The interest of gaining on-line information related to non-metallic inclusions during the steelmaking process has recently increased due to the development as well as the promising results of the Pulse Distribution Analysis with Optical Emission Spectroscopy method (PDA/OES). Even though, the time from sampling to presented results on inclusions is only about 5-10 minutes, the method has also shown limitations with respect to the determination of some inclusion characteristics. Therefore, a first step was to perform a study on other methods such as the cross-section method (CS) on a polished sample surface, the cross-section after etching method (CSE), the bromine-methanol extraction method (BME), and the electrolytic extraction method (EE). This study focused on the evaluation of these methods with respect to the time consumption for preparation and analysis of a sample, the analyzed volume and the determination of inclusion and cluster characteristics such as size, number, particle size distribution (PSD) and composition. The CS and CSE methods were found to be suitable in the determination of the largest cluster in a sample which can be recommended in order to select proper extraction parameters for further studies. The BME method was considered to be fast with the possibility of analyzing a large volume. However, the used solution is chemically stronger compared to electrolytic extraction solutions, which can affect the results. In most aspects, the EE method was found to be the most stable, reliable and accurate method with some limitations regarding the time aspect. Based on this conclusion, the EE method was selected for a comparative study with the PDA/OES method. Reliably detected size ranges by using the PDA/OES method were defined for two low-alloyed steel grades. These are 2.0-5.7 μm and 1.4-5.7 μm for steel samples taken before and after a Ca-addition during the secondary steelmaking, respectively. Moreover, agreements between the EE and PDA/OES methods were observed in the average size and number of detected inclusions when only inclusions with the size &gt; 2 μm were considered. Also, a theoretical minimum size and a maximum number ofinclusions present in the steel sample, which can be detected by using the PDA/OES method, were estimated. The work continued by successfully applying the EE method to study correlations between inclusions observed in the liquid steel samples and in a clogged nozzle (clogging material). It was found that the average sizes of spherical and non-spherical inclusions observed in the steel corresponded well with those observed in the clogging material. However, there were some differences in the frequencies of these inclusions. This was explained by a possible transformation of the present inclusions due to a reoxidation and a reaction with the nozzle refractory of the steel melt. The results of this study may contribute in the selection of proper process parameters or inclusion characteristics for future studies on the improvement and application of on-line methods. Finally, suggestions on how to present and interpret data obtained by the PDA/OES method during production of stainless steels were given in the present thesis. More specifically, the possibilities of defining operating windows with respect to inclusion composition and the use of a B-factor for Al (the total content of Al in inclusions detected by using the PDA/OES method) during the secondary steelmaking were discussed. In addition, a correlation study between B-factors for Al and numbers of inclusions (dV &gt; 4 μm) obtained by using the PDA/OES method on process samples, and corresponding slivers indices from plate products was performed. The results showed a moderate correlation between these parameters as well as an increase of the slivers index with increased values of the chosen PDA/OES data. This indicates that it could be possible to predict when there is an increased risk of having slivers on the final rolled product at an early stage of the steelmaking process. / <p>QC 20150525</p>

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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.

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.

This thesis focus on investigations of the influence of non-metallic inclusions on corrosion in steel samples taken at different stages of the steel production when producing pipeline steels. The electrolytic extraction technique was used to extract inclusions from these steel samples and thereafter studying them using scanning electron microscopy in combination with energy dispersive microscopy. This approach enabled three-dimensional evaluations of different non-metallic inclusions present in two metal samples of low-carbon Ca-treated pipeline steels. The modification of the inclusion characteristics was investigated and compared for steel samples taken from various stages of the smelting production process. Thereafter, the corrosion resistance of these steels was discussed depending on the characteristics of non-metallic inclusions present in the steel. In addition, this study also presents a new method of soft chemical extraction for qualitative and quantitative evaluations of the initial corrosion processes of a steel matrix surrounding various non-metallic inclusions. The results showed that the initial dissolution of the steel matrix started in areas surrounding CaS inclusions or inclusion phases containing a CaS phase. Furthermore, the results showed that no dissolution of the metal matrix surrounding CaO·Al2O3 and TiN inclusions could be detected.     Key words: pipeline steels, Ca-treatment, non-metallic inclusions, electrolytic extraction, corrosion, chemical extraction. / Sammanfattning Denna avhandling fokuserar på påverkan av icke-metalliska inneslutningar på korrosion i stålprover tagna under olika delar av ståltillverkningsprocessen för tillverkning av rör. Den ektrolytiska extraktionstekniken användes för att extrahera dessa inneslutningar från stålprover och därefter undersöka dem med användande av svepelektronmikroskopi i kombination med energidispersiv spektroskopi. Detta angreppssätt möjliggjorde tredimensionella studier av olika icke-metalliska inneslutningar i två lågkolhaltiga kalciumbehandlade metallprover som används för tillverkning av rör. Modifieringen av inneslutningars karakteristik undersöktes i prover tagna från olika delar av ståltillverkningsprocessen. Därefter så undersöktes motståndet mot korrosion baserat på karakteristiken hos de icke-metalliska inneslutningar som återfanns i stålproverna. Denna studie presenterar också en ny metod baserad på en försiktig kemisk extraktion för kvalitativa såväl som kvantitativa utvärderingar av den initiala korrosionsprocessen av stålmatrisen som omger olika typer av icke-metalliska inneslutningar. Resultaten visade att den initiala upplösningen av stålmatrisen började runt CaS inneslutningar eller komplexa inneslutningar innehållande en CaS fas. Samtidigt så visade resultaten att metallmatriser som omger CaO·Al2O3 och TiN inneslutningar eller faser innehållande dessa inte löstes upp.   Nyckelord: stål för tillverkning av rör, kalciumbehandling, icke-metalliska inneslutningar, elektrolytisk extraktion, korrosion, kemisk extraktion.

Nowadays due to large demand for clean and defect-free steels, several techniques based on different characteristics of particles are applied to investigate the steel cleanness. Outokumpu Stainless AB in Avesta has performed extensive work in this field by applying several methods, which all of them have specific advantages and limitations. However, it is necessary to find an accurate technique to investigate real properties of inclusions in duplex stainless steels. For routine analytical methods, calibration and parameters adjustment can be followed by help of these investigation results. The aim of present work is to apply automated INCA-Feature method for controlling cleanness of LDX 6112 duplex stainless steels after electrolytic extractions (EE) as a reference method. Three methods of investigations, INCA-Feature on polished samples as two-dimensional and on film-filter as three-dimensional and EE as three-dimensional analyses, were compared. The results of comparison between running INCA-Feature on polished samples and film filters show an acceptable agreement which proves the possibility of performing EE on this steel grade and using INCA-Feature for investigating this as a fast method. These methods are compared statistically and quantitative results are reported in details.

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

Bifilms is the oxide layer created between two surfaces in the melt of light metals that form an oxide layer. These become planar inclusions in the final casting and are problematic for the mechanical properties such as cracks and crack initiations. Bifilms are too thin to be viewed properly in two dimension cross-section method as they will only appear as thin lines. Because of this, it is relevant to test if it is possible to use electrolytic extraction (EE) as a alternative method to investigate bifilms. Both the deeply etched surface and the inclusions on a filter from the extraction are looked at in the scanning electron microscope (SEM) to get an understanding of the size and shape of the inclusions. With this, a greater understanding of these types of defects can be achieved. After both the filtered inclusions and the surface are examined in SEM with images and Energy-dispersive X-ray spectroscopy (EDS), the images are measured in the software ImageJ. The measurements and analysis show that it is probably bifilms and that they can be relatively large, and not so circular. However, the measurements with the filter have shown high levels of oxygen and carbon. Some levels of chlorine, nitrogen and iron have also been found. But if the surface is compared to the metal surface, it can be concluded that it is likely that bifilms have been found. There are sufficient levels of aluminum and oxygen present. Images in SEM also show the appearance of film-like inclusions. If the method of electrolytic extraction is to be improved to investigate bifilms,optimizations such as filters of other compositions are recommended. / Bifilms är det oxidskikt som skapas mellan två ytor i smältan hos lätta metaller som bildar ett oxidskikt. Dessa blir sedan plana inneslutningar i den slutliga gjutningen och är problematiskt för de mekaniska egenskaperna i form av sprickor och sprickinitieringar. Bifilms är för tunna för att de ska kunna ses korrekt i en tvärsnittsmetod, eftersom de bara kommer att visas som tunna linjer. På grund av detta är det relevant att testa om det är möjligt att använda elektrolytisk extraktion (EE) som en alternativ metod. Både den djupt etsade ytan och inneslutningarna på ett filter från extraktionen tittas på i svepelektronmikroskop för att få en förståelse för inneslutningarnas storlek och form. I och med det kan en högre förståelse uppnås för dessa typer av defekter. Efter att både de filtrerade inneslutningarna och ytan granskats i SEM med bilder och Energy-dispersive X-ray spectroscopy (EDS), mäts bilderna i en mjukvara, ImageJ. De mätningarna och analyserna visar att det antagligen hittats bifilms och att de kan vara förhållandevis stora, samt inte så cirkulära. Däremot har mätningarna med filtret visat höga halter av syre och kol. Även vissa halter av klor, kväve och järn har hittats. Men om ytan jämförs med metallytan så kan en slutsats dras om att det är troligt att bifilms har hittats. Där finns tillräckliga halter av aluminium och syre. Även bilder i SEM påvisar filmliknande inneslutningar till sitt utseende. Om metoden med elektrolytisk extraktion ska förbättras för att undersöka bifilms behövs optimeringar, som till exempel filterav en annan sammansättning.

When producing high strength special steels strict requirements are in place to assure the quality of the final product, both in terms of harmful elements and  the  content  of  non-metallic  inclusions  (NMI).  Achieving  cleanliness  is a  gradual  process  where all  the  steps  of  the  production  process  are  inter- connected, meaning that it is crucial to know the influence of each step in order to assure the contents of the final product.  The purpose of this thesis was to investigate the presence of non-metallic inclusions in wear plate steel, produced through two different process routes, one with an added round of Ca treatment and vacuum treatment. The  investigations  were  performed  using  electrolytic  extraction  of  in- clusions  followed  by  analysis  with  a  scanning  electron  microscope  (SEM). Backscattered electrons (BSE) were used for imaging and morphology anal- ysis and composition analysis was performed using energy dispersive spec- troscopy (EDS). Four different types of inclusions were found in the samples, whereof only one type is present in liquid steel.  It was found that the ini- tial Ca treatment stabilised the composition for the vacuum treated samples, while the sizes of the inclusions found in these samples were scattered.  The reverse was observed in the reference samples, where compositions were scat- tered but a mode value could be found for inclusion size at around 2.5 µm. Inclusions in the reference samples were found to have an average composi- tion lying outside the desired liquid region, not achieving full modification of harmful inclusions, while only modified inclusions could be found in vacuum treated samples. Additionally, around 70% of the analysed inclusions in the vacuum treated samples could be found in the liquid region. It was also found that the use of an electrolytic extraction method was appropriate for the investigated steel grade, while highlighting the need for some parameter adjustments to be made for future investigations in order to extract a sufficient number of inclusions. / Vid tillverkning av höghållfasta specialstål ställs stränga krav för att säkerställa kvaliteten på slutprodukten, både vad gäller skadliga element och innehållet av  icke-metalliska  inneslutningar  (NMI).  Att  uppnå  renlighet  är  en  gradvis  process  där alla  steg  i  produktionsprocessen  är  sammankopplade,  vilket innebär  att  det  är avgörande  att  känna  till  varje  stegs  inverkan  för  att säkerställa innehållet i slutprodukten.  Syftet med detta examensarbete var att  undersöka  förekomsten  av icke-metalliska  inneslutningar  i  slitplåtsstål, producerade genom två olika processvägar, en med en extra omgång av Ca- behandling och vakuumbehandling. Undersökningarna  utfördes  med  hjälp  av  elektrolytisk  extraktion  av  inneslutningar  följt  av  analys  med  ett  svepelektronmikroskop  (SEM).  Tillbakaspridda  elektroner  (BSE)  användes  för  avbildning  och  morfologianalys och sammansättningsanalys utfördes med användning av energidispergerande spektroskopi (EDS). Fyra olika typer av inneslutningar hittades i proverna, varav  endast  en  typ  förekommer  i  flytande stål.    Det  visade  sig  att  den initiala  Ca-behandlingen  stabiliserade sammansättningen  för  de  vakuumbehandlade proverna, medan storleken på inneslutningarna som hittades i dessa prover var spridda.  Det omvända observerades i referensproverna, där sammansättningarna  var  spridda  men  ett  modvärde  kunde hittas  för  inneslutningsstorleken  på  cirka  2,5  µm. Inneslutningar  i referensproverna visade sig  ha  en  genomsnittlig  sammansättning  som  låg  utanför  den  önskade flytande  regionen,  där  fullständig  modifiering  av  skadliga inneslutningar  inte uppnåtts, medan endast modifierade inneslutningar kunde hittas i vakuumbehandlade prover.  Dessutom kunde cirka 70% av de analyserade inneslutningarna i de vakuumbehandlade proverna hittas i den flytande regionen. Det visade sig också att användningen av en elektrolytisk extraktionsmetod var lämplig för den undersökta stålsorten, samtidigt som behovet av att göra vissa parameterjusteringar inför framtida undersökningar framhölls, för att kunna extrahera en tillräcklig mängd inneslutningar.