJ. As a result, five types of inclusions were identified, these include reoxidation, deoxidation, desulphurization, and complex compositions. Each type was represented by specific compounds and elements, such as FeO for reoxidation inclusions and Al2O3 for deoxidation inclusions. Additionally, inclusion morphology and size were significant classification factors, with film inclusions presenting larger sizes compared to other types, while spherical inclusions were observed perfectly, spherical ones were often associated with pure FeO content. Despite successful electrolytic extraction and SEM analysis, the number of inclusions obtained was lower than expected due to the presence of an additional layer of carbides. Future research may benefit from additional heating treatments to facilitate deeper analysis of inclusions. / Reoxidation är ett fenomen som uppstår i stålprodukter under gjutning. Detta leder till bildning av inneslutningar vilket är ett vanligt problem som påverkar egenskaperna, såsom hållfasthet och formbarhet hos stålet, och därmed minskar dess kvalitet. För att undersöka dessa inneslutningar utfördes en elektrolytisk extraktion och en SEM på fyra kolstålprover tagna före och under stränggjutning. För att få en bättre förståelse av inneslutningarna analyserades den kemiska sammansättningen, morfologin och storlekarna, dessa mättes med programvaran ImageJ. Som ett resultat identifierades fem typer av inneslutningar, dessa inkluderar reoxidation, deoxidation, avsvavling och komplexa kompositioner. Varje typ representerades av specifika föreningar och element, såsom FeO för reoxidationsinneslutningar och Al2O3 för deoxidationsinneslutningar. Dessutom var inklusionsmorfologi och storlek signifikanta klassificeringsfaktorer, med filminneslutningar som presenterade större storlekar jämfört medandra typer, medan sfäriska inneslutningar, observerades perfekt sfäriska sådana var ofta associerade med rent FeO-innehåll. Trots framgångsrik elektrolytisk extraktion och SEM-analys var antalet erhållna inneslutningar lägre än förväntat på grund av närvaron av ytterligare ett lager karbider. Framtida forskning kan dra nytta av ytterligare värmebehandlingar för att underlätta djupare analys av inneslutningar.

<div>Defects are unavoidable, life-limiting and dominant sites of damage and subsequent failure in a material. Ni-based superalloys are commonly used in high temperature applications and inevitably found to have defects in the form of inclusions, voids and microscopic cracks which are below the resolution of standard inspection techniques. A mechanistic understanding of the role of defects in such industrially relevant bulk polycrystalline material is essential for philosophies of design and durability to follow and ensure structural integrity of components in the inevitable presence of such defects. The current understanding of defect-mediated damage, in bulk Ni superalloys, is limited by experimental techniques that can capture the local micromechanical state of the material surrounding the defect. In this work, we combine mechanical testing with in-situ, non-destructive 3-D X-ray characterization techniques to obtain rich multi-modal datasets at the microscale to interrogate complex defect-microstructure interactions and elucidate the mechanisms of failure around defects. The attenuated X-ray beam, after passage through the material, is utilized through computed micro-tomography to characterize the defects owing to its sensitivity to density differences in the material. The diffracted X-ray beam, after illuminating the material, is employed through high energy diffraction microscopy in various modes to interrogate the evolving micromechanical state around the discovered defects.</div><div>Three case studies are performed with specimens made of a Ni-based superalloy specially designed and fabricated to have internal defects in the form of: (i) an inclusion, (ii) a microscopic crack, and (iii) voids. In each case, the grain scale information is investigated to reveal heterogeneity in the local micromechanical state of the material as a precursor for the onset of failure. Models and simulations based on finite element or crystal plasticity are utilized, wherever necessary, to assess the factors essential to the underlying mechanism of failure. In the first case study, the detrimental effects of an inclusion in initiating a crack upon cyclic loading is interrogated and the state of bonding, residual stresses, and geometrical stress concentrations around the inclusion are demonstrated to be of utmost importance. In the second case study, the propagation of a short fatigue crack through the microstructure is examined to reveal the crystallographic nature of crack growth through the (i) alignment of the crack plane with the most active slip system, (ii) the correlation between the crack growth rate and the maximum resolved shear stresses, and (iii) the dependence of the crack growth direction on microplasticity within grains ahead of the crack front. In the third case study, the role of voids in ductile failure under tensile loading is explored to illuminate the activation and operation of distinct mechanisms of inter-void shear and necking under the control of the local state of stress triaxiality and the local plasticity within the grains at critical sites of fracture.</div><div>In summary, a grain scale description of the micromechanical state has been unambiguously determined through experiments to examine the heterogeneity around defects in the material. It has enabled us to identify and isolate the nature of factors essential to the activation of specific mechanisms at the onset failure. The grain scale thus provides an ideal physical basis to understand the fundamentals of defect mediated damage and failure instilling trust in the predictive capabilities of models that incorporate the response of the grain structure. The generated datasets can be used to instantiate and calibrate such models at the grain level for higher fidelity. </div>

In this study, the goal is to optimize the process and to reduce the clogging tendency during the continuous casting process. The focus is on clogging when the refractory base material (RBM) in the SEN is in contact with the liquid steel. It is difficult or impossible to avoid non-metallic inclusions in the liquid steel, but by a selection of a good RBM in the SEN clogging can be reduced.   Different process steps were evaluated during the casting process in order to reduce the clogging tendency. First, the preheating of the SEN was studied. The results showed that the SEN can be decarburized during the preheating process. In addition, decarburization of SEN causes a larger risk for clogging. Two types of plasma coatings were implemented to protect the RBM, to prevent reactions with the RBM, and to reduce the clogging tendency. Calcium titanate (CaTiO3) mixed with yttria stabilized zirconia (YSZ) plasma coatings were tested in laboratory and pilot plant trials, for casting of aluminium-killed low-carbon steels. For casting of cerium alloyed stainless steels, YSZ plasma coatings were tested in laboratory, pilot plant and industrial trials. The results showed that the clogging tendency was reduced when implementing both coating materials.   It is also of importance to produce clean steel in order to reduce clogging. Therefore, the steel cleanliness in the tundish was studied experimentally. The result showed that inclusions originated from the slag, deoxidation products and tundish refractory and that they were present in the tundish as well as in the final steel product. / VINNOVA

Die Wirkung nichtmetallischer Einschlüsse auf das temperatur- und beanspruchungsratenabhängige Festigkeits-, Verformungs- und Zähigkeitsverhalten des Stahls G42CrMo4 wird erforscht. Die im Rahmen des SFB 920 entwickelten Filter mit funktionalisierter Oberfläche dienten der Reinigung einer vorher bewusst verunreinigten Stahlschmelze. Diese Stähle werden mit kommerziell verfügbaren Stählen verglichen. Das Festigkeits- und Verformungsverhalten wird durch bekannte Modelle beschrieben, um das Zähigkeitsverhalten zu analysieren. Die Messung der bei schlagartiger Beanspruchung und tiefer Temperatur geringeren Zähigkeit erfolgt durch methodisch weiter- und neuentwickelte Versuchsaufbauten. Die geringere Zähigkeit der Stähle, die im Rahmen des SFB 920 hergestellt wurden, wird auf den höheren Einschlussanteil zurückgeführt. Das Zähigkeitsverhalten wird durch ein neues Modell beschrieben, das die fraktographisch ermittelte Einschlussverteilung einbezieht.

It is well known that inclusions affect the properties of steels and alloys. Therefore, it is important to understand what type of inclusions that exist and how they behave and especially with a focus on large size inclusions. Thus, the large size non-metallic inclusions in ferroalloy FeTi70R were investigated in two dimensions (2D) by using scanning electron microscopy (SEM) in combination with an energy dispersive technique (EDS). It was found that the FeTi70R ferroalloy contain complex oxide inclusions consisting mostly of CaO, SiO2 and TiOx. Furthermore, experimental trials were performed to investigate how these inclusions behaved when entering a melt. More specifically, a comparison between pure Fe and an Alloy 825 grade were made. These results determined the parameters effect on the transformation of the inclusions in the melt. The large size non-metallic inclusions in Alloy 825 during the ladle treatment were investigated during industrial trials by using both two dimensional (2D) and three dimensional (3D) microscopic investigations. The results showed that inclusions consisted of spherical oxides and clusters made up of oxides and nitrides. Further investigations found that the spherical inclusions were transformed from existing NMI in the FeTi70R ferroalloy and slag particles. As for the clusters, they originate from deoxidation products. Furthermore, small inclusions precipitated in the local zones around the added FeTi70R ferroalloy and titanium nitrides. Investigations also found that only Al2O3-MgO and TiN clusters exist after casting. Industrial trials were performed during the last period of the ladle treatment and using a combined electromagnetic (EMS) and gas (GS) stirring. The purpose to investigate the effect of different EMS directions on the agglomeration and on the removal of Al2O3-MgO and TiN clusters. The investigations were then performed in 3D after an electrolytic extraction of the metal samples. The results show that electromagnetic stirring in the upwards direction is best for the agglomeration of the Al2O3-MgO and TiN clusters. However, electromagnetic stirring in the downwards direction is more effective to remove clusters from the melt. This is in agreement with the theoretical predictions based on Stokes’, Brownian and Turbulent collisions. Also, the calculations showed that for Al2O3-MgO clusters with sizes &lt;20 μm the Turbulent collision is the defining factor for agglomeration. However, both Stokes’ and Turbulent collisions are dominant for larger inclusions. For the TiN clusters, turbulent collisions is the dominant factor. Further investigations with more heats and stirring modes were done by using 2D microscopic investigations. More specifically, the number, size, composition and morphology of different inclusions were determined by using SEM in combination with EDS and Inca Feature analyses. The results show that the EMS in downwards direction with a 0.04 m3 min-1 gas flow rate promotes a general removal of Al2O3-MgO and TiN inclusions. Furthermore, that the upwards EMS direction promotes a drastically increase of inclusions having an equivalent size smaller than 11.2 μm. Moreover, the stirring with a 0.02 m3 min-1 gas flow rate has a better removal rate for both downwards and upwards stirring directions compared to the stirring with a 0.04 m3 min-1 gas flow rate. However, no influence on the inclusion composition and morphology could be seen from the different stirring modes. / Det är välkänt att inneslutningar påverkar egenskaperna i stål och legeringar. Därför är det viktigt att förstå vilken sorts inneslutningar som existerar samt hur de beter sig, särskilt stora inneslutningar. Således undersöktes de stora icke-metalliska inneslutningarna i ferrolegeringen FeTi70R i två dimensioner (2D) genom att använda svepelektronmikroskopi (SEM) i kombination med energidispersionsteknik (EDS). Det visade sig att ferrolegeringen FeTi70R innehåller komplexa oxidinneslutningar bestående huvudsakligen av CaO, Si02 och TiOx. Vidare utfördes laborativa försök för att undersöka hur dessa inneslutningar uppträder när de kommer ner i det smälta stålet. Mer specifikt så gjordes en jämförelse mellan rent Fe och Alloy 825 legeringen. Dessa resultat fastställde hur olika parametrar påverkade inneslutningarnas omvandling i smältan. De stora icke-metalliska inneslutningarna i Alloy 825 legeringen under skänkugnsbehandlingen undersöktes vid industriella försök med hjälp av både tvådimensionella (2D) och tredimensionella (3D) mikroskopiska undersökningar. Resultaten visade att inneslutningarna bestod av sfäriska oxider och kluster uppbyggda av oxider och nitrider. Ytterligare undersökningar visade att de sfäriska inneslutningarna omvandlades från befintliga icke-metalliska inneslutningar i ferrolegeringen FeTi70R och slaggpartiklar. När det gäller kluster härrör de från desoxidationsprodukter. Vidare så bildades små inneslutningar i de lokala zonerna kring den tillsatta FeTi70R legeringen och kring titanitriderna. Undersökningarna fann också att endast Al2O3-MgO och TiN-kluster existerar efter gjutning. De industriella försöken utfördes under den sista perioden av skänkugnsbehandlingen och med en kombinerad elektromagnetisk (EMS) och gas (GS) omröring. Syftet med detta var att undersöka effekten av olika riktningar på EMS omrörningen på agglomerationen och avskiljningen av Al2O3-MgO- och TiN klustren. Undersökningarna utfördes sedan i 3D efter en elektrolytisk extraktion av metallproverna. Resultaten visar att en uppåtriktad elektromagnetisk omröring är bäst för agglomereringen av Al2O3-MgO inneslutningar och TiN kluster. Emellertid så är en nedåtriktad elektromagnetisk omröring effektivare för att avlägsna kluster från smältan. Dessa resultat överensstämmer med de teoretiska förutsägelserna baserade på Stokes, Brownian och Turbulent kollisionsvolymer. Dessutom visade beräkningarna att för Al2O3-MgO kluster med storlekar &lt;20 μm är det turbulenta kollisioner som är den avgörande faktorn för agglomerering. Dock är det både Stokes och de Turbulenta kollisionerna som dominerar för större inneslutningar. För TiN klustren är det de turbulenta kollisionerna som är den dominerande faktorn. Ytterligare undersökningar med fler charger av Alloy 825 och olika omrörningsmetoder gjordes baserade på 2D mikroskopiska undersökningar. Mer specifikt så bestämdes antalet, storleken, sammansättningen och morfologin för olika inneslutningar med användning av SEM i kombination med EDS och Inca Feature analyser. Resultaten visar att en nedåtriktad EMS i kombination med ett gasflöde på 0,04 m3 min-1 främjar ett generellt avlägsnande av Al2O3-MgO och TiN inneslutningar. Vidare främjar den uppåtriktade EMS omrörningen en drastisk ökning av inneslutningar med en ekvivalent storlek av 11,2 μm eller mindre. Vidare har omröringen med ett gasflöde på 0,02 m3 min-1 en bättre avskiljningshastighet för inneslutningar i både nedåt och uppåtgående omrörningsriktningar jämfört med omrörningen med ett gasflöde på 0,04 m3 min-1. Emellertid kunde inget inflytande på sammansättningen och morfologin ses från de olika omrörningssätten. / <p>QC 20171122</p>

It is well known that inclusions affect the properties of steels and alloys. Therefore, it is important to understand what type of inclusions that exist and how they behave and especially with a focus on large size inclusions. Thus, the large size non-metallic inclusions in ferroalloy FeTi70R were investigated in two dimensions (2D) by using scanning electron microscopy (SEM) in combination with an energy dispersive technique (EDS). It was found that the FeTi70R ferroalloy contain complex oxide inclusions consisting mostly of CaO, SiO2 and TiOx. Furthermore, experimental trials were performed to investigate how these inclusions behaved when entering a melt. More specifically, a comparison between pure Fe and an Alloy 825 grade were made. These results determined the parameters effect on the transformation of the inclusions in the melt. The large size non-metallic inclusions in Alloy 825 during the ladle treatment were investigated during industrial trials by using both two dimensional (2D) and three dimensional (3D) microscopic investigations. The results showed that inclusions consisted of spherical oxides and clusters made up of oxides and nitrides. Further investigations found that the spherical inclusions were transformed from existing NMI in the FeTi70R ferroalloy and slag particles. As for the clusters, they originate from deoxidation products. Furthermore, small inclusions precipitated in the local zones around the added FeTi70R ferroalloy and titanium nitrides. Investigations also found that only Al2O3-MgO and TiN clusters exist after casting. Industrial trials were performed during the last period of the ladle treatment and using a combined electromagnetic (EMS) and gas (GS) stirring. The purpose to investigate the effect of different EMS directions on the agglomeration and on the removal of Al2O3-MgO and TiN clusters. The investigations were then performed in 3D after an electrolytic extraction of the metal samples. The results show that electromagnetic stirring in the upwards direction is best for the agglomeration of the Al2O3-MgO and TiN clusters. However, electromagnetic stirring in the downwards direction is more effective to remove clusters from the melt. This is in agreement with the theoretical predictions based on Stokes’, Brownian and Turbulent collisions. Also, the calculations showed that for Al2O3-MgO clusters with sizes &lt;20 μm the Turbulent collision is the defining factor for agglomeration. However, both Stokes’ and Turbulent collisions are dominant for larger inclusions. For the TiN clusters, turbulent collisions is the dominant factor. Further investigations with more heats and stirring modes were done by using 2D microscopic investigations. More specifically, the number, size, composition and morphology of different inclusions were determined by using SEM in combination with EDS and Inca Feature analyses. The results show that the EMS in downwards direction with a 0.04 m3 min-1 gas flow rate promotes a general removal of Al2O3-MgO and TiN inclusions. Furthermore, that the upwards EMS direction promotes a drastically increase of inclusions having an equivalent size smaller than 11.2 μm. Moreover, the stirring with a 0.02 m3 min-1 gas flow rate has a better removal rate for both downwards and upwards stirring directions compared to the stirring with a 0.04 m3 min-1 gas flow rate. However, no influence on the inclusion composition and morphology could be seen from the different stirring modes. / Det är välkänt att inneslutningar påverkar egenskaperna i stål och legeringar. Därför är det viktigt att förstå vilken sorts inneslutningar som existerar samt hur de beter sig, särskilt stora inneslutningar. Således undersöktes de stora icke-metalliska inneslutningarna i ferrolegeringen FeTi70R i två dimensioner (2D) genom att använda svepelektronmikroskopi (SEM) i kombination med energidispersionsteknik (EDS). Det visade sig att ferrolegeringen FeTi70R innehåller komplexa oxidinneslutningar bestående huvudsakligen av CaO, Si02 och TiOx. Vidare utfördes laborativa försök för att undersöka hur dessa inneslutningar uppträder när de kommer ner i det smälta stålet. Mer specifikt så gjordes en jämförelse mellan rent Fe och Alloy 825 legeringen. Dessa resultat fastställde hur olika parametrar påverkade inneslutningarnas omvandling i smältan. De stora icke-metalliska inneslutningarna i Alloy 825 legeringen under skänkugnsbehandlingen undersöktes vid industriella försök med hjälp av både tvådimensionella (2D) och tredimensionella (3D) mikroskopiska undersökningar. Resultaten visade att inneslutningarna bestod av sfäriska oxider och kluster uppbyggda av oxider och nitrider. Ytterligare undersökningar visade att de sfäriska inneslutningarna omvandlades från befintliga icke-metalliska inneslutningar i ferrolegeringen FeTi70R och slaggpartiklar. När det gäller kluster härrör de från desoxidationsprodukter. Vidare så bildades små inneslutningar i de lokala zonerna kring den tillsatta FeTi70R legeringen och kring titanitriderna. Undersökningarna fann också att endast Al2O3-MgO och TiN-kluster existerar efter gjutning. De industriella försöken utfördes under den sista perioden av skänkugnsbehandlingen och med en kombinerad elektromagnetisk (EMS) och gas (GS) omröring. Syftet med detta var att undersöka effekten av olika riktningar på EMS omrörningen på agglomerationen och avskiljningen av Al2O3-MgO- och TiN klustren. Undersökningarna utfördes sedan i 3D efter en elektrolytisk extraktion av metallproverna. Resultaten visar att en uppåtriktad elektromagnetisk omröring är bäst för agglomereringen av Al2O3-MgO inneslutningar och TiN kluster. Emellertid så är en nedåtriktad elektromagnetisk omröring effektivare för att avlägsna kluster från smältan. Dessa resultat överensstämmer med de teoretiska förutsägelserna baserade på Stokes, Brownian och Turbulent kollisionsvolymer. Dessutom visade beräkningarna att för Al2O3-MgO kluster med storlekar &lt;20 μm är det turbulenta kollisioner som är den avgörande faktorn för agglomerering. Dock är det både Stokes och de Turbulenta kollisionerna som dominerar för större inneslutningar. För TiN klustren är det de turbulenta kollisionerna som är den dominerande faktorn. Ytterligare undersökningar med fler charger av Alloy 825 och olika omrörningsmetoder gjordes baserade på 2D mikroskopiska undersökningar. Mer specifikt så bestämdes antalet, storleken, sammansättningen och morfologin för olika inneslutningar med användning av SEM i kombination med EDS och Inca Feature analyser. Resultaten visar att en nedåtriktad EMS i kombination med ett gasflöde på 0,04 m3 min-1 främjar ett generellt avlägsnande av Al2O3-MgO och TiN inneslutningar. Vidare främjar den uppåtriktade EMS omrörningen en drastisk ökning av inneslutningar med en ekvivalent storlek av 11,2 μm eller mindre. Vidare har omröringen med ett gasflöde på 0,02 m3 min-1 en bättre avskiljningshastighet för inneslutningar i både nedåt och uppåtgående omrörningsriktningar jämfört med omrörningen med ett gasflöde på 0,04 m3 min-1. Emellertid kunde inget inflytande på sammansättningen och morfologin ses från de olika omrörningssätten.

The presence of non-metallic inclusions (NMIs) have critical effects on both the mechanical properties and machinability of steels. In the present thesis, one focus is to study the characteristics of deformed sulfides (MnS) for a stainless steel (3R65) and a tool steel (42CrMo4). Three groups of MnS inclusions were detected in the samples taken after deformation of the steel: i) type RS (sulfides with a Rod-like geometry), ii) type PS (sulphides with a plate-like geometry) and iii) type OS (oxy-sulfides). Here, the elongated inclusions present in both stainless and tool steels were studied more in detail using SEM to determine the tendency for the inclusions to break.  The results showed that three types of elongated MnS inclusions could be identified, namely UU, UB and BB. Here, ‘U’ represents the unbroken edge(s) of inclusion and ‘B’ represents the broken edge(s) of an inclusion. The presence of these three types of inclusions in samples collected both before and after a heat treatment was studied and the results showed that the heat treatment had a very small effect on the morphologies of the elongated MnS inclusions for both stainless steels (containing &lt;0.1 mass % C) and tool steels (containing 0.42 mass % C).  In the second part of the thesis, the characteristics of chips after machining of a 157REM Ce-treated steel and a 157C reference steel was studied. Furthermore, the effect of the NMIs on the chip breakability during machining was determined. The results show that a Ce modification of a 157C steel transforms the NMIs from large size elongated inclusions to small size inclusion with a spherical shape. This leads to an improved machinability of 157C steels. In addition, a newly developed weight distribution of chips (WDC) method, based on the chip weight measurements, was used to determine the tendencies for breaking of chips. The results of this investigation showed that the chips that were obtained from the machining of 157C and the 157REM steels could be classified into the following three types: i) type I chips (with a geometry containing one arc) and having a weight of less than 0.08 g, ii) type II chips (with a geometry containing two arcs) and having weights between 0.08 g and 0.15 g, and iii) type III chips (with a geometry containing three or more arcs) and having weights larger than 0.15 g. From industrial experience, it is known that a high amount of small type I chips will lead to a good chip breakability. The results from the machining test show that the fraction of type I chips from machining of the 157REM steel (65 %) is smaller than from machining of the 157C reference steel (80 %) when using a lower feed rate of 0.4 mm/rev. However, when using a higher feed rate of 0.5 mm/rev, 40 % of the chips belong to type I small chips for the 157REM steel and 14 % for the 157C steel. Based on the conditions used in this study and the obtained results, the following is clear in order to reach the best machinability: i) it is most advantageous to use the 157C steel when using a lower feed rate of 0.4 mm/rev and ii) it is most advantageous to use the 157REM steel when using a higher feed rate of 0.5 mm/rev. / Närvaron av icke-metalliska inneslutningar (NMIs) har en betydande påverkan både med avseende på mekaniska egenskaper såväl som skärbarhetsförmågan hos stål. I denna avhandling är ett fokus att studera deformerade sulfider (MnS)  i ett rostfritt stål (3R65) och ett verktygsstål (42CrMo4). Tre grupper av MnS inneslutningar återfanns i stålproverna, som togs efter deformation av stålet: i) RS (sulfider som har en cylindrisk geometri), ii) PS (sulfider som har en platt geometri) och iii) OS (oxy-sulfider). Dessutom så studerades utdragna inneslutningar mer i detalj med användande av SEM undersökningar i syfte att studera tendensen till att dessa inneslutningar bröts sönder. Resultaten visade att tre typer av utdragna inneslutningar kunde identifieras, nämligen UU, UB och BB. Här representerar ‘U’ en ände av en inneslutning som inte brutits sönder och ‘B’ representerar en ände av en inneslutning som brutits sönder. Närvaron av dessa tre typer av utdragna inneslutningar studerades i prover som togs både före och efter en värmebehandling, men resultaten visade att en värmebehandling hade en mycket liten påverkan på morfologin hos de utdragna MnS inneslutningarna för både rostfria stål (innehållande &lt;0.1 mass % C) och verktygsstål (innehållande 0.42 mass % C).  I den andra delen av avhandlingen så studerades karakteristiken hos spånor som bildats efter skärande bearbetning av ett 157REM (Ce-behandlat) modifierat stål och ett 157C referensstål som inte modifierats. Dessutom så studerades inverkan av icke-metalliska inneslutningar på spånbrytningen under den skärande bearbetningen. Resultaten visar att en Ce-modifiering av stålet omvandlar inneslutningarna från stora och utdragna geometrier till små inneslutningar med en sfärisk geometri. Detta leder till en ökad skärbarhet hos 157C stål. Spånbrytbarheten bestämdes också med användande av en nyutvecklad metod (WDC metoden) som baseras sig på att bestämma vikten av spånor. Resultaten av denna utvärdering visade att spånorna som erhölls från bearbetning av 157C och 157REM stål kunde klassificeras enligt följande tre typer: i) typ I spånor (en geometri som består av en bågform) som har en vikt som är mindre än 0.08 g, ii) typ II spånor (en geometri som består av två bågformar) som har en mellan 0.08 g och 0.15 g och iii) typ III spånor (en geometri som består av tre eller fler bågformar) som har en vikt som är större än 0.15 g. Baserat på industriell erfarenhet så är det känt att en stor mängd av små typ I spånor är kopplad till en bra spånbrytbarhet. Resultaten från skärbarhetstesterna visar att andelen typ I spånor från bearbetning av ett 157REM stål (65 %) är mindre än vid bearbetning av ett 157C referens stål (80 %), när en lägre matningshastighet av 0.4 mm/rev används. Däremot så visar resultaten att om en högre matningshastighet av 0.5 mm/rev används vid bearbetning, så är andelen typ I spånor 40 % för 157REM stålet och 14 % för 157C referensstålet. I syfte att erhålla bästa möjliga skärbarhet så är det fördelaktigt att använda ett 157C referensstål för den lägre matningshastigheten av 0.4 mm/rev, men att använda ett 157REM stål för en högre matningshastighet av 0.5 mm/rev.