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  • 1.
    Andersson, Sofia
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013).
    Study of Dross in Ductile Cast Iron Main Shafts2015Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The study of dross in ductile cast iron main shafts was performed at Global Castings Guldsmedshyttan AB and presented in this master thesis. The purpose of the study was to obtain answers to why dross defects were present in some of the foundry's casted main shafts, with the main problem located at the flange of the shaft. The chemical composition of the dross formations and which steps in the casting process that increased the dross formation were of interest. The study only included dross in main shafts manufactured at Global Castings Guldsmedshyttan AB.

    Dross particles form when elements such as Mg, Ca, Si and Mn react with O. These elements, which are highly reactive to O, are used in ductile cast irons to achieve the spheroidal graphite nodules that regulate the cast materials ductile properties. If a higher amount of dross particles has formed, the particles will start to cluster, resulting in a growing dross formation. Dross formations works as surface crack initiation points and reduces the castings fatigue strength and ductility.

    During the study it was seen that the cause of dross formations is a combination of many parameters increasing the melts exposure to O resulting in dross defects. The dross formations could be connected to worn out ladles, low melt temperatures, incorrect additions of Mg treatment, lack of an extra slag removal station and finally turbulence as the melt were poured into the mould.

    At Global Castings Guldsmedshyttan AB a greater part of the main shafts containing dross defects were a result of worn out ladles and low melt temperatures. The types of dross found in the main shaft material were mainly Mg, Ca, Si and Al which had reacted with O. S bonded with Mg and Ca was also detected in the dross formations. It was shown that the dross particles could be derived from charge material, Mg treatment and inoculation.

    To avoid dross defects the first step would be to set up an extra slag station, shorten the interval of maintenance of the ladles and to better adjust the melt temperature to the condition of the specific ladle. To minimize dross due to excess Mg a better controlled process would be recommended with an increased number of monitored manufacturing parameters.    

  • 2.
    Andersson, Stefan
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Analysis of welding in comparable steel grades: Influence of steel grade on the welding process2014Independent thesis Advanced level (professional degree), 20 poäng / 30 hpOppgave
    Abstract [en]

    This master thesis is written to examine the influence of different low carbon steel sheet materials on the GMAW welding process. During welding the properties of the base material influence the productivity of the welding process. The purpose of this thesis is to examine how the choice of material and welding speed affect the welding process and the productivity.

    A literature survey was performed to describe the welding technique and the differences in manufacturing for the sheet materials as well as the effect of alloying and welding on the sheet material. Defects in the weld and methods used to determine them are explained. Test pieces of the different sheet materials were welded with the GMAW process and examined.

    The result shows that there is a variation in the welding process regarding weld penetration. Measurements also show that welding speed and gap have little influence on the hardness of the weld and heat-affected zone and that the S355MC is more likely to suffer from a narrower toe transition radius than S355NL and S355MC Si. This and the higher area in the Y2 region for the S355MC could indicate a stronger inward flow in the weld pool during welding possibly a result of surface active agents such as oxygen and sulphur.

  • 3.
    Bergh, Gustav
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik.
    Förslitning av fräsverktyg2014Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
  • 4.
    Birgmark, Anja
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap.
    Wear of Coater Blades2013Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 5.
    Ejnermark, Sebastian
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Mjukglödgning av ett plastformsstål2012Independent thesis Basic level (university diploma), 15 poäng / 22,5 hpOppgave
  • 6.
    Ekengren, Jens
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Large and rare: An extreme values approach to estimating the distribution of large defects in high-performance steels2011Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The presence of different types of defects is an important reality for manufacturers and users of engineering materials. Generally, the defects are either considered to be the unwanted products of impurities in the raw materials or to have been introduced during the manufacturing process. In high-quality steel materials, such as tool steel, the defects are usually non-metallic inclusions such as oxides or sulfides.

    Traditional methods for purity control during standard manufacturing practice are usually based on the light optical microscopy scanning of polished surfaces and some statistical evaluation of the results. Yet, as the steel manufacturing process has improved, large defects have become increasingly rare. A major disadvantage of the traditional quality control methods is that the accuracy decreases proportionally to the increased rarity of the largest defects unless large areas are examined.

    However, the use of very high cycle fatigue to 109 cycles has been shown to be a powerful method to locate the largest defects in steel samples. The distribution of the located defects may then be modelled using extreme value statistics.

    This work presents new methods for determining the volume distribution of large defects in high-quality steels, based on ultrasonic fatigue and the Generalized Extreme Value (GEV) distribution. The methods have been developed and verified by extensive experimental testing, including over 400 fatigue test specimens. Further, a method for reducing the distributions into one single ranking variable has been proposed, as well as a way to estimate an ideal endurance strength at different life lengths using the observed defects and endurance limits. The methods can not only be used to discriminate between different materials made by different process routes, but also to differentiate between different batches of the same material.

    It is also shown that all modes of the GEV are to be found in different steel materials, thereby challenging a common assumption that the Gumbel distribution, a special case of the GEV, is the appropriate distribution choice when determining the distribution of defects.

    The new methods have been compared to traditional quality control methods used in common practice (surface scanning using LOM/SEM and ultrasound C-scan), and suggest a greater number of large defects present in the steel than could otherwise be detected.

  • 7.
    Ekengren, Jens
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Bergström, Jens
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Estimating the volume distribution of large defects using Generalized Extreme Values2011Inngår i: Extremes, ISSN 1386-1999, E-ISSN 1572-915XArtikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    The presence of defects, such as oxides and other non-metallic inclusions, is an important factor in determining the properties of steels. Due to improvements in the manufacturing of high-quality steels, the amount of large defects has decreased and therefore it has become increasingly difficult to accurately determine their distribution using conventional methods. Previously, a method for estimating the distribution of large defects using a conversion from the Gumbel distribution has been presented. However, it has been shown that the Gumbel distribution is not always appropriate for modelling the sizes of the largest defects and that the Generalized Extreme Values (GEV) distribution should be used instead. In this work a more general method for the estimation of the total volume distribution of large defects isproposed, showing how the volume distribution may be calculated from the estimated parameters for the GEV distribution. The new method is applied to the results of a series of specimens made from high-quality tool steel tested in ultrasonic resonance fatigue. Possible methods for obtaining the confidence limits of thevolume distribution are also discussed.

  • 8.
    Ekengren, Jens
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Bergström, Jens
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Extreme value distributions of inclusions in six  steels2012Inngår i: Extremes, ISSN 1386-1999, E-ISSN 1572-915X, Vol. 15, s. 257-265Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    There is a prevailing assumption that the largest inclusions in steel volumes follows mode I of the Generalized Extreme Values (GEV) distribution. In this work, the GEV distributions of non-metallic inclusions in six different high performance steels, of different grades and processing routes, were investigated by means of fractography of inclusions causing failure in ultrasonic fatigue testing to one billion cycles and all three modes of the GEV were found for the different steel grades. Values of the shape parameter ξ of the GEV distribution as high as 0.51 (standard deviation 0.11) were found in one steel grade. Thus, the present results show that the assumption of GEV-I (Gumbel, LEVD) distribution has to be substantiated before being used to estimate the size of the largest inclusions.

  • 9.
    Ekengren, Jens
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Bergström, Jens
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Influence of life length on estimated defect  distribution in a low defect steel material2011Inngår i: Proceedings of the Fifth International Conference on Very High Cycle Fatigue / [ed] C. Berger and H.-J. Christ, 2011, s. 177-182Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper reports on results of very high cycle fatigue tests on a steel with a relatively low number of defects per unit volume. Two series of newly designed dog-bone specimens, with low stress gradients, were tested at two constant stress levels, aiming at providing fatigue life lengths of 106–108 cycles and 107–109 cycles, respectively. Fatigue-initiating defects on the fracture surfaces were measured and the corresponding size distributions were analysed to investigate the influence of the elevated stress level needed to achieve shorter life lengths.The presented results indicate a difference between the distribution of initiating defects in the long and shorter life length test series. The main conclusion is that fixed stress level fatigue testing to life lengths around 107 cycles may be a suitable method to estimate the content of large defects in low defect steel materials, provided a suitable test specimen geometry with low stress gradients is used.

  • 10.
    Ekengren, Jens
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Kazymyrovych, Vitaliy
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Bergström, Jens
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Assessment of strength and inclusions of Tool Steels in Very High Cycle Fatigue2009Inngår i: Proceedings of the 8th International Tooling Conference, Vol 1 / [ed] P. Beiss, C. Broeckmann, S. Franke, B. Keysselitz, Verlag Mainz, Wissenschaftsverlag , 2009Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Fatigue strength is an important material property for many tooling applications, particularly in high performance applications. The research in Very High Cycle Fatigue (VHCF) has demonstrated that the traditional fatigue limit may not be valid for many materials subjected to 107 or more load cycles. Presently, both materials data and mechanism knowledge is missing on VHCF applications, even though many components are run at these life lengths. The fatigue strength is commonly controlled by different defects initiating failure, as in well controlled laboratory experiments may be internal inclusions. In this paper VHCF experimental testing was accomplished by the use of ultrasonic fatigue testing run at 20 kHz allowing long life evaluation within reasonably short test time. Fatigue strength, failure mechanisms and inclusion content were accordingly assessed. Fatigue strength data on H13 tool steel are presented, as well as a statistical approach considering available defect distribution and load distribution in the critically stressed volume, important to both steel supplier and end-user.

  • 11.
    Glaad, Gustaf
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Pressurizing of high-pressure fuel system forsingle cylinder test cell2019Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This master thesis covers the development of a high-pressure fuel system for compression ignitedfuels such as diesel and diesel-like fuels that will be deployed into a single cylinder test cell at AVLMTC Södertälje, Sweden. The test cell is used by AVL to conduct research and testing of new fuelsfor their customers and this new fuel system will widen the span of fuels able to be tested by theequipment.This thesis focuses on pumping and pressurizing of the fuel, ensuring that all ingoing materialsare non-corrosive in this environment and compatible with the necessary fuels and lastly a safetyanalysis of the system with respect to operator and process safety. Other aspects of the projectsuch as mass flow measurements and fuel conditioning is covered in a sister thesis Mass flowrate measurement of compression ignition fuels in high-pressure stand-alone pump unit for singlecylinder test cell written by C. Aksoy [1].The goal of this thesis project was to deliver a finished manufactured fuel system and if the timeallowed for it, also validate its performance and finally installing and incorporating it into the singlecylinder test cell. The development process started with the writing of a product specificationoutlining the requirements and request on the product in a specification of requirements matrix andrelate these to product properties of the system using a quality function deployment (QFD) matrix.This document was then used as a base for further advancement in developing concepts to solveeach product property and weighing these concepts against each other using Pugh’s matrices. Thechosen concepts were then further developed, a flow chart for the system was developed as well asfuel lines and other supporting components were analyzed and chosen.In the end the high-pressure fuel pump from Scania’s XPI fuel system were chosen as well asa pressure transducer in the HP1000 series from ESI. Within the time frame of this thesis, theproject did not end up getting finished to the degree planned, but due to time constraints werehalted before starting manufacturing of the system. Some minor component choices remained aswell as documentation such as drawings and finalizing the physical layout of the system remained.All information regarding the remaining work needed to finalize the project and deploying thesystem in the test cell were outlined and with more time, the fuel system should fulfill its purposeof allowing testing and research of compression ignited fuel to be possible in the test cell.

  • 12.
    Gåård, Anders
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Krakhmalev, Pavel
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Bergström, Jens
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap.
    Hallbäck, Nils
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap.
    Galling resistance and wear mechanisms - cold work tool materials sliding against carbon steel sheets2007Inngår i: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 26, nr 1, s. 67-72Artikkel i tidsskrift (Fagfellevurdert)
  • 13.
    Hidén Rudander, Petter
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik.
    Case hardened steel plates for ballistic armour: A study of ballistic and mechanical properties of case hardened ARMOX® steel2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Protective materials are a necessity to ensure the safety of personnel or property subjected to impacts by bullets, fragments and/or explosions. To shatter an inbound projectile, the surface of the target needs to exhibit a very high hardness but also the ability to prevent crack growth and plastically deform to avoid brittle fracture. The need for a combination of hardness and toughness led to the invention of dual hard steel which can be achieved within a homogeneous plate by modification of the surface through single-sided case hardening. In this work ARMOX® 440T and ARMOX® 500T was case hardened with a case depth of 2 and 2.3 mm and shoot upon with armour piercing rounds P80 to determine the ballistic limit of the material and to compare with the reference ARMOX®. Metallographic investigation was performed together with grain size measurement and mechanical properties were tested including hardness, impact toughness, dimensional deviation and tensile strength.

    A considerable increase of the ballistic performance with 40-70 % was reached by single-sided case hardening even though an irregular failure of the diffusion barrier had led to double-sided cases in various areas. Mass efficiency also increased considerably. Especially ARMOX® 440T was suitable for the treatment since it increased by the largest relative amount despite the fact that it had a thinner case then ARMOX® 500T plates.

    The complete penetrations were caused by formation of adiabatic shear bands and lead to punching of the plates except for hits at areas with double-sided case where back spall also occurred. The backside-case also resulted in a sharp reduction in impact toughness. Crack formation in close proximity to the impact site was found in all case hardened plates perpendicular to the front surface originating from inter-granular oxides near the surface.

    All the conventionally case hardened plates deviated from the reference plate flatness. Most likely because of placement in the furnace.

    Collectively the material is not recommended to be implemented in structural components until further investigations have been made concerning multi-hit threat, heat treat optimisation to minimize dimensional changes and bending because of the formation of perpendicular cracks under tensile load.

  • 14. Jansson, Andreas
    Influence of alloying content and preconditioning on gaseous ferritic nitrocarburizing of steels2011Independent thesis Advanced level (professional degree), 20 poäng / 30 hpOppgave
    Abstract [en]

    Atlas Copco rock drills AB is manufacturing and developing rock drills. These rock drills have steel components that have high requirements. To increase mechanical properties (besides material selection) the components undergoes the in-house technology surface treatment nitrocarburizing. However some material can experience a variation in result after this surface treatment. This study is performed to increase the knowledge on which parameters in the manufacturing process that are influencing on the result of this surface treatment. Several steels were studied including steel grades comparable with the low alloy steels, 50CrMo4C, 42CrMo4, 25CrMo4 and C45E but also three high alloy Cr-Mo-V tool steels with various carbon content. These steels were exposed to different external elements such as air (surface oxidation), cutting fluid and alkaline cleaning fluids to gain knowledge about how chemical composition respond to external elements regarding nitrocarburizing results. The specimens were evaluated with light optical microscopy (LOM), scanning electron microscopy (SEM) and hardness testing. The results of this study demonstrate that steels have similar behaviour as reported in literature in aspect of chemical composition; increased amount of alloying content give a harder but also thinner hardened case. External elements like cutting fluid and delay time in air (surface oxidation) decrease thickness and homogeneity of hardened case in almost all material. An alkaline cleaning process after exposure of these external elements (air, cutting fluid) would, inconsistent, decrease thickness and homogeneity even further. Adding a second step of cleaning the surface with i.e. ethanol after alkaline cleaning process could reduce the negative effect from alkaline wash. Therefore, it is recommended that the wash process at Atlas Copco will be altered to improve the result of this surface treatment by a decrement of passivation media in cleaning process.

  • 15.
    Larsson, Karl
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Nötning av verktygsstål vid plåtformning: Inverkan på arbetsmaterialets sträckgräns och påkletningsmotstånd för verktygsstål2019Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    I dagens industri utsätts verktyg vid plåtformning för allt större krafter. Material som ska formas blir starkare behövs också större krafter för at åstadkomma en geometrisk förändring. Detta har medfört att nötningseffekter vid tillverkning har ökat, och ett av dessa problem är galling. Galling, som är ett av huvudproblemen, är en nötningseffekt på verktygen där både adhesiv och abrasiv nötning förekommer. Detta innebär att material lossnar från värdmaterialet och fastnar på verktyget. Då material har överförts till verktyget har det inte längre ursprungsformen och kan leda till ojämnheter i materialet som ska formas. Hittills har företag använt sig av smörjmedel för att minska galling. Eftersom smörjmedel regleras allt hårdare av miljöskäl, måste industrin hitta nya lösningar. En lösning är att skapa verktygsstål som är motståndskraftiga mot galling genom sin mikrostruktur. Det finns fortfarande begränsad kunskap inom området och den här studien syftar till att jämföra två verktygsstål för att avgöra vilket som är mest beständigt mot galling. Verktygsstålen Caldie och Vancron Superclean kommer glida mot materialen DP600 och DP1000. De sistnämnda är de material som formas vid plåtformningen. Där materialen har olika sträckgränser, detta för att se om den har en inverkan vid plåtformning. För att avgöra vilket verktygsstål som är mest lämpligt vid plåtformning kommer en glidsträcka tas fram med hjälp av SOFS metoden. Glidsträckan kommer att ange hur snabbt galling uppstår och således kan ett bättre material bestämmas. Nötningsspåren hos materialen analyserades med hjälp av ett elektronmikroskop för att se hur galling hade påverkat verktygsstål och ytmaterial.Resultatet visade att Vancron Superclean var mer beständigt mot galling, då verktygsstålen gled över DP600, medan ingen slutsats kunde dras när de gled över DP1000.

  • 16.
    Lind, Sofia
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik.
    Zinklegering i åldrat och kylt tillstånd: Identifiering av parametrar som förändrar materialegenskaperna i Zamak52015Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Bilsäkerhet är en viktig fråga i dagens samhälle. Det enklaste sättet att skydda sig vid en bilfärd är genom att använda säkerhetsbälte. En säkerhetsbältesrulle är uppbyggd av flera olika komponenter, en av dessa kallas torque tube som tar energi när kroppen fångas upp av bältet vid en eventuell kollison. Säkerhetsbältet ska skydda passagerarna i bilen i många år och vid olika temperaturer. Torque tuben är i detta fall gjuten i en zinklegering som heter Zamak5 som förändrar sina materialegenskaper i åldrat och kylt tillstånd. Målet med arbetet är att hitta de parametrar som förändrar materialegenskaperna i Zamak5.

    Olika metoder användes för att få fram ett resultat på en torque tube som är specialtillverkad med försvagad geometri. Provobjekten som testades var både åldrade och oåldade. Ett pendelprov kan motsvara en kollision mellan ett säkerhetsbälte och en tyngd. För att hitta den kritiska temperatur då Zamak5 förändrar materialegenskaperna gjordes det pendelprov vid olika temperaturer för att se vilka provobjekt som gav brott. Brottytorna studerades sedan i mikroskop för att se vilka parametrar som orsakat egenskapsförändringarna.

    Resultatet visade att brottet var sprött. Det beror på att temperaturen understigit omslagstemperaturen. Det åldrade och kylda provobjektet visade på sämre hållfasthet och detta beror på att inkoherenta partiklar bildats och lagt sig i korngränser och i kritiska skjuvplan.

  • 17.
    Ohlsson, Jonas
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Effects of different heat treatments on hardness of Grade 91 steel2014Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [en]

    CCI Valve Technology AB is a company located in Säffle, Sweden, that manufactures and installs bypass valves. Due to requirements outside normal standards on the valve's hardness values, some measurements have had difficulties meeting such requirements. During this thesis work, tests were carried out to determine how to overcome the difficulties. The experiments focused on five different areas that may affect the components hardness, welding method, soaking temperature during post weld heat treatment, measuring procedure, component thickness and number of heat treatment cycles. The Grade 91 steel specimens that were examined consisted of five solid cylinders and three various pipes that were welded together by using shielded metal arc welding (SMAW) or gas tungsten arc welding (GTAW). Each pipe was sawed apart into three equal parts. All specimens were hardness tested and eight of the specimens' microstructure was studied with an optical microscope. The hardness measurement instruments used, LECO V-100-C2 and GE-MIC 10, are Vickers hardness testers, one stationary and the other one portable. The measuring results contain a vast number of different hardness measurement data. From the analyzed data, the conclusions were drawn that the most suitable soaking temperature during post weld heat treatment were 750° C, that the SMAW method creates a more stable hardness profile than the GTAW method, and that one heat treatment cycle is more beneficial than two or more.

  • 18.
    Pernefur, Emil
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013).
    Extremvärdesanalys (SEV) av högkvalitativt verktygsstål: Uppskattning av maximal inneslutningsstorlek i pulverstål2017Independent thesis Basic level (degree of Bachelor), 15 poäng / 22,5 hpOppgave
    Abstract [en]

    This work were requested by Uddeholms AB. Uddeholm is the worldś leading manufacturer of high performance tool steel for industrial tools. The company exists worldwide and is present in over 100 countries. One of the company’s main production processes is manufacturing powder steels with extremely high quality. In this work, one of these steels has been analyzed to evaluate the presence and distribution of non-metallic inclusions.

    Higher demands on quality and more global competition worldwide means that you always have to strive towards perfection in the manufacturing processes. Non-metallic inclusions have severe effects on the mechanical properties of steels. That's why it's of utmost importance to investigate their presence in the tool steel and especially their size. The reason for this is because it's the largest inclusions that's the most dangerous for the material.

    To obtain a statistically number of certainty of the largest of inclusions, very vast areas of steel have to be examined. Therefore a theoretical method of extrapolation is often used instead to approximate the distribution of the largest inclusions. The precision of this method is still very uncertain. Different methods of this kind of analysis do exist. The method applied in this work of degree is extreme values analysis by statistics of extreme values (SEV).

    To ensure the pre-conditions of the extreme values analysis, a large quantity of powder steel was analyzed. This was done by light-optic microscopy (LOM) and exclusively performed by Uddeholms AB at their R&D-facility (Research and development-facility) in Hagfors.

    At Karlstad Universityś test-facility specimens were subjected to ultrasonic fatigue testing at 20 kHz. The specimens derived from the same material as the ones examined in LOM. The result from the ultrasonic fatigue testing were that the largest inclusions in the material were found. This was done by applying very high cycle fatigue (VHCF).

    To calculate the maximum theoretical inclusion size, SEV was used. The extreme values analysis was performed on gathered data from both LOM and VHCF.

    All fracture surfaces from the ultrasonic fatigue testing were then examined in scanning electron microscope (SEM) at Karlstad University. In SEM, the largest inclusion in every fractured surface was identified and measured.

    The maximum real inclusion size from the fractured surfaces was then compared to the maximum theoretically calculated inclusion size from the extreme values analysis. As it turned out the real inclusion size proved to be slightly larger than the theoretical. The difference between them was found to be 3,25 µm.

    Conclusions drawn were that Uddeholms powder steel exhibits very high purity and that extreme values analysis as an analytical method is recommended. However, the analysis should be repeated to underline the chosen solution methodology.

  • 19.
    Rashid, Lezan
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013).
    Overlay welding of FeCrAl alloys2016Independent thesis Advanced level (degree of Master (Two Years)), 300 hpOppgave
    Abstract [en]

    In this master thesis different overlay welding methods suitable for boiler application has been investigated.

    The purpose of this project is to define advantages and disadvantages for each overlay welding methods and suggest some evaluation criteria on some commercial and experimental alloys aimed for overlay welding material.

    Many components in a boiler are made of low alloy steel and the atmosphere in the furnace region can be very complex; therefore many different types of corrosion can occur. Weld overlay is a process where one or multiple layers of corrosion resistant material are applied to a base material.

    The two overlay welding methods investigated in this study were Tungsten Inert Gas welding and Metal Inert/Active Gas welding. Tests were performed with FeCrAl alloys (Kanthal A, Kanthal D and some experimental alloys). FeCrAl alloys in general are ferritic iron-based steels with a typical concentration of 20-23 wt. % chromium and ~5 wt.% aluminum.

    Different overlay welding evaluation was made; visual examination, dye penetrant inspection, macro/micro examination, side bend test and short term corrosion test (~50hours).

    Conclusion of this thesis is that MIG welding is a more productive method than TIG, but more defects such cracks and lack of fusion can be produced for MIG welding. These defects can be “fixed” if welding parameters is optimized. If repairing a certain place TIG welding is a better option. A conclusion about number of layers; one layer with MIG welding is almost as thick as three layers with TIG welding with welding wire Ø 1mm.

    Three welding evaluation that is really important is visual examination, dye penetrant testing and corrosion test in order to choose which overlay welding method is suitable in boiler application.

  • 20.
    Rådberg, Malin
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik, Science, Mathematics and Engineering Education Research (SMEER).
    Design of Experiment for Laser cutting in Superalloy Haynes 2822016Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This project aims to investigate the effect of varying different laser cutting parameters on the laser cut surface. The parameters that were varied were cutting speed, beam effect, gas pressure and focal point. The statistical method Design of Experiment was used to plan the experiments and two full factorial test plans were set up, one with argon as cooling and protective gas and one with nitrogen. Sheet metal consisting of the superalloy HAYNES ® 282 with a thickness of 2,54 mm was investigated. Samples from the material were cut with different laser cutting parameters according to the test plans. The samples were evaluated by measuring cracks, recast layer thickness, surface irregularity, burr height and distance to beam deflection point on the cut surface. The resulting data was inserted as responses into the statistical program Modde 10.1 for analysis.

    Modde 10.1 provided models of high significance for the responses of Recast layer, Tav; Recast layer, Tmax; Burrheight, max and Distance to deflection point for the argon series and Recast layer, Tav and Recast layer, Tmax for the nitrogen series.

    The results showed that both recast layer thickness and burr height decreases with increased values of cutting speed, gas pressure and focal point as well as decreased values of beam effect within the parameter window investigated. They also showed that distance to deflection point increased with increasing values of gas pressure and focal point and with decreased values of cutting speed and beam effect within the parameter window.

    The results also showed that for the samples cut with argon as cooling and assistant gas the parameters that affects the recast layer thickness the most are focal point and gas pressure, whereas for the nitrogen series it is gas pressure and beam effect. The parameter with greatest effect on burr height is the cutting speed and for the distance to deflection point it is focal point and gas pressure that have the greatest effect.

    When comparing the argon and the nitrogen series to each other it can be seen that the argon series generate less recast layer from the entry of the cut until between 60 – 80 % into the cut, after which the argon series bypasses the nitrogen series in amount of recast layer produced in the cutting process in the majority of the places measured.

  • 21.
    Sjöman, Joakim
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Cold drawing of tool steels2011Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Present study is a master thesis in materials engineering and has been performed at Karlstad University and at Uddeholms AB in Hagfors. Uddeholms AB has recently seen a new request from customers, of smaller dimensions of round bars than covered by Uddeholms AB’s dimension program. To get these smaller dimensions Uddeholms AB has up till now, used help from other companies to hot roll and peel the material to the desired dimension. A more efficient way could be to use a cold drawing process on these bars to the desired dimensions.

    The main objectives of this study were to find nearby companies which have suitable draw benches and to find how the material is affected by a cold drawing process. This was performed by a market investigation followed by a technical investigation. The investigated material was Uddeholm THG 2000.

    Cold drawing is an operation in which the cross section of a bar, rod or wire is reduced by pulling it through a die opening. It was soon found that in the desired dimension range the common way to perform this is from wire coil and not from straight bars. This reduced the suitable companies for the Uddeholm THG 2000 bars greatly.

    Some of the conclusions from the present study are:

    • Cold drawing of bar to bar is not the normal practice in the desired dimension range. Only three suitable companies were found to be able to perform bar to bar drawing, Boxholm Stål AB, Kiveton Park Steel and Erasteel Champagnole.
    • THG 2000 could be drawn from Ø25 mm to Ø10 mm, but this would require as many as 8-10 drawing processes, with annealing heat treatments between every second drawing process. This would not be economically efficient, but could result in an extremely fine grain size.
    • The cold drawing process of small dimensions affects the entire cross section of the material. 
    • The direct effects (hardness and internal stress) of a cold drawing operation will disappear in the quench and temper treatment, and in that aspect there are no differences between cold drawn and hot rolled material. Anyhow, indirect effects such as grain size and material distortion can affect material properties even after a quench and temper heat treatment.
  • 22.
    Tofique, Muhammad Waqas
    et al.
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik.
    Bergström, Jens
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap.
    Burman, Christer
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik.
    Hallbäck, Nils
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap.
    Gåård, Anders
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Fatigue strength, crack initiation, and localized plastic fatigue damage in VHCF of duplex stainless steels2016Inngår i: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 87, nr 7, s. 899-910Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The fatigue strength of two-duplex stainless steel grades, 2304 SRG and LDX 2101, with austenitic–ferritic microstructure is tested using ultrasonic fatigue testing equipment operating at 20 kHz. The testing is conducted in tension-compression mode with the load ratio R=-1. The fatigue strength is evaluated at 107, 108, and 109 load cycles and the estimates of fatigue strength are higher for the LDX 2101 grade. The fatigue crack initiation mechanisms are analyzed using a scanning electron microscope. The fatigue cracks, in all cases, appear to initiate due to accumulation of plastic fatigue damage at the surface. In the 2304 SRG grade, accumulation of fatigue damage occurs at the external surface of fatigued specimens in the form of extrusions at the grain/phase boundaries and in the form of individual slip lines in the austenite phase. Meanwhile, in the LDX 2101 grade accumulation of plastic fatigue damage in the form of extrusions and intrusions occurs mainly within the ferrite grain. When the crack is microstructurally short, the crack growth appears to be crystallographic in nature and the crack appears to change its direction propagating from one grain into another.

  • 23.
    Van Meensel, Kim
    et al.
    Katholieke Universiteit Leuven, Belgium.
    Lietaert, Karel
    Katholieke Universiteit Leuven, Belgium; 3D Systems Leuven, Belgium.
    Vrancken, Bey
    Katholieke Universiteit Leuven, Belgium.
    Dadbakhsh, Sasan
    Katholieke Universiteit Leuven, Belgium.
    Xiaopeng, Li
    Katholieke Universiteit Leuven, Belgium; University of New South Wales, Sydney, Australia.
    Kruth, Jean Pierre
    Katholieke Universiteit Leuven, Belgium.
    Krakhmalev, Pavel
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Yadroitsev, Igor
    Central University of Technology, Bloemfontein, South Africa.
    Van Humbeeck, Jan
    Katholieke Universiteit Leuven, Belgium.
    Additively manufactured metals for medical applications2018Inngår i: Additive Manufacturing: Materials, Processes, Quantifications and Applications / [ed] Jing Zhang, Yeon-Gil Jung, Kidlington, U.K.: Butterworth-Heinemann, 2018, 1, s. 261-309Kapittel i bok, del av antologi (Fagfellevurdert)
  • 24. Yadroitsev, Igov
    et al.
    Krakhmalev, Pavel
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Yadroitsava, Inna
    Titanium Alloys Manufactured by In Situ Alloying During Laser Powder Bed Fusion2017Inngår i: JOM: The Member Journal of TMS, ISSN 1047-4838, E-ISSN 1543-1851, Vol. 69, nr 12, s. 2725-2730Artikkel i tidsskrift (Fagfellevurdert)
  • 25.
    Åsberg, Mikael
    et al.
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Fredriksson, Gunnel
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Hatami, Sepehr
    Swerea IVF AB.
    Fredriksson, Wendy
    Bodycote Hot Isostatic Pressing.
    Krakhmalev, Pavel
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Influence of post treatment on microstructure, porosity and mechanical properties of additive manufactured H13 tool steel2019Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 742, s. 584-589Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Additive manufacturing (AM) is an attractive manufacturing technology in tooling applications. It provides unique opportunities to manufacture tools with complex shapes, containing inner channels for conformal cooling. In this investigation, H13, a widely used tool steel, was manufactured using a laser powder bed fusion method. Microstructure, tensile mechanical properties, hardness, and porosity of the AM H13 after stress relieve (SR), standard hardening and tempering (SR + HT), and hot isostatic pressing (SR + HIP + HT) were investigated. It was found that the microstructure of directly solidified colonies of prior austenite, which is typical for AM, disappeared after austenitizing at the hardening heat treatment. In specimens SR + HT and SR + HIP + HT, a microstructure similar to the conventional but finer was observed. Electron microscopy showed that SR and SR + HT specimens contained lack of fusion, and spherical gas porosity, which resulted in remarkable scatter in the observed elongation to break values. Application of HIP resulted in the highest strength values, higher than those observed for conventional H13 heat treated in the same way. The conclusion is that HIP promotes reduction of porosity and lack of fusion defects and can be efficiently used to improve the mechanical properties of AM H13 tool steel.

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