Rozprawy doktorskie: „Steel – Inclusions”

1

Douglas, Brent A. "Nonmetallic inclusions in HSLA steel weldments". Thesis, Monterey, California. Naval Postgraduate School, 1989. http://hdl.handle.net/10945/27164.

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Gregg, John Martin. "Ferrite nucleation on non-metallic inclusions in steel". Thesis, University of Cambridge, 1995. https://www.repository.cam.ac.uk/handle/1810/221878.

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3

Kuyucak, Selçuk. "Direct detection of non-metallic inclusions in molten iron". Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63356.

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4

Ruoru, Ke. "Pitting corrosion on sulphide inclusions in stainless steel 316". Thesis, University of Surrey, 1988. http://epubs.surrey.ac.uk/847585/.

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Pits have been observed to initiate at certain inclusions in stainless steel, which affect the composition and properties of the passive film in that region. In this thesis, the VG MA500 high resolution scanning Auger microscope associated with Link EDX is used to investigate the surface chemistry of inclusion groups in stainless steel 316 relative to the bulk composition, before and after exposure to sodium chloride solution. The work demonstrates that careful control of experimental conditions allows the progress of initiation of pits to be observed systematically. The role of inclusions as initiators of pitting corrosion has been studied from the very inception of attack. Detailed observation have been taken from separate manganese sulphide as well as mixture of manganese sulphide and multi-element oxide at various pH values of solutions to trace the behaviour of these inclusions during exposures. It is suggested from this investigation that corrosive attack starts on MnS inclusion proper. The dissolution of MnS takes place in sodium chloride solution followed by the acidification in the microarea and dissolution of metal in the region adjacent to the inclusion. The mechanism for the crevice corrosion is of importance after the microcrevice forms. The observations showed that sulphur precipitated on the area surrounding the inclusion group in acidic sodium chloride solution. This is in contrast to the finding in prior studies by electron probe or EDX analyses in which sulphur precipitation was only observed on the inclusion. Because pitting normally occurs on surfacesthat are initially exposed to air before being immersed in the corrosive solution, an understanding of the change of surface film associated with the change of medium is very important. XPS was used in this work to study the air formed and aqueous films, the transformation when the specimens were immersed in solutions. The study of the energy-loss structure of photoelectron peaks has lead to a better understanding of these various films. It has been used to study in greater detail the composition and properties of the films formed on Fe-Cr alloys during oxidation, vacuum annealing, and to find the relationship between the depth distribution of the components in the films and energy loss background of photoelectron peaks. Three features are of particular importance: the background loss tail height, the baseline slope and the post-peak loss structure. These features have been related quantitatively to the relative amounts of the element and the surrounding matrix in the layers which contribute the greatest signal at any given take-off angle. The present work illustrates that the additional depth information available from closer inspection of the inelastic loss background feature may aid an understanding of the change from the air-formed film to the aqueous film as well its effect on the initiation of pits in stainless steel 316. The combination of AES and EDX with high spatial resolution gave an opportunity to re-investigate the initiation of pits at the site of inclusion on stainless steel by offering both bulk and surface information. The use of AES and XPS associated with the energy loss structure of photoelectron peaks facilitates a comprehensive understanding for the whole surface of various films and the local areas which are involved in the formation of pits.

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5

Nakajima, Hidemasa. "On the detection and behaviour of second phase particles in steel melts". Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75341.

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The behaviour of second phase particles in molten steel processing vessels was investigated, using the E.S.Z. (Electric Sensing Zone) method, in conjunction with aqueous modelling and molten steel systems.
1. Slag droplet entrainment/dispersion is an axisymmetric gas injection stirred system was investigated: A tank containing a water-olive oil simulation of stirred ladles of molten steel was used. Extensive numerical predictions of the oil (slag) droplet population distributions within the vessel were also carried out, and reasonable agreement with the experimental data achieved. Droplet dispersions were shown to be time and spatially dependent.
2. Inclusion separation characteristics in tundishes of continuous steel casting operations were investigated. The mixed reactor model proved to be adequate for predicting particle separation behaviour, proved that the effective upper surface area of the dispersed plug flow region is known, a priori.
3. An on-line method for the detection and measurement of inclusions in molten steel systems was developed. Inclusion removal rates within an induction furnace, as well as inclusion separation behaviour in a commercial scale tundish for continuous billet casting, were measured.

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6

Hussain, I. "A comparison of the cleanliness of steels treated with calcium-silicon and magnesium". Thesis, University of Wolverhampton, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234259.

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7

Deng, Zhiyin. "Study on the Interaction between Refractory and Liquid Steel Regarding Steel Cleanliness". Doctoral thesis, KTH, Mikro-modellering, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-190071.

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The present thesis focuses on the interaction between refractory and liquid steel. The aim of this work is to understand the interaction behavior between refractory and liquid steel regarding steel cleanliness. The effect of different refractories on different inclusions in Al-killed steel was studied in a furnace. The sintering mechanism of filler sand were also investigated in laboratory. In the industrial trials, the attachments of different oxides on the walls of submerged entry nozzle (SEN) were discussed in the cases of high strength low alloy steel (HSLA) and ultra-low carbon steel (ULC). It is found that the effect of alumina and spinel refractory on all the three types of inclusions is very little, while MgO refractory influences the inclusions depending on the activity of dissolved oxygen in liquid steel. At low oxygen level, alumina inclusions could transform into spinel inclusions with the help of MgO refractory, while the effect on spinel and calcium aluminate inclusions is not evident. On the other hand, when the activity of dissolved oxygen is high enough, the evolution of spinel inclusions from alumina inclusions could not be seen. The reaction between chromite and silica grains leading to liquid formation is the main mechanism for the sintering of filler sand. The factors viz. steel composition, silica size and content, operation temperature and process holding time have a strong influence on the sintering of the filler sand. Smaller size and higher content of silica in sand, steel grades containing higher Mn and Al contents, higher temperature and longer holding time would result in serious sintering. The choice of the sand needs to take those factors into account. The results show that solid alumina particles are always agglomerated on the inner wall of SEN in the case of ULC steel. The top slag with high FeO and MnO contents is considered as the main reason of this kind of attachments. The removal of slag might be a good method to avoid the attachments. In the case of HSLA steel, liquid calcium aluminate inclusions could attach on the inner wall of SEN as well. The smoothness of the inner wall of the SEN holds the key of liquid attachments. In addition, the attachment situation on the outer wall of SEN depends on the operations. The oxygen entrainment through the mold powder would result in the formation of plate-like alumina attachments. The control of reoxidation due to oxygen entrainment would help to avoid this situation.

QC 20160816

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8

Söder, Mats. "Growth and removal of inclusions during ladle refining". Doctoral thesis, KTH, Materials Science and Engineering, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-45.

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The overall purpose of this thesis work has been to further our understanding of the growth and removal of inclusions in gas- and induction-stirred ladles. The primary focus has been on alumina inclusions.

Growth mechanisms were studied using data from fundamental mathematical models of gas- and induction-stirred ladles. The results showed the turbulence mechanism to be the most dominant in alumina inclusion growth. The dynamic growth and removal of inclusions in a gas-stirred ladle was studied using mathematical modelling. The model results showed concentration gradients of inclusions. The effect was most obvious in the steel flow past the removal sites: top slag, ladle refractory, and gas plume (bubble flotation). A new removal model was developed for large spherical caps bubbles.

In order to verify the predicted concentration gradients for the size population of inclusions, three experiments were carried out in production. The sampling equipment enabled sampling at five different positions and different locations at the same time. The results showed that concentration gradients of inclusions do exist both in induction-stirred and gas-stirred ladles. A theoretical analysis showed that the drag force on the inclusions to be the dominating force and that therefore inclusions follow the fluid flow.

The cluster behaviour of alumina inclusions were examined on steel samples taken in an industrial-scale deoxidation experiment in a ladle. The samples were examined by microscope and the results used to study cluster growth. It was found that there was rapid cluster growth due to collision during stirring and that at the end of the deoxidation experiment a majority of the small inclusions were bound in clusters. The cluster growth data determined using the microscopic results were compared with predicted cluster-growth data. A method was developed for converting the experimental data observed per unit area into data given per unit volume and vice versa. An expression for the collision diameter of the cluster was also developed. The results showed that the predicted cluster growth agreed well with the microscopic observations for the assumptions made in the growth model.

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9

Tian, Chenguo. "On the removal of non-metallic inclusions from molten steel through filtration". Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=59991.

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Non-metallic inclusions in steel such as alumina, silicates, etc. are detrimental to many steel properties. Elimination of these inclusions has long been a major target in steelmaking.
In this investigation, attempts have been made to remove these non-metallic inclusions by passing the liquid steel through a ceramic filter. It was found that this approach is very effective for removing solid non-wetting inclusions such as alumina. It appeared that liquid silicates could also be removed to some degree.

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10

Dey, Arghya. "The effect of steel composition on the behaviour of inclusions during steelmaking". Thesis, University of Sheffield, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.500451.

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11

Holman, Alan Edwin Lee. "Fatigue of a spring steel with varying levels of non-metallic inclusions". Thesis, University of Plymouth, 2001. http://hdl.handle.net/10026.1/1980.

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Plain specimens of two batches of the commercial spring steel BS 251A58 of nominally identical processing but significantly differing levels of non-metallic inclusion levels, have been tested in rotating bending. The data produced has been analysed against some recent methods for the prediction of fatigue properties in high strength materials containing defects. The materials tested were specifically selected for their disparate cleanliness levels, yielding specimens with differing inclusion distribution and maxima. The morphology of critical inclusions is identical between the two material batches. Material microstructure is tempered martensite with ultimate tensile strength of approximately 2000 MPa, which renders it well above the strength level where sensitivity to defects causes variability in fatigue behaviour. Models have been selected from the literature for the prediction of fatigue limit using characterisation of the local microstructural state and the size and critical position of non-metallic inclusions. These models have been validated by the analysis of specific failures after fractographic analysis. It has been shown that these models are acceptably accurate and generally conservative. Difficulties in experimental work have precluded the planned measurement of crack growth rates during the current test work. These difficulties have yielded a superimposed mean stress to the rotating bend test. This mean stress has been quantified for each test and the result coupled with a parameter for mean stress correction. The validity of the mean stress correction has been proven in this work to be valid. More consistent results are observed for the mean stress corrected data. A statistical method for the prediction of maximum non-metallic inclusion size for a given number of specimens or components from small sample microsection analyses has yielded good results when compared to the fractographic observations. This work has investigated the effect of varying magnification level and number of fields surveyed on the accuracy of prediction and recommendations are made for the method for obtaining best accuracy. A 'unified' crack propagation life model from the literature has been applied which combines long and short crack growth regimes. The model has shown good correlation to the current data but only after fitting of constants and only within the low cycle regime. Relationships presented in the literature between constants and the material ultimate tensile strength were found to be inapplicable to the current material at this strength level.

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12

Corrigan, Martin Robert. "The effect of nitrogen and inclusions on fracture and fatigue of steel". Thesis, Sheffield Hallam University, 2007. http://shura.shu.ac.uk/19502/.

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The dynamic strain ageing behaviour of seven heats of C-Mn steel and an interstitial free steel has been examined from 20°C to 350°C, using slow strain rate tests (SSRT's) at strain rates of 2 x 10[-6] s[-1] and 2.67 x 10[-6] s[-1]. The steels were chemically analysed for the key elements, and additional specialised testing was carried out using internal friction to determine the free nitrogen and carbon content. The effects of temperature on the mechanical properties were investigated in detail. In agreement with previous studies, work hardening peaks, minima in ductility, and negative strain rate dependences of the flow stress were observed between 100°C and 350°C. The positions of which depended on the free nitrogen content and strain rate. It was found that the DSA strengthening due to interstitials was found to be proportional to the log of the free carbon plus free nitrogen. An investigation has been undertaken to examine the ductility and J[1c], dJ/da response of a range of experimental steels containing a range of carbon, nitrogen and sulphur values on 25 mm CT specimens. The tests were carried out at 20°C and 200°C, in the so called blue - brittle range. It was found that the crack initiation resistance J[1c] and the crack growth resistance dJ/da in the dynamic strain ageing region were 30% - 40% lower than at room temperature. Increasing the sulphur content resulted in a 5% -10% reduction of these values. With a further reduction of 8% of these values in a 8 ppm DOW environment at 200°C. Environmental testing was done in a chamber specifically designed for the purpose. It was also found that a linear relationship approximates the relationship between the integral of the J vs Qa curve and the Charpy upper shelf energy. From Charpy tests carried out it was found that the Impact Transition Temperature is proportional to the square root of the free nitrogen content, and that a reciprocal type relationship exists between the Charpy upper shelf energy and volume fraction of inclusions. In agreement with previous studies. Fatigue testing was done at 150°C in air on 11.85 mm thickness specimens. Post test examination of fracture surfaces was carried out using scanning electron microscopy. It is shown that increased levels of free nitrogen and carbon reduced fatigue crack growth rates. This is also confirmed by reduced striation spacing. The effect of interstitials on da/dN is shown to be related to increased yield strength. A modified Ashby model is presented which enables engineering evaluations of the effect of volume fraction of MnS inclusions (V[f]), and free interstitial content (N[f]) on the strain to fracture from 20°C to 300°C. When the model was compared to two sets of published data it was found that, within an error bar tolerance of +/-20%, that 66% and 75% of the data points fell within them.

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13

Mazumdar, Dipak 1932. "Fluid flow, particle motion and mixing in ladle metallurgy operations". Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=72064.

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Extensive computer predictions have been carried out by the author to study flow, addition dispersion and particle motion during central gas injection into cylindrical vessels. In conjunction with numerical computations, experiments were conducted in a 0.30 scale water model of a 150 ton steel processing ladle, using a Froude number scaling criterion. Two typical gas injection configurations (i.e., conventional central injection and C.A.S. alloy addition procedure) were investigated.
Flow visualization studies were carried out using a suspended network of silken threads, mean velocity vectors and overall flow patterns were determined by video recording techniques, while mean velocity vectors and associated turbulence level were also measured with laser doppler velocimetry. These measurements show very reasonable agreement with equivalent numerical predictions.
To simulate the subsurface motion of additions, spherical wooden balls of various densities were dropped from typical heights, and their subsurface trajectories, immersion times, etc., recorded by means of a video recorder. Frame by frame analysis of the video tapes showed trends which are in good accord with computed trajectories.
Mixing times of simulated molten additions were measured by the conductivity measurement technique. These were compared with prediction from an equivalent tracer dispersion model and excellent agreement achieved.
For industrial application, flow, particle motion, and mixing times in a 150 ton steel processing ladle have been predicted and their technological significance discussed.

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14

Safa, Meer. "3D study of non-metallic inclusions by EEmethod and use of statistics for the estimationof largest size inclusions in tool steel". Thesis, KTH, Materialvetenskap, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-93770.

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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.

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15

Beskow, Kristina. "Formation and Chemical Development of Non-metallic Inclusions in Ladle Treatment of Steel". Doctoral thesis, KTH, Materials Science and Engineering, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3598.

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The present study was carried out to investigate theformation and chemical development of non-metallic inclusionsduring ladle treatment of steel.

To begin with, an investigation of the deoxidation processand the impact of aluminium addition was carried out. For thispurpose, a new experimental setup was constructed. The setupallowed the examination of the deoxidation process as afunction of time by using a quenching technique. Preliminaryexperiments showed that homogeneous nucleation of alumina tookplace in the areas supersaturated with aluminium. Theseexperiments also showed that agglomeration of alumina particleswas a very rapid process, even when the convection in the meltwas negligible.

In order to examine whether aluminium supersaturation occursduring industrial practice, the deoxidation of liquid steelwith aluminium wire injection in a gas-stirred ladle wassimulated by mathematical modeling using a Computational FluidDynamics (CFD) approach. The results showed that theconcentration of aluminium in the vicinity of the aluminiumwire injection was high enough to generate homogeneousnucleation of alumina.

Aiming at an understanding of the inclusion chemistry duringthe ladle process, an industrial study was performed atUddeholm Tooling AB. The impact of slag-lining reactions andladle glaze as a source of inclusions in the melt was alsostudied. The experimental results were analysed from athermodynamic viewpoint to gain an insight into the origins ofthe inclusions and their changes along the process of the ladletreatment. Six types of inclusions were found in the steel. Thetypes of inclusions present varied along the history of theladle treatment. Three types of inclusions were found in theliquid steel before deoxidation, namely type A (a liquidinclusion with high SiO2 concentration), type B (spinel) andtype C (a combination of type A and type B). Thermodynamicanalysis indicated that these types of inclusions could begenerated by the reaction between the Electric Arc Furnace(EAF) slag and the ladle glaze, during the filling of theladle. The addition of aluminium resulted in the formation ofalumina inclusions (type E), which agglomerated and separatedfrom the steel very fast. The spinel inclusions of type B werefound to be unstable at low oxygen potentials. The inclusionsof this type would react with the liquid metal forming theinclusions of type F (spinel in the centre surrounded by anoxide solution containing Al2O3, CaO and MgO). Further,reaction between the liquid metal and inclusions of type Fwould result in the inclusions of type G, an oxide solutionmostly consisting of Al2O3 and CaO with small amounts of MgOand SiO2. The inclusions of type G were the only inclusionsfound in the steel before casting.

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16

Daly, Deryck C. "Infulence [sic] of inclusions on the ductile tearing resistance of AISI 303 stainless steel". Thesis, Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/11186.

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17

Luo, Chunhui. "Modeling the behavior of inclusions in plastic deformation of steels". Doctoral thesis, Stockholm, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3158.

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18

Riyahimalayeri, Kamrooz. "Slag, Steel, Ladle and Non-metallic Inclusions Equilibria in an ASEA-SKF Ladle Furnace". Doctoral thesis, KTH, Termodynamisk modellering, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-102149.

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This study explores the possibility of prediction and modification of some of the physicochemical properties of non-metallic inclusions by considering top slag-steel-ladle equilibria in an ASEA-SKF ladle furnace. To test the reliability of an available computational thermodynamic computer program, the first sub project was done. It was concluded that LiMeS, an interface for Thermo-Calc, is a useful tool for slag-steel equilibrium calculations. The second sub project was set out to find some model/s that could calculate the most accurate oxygen activity of molten steel compared to the measured one. This study concluded that both Wagner’s and Turkdogan's equations are useful. It was further seen that increasing the Al contents in the molten steel, increasing the CaO/Al2O3 ratio in the top slag, and reducing the temperature, resulted in reduction of the oxygen activity of the molten steel. In the third sub project a comparison was made between measured CaO and Al2O3 (normalised to CaO-Al2O3) in top slag, calcium aluminate inclusions, and the results of theoretical calculations. The average contents of CaO and Al2O3 in all inclusions were close to the composition of the phase Ca12Al14O33 and the contents of CaO and Al2O3 in the slags were close to the composition of the phase Ca3Al2O6 in the binary phase diagram of CaO-Al2O3. The forth sub project set out to study the effect of vacuum degassing time on non-metallic inclusions. It was concluded that during the vacuum degassing process the share of calcium aluminates compared to spinels, Ca content of the oxides, and the average equivalent circle diameters of the oxides were increasing, and oxides tended to form spherical shapes. Finally, based on the preceding four sub projects, the fifth sub project aimed to optimize the steel treatment in an ASEA-SKF ladle furnace. The final results showed that by adding 200 kg fluorite to the top slag of 1200 kg, it was possible to achieve a sulphur content of less than 10 ppm in the steel and a sulphur ratio between slag and steel of 1570, and at the same time reduce the oxygen activity of the molten steel and the degassing time.

QC 20120917

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19

Safavi, Nick Arash. "A theoretical analysis of the interaction betweenpores and inclusions during the continuouscasting of steel". Licentiate thesis, KTH, Metallernas gjutning, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-174077.

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The possibility of cluster formation during solidication of steel is explored to explain structures that are seen on the fracture surface of the steel. A hypothesis is built that postulates porosities provide favourable locations for inclusions to agglomerate and form clusters. A thermodynamic model is constructed to describe precipitation of porosity and inclusions. Formation of inclusions follow a nucleation and growth mechanism. Porosities on the other hand are the product of pressure balance in the liquid. Motion of pores and inclusions is analysed based on the drag force and surface stresses. Gradient of surface tension is also identied as a driving force which acts on the pore surface and would cause motion. It is shown that relative motion of pores and inclusions coupled with the inclusion tendency to get attached on pore surface makes or a viable mechanism explaining agglomeration of inclusion particles to clusters

QC 20150930

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20

Du, Hongying. "THE EVALUATION OF NON-METALLIC INCLUSIONS IN CALCIUM-TREATED STEEL BY USING ELECTROLYTIC EXTRACTION". Thesis, KTH, Materialvetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-191786.

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This study aims on characterization of non-metallic inclusions (oxides and sulfides) in steel with and without Calcium treatment. In this paper, the three-dimensional (3-D) investigation method of inclusions on film filter after Electrolytic Extraction (EE) of steel samples is applied on two different steel grades (280, 316L). Image analysis of non-metallic inclusions is carried out on Scanning Electron Microscope (SEM) images following with inclusion characteristic analysis. Steel samples with calcium treatment in the production process and reference samples was investigated and compared in density, size and composition. It shows that higher magnification and larger inclusion size correspond to more accurate result. With restriction of equipment and measurement, 2μm is the smallest size could be measured in ×500 magnification within 5% error. The comparison of distribution of inclusions varies with different zones: center has the largest size with least number of NMI; surface has the smallest size with largest number of NM; middle part has the median properties. In 316L steel, Ca treatment increases the number of oxides inclusions significantly; the content of Ca and Si in oxides inclusions is also increased. Two shapes of oxides inclusions, oval and elongated ones, are found with Ca treatment. In 280 steel, the total amount of NMI decreases slightly with Ca treatment; CaS is found in spherical inclusions; Because of earlier formation of larger size spherical inclusions, higher Ca content is found than that in smaller size spherical inclusions.

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21

Isaksson, Henrietta. "Evaluation of 25 MHz Ultrasonic Testing for Detection of Non-Metallic Inclusions in Steel". Thesis, KTH, Materialvetenskap, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-297638.

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Quantification of inclusions is important since it is correlated to the steel’s fatigue properties. One method that could be further developed for detection of inclusions in steel is ultrasonic testing (UST). The aim of this study is to investigate what type of inclusions, in terms of size, morphology and chemical composition, that can be detected with 25 MHz UST, and what type of inclusion that cannot be detected. This was done by firstly scanning 74 steel samples with 25 MHz UST, and then fatigue test the same samples until fracture. The inclusion that caused the fracture was then analysed with microscopy and compared with the results from the 25 MHz UST. It was found that Mn-Mg-sulphides, Ca-sulphides, oxy sulphides and complex oxides are difficult to detect with 25 MHz UST. Globular oxides can be detected with 25 MHz UST, at least down to an area of 8300 μm2 and if they are not too fragmented due to rolling. The results indicate that oxy sulphide stringers can be detected with 25 MHz UST if the inclusion have oxides in direct contact with the steel matrix, rather than oxides encapsulated by sulphides.
Kvantifiering av inneslutningar är viktigt då det korrelerar med stålets utmattningsegenskaper. En metod som kan utvecklas för detektering av inneslutningar i stål är ultraljudstestning (UT). Syftet med den här studien är att undersöka vilken typ av inneslutningar, med avseende på storlek, morfologi och kemisk sammansättning, som kan detekteras med 25 MHz UT, och vilken typ av inneslutningar som inte kan detekteras. Detta gjordes genom att först skanna 74 stålprover med 25 MHz UT och sedan utmattningstesta samma prover tills de gick till brott. Inneslutningen som orsakade brottet analyserades sedan med mikroskopi och jämfördes med resultaten från 25 MHz UT. Det visade sig att Mn-Mg-sulfider, Ca-sulfider, oxisulfider och komplexa oxider är svåra att upptäcka med 25 MHz UT. Globulära oxider kan upptäckas, åtminstone ner till en area på 8300 μm2 och om den inte har blivit för fragmenterad av valsning. Resultaten indikerar att oxisulfider kan detekteras om oxiderna är i direkt kontakt med stålmatrisen, i stället för att oxiderna är inkapslade av sulfider.

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22

Collins, Sunniva Refsnes. "Forging effects on manganese sulfide inclusions as fatigue initiation sites in AISI 4140 steel". Case Western Reserve University School of Graduate Studies / OhioLINK, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=case1057696631.

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23

Jansson, Sune. "A study on molten steel/slag/refractory reactions during ladle steel refining". Licentiate thesis, Stockholm, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-312.

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24

Kumar, Deepoo. "Development of a Reliable Kinetic Model for Ladle Refining of Steel". Research Showcase @ CMU, 2018. http://repository.cmu.edu/dissertations/1169.

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The advancement in computational thermodynamics can help researchers to test their hypotheses regarding complex steelmaking operations in a more quantified manner. The main aim of the current work was to use develop a kinetic model that can predict changes in steel, slag and inclusions during ladle refining and use this model as a tool to develop better understanding of the steelmaking process itself. The important reactions during ladle refining are: steel-refractory reaction, slag-refractory reaction, flotation of inclusions to slag, steel-inclusion reaction, steel-slag reaction and inclusions originating from slag. The chemical reactions between two phases were considered to be mass transfer controlled. The macro-processing feature in FactSage was used to do multiple equilibrium calculations and calculate the change in steel, slag and inclusion composition. Targeted experiments and industrial trials were conducted to find model parameters. For laboratory experiments, the rate of magnesium-transfer to oxide inclusions in steel due to steel-crucible and steel-slag reaction was studied. It was concluded that the presence of spinel layer on MgO crucible at the steel-crucible reaction can help in significantly reduce the rate of Mg pick-up due to steel-crucible reaction. For industrial trials, a comparison between the rate of steel-slag reaction and inclusion flotation rate showed that the steel-slag reaction could be significantly slowed due to slag inhomogeneity. The kinetic model was also used to identify artifacts in steel and slag sampling during ladle refining. One of the main limitations of the kinetic model was the over-prediction of calcium pick-up in steel due to steel-slag reaction. Induction furnace experiments were conducted using MgO, ZrO2 and CaO crucible with different slag composition and silicon concentration to study the extent of calcium pick-up due to steel-slag and steel-crucible reactions. The steel-CaO crucible equilibrium experiment was used to estimate Ca-O interaction parameter. The equilibrated steel was reoxidized with known amount of oxygen to allow all the dissolved calcium to precipitate as oxide inclusions. Inclusion analysis of sample taken after reoxidation was used to estimate dissolved calcium in steel. The measured dissolved calcium was used to estimate Ca-O interaction parameter. A private database for liquid steel was created in FactSage and used for kinetic modeling of laboratory scale steel-slag-crucible experiments. The use of private database for kinetic model helped in avoiding excess calcium pick-up in steel due to steel-slag reaction. However, the model and database should be tested for conditions where significant calcium pick-up is experimentally observed. In the present work, the inclusion removal was assumed to be first order reaction with fixed rate constant. In practice, the inclusion removal is expected to be a more complicated process of agglomeration and flotation. Similarly, the steel-inclusion reactions were considered in equilibrium for each time step of calculation. Sometimes, the composition difference inside single inclusions was found. Some characterization tools were used that could be useful in future to study the agglomeration of inclusions and composition differences inside single inclusion. The agglomeration behavior of inclusions at the steel-argon interface inside confocal laser scanning microscope was compared to the agglomeration in bulk samples from laboratory and industrial steel samples. The size and morphology of inclusion clusters were studied using X-ray micro CT. The composition and morphology of single inclusion was studied using focused ion beam methods: Ga-FIB instrument and plasma-FIB instrument.

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Hekkanen, Mikko. "Inclusion Rating of Clean Steels". Thesis, Örebro University, Department of Technology, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:oru:diva-7786.

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The main part of this work has been a literature survey, reviewing scientifical reports forinformation on how steel cleanness is evaluated today, and also how the steel cleanness is related tothe fatigue performance of clean steels.

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Tripathi, Nagendra. "A Study on the Population and Chemical Development of Non-Metallic Inclusions in the Tool-Steel Making Process". Doctoral thesis, KTH, Materials Science and Engineering, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3827.

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The present work was to study the population and chemicalcharacterization of the inclusions at different steps of thetool steel making process based on industrial trialexperiments. The inclusion populations were found to increasewith ladle age (number of heats ladle being used) beforealuminium deoxidation and before casting. A substantialincrease in inclusion population was noticed after a certainladle age. The analyses of the steel samples from thesolidified ingot revealed a non-uniform distribution ofinclusions. The inclusion populations in the final productswere also found to increase with the ladle age.

Totally four types of inclusions, viz. Type-1 (MgO), Type-2(an oxide solution), Type-3 (spinel), and Type-4 (spinel in thecenter surrounded by the oxide solution of Type-2) wereobserved before deoxidation. Thermodynamic calculation revealedthat the Type-2 and Type-4 inclusions were generated by thereactions between EAF slag and ladle glaze. Three types ofinclusions were found before casting, viz. Type-6 (spinel inthe center surrounded by the oxide solution of Type-7), Type-7(oxide solution with low contents of MgO and SiO₂), and Type-8 (small MgO islands embedded in anoxide solution). Inclusions of both Type-6 and Type-7 were theproducts of the reaction between inclusions of Type-3 and theliquid metal. On the other hand, the occurrence of pieces ofMgO having sharp edges in the oxide solution suggested that theType-8 inclusions were generated by the ladle glaze. In thesteel samples during mould fillings, totally three types ofinclusions namely, Type-6, Type-7, and Type-9 (alumina basedinclusions) were found. The Type-9 inclusions were originatedfrom the erosion of the nozzles and the closing gates duringthe mould filling. The steel samples after casting were foundto contain inclusions of Type-6, Type-7, Type-9, Type-10(alumina-silicate oxide solution), and Type-11 (spinel phasewith calcium sulphide). The types of inclusions were found tovary with the position in the ingot. In the final productsType-6, Type-7, and Type-11 inclusions were found. While almostall the inclusions in the final products were originated in theladle before casting, sulphur was detected in all types ofinclusions. The increase in the sulphur activity of the steelmelt during casting was the cause of the formation ofoxide-sulphide and calcium sulphide phases in the inclusionsdetected after casting and in the final products.

A preliminary examination on the possibility of inclusionseparation by bubble floatation using cold models was alsocarried out. Deionised water and silicon oil were used as thebulk phase. Charcoal particles of different size ranges wereemployed as the dispersed phase. The examination of thecharcoal-water-gas system indicated that the positivefloatation coefficient was not a sufficient condition for theinclusion separation. The experimental results were found to bein contradiction with the prediction of a typical model thatconsiders interfacial energies. The omitting of the drag forcewas believed to be the reason causing the failure of the modelprediction in the charcoal-water-gas system. The failure of themodel prediction suggested a need of a new model taking intoaccount interfacial energies, drag force, buoyancy force andgravity force.

Key words:non-metallic inclusions, ladle metallurgy,ladle glaze, inclusion population, ladle age, ingot casting,interfacial tension, inclusion separation

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Sjökvist, Thobias. "Influence of Ferrochromium and Ferromanganese Additions on Inclusion Characteristics of Steel". Doctoral thesis, KTH, Materials Science and Engineering, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3150.

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Zhiyue, Wan. "Application of some modern analytical techniques for investigations of non-metallic inclusions in steel samples". Thesis, KTH, Materialvetenskap, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-231963.

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The non-metallic inclusions (NMI) have large influence on steel properties. Therefore, evaluation of inclusion size, number, composition and morphology by using modern analytical techniques are very important for control of steel production and steel quality. Three dimensional analysis method of electrolytic extraction is applied in this work. Metals are dissolved and undissolved inclusions are collected on the film filter. Scanning Electron Microscope (SEM) with Energy Dispersive Spectrometer (EDS) is applied to observe different non-metallic inclusions. Apart from electrolytic extraction, several other different methods can be used to analyse the inclusions. Each of them has their advantages and drawbacks. A part of this work compares different methods for investigation of inclusions. To modify the inclusion size, number and morphology, calcium or zirconium can be added in to the steel with certain amount according to the steel grade. This work discussed how inclusion size, number and morphology changed after the modification. In samples of Heat A, the addition of Zr leads to the appearance of ZrO2 clusters. Large size particles disappeared while the peak value for the number of inclusions per unit volume didn’t decrease. The electrolytic extraction and fractional gas analysis (FGA) results show some differences on the inclusion compositions. In samples of Heats B and C, the effect of calcium treatment is investigated. Calcium treatment modified the spinels with large content of Al2O3 into spherical CaS+CaO-MgO-Al2O3 inclusions. Large size inclusions were removed after calcium treatment.Key

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Adolfi, Sofia. "Slag inclusion formation during solidification of steel alloys and in cast iron". Licentiate thesis, Stockholm : Materialvetenskap, Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4371.

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Björklund, Johan. "A study of slag-steel-inclusion interaction during Ladle treatment". Licentiate thesis, KTH, Materials Science and Engineering, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4018.

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The thesis is based on two supplements with two major objectives. In the first supplement equilibrium top slag-steel bulk and inclusions-steel bulk were investigated by comparison between calculated and measured oxygen activity values. This was done by applying different oxide activity models for slags combined with thermodynamic calculations. In the second supplement the inclusion composition is studied during the ladle refining process. The inclusion composition is related to top slag composition and other parameters during ladle

treatment.

The work was carried out by collecting data during well controlled sampling procedures at two different steel plants. Extensive inclusion analyses in Scanning Electron Microscope, SEM, were done. The data was used together with thermodynamics for a description of the interaction between slag-steel-inclusion interaction during ladle treatment.

Evaluation of inclusion composition during the ladle refining have revealed that the majority of the inclusions belonged to the system Al₂O₃-CaO-MgO-SiO₂and showed a continuous composition change throughout the ladle refining process, from high Al₂O_3, via MgO-spinel to finally complex types rich in CaO and Al₂O_3. The final composition after vacuum treatment was found to be close to the top slag composition. Small process parameter changes and practical variations during ladle refining were proven to give large differences of the inclusion composition.

Finally, it was concluded that equilibrium does not exist between top slag and steel bulk, with respect to oxygen, for the studied conditions. However, the equilibrium does exist between the steel bulk and inclusion.

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Godon, Julie. "Influence of steel cleanliness on the wire drawing of hypereutectoid steel fine filaments". Thesis, Lille 1, 2020. http://www.theses.fr/2020LIL1R005.

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La fabrication de très fins filaments (60 µm de diamètre) d’aciers à haute teneur en carbone et à haute résistancereste un défi technologique. En effet, durant le tréfilage de ces filaments, des ruptures ont été observées limitantainsi l’obtention de bobines de grande longueur. Le but de cette étude en partenariat avec la société BEKAERTNV est de comprendre le rôle de la microstructure de l’acier, et plus précisément la propreté inclusionnaire, surl’occurrence des ruptures lors du tréfilage humide.Il est clairement montré que la rupture lors du tréfilage est essentiellement associée à la présence d’inclusions.Ainsi, une première étape a consisté à développer une méthodologie pour identifier ces inclusions. 90% desfilaments rompus impliquent les inclusions suivantes : SiO2, ou SiO2-CaO ou SiO2-MgO. La rupture des fils résultede la décohésion de l'inclusion de la matrice. Les inclusions présentent une large distribution de taille maismesurent en moyenne 6 µm. Les paramètres critiques liés aux inclusions pour l’occurrence de la rupture sontmultiples : densité d'inclusions, taille et composition chimique. La taille critique de l’inclusion dépend de lacomposition chimique. De plus, les paramètres du procédé de tréfilage jouent également un rôle important dansl’occurrence des ruptures. Les propriétés mécaniques du fil et l’angle de filière apparaissent comme des paramètresimportants pour réduire le taux de rupture.Une analyse plus approfondie des changements microstructuraux autour de l'inclusion par EBSD et la modélisationsoulignent un impact réel de l'inclusion sur la déformation locale autour de l'inclusion. L'analyse locale (MET etACOM - Automated Crystal Orientation Mapping) de l'interface inclusion/matrice montre une différence demicrostructure près du bord de l'inclusion le long de l'axe de tréfilage et une déformation locale plus élevée.L’étude de ces différents paramètres permet la proposition d’un mécanisme de rupture qui prend en compte dansle fil la part de matière cisaillée et la part de matière soumise à de la traction
The production of very fine filaments (60 µm in diameter) of high carbon and high strength steels remains atechnological challenge. Indeed, during the drawing of these filaments, fractures have been observed limiting theobtaining of coils of great length. This study, in collaboration with company BEKAERT NV, is to understand therole of the microstructure of steel, and more specifically the steel cleanliness on the occurrence of fracture duringwet drawing.Methodologies for inclusion identification and for inclusion count were developed. 90 % of the fractured filamentswere associated with an inclusion which was SiO2, or SiO2-CaO or SiO2-MgO. The fracture of the wires resultedfrom debonding of the inclusion from the matrix. Inclusions exhibited a wide range of sizes but mostly around6µm. The inclusion density did not appear as the only parameter that affects the fracture occurrence. An importanteffect of size and of chemical composition inclusion of the inclusions was found. A critical size of inclusions forfracture was observed but it depends on the chemical composition of inclusions. The drawing parameters also playan important role in the fracture occurrence. The wire mechanical properties and the die angle appears to beimportant parameters in view to reduce the fracture ratio.A deeper analysis of the microstructural changes around the inclusion by EBSD and modelling underlines a realimpact of the inclusion on the local deformation around the inclusion. The local analysis (TEM and ACOM -Automated Crystal Orientation Mapping) of inclusion/matrix interface shows a difference of microstructure at theinclusion edge along the drawing axis and a higher local deformation. The study of these different parametersmakes possible to propose a fracture mechanism that takes into account the part of the material subjected to shearand the one subjected to tensile stress

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Bannister, S. R. "The effect of inclusions and matrix hardenability upon the microstructural development of carbon manganese steel weld metals". Thesis, University of Southampton, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.378675.

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Amuzuga, Kwassi. "Damage mechanism related to plasticity around heterogeneous inclusions under rolling contact loading in hybrid bearings ceramic/steel". Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI154.

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La durée de vie des pièces mécaniques en contact est fortement affectée par la présence d'hétérogénéités dans le matériau, comme des renforts (fibres, particules), des précipités, des porosités, ou encore des fissures. Des hétérogénéités dures et de formes complexes peuvent créer des surcontraintes locales, initiatrices de fissures par fatigue à proximité de la surface de contact. Une analyse quantitative des surcontraintes créées par les hétérogénéités est nécessaire à la compréhension des mécanismes d'endommagement. Cette étude s'applique à des roulements de ligne d'arbre qui font partie des éléments critiques de moteurs en aéronautique. Elle vise à déterminer précisément la distribution du champ de pression sur l'aire effective de contact et à prédire le profil et l'évolution des champs de contraintes/déformations à chaque passage de la charge sur un volume élémentaire représentatif prenant en compte le gradient de dureté, la présence de carbures et l'existence des contraintes initiales d'origine thermochimique. Une partie de l’étude est consacrée au développement d’un solveur du problème de contact roulant élasto-plastique avec présence d’hétérogénéité par les méthodes semi analytiques assurant un excellent gain en temps et ressources de calculs. Ensuite, un algorithme homogénéisation a été conçu pour analyser le comportement effectif d’un massif élasto-plastique hétérogène sous indentation. Enfin une partie expérimentale est dédiée à la caractérisation microstructurale des aciers étudiés dans le but de déterminer leurs propriétés. Les analyses des résultats de cette étude concourent à soutenir que bien que les inclusions de particules non métalliques soient responsables de la haute résistance de ces matériaux, certaines d’entre elles (celles de longueur dépassant les dizaines de micromètre ou celles qui forment des chaines dans une direction particulière) deviennent, au cours des cycles de fatigue, les principales sources d’endommagement depuis l’échelle locale jusqu’à la rupture globale de la structure
The lifetime of contacting mechanical parts is strongly affected by the presence of heterogeneities in their materials, such as reinforcements (fibers, particles), precipitates, porosities, or cracks. Hard heterogeneities having complex forms can create local overstress that initiating fatigue cracks near the contact surface. The presence of heterogeneities influences the physical and mechanical properties of the material at microscopic and macroscopic scales. A quantitative analysis of the over-stresses generated by heterogeneities is necessary to the comprehension of the damage mechanisms. The present study is applied to rolling bearings which are the critical elements of the aero-engine's mainshaft. The performance required for these bearings, led SKF Aerospace to introduce a new technology of hybrid bearing with ceramic rolling elements on high-strength steels having experienced a double surface treatment (carburizing followed by nitriding). The study aims to precisely determine the pressure field distribution on the effective contact area and to predict the profile and the evolution of the stress/strain fields at each loading cycle on a representative elementary volume that takes into account the gradient of hardness, the presence of carbides and the existence of an initial compressive stress from thermochemical origin. A major part of this study is devoted to develop a heterogeneous elastic-plastic rolling contact solver, by semi-analytical methods ensuring an excellent saving of calculation time and resources. Thereafter, a homogenization algorithm was built to analyze the effective behavior of a heterogeneous elastic-plastic half-space subjected to an indentation loading. Finally, an experimental part is dedicated to the microstructure characterization of the studied steels with intent to determine their properties. A description of the carbides behavior inside the matrix during micro-tensile tests was carried out under SEM in-situ observation. In the scheme of all analyses conducted in the present work, it can be argued that, although the heterogeneities (such as carbides or nitrides) are responsible for the high resistance of the studied materials, some of them (those whose length exceeds tens of micrometer or those which form stringers in a particular direction) become, over fatigue cycles, the main sources of damage, from their local scale up to the macroscopic failure of the structure

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Ånmark, Niclas. "Inclusion Characteristics and Their Link to Tool wear in Metal Cutting of Clean Steels Suitable for Automotive Applications". Licentiate thesis, KTH, Tillämpad processmetallurgi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-164875.

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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.

QC 20150422

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Juneblad, Oscar. "Three-dimensional investigation of mangan sulfides in steels by using electrolytic extraction". Thesis, KTH, Materialvetenskap, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-124127.

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Moraes, Luís Augusto Batista de. "Caracterização de macro e micro-inclusões em aços acalmados ao alumínio produzidos por lingotamento contínuo". Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-18112009-102050/.

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Neste trabalho foram estudadas 10 corridas em duas usinas siderúrgicas semi-integradas, de aço baixa liga para uso em construção mecânica. Em cada uma das corridas foram retiradas 9 amostras, cada uma ao final de uma etapa do processo de produção: após a remoção de escória na panela, antes da desgaseificação a vácuo, após a desgaseificação a vácuo, após a adição de arame de Al, após a adição de arame de CaSi, após a adição de arame de S, após o fim da turbulência no distribuidor no lingotamento contínuo, 30 minutos após o fim da turbulência no distribuidor no lingotamento contínuo, e 60 minutos após o fim da turbulência no distribuidor no lingotamento contínuo. As amostras foram preparadas metalograficamente e analisadas ao microscópio eletrônico de varredura (MEV) com espectrometria de dispersão de energia (EDS), a fim de se identificar as inclusões presentes no aço em cada etapa do processo. Com isto pode-se fazer a caracterização das inclusões encontradas em cada etapa do processo e a sua classificação segundo a composição química e morfologia. Através da comparação da composição química das inclusões encontradas ao final do refino e no lingotamento contínuo foi possível verificar uma tendência de formação de inclusões de espinélio, e através da composição química das inclusões encontradas no lingotamento contínuo foi possível identificar em quais das corridas estudadas houve a presença de inclusões de aluminatos de cálcio formados no estado líquido.
In the present work it was studied 10 heats in two steelworks, of low alloyed steel for use in mechanical construction. From each heat were taken 9 samples, each one of them at end of one production stage: after deslagging in the ladle; before vacuum degassing; after vacuum degassing; after Al wire addiction; after CaSi wire addiction; after S wire addiction; after the end of tundish turbulence at continuously casting; 30 minutes after the end of tundish turbulence at continuously casting; and 60 minutes after the end of tundish turbulence at continuously casting. Samples were metallographic prepared and analyzed by scanning electronic microscopic (SEM) with energy dispersive X-ray spectroscopy (EDX), in order to identify the inclusions present in steel in each process stage. This allowed the founded inclusions in each process stage to be characterized and classified according to chemical composition and morphology. By comparing founded inclusions chemical composition at end of refining and continuous casting was possible to observe a tendency of formation of spinel inclusions, and by founded inclusions chemical composition in continuous casting was possible to identify in which studied heats there were presence calcium aluminates inclusions formed in the liquid state.

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Ånmark, Niclas. "Steel characteristics and their link to chip breaking and tool wear in metal cutting". Doctoral thesis, KTH, Tillämpad processmetallurgi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-187156.

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The vision of this thesis is to study how it is possible to obtain optimised workpieces during metal cutting processes in industry. Specifically, the work is aimed to increase the understanding between the steel characteristics and their link to the chip breaking and tool wear during metal cutting. The emphasis is on the influence of the cleanliness and the characteristics of non-metallic inclusions in the workpiece on the machinability of carburising steel grades. The machinability of a case hardening steel is improved by a M-treatment (additions of Ca). Also, the improved machinability of the M-steels offers an attractive potential to save money which makes it possible to reduce the tooling costs with up to 50%. The improved machinability of Ca-treated steels is correlated to the formation of lubricating slag layers consisting of Ca-enriched sulfide inclusions and oxy-sulfide inclusions, which are formed on the rake face during the machining operation. It is proposed that the formations of slag layers from the workpiece constituents are essential to minimise the chemical degradation of the tool edge due to a contact with the chip. During this process, sulfur minimises the material transfer from the chip flow, whilst Ca-treated impurities have a stabilising effect on the protective deposits made of slag layers. Since there is a remaining industrial need to increase the production rate, whilst maintaining a high quality of the finished parts, the future production will continue to require extreme demands on the quality of workpieces. If the emphasis is focused on the workpiece, it should be possible to obtain a robust manufacturing process. Therefore, the challenge for future steel metallurgists is to develop high performance grades with optimised combined properties.
Syftet med denna avhandling är att studera hur det är möjligt att framställa optimala ämnen för skärande bearbetning i industriell skala. Målsättningen med arbetet är att öka förståelsen för ståls egenskaper och dess inverkan på spånbrytning och slitage av verktyg vid skärande bearbetning. Avhandlingen fokuserar på kopplingen mellan arbetsstyckets renhet och inneslutningskarakteristik och dess inverkan på skärbarhet hos sätthärdningsstål. Skärbarheten hos vanligt sätthärdningsstål kan förbättras markant genom en Ca-behandling, dvs. en så kallad M-behandling. Den förbättrade skärbarheten hos M-stål möjliggör stora kostnadsbesparingar, som uppskattas kunna reducera verktygskostnader med upp till 50%. Den förbättrade skärbarheten hos M-stål beror på bildningen utav tribologiska skikt som är anrikade med (Mn,Ca)S- och (CaO)x-Al2O3-S-slagg. Dessa tribologiska skikt bildas på skärverktygets spånsida under ingrepp vid skärande bearbetning och består utav vissa atomer som överförts från det bearbetade ämnet till skäret. Bildandet av ett skyddande skikt anses nödvändigt för att undvika att verktygets skäregg utsätts för ett kemiskt angrepp i kontaktytan med spånflödet. Svavel anses minimera att rent arbetsmaterial överförs till skärverktyget medans kalcium-berikade inneslutningar hjälper till att bilda ett stabilt och skyddande tribologiskt skikt. Det eviga behovet att öka produktionstakten, utan att för dess skull riskera slutproduktens kvalité ställer stora krav på framtidens material. Med utgångspunkt från arbetsstycken så ska det vara möjligt att uppnå en robust industriell produktion. Utmaningen är därför att utveckla högpresterande stål med en förhöjd kombinerad funktionsegenskap.

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Prasannavenkatesan, Rajesh. "Microstructure-sensitive fatigue modeling of heat treated and shot peened martensitic gear steels". Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31713.

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Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2010.
Committee Chair: David L. McDowell; Committee Member: G. B. Olson; Committee Member: K. A. Gall; Committee Member: Min Zhou; Committee Member: R. W. Neu. Part of the SMARTech Electronic Thesis and Dissertation Collection.

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Alatarvas, T. (Tuomas). "Evolution of inclusion population in calcium treated ultra-high strength steels:novel applications of sample data treatment". Doctoral thesis, Oulun yliopisto, 2018. http://urn.fi/urn:isbn:9789526220987.

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Abstract Non-metallic inclusions are unavoidable particles in steel and are often detrimental to the steelmaking process and the mechanical properties of the steel. While it is not feasible to remove all inclusions, in the well-established calcium treatment of aluminium-killed steel, solid aluminium oxides are transformed into less harmful liquid calcium aluminates. The main objective of this work was to develop a new inclusion identification and classification method. The presented method offers valuable information on phases of the inclusions. This data is often buried within simple inclusion classification criteria. The method offers the best approximation of the phases in each inclusion detected with minimal time, if no time-consuming elemental map analyses are available. In this work, applications for the inclusion phase identification method are presented. Utilising the method, the dispersion and evolution of inclusions during the sampling of liquid steel in lollipop samples is investigated, as well as the evolution of inclusions during continuous casting. New information is obtained on the elongation of inclusions and formation of oxide–sulphide stringers during hot rolling. The results for the investigated steels show that with sulphur contents higher than 10 ppm, calcium aluminates were back-modified to alumina and spinel inclusions during casting. However, with decreasing sulphur contents, and adequate simultaneous calcium treatment of oxides, Al₂O₃ and spinel formation is hindered or even avoided. The most elongated inclusions are often also found in stringers. According to the results of this study, low melting calcium aluminate inclusions are not the most elongated oxide inclusions in the hot rolled product. With moderate calcium treatment, an optimal oxide composition can be obtained, found within the C12A7–CA–MgO composition. These liquid inclusions ensure good castability, while they do not easily elongate or fragment into detrimental stringers after continuous casting
Tiivistelmä Epämetalliset sulkeumat ovat väistämättä osa terästä, ja ne aiheuttavat ongelmia prosessille ja teräksen mekaanisille ominaisuuksille. Sulkeumien poiston sijaan niiden koostumusta muokataan kalsiumkäsittelyllä. Tällöin kiinteät alumiinioksidit muuttuvat vähemmän ongelmallisiksi suliksi kalsiumaluminaateiksi. Tämän työn päätavoitteena oli kehittää uusi sulkeumien tunnistus- ja luokittelumenetelmä. Sulkeuma-analyysien data voi jäädä hyödyntämättä, jos luokitteluun käytetään yksinkertaisia kriteerejä. Työssä esitetty menetelmä antaa parhaan arvion sulkeumissa olevista faaseista, mikäli sulkeumista ei ole alkuainekarttoja, joiden muodostaminen vie huomattavasti aikaa. Väitöskirjassa esitetään sulkeumien tunnistus- ja luokittelumenetelmän soveltamiskohteita. Menetelmän avulla tutkitaan sulkeumien muutosta ja jakaantumista sulan teräksen näytteenotossa ja sulkeumakuvan muutosta jatkuvavalun aikana. Uutta tietoa esitetään oksidi-sulfidiketjujen muodostumisesta kuumavalssauksen aikana. Tutkituilla teräksillä rikkipitoisuuden noustessa yli 10 ppm:n sulat kalsiumaluminaatit takaisinmuokkautuvat kiinteiksi alumiinioksideiksi tai spinelleiksi jatkuvavalun aikana. Riittävän matalalla rikkipitoisuudella ja kohtuullisella kalsiumkäsittelyllä alumiinioksidien ja spinellien muodostumista voidaan hillitä tai jopa estää se. Tutkimuksessa esitetään, että kuumavalssauksessa venyvimmät sulkeumat muodostavat myös lukuisten sulkeumien oksidi-sulfidiketjuja, jotka ovat tuotteen ominaisuuksien kannalta haitallisia. Tulosten mukaan kalsiumaluminaatit, jotka sulavat matalimmissa lämpötiloissa, eivät kuitenkaan ole taipuvaisimpia venymään valssauksessa. Maltillisella kalsiumkäsittelyllä saavutetaan optimaalinen oksidikoostumus C12A7–CA–MgO-faasiseurueesta. Nämä sulkeumat ovat sulia jatkuvavalussa varmistaen teräksen valettavuuden. Toisaalta ne eivät helposti veny tai rikkoonnu ketjuiksi valssauksessa jatkuvavalun jälkeen

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40

Beckius, Fredrik, i Kevin Hartelius. "Kontrollerad gjutprocess för renare stål". Thesis, Tekniska Högskolan, Högskolan i Jönköping, JTH, Maskinteknik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-24063.

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In a multi-year project at Swerea Swecast AB studies on influence of dissolved gas on inclusions have been made. The knowledge about these parameters could be used to increase the quality of the final steel casting. The purpose of this thesis was to closer examine the impact of the oxygen level on inclusions. The questions asked were:  What was the amount of inclusions at different levels of oxygen?  What was the size of these inclusions at different levels of oxygen?  What does the inclusions consist of at different levels of oxygen? This was studied by measuring and sampling, sample preparation and microscopic analysis using an optical microscope and a scanning electron microscope (SEM). Measurements and sampling was performed at Smålands Stålgjuteri AB in Eksjö and at Swerea Swecast AB in Jönköping. At Smålands Stålgjuteri AB the measurements were performed in production while at Swerea Swecast AB the measurements were made in a way that the oxygen levels were provoked. The sample preparations were made at Swerea Swecast AB’s workshop and lab. Scanning electron microscopy (SEM) and light optic microscopy was used for the analysis. The data from these analyses were processed and charts and tables were prepared. The results from the light microscopy shows a difference in microstructure between the two samplings. The charts and tables that were obtained indicated that the number of inclusions correlated with the oxygen level. However, only to a certain extent because other parameters such as time and amount of deoxidizer have a greater effect. The size of the inclusions decreased with decreased oxygen level during deoxidation. As mentioned in the pre-study, oxides are the most common type of inclusions in steel. This was also the case in the current study. The results showed that the oxygen level can be used as an indicator of the necessary addition of deoxidiser.
I ett flerårigt projekt på Swerea Swecast AB har undersökningar kring gasers inverkan på mängden inneslutningar i gjutstål genomförts. Kunskap kring hur parametrarna ser ut skulle användas för att höja kvaliteten på gjutgods. Syftet med det här arbetet var att noggrannare undersöka den fria syrehaltens påverkan på inneslutningar. Frågeställningarna var:  Hur stort antal inneslutningar fanns vid olika syrehalter?  Hur stora var dessa inneslutningar vid olika syrehalter?  Vad innehöll dessa inneslutningar vid olika syrehalter? Detta undersöktes genom mätning och provtagning, provberedning och analys. Mätning och provtagning utfördes på Smålands Stålgjuteri AB i Eksjö och på Swerea Swecast AB i Jönköping. Vid Smålands Stålgjuteri AB utfördes mätningar under ordinarie produktion medan mätningarna på Swerea Swecast AB gjordes så att olika syrehalter provocerades fram. Provberedningen och analysen gjordes i Swerea Swecast ABs verkstad och labb. Analysen gjordes med hjälp av svepelektronmikroskop (SEM) och ljusmikroskop. Data från dessa analyser bearbetades i Excel och diagram samt tabeller togs fram. Resultatet från ljusmikroskopbilderna visar en skillnad i mikrostrukturer mellan de två gjutförsöken. Ur diagram och tabeller kan utläsas att antalet inneslutningar korrelerar med syrehalten. Dock bara till viss del eftersom andra parametrar såsom tid och mängd desoxidationsmedel har större påverkan. Storleken på inneslutningarna minskade tillsammans med syrehalten vid desoxidation. Vid en överdriven desoxidation kunde inneslutningar ansamlas i korngränserna vilket kraftigt försämrar de mekaniska egenskaperna. I förundersökningen nämndes att oxider var de vanligaste inneslutningarna i stål. Så var fallet även här. Resultatet visar tydligt att syrehalten kan användas som indikator för hur stor tillsats av desoxidationsmedel som behövs.

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41

Walters, Jon D. "Microchemical analysis of non-metallic inclusions in C-MN steel shielded metal arc welds by analytical transmission electron microscopy". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1998. http://handle.dtic.mil/100.2/ADA350613.

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42

Almansour, Mansour A. "Sulfide stress cracking resistance of API-X100 high strength low alloy steel in H2S environments". Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/267.

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Sulfide Stress Cracking (SSC) resistance of the newly developed API-X100 High Strength Low Alloy (HSLA) steel was investigated in the NACE TM0177 "A" solution. The NACE TM0177 "A" solution is a hydrogen sulfide (H2S) saturated solution containing 5.0 wt.% sodium chloride (NaC1) and 0.5 wt.% acetic acid (CH3COOH). The aim of this thesis was to study the effect of microstructure, non-metallic inclusions and alloying elements of the X100 on H2S corrosion and SSC susceptibility. The study was conducted by means of electrochemical polarization techniques and constant load (proof ring) testing. Microstructural analysis and electrochemical polarization results for X100were compared with those for X80, an older generation HSLA steel. Uniaxial constant load SSC testing was conducted using X100 samples and the results were compared with those reported for older generation HSLA steels. Addition of H2S to the NACE TM0177 "A" solution increased the corrosion rate of X100from 51.6 to 96.7 mpy. The effect of H2S on the corrosion rate was similar for X80. The corrosion rate for X80 increased from 45.2 to 80.2 mpy when H2S was added to the test solution. Addition of H2S enhanced the anodic kinetics by forming a catalyst (FeHSads) on the metal surface and as a result, shifted the anodic polarization curve to more current densities. Moreover, the cathodic half cell potential increased due to the decrease in pH, from 2.9 to 2.7, which shifted the cathodic polarization curve to more current densities. The increase in both the anodic and cathodic currents, after H2S addition, caused the rise in the corrosion current density. In H2S saturated NACE TM-0177 "A" solution, the X100 steel corrosion rate was higher than the X80 steel by 20%. Longer phase boundaries and larger nonmetallic inclusions in the X100 microstructure generated more areas with dissimilar corrosion potentials and therefore, a stronger driving force for corrosion. Higher density of second phase regions and larger nonmetallic inclusions acted as an increased cathode area on the X100 surface which increased the cathodic current density and consequently, increased the corrosion current density. Proof ring tests on the X100 gave a threshold stress value, C5th, of 46% YS, 343.1 MPa(49.7 ksi). The main failure was caused by SSC cracking. SSC nucleated at corrosion pits on the metal surface and microcracks in the metal body and propagated perpendicular to the applied stress. Hydrogen Induced Cracking (HIC) was observed in the X100. HIC cracks nucleated at banded martensite-ferrite interfaces and propagated along the rolling direction parallel to the applied tensile stress through the softer ferrite phase. When compared to older HSLA grades, the X100 tested in this study had a high SSC susceptibility and therefore, is not be recommended for H2S service applications. The high X100 SSC susceptibility was caused by the material high corrosion rates in H2Smedia which formed corrosion pits that acted as crack initiation sites on the metal surface and provided more hydrogen that migrated into the steel. In addition, the X100 inhomogeneous microstructure provided a high density of hydrogen traps in front of the main crack tip which promoted SSC microcrack formation inside the metal. Microcracks in the metal body connected with the main crack tip that originated from corrosion pits which assisted SSC propagation.

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43

Ahlin, Björn, i Marcus Gärdin. "Automated Classification of Steel Samples : An investigation using Convolutional Neural Networks". Thesis, KTH, Materialvetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-209669.

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Automated image recognition software has earlier been used for various analyses in the steel making industry. In this study, the possibility to apply such software to classify Scanning Electron Microscope (SEM) images of two steel samples was investigated. The two steel samples were of the same steel grade but with the difference that they had been treated with calcium for a different length of time. To enable automated image recognition, a Convolutional Neural Network (CNN) was built. The construction of the software was performed with open source code provided by Keras Documentation, thus ensuring an easily reproducible program. The network was trained, validated and tested, first for non-binarized images and then with binarized images. Binarized images were used to ensure that the network's prediction only considers the inclusion information and not the substrate. The non-binarized images gave a classification accuracy of 99.99 %. For the binarized images, the classification accuracy obtained was 67.9%. The results show that it is possible to classify steel samples using CNNs. One interesting aspect of the success in classifying steel samples is that further studies on CNNs could enable automated classification of inclusions.
Automatiserad bildigenkänning har tidigare använts inom ståltillverkning för olika sorters analyser. Den här studiens syfte är att undersöka om bildigenkänningsprogram applicerat på Svepelektronmikroskopi (SEM) bilder kan klassificera två stålprover. Stålproven var av samma sort, med skillnaden att de behandlats med kalcium olika lång tid. För att möjliggöra den automatiserade bildigenkänningen byggdes ett Convolutional Neural Network (CNN). Nätverket byggdes med hjälp av öppen kod från Keras Documentation. Detta för att programmet enkelt skall kunna reproduceras. Nätverket tränades, validerades och testades, först för vanliga bilder och sedan för binariserade bilder. Binariserade bilder användes för att tvinga programmet att bara klassificera med avseende på inneslutningar och inte på grundmatrisen. Resultaten på klassificeringen för vanliga bilder gav en träffsäkerhet på 99.99%. För binariserade bilder blev träffsäkerheten för klassificeringen 67.9%. Resultaten visar att det är möjligt att använda CNNs för att klassificera stålprover. En intressant möjlighet som vidare studier på CNNs kan leda till är att automatisk klassificering av inneslutningar kan möjliggöras.

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44

Janis, Jesper. "Inclusions and/or Particles Engineering for Grain Refining Purposes in Ferritic Fe-20mass%Cr alloys". Doctoral thesis, KTH, Tillämpad processmetallurgi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-13012.

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Compared to more common used austenitic stainless steels, ferritic stainless steels contain very low amounts of the expensive alloying element Ni. In addition, they have good corrosion properties, but are sometimes suffering from poor weldability and bad mechanical properties. This is mainly due to the presence of large grains after casting and large grain growth during heat treatment or welding. Processes for reducing the grain size (grain refining) of metal alloys are widely known and proven before to be suitable for many alloys. A successful grain refining process can increase the strength of an alloy without decreasing the ductility. This can be achieved by different methods, such as rolling or cooling. In this work, the focus has been on studying the aspect from a metallurgist point of view, to analyse the possibilities to create small particles in the liquid stage to enhance the solidification. The focus has been on oxide and nitride formation for nucleation of smaller grains during solidification. This study was made by forming particles, develop the analysis methods and thereafter to study the effect of particles on the structure of a ferritic stainless steel. The particles were formed by additions of Ti, Ce and Zr in to a liquid Fe-20mass% Cr alloy containing different amounts of oxygen and nitrogen. The electrolytic extraction technique was used to achieve a good understanding of the reaction processes and the particles size, number, composition and morphology. The grain sizes and the particles were then studied in as-cast samples as well as in specimens heat treated for 60 minutes at 1200, 1300 and 1400°C in a Confocal Scanning Laser Microscope (CSLM). Also, based on Scanning Electron Microscope (SEM) determinations and Thermo-Calc calculations, the precipitated particles were divided as primary and secondary particles. Thereafter, the grain refining potential was studied for each of these types. In this work, particles engineering by using small particles have been proven suitable for the Fe-20mass% Cr ferritic stainless steel alloys. Although the work has been based on small-scale samples and experiments, the results show good tendencies with respect to grain refining as well as a clear relationship between the particles in the steels and the microstructures. It was found that Ti-Ce additions in Fe-20mass% Cr alloys resulted in complex oxides including Ti, Ce and Cr. These oxides were observed to have high agglomeration tendencies and therefore to form larger particles or clusters. The grain refining potential on the solidification structure was insignificant, despite a relatively large amount of particles. However, Ti-Zr additions in Fe- 20mass% Cr alloys on the other hand resulted in primary precipitated particles such as ZrO2 and ZrO2+ZrN. Furthermore, ZrN nucleated ferrite during solidification, which lead to a clearly observed grain refining effect. This effect was also increased with an increased number of particles. The amount of particles (primary and secondary) was also found to increase with an increased amount of nitrogen. Secondary particles (mostly TiN) were precipitated near grain boundaries, which lead to a location based pinning effect of the grain growth during heat treatment at 1200 °C. This pinning effect was increased by an increased nitrogen content and thereby an increased number of particles. Finally, the pinning effect was clearly reduced during heat treatment at 1400 °C.
QC20100524

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45

Ragnarsson, Lars. "Formation of non-metallic inclusions and the possibility of their removal during ingot casting". Doctoral thesis, KTH, Mikro-modellering, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-12458.

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The present study was carried out to investigate the formation and evolution of non-metallic inclusions during ingot casting. Emphasize have been on understanding the types of inclusions formed and developed through the casting process and on the development of already existing inclusions carried over from the ladle during casting. Industrial experiments carried on at Uddeholm Tooling together with laboratory work and Computational Fluid Dynamics (CFD) simulations. Ingots of 5.8 tons have been sampled and the types of inclusions together with their distribution within the ingot have been characterized. Two new types of inclusions have been found. Type C1 is found originated from casting powder and in the size from a few μm to 30 μm. Type C2 is of macro inclusion type sizing up to 70 μm. The presence of C2 inclusions are few but very detrimental for the quality of the steel. Both types, C1 and C2 consist of alumina, indicating that reoxidation is the main reason for their existence. The protecting argon shroud has been studied by the use of a 1:1 scaled 2D model. Both flow pattern and oxygen measurement have been carried out. CFD has also been used as an auxiliary tool. It has been found that the oxygen pickup through argon gas shroud depends mostly on the distance between the ladle and the collar placed on top of runner. Further increase of gas flow rate above 2.5 m3.h-1 had very little effect on the oxygen distribution since both the flushing effect and the entraining effect with respect to oxygen are enhanced by further increase of inert gas flow rate. In the case of dual gas inlet, the flow in the shroud was found much less diffused compared with either vertical or horizontal injection system. The oxygen content in this arrangement was also greatly reduced. Studies of the runner after casting revealed a sparse non-metallic network structure around the periphery of the steel rod remained in the runner. The surface of the refractory had been severely attacked by the mechanical force from the streaming steel. The erosions of the centre stone and the end stone were on the other hand negligible. CFD calculations showed that the flow at those locations is almost stagnant. The surface of the refractory in contact with the steel was found to have an increased content of alumina. The source for the alumina could come from either exchange reaction of dissolved aluminium replaces the silica or reoxidation products origin from oxygen pick up during the transfer from the ladle to the vertical runner. Inclusions were also found entrapped in the steel refractory interface. It was also found that a formation of a liquid slag film as early as possible during casting would increase the possibility to remove inclusions and especially inclusions generated by the casting powder.
QC 20100617

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46

Doostmohammadi, Hamid. "A Study of Slag/Metal Equilibrium and Inclusion Characteristics during Ladle Treatment and after Ingot Casting". Doctoral thesis, KTH, Materialvetenskap, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-11596.

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Today, there is a high demand on clean steel for high performance materialproperties. Thus, steel producers try to deliver a steel product with the highestquality and cleanliness to the market. The number of parameters that affect thesteel cleanliness may vary depending on the required material properties of thefinal product. However, the non-metallic inclusion characteristics represent one ofthe most important parameters. More specifically, the composition, size, numberand morphology affect steel cleanliness. In this work, selected parameters affectingthe inclusion characteristics were studied using the following methods: i)thermodynamic calculations (including computational thermodynamiccalculations), ii) inclusion determinations using a cross sectional (CS) method (2Dinvestigations) and iii) inclusion determinations using an electrolytic extraction(EE) method (3D investigations). The computational thermodynamic calculations of the slag-steel and inclusion-steelequilibriums were carried out using the Thermo-Calc software. With the help ofthese calculations, the influence of the slag carryover on the top slag, aluminumcontent in steel and sulfur distribution ratio as well as predictions of stable phasesof inclusions were studied. In addition, inclusion determinations of tool steel gradesamples collected during various stages of the ladle treatment in a scrap-based steelplant were carried out using both 2D and 3D methods. Furthermore, inclusiondeterminations of bearing steel grade samples from a runner system after ingotcasting were performed using a 2D metallographic method (CS-method). Also, theINCAFeature software was used, when using cross sectional method, in order tocollect more statistics of the inclusion characteristics. It was found that slag carryover has a large influence on the composition of theactual top slag as well as the aluminum content in the steel as well as the sulfurdistribution ratio. In addition, steel and slag were found to be in “near”-equilibriumconditions, after the completion of the vacuum degassing operation. Furthermore,the composition of small-size inclusions in samples taken from tool steel was foundto be very scattered. Moreover, the composition of the large-size inclusions wasfound to be less scattered. Furthermore, closer to the top slag composition insamples collected after vacuum degassing. Finally, the accuracy of the inclusioncomposition determinations of tool steel samples using the electrolytic extractionmethod was found to be better than for the cross sectional method. The worseaccuracy of the CS-method is due to a considerable effect of matrix elements oninclusion composition.
QC 20100709

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47

Guo, Shuo. "Evaluation of deformed MnS in different industrial steels by using electrolytic extraction". Thesis, KTH, Materialvetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-217880.

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The inclusions have a different chemical composition and give the steel different mechanical properties. These inclusions affect several properties of steel. In order to understand how the inclusions will affect the steel properties, the electrolytic extraction of 3D investigate method is applied on the steel grade of 42CrMo4. Then follow with Scanning Electron Microscope (SEM) observation. Steel samples from both ingot and rolling with and without heat treatment are observed and compared with different ratios. The result shown that, heat treatment can be applied for removing carbides successfully. And most inclusions are belonging to Type RS which is rod like MnS. The percentage of broken particles can be up to 80%, which means that the reason for the inclusions broken should be find. And heat treatment can affect the characteristics of elongated MnS.

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48

Gjønnes, Anders Welde. "Effect of Sulfide Inclusions in Austenitic Stainless Steel on the Initiation of Pitting in Base Metal and Heat Affected Zone after Welding". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-19594.

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The predominant site for the initiation of pitting on austenitic stainless steel has been shown to be sulfide inclusions and notably the manganese types of sulfides. Dissolution of inclusions has been observed and suggested to be the initial step for pit initiation, though several explanations for the mechanisms causing initiation has been proposed. Regarding welded stainless steels, several microstructural changes have been described and suggested to contribute to the decreased corrosion resistance in the weld zone. An area which has not been investigated much is the contribution of inclusions, in particular MnS inclusions, to the reduced corrosion resistance and the initiation of pitting in the weld zone. In the present work a literature review of the investigations focusing on the initiation of pitting by sulfide inclusions in austenitic stainless steels has been provided. A literature review of investigations focusing on the effects of welding on the microstructure, inclusions and the corrosion properties in the weld zone of austenitic stainless steels has also been provided.Experimental work was performed to obtain results which could be compared to or verify findings and suggestions from the reviewed literature regarding the initiation of pitting by inclusions. Observations of MnS inclusions as the preferential site for pit initiation in austenitic stainless steel was tried recreated. The hypothesis saying that dissolution of MnS inclusions occur prior to the initiation of pitting was also tried verified. It was also performed experiments to obtain results which could give knowledge about the effects of MnS inclusions on the corrosion properties and the initiation of pitting in the weld zone of an austenitic stainless steel. Along with this, the corrosion behaviour and microstructural changes in the weld zone in general and compared with the base metal were studied. A part of the work was also to study the effect of a lacking inert shielding gas during welding.Samples of a 316L stainless steel were first examined in SEM to study the microstructure and to identify inclusions. Then, some samples were welded, followed by SEM examination. Then all samples were polarized electrochemically in synthetic seawater with the purpose of initiating pitting. After the polarization, all samples were examined in SEM again to correlate pitting attack to inclusions and to compare microstructural changes and the corrosion behaviour in the base metal and the weld zone.It was verified that the main initiation site for pitting in the base metal was MnS inclusions. It was indicated that dissolution of the MnS inclusions started the pit initiation process, with the contribution of released compounds from the inclusions. An average percent of inclusions showing an inactive behavior regarding the initiation of pitting was 38 %, verifying similar observations reported in earlier investigations. A nitric acid treatment to remove MnS inclusions improved the pitting resistance significantly.The welding caused the initiation of corrosion at lower potentials when performing electrochemical polarization in synthetic seawater. The corrosion mechanism was probably grain boundary corrosion caused by precipitation of chromium carbides in the grain boundaries. A lacking inert shielding gas during welding did not have any effect on the potential for the initiation of corrosion when comparing two samples welded with and without shielding gas.It was indicated that compositional changes had occurred for MnS inclusions in a certain distance from the fusion line. These changes may have caused the inclusions to be more prone to initiate pitting. Further investigation should be performed to clarify the behaviour of such inclusions, and their susceptibility towards the initiation of corrosion. Grain boundary corrosion in various grades had occurred in the HAZ in certain distances from the fusion line. In a further distance from the fusion line pitting-like corrosion in clusters, possibly induced by chromium depletion after forming chromium oxides combined with a thin oxide film, had occurred. The grain boundary corrosion and the pitting cluster attack are from the experimental results believed to be more important for the failure of the welded stainless steel investigated in this work, than pitting initiated at MnS inclusions changed by the welding process.

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49

Song, Minho. "A Study on the Correlation between Ladle Glaze and Non-Metallic Inclusions in the Ladle Treatment". Doctoral thesis, KTH, Mikro-modellering, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-27640.

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In the present thesis, the correlation between ladle glaze and non-metallic inclusions in the ladle treatment was studied. A number of industrial trials with full scale ladle and laboratory works were performed to investigate the inclusions in the ladle treatment. BaO was used as tracer in the ladle slag to investigate the effect of slag on inclusion composition and the formation of non-metallic inclusions by ladle glaze. BaO was detected in the inclusions of all followed heats. This observation showed strong evidence for the generation of non-metallic inclusions by the ladle glaze. The increase of the fractions of BaO containing inclusions and their average content of BaO in the first heat with tracer suggested that the effect of slag on the composition of inclusions was a very slow process. The detachment of ladle glaze and the chemical transformations of oxide solution in the MgO matrix were investigated. The experimental results evidently showed that the ladle glaze could be the source of inclusions continually during the ladle treatment. Samples of liquid oxide solution to simulate the liquid oxide inclusions carried over from EAF were equilibrated with molten steel under controlled atmosphere. The results along with thermodynamic calculation suggested that the SiO2 content of inclusions from EAF could be considerably reduced by dissolved aluminium in the steel. This would explain the vanishing of inclusions containing high SiO2 content after deoxidation. Due to the lack of experimental data, the viscosities of slags in the Al2O3-CaO-MgO-SiO2 system were measured using the rotating cylinder method in the temperature range of 1720 to 1910 K. Eight different slag compositions related to the secondary steel making operations were selected. Viscosities in this system and its sub-systems were expressed as a function of temperature and composition based on the viscosity model developed earlier at KTH. The activities of oxide components in the Al2O3-CaO-MgO-SiO2 systems at 1873 K were measured by equilibrating liquid slag and metal. Either silicon or copper was used as the metal phase and the oxygen partial pressure was controlled with different mixing rates of Ar and CO gas flow in equilibrium with graphite. Iso-activity lines were drawn from the measured activity values in the isothermal section of the slag systems. Nine series of industrial trials were carried out using the same ladle in each series to examine the effect of ladle slag on the number of non-metallic inclusions in the next heat. It was found that the number of inclusions increased with SiO2 content of the ladle slag in the previous heat. No clear trends were found for the effects of viscosity and MgO activity of the previous slag on the number of inclusions. Theoretical analysis based on the experimental results suggested that the formation of 2CaO∙SiO2 followed but the dusting of the compound made the refractory more porous, which was reasonable for the number of non-metallic inclusions.

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50

Zhong, Yuan. "Sub-grain structure in additive manufactured stainless steel 316L". Doctoral thesis, Stockholms universitet, Institutionen för material- och miljökemi (MMK), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-144519.

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The thesis focuses on exploring the sub-grain structure in stainless steel 316L prepared by additive manufacturing (AM). Two powder-bed based AM methods are involved: selective laser melting (SLM) and electron beam melting (EBM). It is already known that AM 316L has heterogeneous property and hierarchy structure: micro-sized melt pools, micro-sized grains, nano-sized sub-grain structure and nano-sized inclusions. Yet, the relation among these structures and their influence on mechanical properties have not been clearly revealed so far. Melt pool boundaries having lower amount of sub-grain segregated network structures (Cellular structure) are weaker compared to the base material. Compared with cell boundaries, grain boundaries have less influence on strength but are still important for ductility. Cell boundaries strengthen the material without losing ductility as revealed by mechanical tests. Cellular structure can be continuous across the melt pool boundaries, low angle sub-grain boundaries, but not grain boundaries. Based on the above understanding, AM process parameters were adjusted to achieve customized mechanical properties. Comprehensive characterization were carried out to investigate the density, composition, microstructure, phase, magnetic permeability, tensile property, Charpy impact property, and fatigue property of both SLM and EBM SS316L at room temperature and at elevated temperatures (250°C and 400°C). In general, SLM SS316L has better strength while EBM SS316L has better ductility due to the different process conditions. Improved cell connection between melt pools were achieved by rotating 45° scanning direction between each layer compared to rotating 90°. Superior mechanical properties (yield strength 552 MPa and elongation 83%) were achieved in SLM SS316L fabricated with 20 µm layer thickness and tested in the building direction. Y2O3 added oxide dispersed strengthening steel (ODSS) were also prepared by SLM to further improve its performance at elevated temperatures. Slightly improved strength and ductility (yield strength 574 MPa and elongation 90%) were obtained on 0.3%Y2O3-ODSS with evenly dispersed nanoparticles (20 nm). The strength drops slightly but ductility drops dramatically at elevated temperatures. Fractographic analysis results revealed that the coalescence of nano-voids is hindered at room temperature but not at elevated temperatures. The achieved promising properties in large AM specimens assure its potential application in nuclear fusion. For the first time, ITER first wall panel parts with complex inner pipe structure were successfully fabricated by both SLM and EBM which gives great confidence to application of AM in nuclear industry.

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Manuscript. Paper 5: Manuscript.

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Rozprawy doktorskie na temat „Steel – Inclusions”

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