| 1. |
- Ahlström, Johan
(författare)
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Aluminium i betong - Litteraturstudie och experimentella försök
- 2012
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Rapport (refereegranskat)abstract
- I dagens byggprojekt används en mängd olika material för att bygga konstruktioner. Det förekommer att komponenter av aluminium gjuts in i betong vilket medför en risk att täckskiktet spricker p.g.a. korrosionsprodukternas stora volym. Därför är det viktigt att klargöra vilka korrosionsegenskaper aluminium har ingjuten i betong.
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| 2. |
- Ahlström, Johan
(författare)
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Atmosfäriska korrosionsegenskaper för rostfritt stål med olika ytstruktur
- 2011
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Rapport (refereegranskat)abstract
- Generellt sett så har rostfria stål en hög korrosionsresistens i atmosfärisk miljö p.g.a. den mycket tunna oxidfilmen på ytan, en film som fungerar som en barriär och försvårar initieringen av en korrosionsprocess på stålets yta. Dock så kan rostfria stål få svåra gropfrätningsangrepp i vissa aggressiva atmosfärer där t.ex. klorider och SO2 finns närvarande. Olika ytstrukturer kan ge ytan olika egenskaper som vätbarhet, ytråhet och ytsammansättning. En yta som har hög vätbarhet har en tjockare fuktfilm på ytan jämfört med en yta som har låg vätbarhet. Det är i fuktfilmen på ytan som korrosionsprocesserna sker, aggressiva partiklar och gaser kan tas upp i fuktfilmen från atmosfären och öka korrosionshastigheten. Ytråheten påverkar både vätbarhet och hur mycket partiklar som fastnar på en yta, därmed påverkar ytråheten korrosionshastigheten. Ytsammansättning anger vilka och hur mycket det finns av ett ämne i den skyddande oxidfilmen, ämnen som kan ha betydelse för hur lätt korrosion uppstår, t.ex. så kan olika sulfider fungera som initieringsyta för korrosionsangrepp. I litteraturen har det dragits olika slutsatser om vilken ytegenskap som har störst betydelse för korrosionens omfattning. Vissa studier säger att ytråheten har störst betydelse medan andra säger att ytsammansättningen har störst betydelse. Särskilt låglegerade ferritiska rostfria stål kan få svår gropfrätning i aggressiva miljöer och då har typen av ytstruktur liten betydelse för hur stora korrosionsangreppen blir. För de mer legerade austenitiska stålen kan typen av ytstruktur ha stor betydelse för storleken på korrosionsangrepp. Höglegerade stål som innehåller molybden har generellt sett små korrosionsangrepp och typen av ytstruktur har liten betydelse för korrosionsangreppens omfattning. Sammantaget tycks det dock vara så att ytråheten ändå har relativt stor inverkan på korrosionsresistensen, dock har relativt få studier genomförts där ytråheten verkligen mätts.
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| 3. |
- Ahlström, Johan
(författare)
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Rostfritt stål i betong med hög fukt och kloridhalt - Provningsmetod för rostfritt stål i betong: Delrapport IV
- 2011
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Rapport (refereegranskat)abstract
- För betongkonstruktioner som är exponerade i aggressiva miljöer kan korrosionsskador uppstå som kräver kostsamma reparationer. Aggressiva miljöer kan t.ex. vara konstruktioner i kontakt med havsvatten där klorider kan transporteras genom betongskiktet fram till armeringen och där orsakar korrosionsskador. För att förhindra vissa korrosionsskador kan armering av kolstål (som är det vanligaste armeringsmaterialet) bytas ut mot armering i rostfritt stål. Idag finns en mängd olika rostfria stål, med olika korrosionsegenskaper, tillgängliga på marknaden och det är därför viktigt att kunna klassificera korrosionshärdigheten för dessa stål. I en tidigare litteraturstudie ”Elektrokemiska metoder för utvärdering av armeringskorrosion samt kritisk kloridjonkoncentration för rostfritt stål i betong” [1] så undersöktes vad som har rapporterats i litteraturen om provningsmetoder för att undersöka korrosionshärdigheten för rostfritt stål i betong. Det framgick av litteraturstudien att en potentiostatisk metod med polarisering till +200 mV kan vara lämplig. I denna studie har en liknande potentiostatisk metod tillämpats och utvärderats. Provkropparna placerades i ett vattenbad där temperaturen ökade med 5°C per 14 dagar från lägst 20°C till maximalt 40°C. Två austenitiska och tre duplexa stål har undersökts och resultaten visar att stålen EN 1.4301 (304), EN 1.4162 (2101), EN 1.4436 (316) fick korrosionsangrepp vid 4 vikt-% Cl per cementvikt när temperaturen på vattenbadet var mellan 20 och 30°C. Det mer legerade duplexa stålet EN 1.4362 (2304) fick korrosionsangrepp vid 6 vikt-% Cl per cementvikt vid en temperatur på 35°C. Det högst legerade stålet EN 1.4462 (2205) fick inga korrosionsangrepp vid10 vikt-% Cl per cementvikt som var den högsta kloridkoncentrationen.
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| 4. |
- Allvar, Marie
(författare)
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MIG/MAG brazing with cold metal transfer
- 2012
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Rapport (refereegranskat)abstract
- In the automotive industry a commonly used material is thin steel sheets coated with a thin layer of zinc for corrosion resistance purposes. Welding of this material, with the high temperatures involved, causes problems with zinc burn-off leading to reduced corrosion resistance. The zinc evaporation also causes arc disturbances leading to spatter formation, pores and difficulties achieving good visual weld quality. The joints are in many cases visible or semi-visible (e.g. visible after opening a door) and “A-grade” quality is demanded, meaning no visible discontinuities are allowed. It also implies a smooth and generally appealing appearance of the joint. An alternative to welding is brazing, and laser brazing meets the requirements but the process is associated with high costs. In the national project “LEX-B”, funded by Vinnova, the possibilities of using arc brazing, in particular one MIG/MAG brazing and two TIG brazing processes, for some automotive applications are investigated. This master thesis is connected to the first part of the project and aims at compiling data for making a selection of the most promising process to investigate and optimise further. LEX-B is conducted in cooperation between Swerea KIMAB AB, Volvo Trucks, Scania CV and University West. The joint of interest is a lap joint between bottom and upper sheets of 1.2 mm and 0.8 mm respectively that represents a joint on the side of a truck cabin. The requirements are visual A-grade quality and tensile shear strength of 300 MPa. In the project the MIG/MAG process Cold Metal Transfer (CMT) was compared to the TIG processes forceTIG and Plasmatron. CMT was experimentally investigated while the results for the other two processes were obtained partly from a previous study and partly from Volvo Trucks where tests were performed simultaneously. A system for measuring data for the process was developed, test specimens were brazed and examined visually and mechanical destructive testing was performed to ensure the tensile shear strength. Parameter studies were done for further process optimisation.
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| 5. |
- Bengtson, Arne, et al.
(författare)
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Comparison of GD-MS and LA-ICPMS direct solid sampling techniques for trace elemental analysis of steels
- 2013
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Rapport (refereegranskat)abstract
- The objective of this project is to evaluate commercially available techniques for trace elemental analysis of steels using direct solid sampling. Such methods have the potential to increase sample throughput and thereby reduce analysis costs. Glow Discharge Mass Spectrometry (GD-MS) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) were evaluated. Five certified reference materials (CRM) were selected for the experimental work; a high purity iron, a carbon steel and three high alloy steels. For both types of instruments, the sample set was first used for calibration, then run as unknowns several times in order to get sufficient statistics for the evaluation. The GD-MS measurements were carried out at the Thermo Fisher Scientific applications laboratory in Bremen. The LA-ICPMS work was carried out at KIMAB. Prior to the measurements reported here, the effects of varying instrumental parameters of LA-ICPMS were investigated in order to develop a suitable method for steels. The results show that both techniques are powerful methods for simultaneous determination of a large number of trace elements in steels. A limitation is that none of the techniques is capable of analysing C, N and O, due to gas leaks and contamination from materials in the sources. The overall performance in terms of precision and detection limits is better for GD-MS, but for several applications LA-ICPMS provides sufficient performance. Both techniques have instrumentally limited detection limits at the ppb level or below, but the results on the test samples mostly give considerably higher standard deviations, also at very low concentration levels. Therefore, the analytical accuracy for traces is more limited than one would expect based on the instrumental capabilities; typically in the low ppm range or slightly below. The most likely reason for this is the combination of material inhomogeneity and small sampling volumes. This affects LA-ICPMS the most, due to considerably lower sampling volume than GD-MS.
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| 6. |
- Bengtson, Arne, et al.
(författare)
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Further Development of GD-OES for Surface and Depth Profile Analysis
- 2014
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Rapport (refereegranskat)abstract
- Glow Discharge Optical Emission Spectroscopy (GD-OES) is a well established technique for Compositional Depth Profiling (CDP), very useful for in-depth elemental analysis of surface layers from 10 nm to 100 µm. It is fast, sensitive and fully quantitative. However, there are a few artefacts requiring further study to improve the accuracy and trueness of the method further, primarily for near-surface applications. Outgassing of volatile compounds present inside the source, mainly water and hydrocarbons, has been established to be a major cause of such artefacts. The most “problematic” element is hydrogen, for the following two reasons: 1) it “cools” the plasma even when present in small quantity and thereby affects the intensities of the emission from almost all other elements; 2) it is very reactive and forms molecular species with other light elements e.g. CH, NH and OH, having emission spectra overlapping several atomic analytical lines; causing “false” or exaggerated surface peaks of the corresponding elements. In this work, methods to reduce the outgassing of volatile compounds have been studied. Attempts to dry and clean the argon gas flowing into the source by means of a chemical filter gave no significant improvement. On the other hand, replacing the “standard” anode made of a copper-beryllium alloy with a pure copper anode was shown to reduce the outgassing significantly. To be more specific, the background signal from atomic hydrogen and associated artefacts are reduced, it is still possible that the amount of molecular hydrogen remains almost constant, without observable effects on the analytical signals. Since molecular emission can originate from the sputtered material of the sample itself, particularly organic coatings, an in-depth study of molecular emission in GD-OES was carried out. It was shown that background signals from such emission can be significantly reduced, provided that the instrument has spectral channels for the emitting molecular species installed. With such channels available, conventional “line interference correction” methods was found to be effective in reducing false elemental signals from molecular emission. Application of the pure copper anode and reduction of molecular background techniques to a heat treated zinc-base coating showed expected improvements in the near-surface part of the depth profile. However, for the major elements of technical importance, the difference compared with the original anode and analytical method was marginal. This is reassuring, since it means that the near-surface artefacts normally do not cause major analytical errors. The element that is most difficult to establish the “trueness” of depth profiles is nitrogen, especially if the surface layer is slightly porous. There are samples where an elevated signal from nitrogen in the top surface cannot be correlated to a vacuum leak, trapped air or molecular emission (CO). Investigations where samples are measured for total nitrogen with conventional techniques are very difficult, since the surface layers showing an elevated content are very thin. Further investigation of such samples with high vacuum techniques, e.g. SIMS, would be of interest. A second part of the project deals with advanced evaluation of depth profile data by means of “expert systems”. An expert system is a computer application that is able to perform tasks which are normally performed by human experts; in this case the aim is to be able to perform e.g. quality control with GD-OES without the need for a qualified human expert to interpret the data. There are several types of “computational statistics” methods that can be employed for such purposes, the most well known is probably multivariate analysis. Other methods can evaluate both numerical and other types of input related to classification based on technical properties, e.g. paint adhesion, scratch resistance etc. The objective of this work is to be able to classify samples according to such technical properties. All such systems need a “training set” of samples with known technical properties. In this work, a relatively large set of steel sheet samples with various zinc-based coatings were classified according to corrosion resistance. Form the GD-OES depth profiles, the coating weights of zinc, aluminium and magnesium were extracted in a data pre-treatment step. Using the rule-based classification algorithm “decision tree” 25 out 29 samples was correctly classified. This “proof of concept” work has shown that it is possible to predict certain technical properties based on a multi-element depth profile. This opens up the possibility for e.g. automated quality inspection of complex coating systems, but also the possibility to use GD-OES depth profiling more effectively as a tool in product development.
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| 7. |
- Bengtson, Arne, et al.
(författare)
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Investigation of computational statistics for evaluation of PDA-OES data – final report of the project Innestyr 3
- 2014
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Rapport (refereegranskat)abstract
- The aim of this project was to investigate the potential of applying computational statistics (“data mining”) methods to PDA – OES data to find correlation to defects in the final products as well as changes of parameters during the steelmaking process. The computational methods used were multivariate (MVA) data analysis and the rule-based methods “decision trees” and “neural nets”. The project was carried out in close cooperation with Outokumpu Stainless Avesta and the Royal Institute of Technology (KTH). PDA – OES data from sheet samples with and without surface defects were processed by all three methods, all showing statistically significant and consistent correlation. The formation of surface defects is positively correlated to the number of “medium” to “large” inclusions of the classes AlCaMg and AlCa i.e. mixed oxides of these elements. The second part of the research was an evaluation of variations in inclusion characteristics in different process stages using synthetic slags. A large number of samples were collected from experimental trials with two types of synthetic slags, and the conventional process without slag addition for reference. The samples were taken in the ladle furnace at three stages, and in the tundish in connection with the final test sample before casting. PDA – OES data from these samples were evaluated with MVA and decision tree methods. The results showed that the different process stages can be identified from the PDA-OES data with rather good certainty. No significant difference between the use of synthetic slags and the conventional process was detected. In the course of the evaluation work, it was also found that the computational statistics methods must be used with caution. The reason is that data due to “statistical noise” can be identified as significant, giving misleading results. Further work to reduce this problem will be necessary.
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| 8. |
- Bengtson, Arne, et al.
(författare)
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Optical Emission – Pulse Distribution Analysis (PDA/OES) for applications to Aluminium alloys
- 2012
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Rapport (refereegranskat)abstract
- The technique PDA/OES is briefly reviewed. It is based on detection of the signals from individual sparks in OES analysis, which usually comprises a few thousand sparks in each burn. Sparks hitting inclusions/particles of characteristic elemental composition give rise to “outliers” of higher intensity for “marker” elements characteristic of the particle type. The outliers are extracted by statistical analysis, and processed by the software to identify and quantify the particles. PDA/OES is used mainly in the steel industry, where the main interest is to detect and analyse non-metallic inclusions (NMI). In this work, PDA/OES has been tested for applicability to aluminium alloys. In this case the main interest is metallic particles, but there are also some types of NMI’s of interest. It was found that PDA functions in the same way as in steels, but there are several factors limiting the applicability. Firstly, the smallest detectable particles are about 1 μm diameter, and the particle number density should not exceed about 20000/mm3 for PDA to detect then as individual particles. In aluminium, many particles (precipitates) of interest are much smaller and present in much higher number densities. Secondly, the elements present in the metallic particles also exist as dissolved in the surrounding metal, giving a high and noisy background which limits the possibility to detect signals from the particles as outliers. These constraints has limited the applicability to metallic particles in the several μm range, using Fe as the “marker” element. However, for certain types of NMI it is likely that very small particles down to 1 μm can be detected. The experimental work has shown that the scanning spark technique OPA can provide additional useful analytical information. Macroscopic segregation at the mm – several cm ranges can rapidly be investigated in two dimensions. In combination with PDA, macroscopic “clusters” of particles can be mapped.The spark optical emission techniques PDA/OES and Original Position Analysis (OPA) have been investigated for application to aluminium alloys. PDA/OES has been optimised for detection and quantification of metallic particles in the several µm range with. The OPA technique has been evaluated for rapid determination of macroscopic segregation.
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| 9. |
- Bengtson, Arne, et al.
(författare)
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Synthetic standards for determination of trace elements in steels by solid sampling techniques
- 2015
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Rapport (refereegranskat)abstract
- Accurate determination of trace elements in steels is of importance for several reasons. Some trace elements are added on purpose to influence the metallurgy of the steel, and it is important to control the content to the correct level. Other trace elements are deleterious to certain steel properties and must be controlled to be below maximum levels in order to ensure the quality. In more recent years, national and international legislation demand from steel producers to declare the content of certain environmentally hazardous elements, mainly heavy metals such as Hg, Pb and Cd. Multi-element techniques based on direct solid sampling is of great interest due to the short analysis times, but there is a lack of suitable reference materials (RM) for calibration. Bundesanstalt für Materialprüfung (BAM) in Berlin has therefore developed a technique to produce synthetic solid RM’s for trace analysis. The technique is based on mixing metal powder with small amounts of trace elements in liquid solution, drying and compacting the powder into solid briquettes. A few stainless steel RM’s produced at BAM were used at KIMAB to determine Ce, La, Nd and Pr in a stainless steel CRM, using an LA-ICPMS instrument. The results showed very good agreement with certified values. Six RM’s of the same type were subsequently prepared at KIMAB, doped with Pb, Cd and Hg at levels from 0,1 μg/g to 30 μg/g. The RM’s were first analysed by wet chemical ICP-MS at ALS in Luleå. The results showed nearly 100% recoveries of Pb and Cd, while most of the Hg had been lost in the sample preparation. The samples were then used to calibrate the LA-ICPMS instrument for Pb and Cd. It was found that the signals from the top surface of the samples were very high, indicating a considerable degree of “elemental fractionation. A “preburn” in the form of an ablation linear scan across the sample surface was therefore needed prior to the analysis scan. Very good linear calibration curves were obtained for Pb and Cd, but with apparently higher background levels than in solid steel. Three stainless steels with previously determined contents of Pb just below 2 μg/g were analysed together with the synthetic RM’s, giving intensities significantly below the calibration curve. Assuming a zero background level give calculated mass fractions in near agreement with certified values, but this is not a satisfactory calibration method. It is therefore concluded that in present form, synthetic RM’s are only reliable as calibration samples for LA-ICPMS measurements at trace levels larger than 10 μg/g. Further work is necessary in order to reduce this limit
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| 10. |
- Caddéo, Sophie, et al.
(författare)
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Study on oxygen reduction effects due to sintering parameters for sintered steel materials
- 2012
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Rapport (refereegranskat)abstract
- Three sinter steel materials, AD15, AD4 and Astaloy CrM, have been under evaluation in this study. The study has been focusing on three types of trials in order to see how the sintering parameters influence the reduction of oxides. The first series of trails were focused on how the green body density affects the reduction rate. The second and third series of trail were more focused on the sintering parameters, i.e. sintering time and sintering atmospheres, respectively. For sinter steel pellets a clear effect of the green body density can be seen on PAS and oxygen analyses. A higher green body density decreases the oxygen reduction reactions during sintering and results in higher oxygen content in the final pellet. How the hydrogen content in the sintering atmosphere affects the reduction efficiency is still not clear as the results from the PAS and the chemical and microstructure analysis had different outcome. Further studies are required. The total reduction time has effect on the reduction result i.e. a longer reduction time will reduce more than a faster reduction time.
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