The Powder Bed Fusion using Electron Beam (PBF-EB) process is a highly complex additive manufacturing process. There are a very limited number of materials that have been used successfully, which limits the applications of the process, despite its well-documented advantages over conventional manufacturing. However, the development of new materials is hindered due to a lack of understanding of the fundamental phenomena in the process. The goal of this work has been to develop a model that is able to predict the process parameters that will lead to the manufacture of a fully dense component.   The model is based on 1285 empirical datasets of process parameters and the physical properties of the printed materials. Nine different materials were included in the data. By inputting a pre-defined set of process parameters and materials properties the model will output the beam power at which it is predicted a dense component may be manufactured. This novel approach will shorten the development of new process parameters by providing a first approximation of suitable parameters to iterate from. A tool steel powder supplied by Uddeholms AB was printed, using parameters proposed by the model. Two sets of pre-defined process parameters were used with several beam velocities and resulted in a number of correct predictions.   This model is a first step in predicting process parameters and presents a simple, transparent and new method of obtaining the process window for novel materials in Powder Bed Fusion using Electron Beam. / Powder Bed Fusion med Electron Beam (PBF-EB) är en mycket komplex additiv tillverkningsprocess. Det finns ett fåtal antal material som går att använda i processen. Detta är ett förhinder för applikationer trots processens väldokumenterade fördelar över konventionell framställning. Framtagning av nya material är dock hejdad på grund av okunskap kring de grundläggande fenomenen inom processen. Målet med detta arbete har varit att utveckla en modell som kan förutse processparametrar vilka ger helt kompakta komponenter.   Modellen är baserad på totalt 1285 data uppsättningar av processparametrar och de fysiska egenskaperna av de printade materialen. Data på nio olika material har samlats in. Genom att mata in ett par förbestämda processparametrar och materialets specifika materialegenskaper så beräknar modellen kraften på strålen vid vilken det förutspås att goda resultat framställs. Denna nya metod kortar ned tiden inom traditionell processparameterutveckling genom att bistå med en första iteration att arbeta utifrån. Ett verktygsstålspulver tillverkat av Uddeholms AB vart printat med hjälp av modellen. Två uppsättningar av förbestämda processparametrar användes vid flera olika stråles hastigheter och resulterade i åtskilliga lyckade förutsägelser.   Denna modell är ett första steg i att förutspå processparametrar och presenterar en simpel, transparant och ny metod till att finna process fönstret för nya material i Powder Bed Fusion med Electron Beam processen.

Steel cleanliness as a function of stirring practice during vacuum degassing treatment have been investigated in industrial studies at the steel plants of SSAB Special Steels in Oxelösund and Uddeholm AB in Hagfors. The cleanliness was examined with regards to the contents of sulphur, nitrogen and large inclusions (&gt;10µm). The stirring practice during the vacuum degassing treatment has been studied with respect to time, namely by shortening the vacuum degassing treatment time from 24 to 15 minutes. Furthermore, the effect of the stirring intensity was studied by measuring the open eye zone using camera recordings. The focus has been to study the effect of a shortened vacuum degassing time as well as a controlled stirring intensity on the steel cleanliness. Moreover, study the effect of subsequent induction stirring, after vacuum degassing, on the amount of inclusions. By taking steel and slag samples taken before and after the vacuum degassing treatment, the different stirring practices could be investigated. It should be noted that all heats reached the desired composition regardless of the treatment time and stirring practice. The results from the trials at SSAB Special Steels showed that the stirring practice during vacuum degassing have an effect on the total number of inclusions. The strong argon stirring during vacuum degassing with visible open eyes resulted in an average increase of 400% of the total amount of inclusions &gt;10µm. However, no difference between a vacuum degassing time of 24 or 15 minutes was seen with respect to the increased amount of inclusions, denitrogenization or desulphurization. During the subsequent induction stirring, which was softer with no open eyes, the effect of the stirring practice was unclear due to overlapping confidence intervals. An average decrease of 65% of the total amount of inclusions &gt;10 µm was seen for the heats  with non-overlapping confidence intervals. Based on these results it can be suggested that the use of a soft induction stirring after the vacuum degassing treatment as a possible process change to reach lower amounts of large inclusions. The stirring intensity during the vacuum degassing treatment was measured as the average ladle eye size during the trials at Uddeholm AB. This, due to that stronger stirring results in larger ladle eye zone. The results show that the amount of smaller inclusions (&lt;11.2 μm) decrease by up to 90% compared to the original amount, regardless of the stirring intensity. A stronger stirring showed tendency to increase the amount of large inclusion (&gt;22.4 μm). Moreover, the denitrogenization and desulphurization was not affected by the changed stirring intensity during vacuum degassing. It was also found that the average ladle eye size did not correlate to the logged average argon flow. / <p>QC 20150522</p>

The influence of ladle-slag additions on the BOF-process performance were investigated in plant trials. The aim of the study was to recycle ladle slag from secondary steelmaking to the LD-converter to save lime and improve the slag formation. More specifically, two plant trial campaigns covering in total 83 heats, whereof 47 with ladle-slag additions and 36 without ladle-slag additions, were performed.  Slag and steel sampling of the process were performed at tapping as well as during blowing at 15, 35, and 65% of the total blowing time. During the first campaign, ladle slag was added through the chute and lime reductions were made manually to correct for the ladle-slag addition.  In the second campaign, a development of the approach was made to suite a normal production practice. More specifically, the ladle slag was added through the weight-hopper system and implemented in the process-control system. In this way, the lime additions were reduced automatically by approximately 260 kg per heat. Moreover, the heat balance was compensated with a reduction in the iron-ore consumption. Additionally, the lance program was modified and the lance was lowered in the initial stages of the blow.  On the positive side, it was found that no demerits in the metallurgical performance of the process occur when ladle slag is recycled to the BOF-process. Furthermore, only slight affections on the slag composition were found, mainly with respect to the Al2O3 and FeO-content. In addition, the ladle slag was shown to melt during the initial stages of the blow. This contributed to an increased slag weight both during the blow and at tapping. However, a negative effect on the blowing time was experienced during the trials. Although, this effect was more pronounced during the first campaign and could be reduced with a controlled heat balance during the second campaign. / QC 20110503

The metallurgic process, Vacuum Oxygen Decarburization (VOD) process, is used for producing stainless steels with ultra-low carbon grades. In a VOD process, an oxygen lance is equipped with a De Laval nozzle which injects high speed oxygen gas. The aim of this work is to increase the knowledge of the flow behavior in the harsh environment of VOD vessels. Two real VOD nozzles from industry were numerically studied and compared at different temperatures and ambient pressures.  Flow patterns of the oxygen jet under different ambient pressures were studied and the flow information at different positions from the nozzle was analyzed. In addition, the study compared the effects of different ambient temperatures on the jet velocity and the dynamic pressure. The predictions revealed that the modeling results obtained with the CFD modeling showed an incorrect flow expansion, which agreed well with the results from the De Laval theory. Moreover, a little under-expansion is somewhat helpful to improve the dynamic pressure. The jet dynamic pressure and its width for the specific nozzle geometry have also been studied. It has been observed that a variation in the ambient pressure can influence the jet momentum and its width. In addition, a high ambient temperature has a positive effect on the improvement of the jet dynamic pressure. For the comparison between the two nozzles concerned, the modeling results showed that one of the nozzles was more applicably proper for lower pressures, displaying a more stable flow pattern. Furthermore, it was found that a change in ambient pressure has a stronger effect on the jet force than a change in ambient temperature. In addition, it was proved that the profiles of the dynamic pressure at a certain blowing distance fit well to Multi-Gaussian curves. / QC 20110920

This study intends to better control the final composition of steel by trying to have a better knowledge of elements including copper, nickel, molybdenum, manganese, tin and chromium in the scrap. This objective was approached by applying probability and statistical concepts such as normal distribution, multiple linear regression and least square and non-negative least square concepts. The study was performed on the raw materials’ information of Ovako Smedjebacken and Ovako Hofors, two steel production plants in Sweden. The information included but were not limited to the amount of the different scrap types used in the charge, total weight of the charge and the final composition of the produced steel.  First, the concept of normal distribution was used as to consider the variations of the alloying elements between the estimated and measured alloy contents. The data were then used to consider a model for distribution factor of the studied elements. Also, an estimation of the alloy contents in the scrap type given the final steel composition was carried out using the concept of probability and statistics. At the end, a comparison of the results from the different concepts was done.

Surface treatment processes of stainless steel, such as pickling, produces acidic waste water consisting of Na⁺, Cl⁻, F⁻, NO⁻3, SO42-, PO43-, Fe3+, Cr6+ and Ni2+. At Sandvik ABs steel works in Sandviken, this waste water is treated and neutralized using slaked lime before being released into the lake Storsjön. The aim of this report was to make a literary review of previous work in using slag as a neutralizing agent for acidic waste water. Furthermore, to see if it’s possible to replace some or all of the slaked lime in the neutralization process with slag and to study what slag that might be suitable to use. Since the waste water contains HF acid, the focus of this report was on different materials used for fluoride adsorptions. The literary study showed that the fluoride adsorption process with BOF slag, quick lime and magnesium oxide as adsorbents were endothermic. Therefore, it benefitted from an increased temperature. Furthermore, the literature study showed that many materials follow a pseudo-second-order kinetic model as well as a Langmuir or Freundlich isotherm for a fluoride adsorption. A previous experiment showed that a mixture of BF slag and slaked lime had the best HF acid neutralization among the tested materials. A fluoride adsorption experiment was made at different temperatures (25 – 55 °C) by using a slag from an aluminium reduced steel melt and a slag from a silicon reduced steel melt from the AOD converter in Sandviken. The silicon reduced steel melt slag showed an increase of fluorides in the solution, due to the presence of calcium fluoride in the slag. This was observed for all temperatures. The aluminium reduced steel melt slag also increased the fluoride content in the solution at 25 and 30 °C. At higher temperatures the fluoride content in the solution decreased with 93.6 to 94.9 %. Na⁺, Cl⁻, F⁻, NO⁻3, SO42-, PO43-, Fe3+, Cr6+, and Ni2+

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. / <p>QC 20150422</p>

This bachelor degree project is about determining the impact that additional bottom stirring may have on the desulphurization process at SSAB Luleå. During one week of field work steel samples were collected from 39 different heats. 31 of the heats were samples with the bottom stirring function enabled and the remaining 8 heats without the bottom blowing function, which is the standard method today at SSAB Luleå and they can be referred as references. Data from 15 old reference heats were also used for analysis.Two different behaviors of bottom stirring appeared and they were therefore separated to type 1 and type 2 bottom stirring. Type 1 bottom stirring turned out to have highest possibility of all methods to reach dissolved sulfur content of maximum 0.001%. If the ingoing dissolved sulfur content is around 0.03% has type 1 bottom stirring 33% chance to reach 0.001% dissolved sulfur content already after 13.3 minutes of injection and that can save sulfur reagents. The method with highest reagent efficiency showed type 1 bottom stirring to have, on second place came type 2 bottom stirring and the references showed to have lowest reagent efficiency.

It is well known that REMs are strong oxide and sulphide formers that can easily form large clusters which have harmful effect on the casting process as well as the quality of the final steel product. By adding these elements right before casting, the number of narrow transfer parts are eliminated (compared to if added in ladle) Also, the REM inclusions has less time to sinter together to form large clusters, preventing clogging. The general idea behind this alloying method in the continuous casting machine is to feed a wire of FeSiRE powder blend, coated with a metal strip, into the melt in the chilled Cu mold (CC mold) Adding REMs to the steel, in particular Ce, can increase the resistance to oxidation at high temperatures by improving the properties of the chromia layer. This is of big interest for SANDVIK as it can improve their corrosion resistant grades and may also, in the future, enable alloying in with other volatile elements such as Zr. This master thesis has the objective to find out the dissolution time of the wire, coated with three different metal strips; Steel, Cu and Al. The experiments were performed with steel grade 316L, provided by SMT, in a 2kg melt in a lab scaled induction furnace at 1500oC, 1510oC and 1530oC. The operations were performed both with and without FeSiRE powder inside. The results obtained with powder inside at 1500oC showed that the Al wire experienced the shortest dissolution time ( 0,5 to 1s) followed by Cu (≤10s) and Steel (18 to 20s). In addition to this, sampling procedures was implemented ( 1, 1, 3, 5 10 and 29mins after wire addition) in a depth of 40mm for each wire. Here, the yield of Ce 1 minute after wire addition was highest for the Steel wire (41.9%) followed by Cu wire (25%) and Al wire (&lt;14.8%). From samples taken 1 and 5mins after wire addition in the Al wire experiment, inclusions were extracted and collected on a film filter after electrolytic extraction and filtration. The film filter was observed in SEM. The morphology and compositions were analysed and compared. It was found that Ce and La was present as Ce La oxy sulfides both individually and on Al Mg O clusters.

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.