Search

A number of carbon-rich (containing up to 47 wt% C) and lime-rich (containing up to 96 wt% of CaO-compounds) waste products from the pulp and paper industries can be used in iron and steel industry as fuels and slag formers for various metallurgical processes such as blast furnaces (BF), cupola furnaces (CF), argon oxygen decarburization (AOD) converters and electric arc furnaces (EAF). In most cases, these wastes consist of different size powders. In order to facilitate loading, transportation and charging of these powder wastes, briquetting is required. In this study, a pulverized AOD slag was tested as a binder component for briquetting of CaO-containing wastes (such as mesa, lime mud and fly ash) from pulp and paper industries. Moreover, mechanical testing of the possibilities for loading, transportation and unloading operations were done, specifically drop test trials were done for briquettes with different chemical compositions and treatments such as heating and storage. The results showed that an addition of 10-20% of AOD slag as a binder component followed by heat-treatment at 850 °C significantly improved the mechanical properties of the CaO-containing briquettes. An application of these briquettes will significantly reduce the consumption of natural resources (such as nature lime) in the metallurgical processes. Moreover, it can reduce the landfill area of wastes from pulp and paper industries, which is important from an environmental point-of-view., QC 20191017

The dimension quality of the strip within the hardening process is an essential parameter, which great attention needs to be paid. The flatness of the final product is influenced by the temperature distribution of the strip, specifically across the width direction. Therefore, based on physical theories, a numerical model was established. The temperature of the strip for the section before the martensitic transformation was objected in the predicted model by using a steady state approach. In addition an infrared thermal imaging camera was applied in the real process in order to validate the results and to improve the boundary conditions of the numerical model. The results revealed that the temperature of strip decreased up to 250 degrees C within the area between the furnace and the quenching bath. This, in turn, resulted in significant temperature difference across the width of the strip. This difference can be up to 69 degrees C and 41 degrees C according to the numerical results and thermal imaging data, respectively. Overall, this study gave a better insight into the cooling step in the hardening process. In addition, this investigation can be used to improve the hardening process as well as an input for future thermal stress investigations., QC 20190805

The flow pattern plays a crucial role in the uphill teeming process. The non-metallic inclusion generation due to interaction with the mold flux is believed to be influenced by the flow pattern. In this study, a three-dimensional mathematical model of the filling of a gating system for 10, 20, and 30 degrees angled runners was used to predict the fluid flow characteristics. Moreover, a mathematical model with a horizontal runner was applied as a reference. The predictions indicate that the angled-runner-design decreases the hump height during the initial filling stage, which results in less entrapment of mold flux into the mold. Nevertheless, increasing the angle of runner can result in a lower hump height, while the 30 degree angled runner gives a much more stable increase of the hump height during the initial filling stage. Besides CFD calculations, some thermodynamic calculations are taken into account for the chemical reactions between liquid steel and gas. The results show that the bubble shrinks due to the fact that N and O are dissolved into steel. The present findings strongly suggest that changing the horizontal runner to an angled runner would be an effective means of reducing flow unevenness during the initial filling of ingots, if the added steel losses are deemed acceptable., QC 20190802

Ferroalloys are integral constituents of the steelmaking process, since non-metallic inclusions (NMIs) from ferroalloys significantly influence the transformation of inclusions present in liquid steel or they are directly involved in casted steel. In this study, the characteristics of inclusions (such as the number, morphology, size, and composition) in different industrial ferroalloys (FeV, FeMo, FeB, and FeCr) were investigated using the electrolytic extraction (EE) technique. After extraction from the ferroalloy samples and filtration of the solution, the inclusions were investigated on a film filter. The three-dimensional (3D) investigations were conducted using a scanning electron microscopy in combination with energy dispersive spectroscopy (SEM-EDS). The characteristics of inclusions observed in the ferroalloys were compared with previous results and discussed with respect to their possible behaviors in the melt and their effects on the quality of the cast steels. The particle size distributions and floatation distances were plotted for the main inclusion types. The results showed that the most harmful inclusions in the ferroalloys investigated are the following: pure Al2O3 and high Al2O3-containing inclusions in FeV alloys; pure SiO2 and high SiO2-containing inclusions in FeMo alloys; Al2O3 and SiO2-containing inclusions in FeB alloys; and MnO-Cr2O3, Al2O3, and Cr2O3-based inclusions in FeCr alloys., QC 20190802

A 1:4.6 scale physical model of a production argon oxygen decarburisation (AOD) converter was used to study the influence of top slag on the AOD process. Specifically, the gas penetration depth, fluid flow and slag behaviour under different nozzle diameters, nozzle numbers and gas flow rates were studied. The results show that the relative gas penetration depth generally increases linearly with an increased gas flow rate and a decreased nozzle size. Furthermore, the slag thickness increases linearly with an increased gas flow rate. In addition, the open-eye size was found to increase exponentially with an increased gas flow rate. Overall, three kinds of fluid flow patterns were found in the experiments: (i) a counter-clockwise rotation, (ii) a clockwise rotation and (iii) a double circulation with the plume in the middle of the converter. A counter-clockwise rotation was most common for the current experimental conditions., QC 20190107

The possibilities of obtaining a good process control in order to reach a good cleanliness of the steel were studied based on plant trials. Steel and slag samples were taken from two steel grades with a slightly different composition, but with similar processing conditions. Thereafter, the chemical compositions of the steel and slag samples were determined. The results show that the sum of the FeO and MnO was found to be a clear indicator for when reoxidation had taken place. No conclusive indicator was found to predict the extent of slag carry-over from the electric arc furnace. However, most of the variation in deoxidation seem to originate from the accuracy of the slag raking. Steel grades with low amounts of deoxidisers such as C and Si naturally were found to result in higher oxygen contents at the start of deoxidation. Furthermore, calculations of oxygen activities in the steel melt were made and the results were compared to measurements with varying results. Overall, the results indicate that calculation of oxygen activities with multivalence slag species such as Fe and Cr requires additional measurements to obtain accurate results., QC 20180802

There is no known example of an AOD converter with oblong cross sections in the literature. Changing the geometry of the converter vessel, from the traditional circular cross sections, to increase converter volume could potentially influence the performance of the converter and in particular the decarburisation rate. To study the feasibility of implementing an oblong converter, physical modelling was used to study the fluid flow of the proposed converter configuration, geometry and number of tuyeres, and the potential influence on the decarburisation rate. Two water models were employed using water containing NaOH and gas injected through six or eight tuyeres as fluids. In the model, CO2 gas was injected and the reaction of CO2 and NaOH was indirectly measured by detecting the pH value of the water. The mixing time is considered to be a good indicator of the decarburisation as kinetics will be diffusion controlled in the latter period of the process. The following three configurations were studied: (i) a circular converter with six tuyeres, (ii) an oblong converter with six tuyeres, and (iii) an oblong converter with eight tuyeres. The mixing time can be used to evaluate the different converter configurations. The average CO2 concentrations based on several experiments, differed by less than 5% between the circular and oblong models after 165 s of injection of air and CO2. The results also showed that no difference in mixing time could be found when using 6 and 8 tuyeres, respectively in the oblong model, where the CO2 concentrations differed by less than 2% after 165 s of injection time of air and CO2. Based on the findings, it has been observed that the influence of converter geometry on mixing time is small, it was concluded that decarburisation rate is likely to be the same irrespectively of converter geometry., QC 20180802

Lamellar graphite iron (LGI) is an important technical alloy used to produce cast components for the automotive and the marine industry. The performance of the component is defined by the solidification sequence. Therefore, a lot of research work has been done in the field of solidification. The present work introduces a new measurement approach that combines advanced dilatation measurements with thermal analysis to investigate the solidification of LGI. The method involves a thermally balanced spherical sample. The temperature values are measured in the geometrical center and on the surface of the sample. The released heat of solidification is calculated by using the Fourier Thermal Analysis (FTA) method. The displacement values are measured on the surface of the sample. The volume change is calculated from the displacement data. The dilatation results clearly shows the advantage of the multidirectional measurement.

Full dense ZrN substrates with a relative density of 96% were prepared by using the Spark Plasma Sintering (SPS) method. Thereafter, the wettability and corrosion behavior of ZrN by liquid iron and steel were studied using a sessile drop technique. The nitrogen diffusion from the ZrN substrate into pure Fe/steel was identified. A strong wetting behavior of the liquid iron and steel in contact with the ZrN substrate was found. This is due to the nitrogen diffusion into the melt. The mechanism of the nitrogen diffusion is mainly due to the ZrN substrate oxidation rather than due to a ZrN dissolution., Funding Details: KTH, KTH Royal Institute of TechnologyQC 20160524

In this study a newly developed method called the Progressing and Backcasting models were used to evaluate the annual resource utilizations of steel scrap in Sweden and globally. The model results show that it is possible to assess the amounts of steel scrap available for steelmaking at a given point in time, based on statistical dynamic material flow models. By a better mapping of the available amounts of steel scrap reserves on a country basis, it is possible to ease the trade of scrap across country boarders. This in turn can optimize the supply of recyclable metals as a raw material used in the industry. The results for Swedish steel consumption show that export bans used to secure the domestic market of steel scrap do damage the internal market due to increased amounts of losses. This suggests that export bans should be lifted to optimize recycling in countries. The model results also show that the global losses of steel are higher than for an industrialized country such as Sweden. Furthermore, the results show that the Backcasting and Progressing models can be used to calculate robust forecasts on the long term availability of steel scrap assets. This information could be used for future structural plans of scrap consuming steelmaking mills and waste management facilities. Hence, it is possible to contribute to a sustainable industrial development and a circular economy., QC 20161129

This paper presents computational fluid dynamics (CFD) simulation results of inclusions macroscopic transport as well as dynamic removal in tundishes. A novel treatment was implemented using the deposition velocity calculated by a revised unified Eulerian deposition model to replace the widely used Stokes rising velocity in the boundary conditions for inclusions removal at the steel–slag interface in tundishes. In this study, the dynamic removal for different size groups of inclusions at different steel–slag interfaces (smooth or rough) with different absorption conditions at the interface (partially or fully absorbed) in two tundish designs was studied. The results showed that the dynamic removal ratios were higher for larger inclusions than for smaller inclusions. Besides, the dynamic removal ratio was higher for rough interfaces than for smooth interfaces. On the other hand, regarding the cases when inclusions are partially or fully absorbed at a smooth steel–slag interface, the removal ratio values are proportional to the absorption proportion of inclusions at the steel–slag interface. Furthermore, the removal of inclusions in two tundish designs, i.e., with and without a weir and a dam were compared. Specifically, the tundish with a weir and a dam exhibited a better performance with respect to the removal of bigger inclusions (radii of 5, 7, and 9 μm) than that of the case without weir and dam. That was found to be due to the strong paralleling flow near the middle part of the top surface. However, the tundish without weir and dam showed a higher removal ratio of smaller inclusions (radius of 1 μm). The reason could be the presence of a paralleling flow near the inlet zone, where the inclusions deposition velocities were much higher than in other parts., QC 20160518

As an alternative to some traditional methods to generate a swirling flow in the continuous casting process, the use of a new swirling flow generator, TurboSwirl, was studied. Specifically, a reversed TurboSwirl device was designed as part of a submerged entry nozzle (SEN) for a round billet continuous casting process. Mathematical modelling was used to investigate this new design and a water model experiment was carried out to validate the mathematical model. The predicted velocities by the turbulence models: realizable k-ε model, Reynold stress model (RSM) and detached eddy simulation (DES) were compared to the measured results from an ultrasound velocity profile (UVP) method. The DES model could give the best prediction inside the SEN and had a deviation less than 3.1% compared to the measured results. Moreover, based on the validated mathematical model and the new design of the SEN, the effect of the swirling flow generated by the reverse TurboSwirl on the flow field of the SEN and mold was compared to the design of the electromagnetic swirl flow generator (EMSFG). A very strong swirling flow in the SEN and a stable flow pattern in the mold could be obtained by the reverse TurboSwirl compared to the EMSFG., QC 20161123

A swirling flow has been demonstrated to be beneficial for making the flow pattern even and to reduce turbulence during filling in ingot casting. A new swirling flow generation device, TurboSwirl, was applied to improve the flow pattern of the liquid steel as it flows into the mold so that a more stable flow could be obtained. A water model was built including the TurboSwirl with different flaring angles of the divergent nozzle, according to a former numerical study indicating that a much more beneficial flow pattern could be obtained by reducing the flaring angle. To validate the mathematical model, the air-core vortex formed in the water model experiment was used, and the length of the vortex was measured and compared to the numerical predictions. Different turbulence models including the standard k-epsilon, realizable k-epsilon and Reynolds stress model were tested. It was found that only the Reynolds stress model could most accurately simulate the high swirling flow including a vortex. In addition, the radial velocity of the water around the vortex was measured by an ultrasonic velocity profiler (UVP). The experimental results revealed a high turbulence of the swirling flow and strong fluctuations of the vortex. The radial velocity of the water around the upper part of the vortex could be predicted well compared to the experimental results by the UVP measurements., QC 20160926

The characteristics of non-metallic inclusions (such as number, size and volume fraction) in liquid steel samples taken during ladle treatment and casting of industrial heats of two low-alloyed Ca-treated steel grades were evaluated by using the Pulse Distribution Analysis with Optical Emission Spectroscopy (PDA/OES) method. These results were compared to data obtained by Scanning Electron Microscope observations of inclusions after electrolytic extraction from steel samples (the EE method). It was found that the PDA/OES method can be used for a relative estimation of the homogeneity of the distribution of non-metallic inclusions in steel samples. Bottom and middle parts of the steel samples showed more homogeneous results with respect to the characteristics of the investigated Al2O3, CaO-Al2O3 and CaO-Al2O3-CaS inclusions. The numbers of inclusions in the size ranges 2.0-5.7 mu m and 1.4-5.7 mu m in samples taken before and after a Ca addition, respectively, showed a relatively good agreement between both methods. Furthermore, the calculated volume fractions for inclusions in the size range 2-13 mu m obtained by the PDA/OES method agreed satisfactorily well with those obtained from the EE method. Finally, the minimum sizes of inclusions in steel samples, which can reliably be detected by the PDA/OES method, were estimated for steels with different concentrations of Al in steel and Al2O3 in inclusions., Updated from manuscript to article.QC 20151202

In this work, the placement of an electromagnetic swirl flow generator (EMSFG) around a submerged entry nozzle (SEN) was proposed as a method for generating a rotating electromagnetic field in a continuous casting (CC) process of steel. First, two kinds of a full type EMSFG and a half type EMSFG were designed based on mathematical modeling. Then, distributions of magnetic flux intensity in an EMSFG as well as distributions of Lorentz force in molten steel were simulated. It was found that the EMSFG structure and electromagnetic parameters have an important effect on magnetic flux intensity and Lorentz force distributions. For both a full type and a half type EMSFG, the magnetic flux intensity and Lorentz force increases as the magnetomotive force increases. Especially, for a full type EMSFG, the magnetic flux intensity is distributed evenly in molten steel. Moreover, the Lorentz force increases along a radial direction in the molten steel in the SEN. However, for a half type EMSFG, the magnetic flux intensity and Lorentz force decreases gradually towards the region without an EMSFG. Consequently, a full type EMSFG with a 44 000 AT magnetomotive force and a 50 Hz frequency is more suitable to apply in the operation of an EMSFG under actual production conditions., QC 20150511. Updated from manuscript to article in journal.

Previous studies have verified that a swirl flow generated in a submerged entry nozzle (SEN) can effectively improve a flow pattern and a heat transfer in a continuous casting (CC) process. In order to obtain a further in-depth understanding with respect to the effect of a swirl flow on a CC process, the inclusion behavior in a SEN and a mold was studied in the present work. The flow field and the temperature field of molten steel as well as the inclusion behavior in a SEN and a square bloom mold were simulated under the influence of a rotating electromagnetic field (swirl generator). Also, the influence of different inclusion parameters such as the densities, sizes, and boundary conditions, on the inclusion behavior was studied. The results show that a flow pattern in a SEN can be characterized into three distinct flow regions: an accelerating flow of molten steel from an electromagnetic swirl flow generator (EMSFG) inlet to an EMSFG center, a decelerating flow of molten steel from an EMSFG center to an EMSFG outlet, and a recirculation flow of molten steel from an EMSFG outlet to an SEN outlet. In addition, it was found that light Al2O3 inclusion moves towards the rotational center by a centrifugal force, and that a swirl flow prevents nozzle clogging. Moreover, it was also found that the inclusion separation to a mold meniscus increased and that the inclusions trapped into a solidified shell wall decreased when using a swirl flow., QC 20150508

The effect of different stirring conditions during ladle treatment on the steel cleanliness was studied in the steel plant of SSAB Special Steels in Oxelosund, Sweden. The cleanliness was examined with regards to the contents of sulfur, nitrogen, and large inclusion (>10 mu m). The results showed that vacuum degassing increased the amount of inclusions larger than 10 mu m and that subsequent induction stirring suggested a possible positive effect on the inclusion removal. A shortening of the vacuum degassing time from 24 to 15 min did not affect the nitrogen or sulphur refining. Overall, all heats reached the desired composition and cleanliness levels regardless of the treatment time., QC 20160216

The protonic conductors BaZr(x)Ce(0.8-x)Ln(0.2)O(3-delta) (x=0.8, 0.5, 0.1; Ln=Y, Sm, Gd, Dy) were successfully prepared using a solid-state reactive-sintering method. NiO (1 wt.%) was added as a sintering aid, and it was proven that NiO produced tremendous enhancement in the densification process. The morphologies of the variously doped BaZr(0.8)Ln(0.2)O(3-delta), BaZr(0.5)Ce(0.3)Ln(0.2)O(3-delta) and BaZr(0.1)Ce(0.7)Ln(0.2)O(3-delta) ceramics, as well as their sintering behaviour, were investigated. The results show that the Ce content in the BaZr(0.8)Ln(0.2)O(3-delta), BaZr(0.5)Ce(0.3)Ln(0.2)O(3-delta) and BaZr(0.1)Ce(0.7)Ln(0.2)O(3-delta) compounds influences the sintering temperature significantly, and a larger Ce content will lead to a lower sintering temperature. In addition, ionic radii of the dopants that are similar to the ionic radii of the B-site will also result in a lowered sintering temperature. Based on the present study, NiO has no influence on the lattice parameters., QC 20150324

A pure and well-crystallized Hf0.7Y0.3O2-delta (YSH) powder was synthesized using a modified solid-state reaction method. Water-based milling and freeze drying process were implemented to facilitate powder synthesis and final densification process. The improved powder performance, in aspects of phase development and sintering behaviour, was investigated by systematic comparison between different powder processing procedures. Dense YSH ceramic material with a relative density of 0.975 was successfully obtained using conventional sintering at 1650 degrees C for 10 h. XRD, SEM and EDS were employed to characterize the synthesized powder and dense YSH ceramics. Dense YSH ceramic possesses a fluorite cubic structure with an a value of 5.1406 angstrom, and the ionic radius of Y3+ in YSH was determined to be 0.1006 nm., QC 20150324

Clusters of Al2O3 inclusions in a liquid stainless steel (18/8) and in a clogged ZrO2 nozzle after casting were studied during a pilot plant trial. Samples were taken from the melt at different holding times after an addition of 0.1 mass% Al. The characteristics (composition, size, number, and morphology) of clusters and clustered inclusions in the steel samples and in the clogged nozzle were investigated after electrolytic extraction and etching by using SEM. It was found that the Al2O3 inclusions in the clusters are transformed from a spherical into irregular and regular (with sharp edges) shape during the holding time. Most of the inclusions in the clusters (>80%) after a 6 min holding time are regular inclusions, which have sharp edges and flat faces. The size of the inclusions in clusters in the melt increased on average from 1.0 μm at a 1 min to 5.2 μm at a 12 min holding time. While the sizes of different types of inclusions in the clogged nozzle correspond to those present in the liquid steel at respective time, the frequency of spherical inclusions in the clogged nozzle is about 2–4 times larger (particularly near the nozzle wall) compared to that in the melt. Growth and transformation of Al2O3 clusters in the liquid steel at different holding times after an addition of Al and during casting were considered based on the obtained results., QC 20151120