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  • 51.
    Engberg, Göran
    Dalarna University, School of Technology and Business Studies, Materials Technology. Dalarna University, School of Technology and Business Studies, Material Science.
    Constitutive models, physically based models for plasticity2014In: Encyclopedia of Thermal Stresses / [ed] Hetnarski RB, Dordrecht, Heidelberg, New York, London: Springer, 2014, p. 649-662Chapter in book (Refereed)
    Abstract [en]

    Physically based models for the plastic behavior of crystalline, metallic materials are discussed. However, deformation by twinning and phase transformations as well as the evolution of texture are omitted. 

  • 52.
    Engberg, Göran
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Karlsson, Lars
    Dalarna University, School of Technology and Business Studies, Material Science.
    Analysing metal working processes2005In: Fundamentals of metallurgy / [ed] Seetharaman, Seshadri, Cambridge: Woodhead Publishing ltd , 2005, p. 453-470Chapter in book (Other academic)
    Abstract [en]

    Metal working processes encompass a wide range of strain, strain rates and temperatures. Strains range from less than 0.01 (for example in skin-pass rolling of interstitial free steel) up to around 1 (cold rolling of strip, extrusion, etc.). Typical strain rates and temperatures are given in Table 11.1 (which is partly an extract from Frost and Ashby (1982). For plastic forming processes the most important characteristics of the material are: the ability to distribute strains; the deformation resistance; and the resulting properties of the formed part. The ability to distribute strains is mainly governed by the work hardening and strain-rate sensitivity. It is also affected by the strain path. The purpose of this paper is to outline the, in our view, most essential material properties for metal working processes and the microstructural reasons for them. We recognise that the presence and development of crystallographic texture is quite an important part but our purpose is not to give an extensive description of this, only to point out some consequences. For further reading we recommend a book by Kocks, Tomé and Wenk (1998). Another aspect that is only briefly covered is the influence of stress states and changes in strain paths during processing or between consecutive process steps.

  • 53.
    Engberg, Göran
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Lissel, Linda
    A Physically based Microstructure Model for Predicting the Microstructure Evolution of a C-Mn Steel during and after Deformation2008In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 79, no 1, p. 47-58Article in journal (Refereed)
    Abstract [en]

    A physically based model for predicting microstructural evolution has been developed. The model is based on a physical description of dislocation density evolution, where the generation and recovery of dislocations determine the flow stress and also the driving force for recrystallization. In the model, abnormally growing subgrains are assumed to be the nuclei of recrystallized grains and recrystallization starts when the subgrains reach a critical size and configuration. To verify that the model is able to describe dynamic, static and metadynamic recrystallization of C-Mn steels, hot compression tests combined with relaxation were performed at various temperatures, strains and strain rates. The model showed reasonable agreement with the experimental data for the compression tests performed at temperatures ranging from 850?C to 1200?C and strain rates ranging from 0.1 to 10 s-1. Also, the calculations of the stress relaxation tests show good agreement with experimental data. A validation of the model was done by calculating a multi-step test where good agreement with both flow-stress values and grain sizes was obtained. The main purpose of the model is to be able to predict the microstructural evolution during hot rolling and this investigation presents very promising results.

  • 54.
    Engkvist, Josefin
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Material Science.
    Grehk, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    High temperature oxidation of FeCrAl-alloys: influence of Al-concentration on oxide layer characteristics2009In: Materials and corrosion - Werkstoffe und Korrosion, ISSN 0947-5117, E-ISSN 1521-4176, Vol. 60, no 11, p. 876-881Article in journal (Refereed)
    Abstract [en]

    The superior high temperature oxidation resistance of FeCrAl alloys relies on the formation of a dense and continuous protective aluminium oxide layer on the alloy surface when exposed to high temperatures. Consequently, the aluminium content, i.e. the aluminium concentration at the alloy–oxide layer interface, must exceed a critical level in order to form a protective alumina layer. In the present study the oxidation behaviour of six different FeCrAl alloys with Al concentrations in the range of 1.2–5.0wt% have been characterised after oxidation at 900 8C for 72 h with respect to oxide layer surface morphology, thickness and composition using scanning electron microscopy, energy dispersive X-ray spectroscopy and Auger electron spectroscopy.The results show that a minimum of 3.2wt% Al in the FeCrAl alloy is necessary for the formation of a continuous alumina layer. For Al concentrations in the range of 2.0–3.0wt% a three-layered oxide layer is formed, i.e. an oxide layer consisting of an inner alumina-based layer, an intermediate chromia-based layer and an outer iron oxide-based layer. In contrast, the 1.2wt% Al FeCrAl alloy is not able to form a protective oxide layer inhibiting extensive oxidation.

  • 55.
    Engkvist, Josefin
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Material Science.
    Grehk, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    ToF-SIMS Analysis of a FeCrAl Alumina Forming Alloy2004In: SIMS Europe 2004, Münster, Germany, 2004Conference paper (Other academic)
  • 56.
    Engkvist, Josefin
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Material Science.
    Grehk, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    ToF-SIMS Depth Profiling of Alumnia Formed on a FeCrAl High Temperature Alloy2003In: Proceedings of the 14th International Conference on Secondary Ion Mass Spectrometry, San Diego, California, USA, 2003Conference paper (Refereed)
  • 57.
    Engkvist, Josefin
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Canovic, Sead
    Hellström, Kristina
    Järdnäs, Anders
    Svensson, Jan-Erik
    Johansson, Lars-Gunnar
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Halvarsson, Mats
    Alumina scale formation on a powder metallurgical FeCrAl alloy (Kanthal APMT) at 900-1100 °C in dry O2 and in O2 + H2O2010In: Oxidation of Metals, ISSN 0030-770X, E-ISSN 1573-4889, Vol. 73, no 1-2, p. 233-253Article in journal (Refereed)
    Abstract [en]

    A Rapidly Solidified Powder (RSP) metallurgical FeCrAl alloy, Kanthal APMT, was exposed in dry and humid O2 for 72 h at 900–1,100 °C. The formed oxide scales were characterized using gravimetry in combination with advanced analysis techniques (SEM, EDX, TEM, XRD, AES andSIMS). The oxide scales were at all exposures composed of two-layered α-Al2O3 scales exhibiting a top layer of equiaxed grains and a bottom layer containing elongated grains. A Cr-rich zone, originating in the native oxide present before exposure, separated these two layers. The top α-Al2O3layer is suggested to have formed by transformation of outwardly grown metastable alumina, while the inward-grown bottom α-Al2O3 layer had incorporated small Zr-, Hf- and Ti-rich oxide particles present in the alloy matrix. The scale also contained larger Y-rich oxide particles. Furthermore, in the temperature range studied, the presence of water vapour accelerated alloy oxidation somewhat and affected scale morphology.

  • 58. Engkvist, Josefin
    et al.
    Canovic, Sead
    Järdnäs, Anders
    Svensson, Jan-Erik
    Johansson, Lars-Gunnar
    Halvarsson, Mats
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Microstructural investigation of the effect of watr vapour on the oxidation of a FeCrAl alloy (Sandvik APMT)2008In: 214th Meeting of ECS-The Electrochemical Society, Honolulu, Hawaii, 2008Conference paper (Other academic)
  • 59.
    Engkvist, Josefin
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Canovic, Sead
    Liu, Fang
    Götlind, Helena
    Svensson, Jan-Erik
    Johansson, Lars-Gunnar
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Halvarsson, Mats
    Oxidation of FeCrAl foils at 500-900 C in dry O2 and O2 with 40% H2O2009In: 7th Int. Conf. on the Microscopy of Oxidation, Chester, UK, 2009Conference paper (Other academic)
  • 60.
    Engkvist, Josefin
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Grehk, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Material Science.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Early stages of oxidation of uncoated and PVD SiO2 coated FeCrAl foils2009In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 203, no 19, p. 2845-2850Article in journal (Refereed)
    Abstract [en]

    The high temperature oxidation characteristics of uncoated and SiO2 PVD-coated FeCrAl foils have been investigated when exposed to laboratory air at 1000 °C during 1, 2, 4, 8, 16, 32 and 60 min. The oxidized samples were characterized using SEM, EDS, AES and SIMS. The results show that the presence of a 100 nm thin SiO2 PVD coating significantly reduces the oxidation rate of the FeCrAl foil during early stages of oxidation. The decreased oxidation rate displayed by the SiO2 coated FeCrAl foil is the result of the SiO2 coating acting as an initial diffusion barrier promoting the formation of a predominantly inward growing Al2O3 layer during oxidation. Additionally, by using EDS analysis together with AES and SIMS depth profiling it was shown that the total concentration of Si in the grown oxide scale decreased during oxidation.

  • 61.
    Engkvist, Josefin
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science. Chalmers University of Technology, Göteborg, Sweden.
    Israelsson, Niklas
    Chalmers University of Technology, Göteborg, Sweden.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    The initial effect of KCl deposit on alumina scales characterized by ToF-SIMS and AES2013In: Surface and Interface Analysis, ISSN 0142-2421, E-ISSN 1096-9918, Vol. 45, no 1, p. 445-448Article in journal (Refereed)
    Abstract [en]

    A FeCrAl alloy was preoxidized to form a protective alumina scale, and the effect of KCl deposits on the alumina scale was investigated while exposed during 1 and 24 h at 600 °C. However, impurity concentrations in the alumina scale change the ion conductivity and hence affect its protective properties. Therefore, Auger electron spectroscopy and time-of-flight secondary ion mass spectrometry were used to characterize the alumina scales and detect traces of K and Cl. The results showed that K and Cl existed as large sharp-edged crystals surrounded by a dendritic network after 1 h. However, after 24 h, those were dissolved, and K together with Cl was detected only in the outer layer of the duplex alumina scale, which was formed during preoxidation.

  • 62. Eriksson, C.
    et al.
    Börner, K.
    Nygren, H.
    Ohlson, K.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Material Science.
    Billerdahl, N.
    Johansson, M.
    Studies by imaging ToF-SIMS of bone mineralization on porous titanium implants after 1 week in bone2006In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 252, no 19, p. 6757-6760Article in journal (Refereed)
    Abstract [en]

    Anodic oxidation was used to grow porous layers on titanium discs. Six different oxidation procedures were used producing six different surfaces. The implants were inserted in rat bone (tibia) for 7 days. After implant retrieval, mineralization (hydroxyapatite formation) on the implant surfaces was investigated using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Bone tissue around the implants was sectioned and stained. The amount of bone in close apposition to the implant was calculated. The porosity showed great variation between the surfaces. Hydroxyapatite was detected on all surfaces. A slight positive correlation between porosity and mineralization was found, although the most porous surface was not the best mineralized one. Bone had formed around all implants after 7 days. The bone-to-metal contact for the porous implants did not differ significantly from the non-porous control. Porosity is known to influence cellular events. The results indicate that porosity could have an initial, positive influence on bone integration of implants, by stimulating the mineralization process. The methods used were found to be suitable tools for investigation of initial healing around implants in bone.

  • 63.
    Eriksson, Dennis
    Dalarna University, School of Technology and Business Studies, Material Science.
    Intrimning och evaluering av processparametrar samt tillsatser för reduktionsspruta2006Independent thesis Basic level (degree of Bachelor)Student thesis
    Abstract [sv]

    Syftet med examensarbetet var att förbättra legeringsutbytet i ljusbågsugnen, detta med hjälp av en reduktionsspruta. Två stålsorter har följts upp. Provtagningar och beräkningar har gjorts för att få fram rätt tillsatsmängder. Slaggen i stålsort typ 1 innehöll enligt analys mellan 44 och 256 kg Cr2O3. I snitt torde det behövas en tillsats med reduktionssprutan av 34 kg SiC eller 45 kg FeSi75 för att reducera den mängd Cr2O3 som finns i kvar slaggen. Stålsort typ 2 hade i slaggen enligt analys mellan 921 kg och 1147 kg Cr2O3. Efter ändring av kalktillsatsen var det 628 kg Cr2O3 i slaggen enligt analys. I snitt torde det behövas en tillsats med reduktionssprutan av 170 kg SiC, samtidigt som det tillsätts 224 kg kalk. Eller 220 kg FeSi75, samtidigt som det tillsätts 310 kg kalk. Detta för att reducera den mängd Cr2O3 som finns i kvar slaggen.

  • 64.
    Eriksson, Jenny
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Evaluation of galling resistance for some selected combinations of tool steels/stainless steel sheet materials/lubricants using pin-on-disc testing2010In: NordTrib 2010, Storforsen, 2010Conference paper (Other academic)
    Abstract [en]

    Stainless steels are well known to be prone to cold welding and material transfer in sliding contacts and therefore difficult to cold form unless certain precautions as discussed in this paper are taken. In the present study different combinations of tool steels/stainless steels/lubricants has been evaluated with respect to their galling resistance using pin-on-disc testing. The results show that a high galling resistance is favored by a high stainless steel sheet hardness and a blasted stainless steel sheet surface topography. The effect of type of lubricant was found to be more complex. For example, the chlorinated lubricants failed to prevent metal-to-metal contact on a brushed sheet surface but succeeded on a blasted sheet surface of the same stainless steel material. This is believed to be due to a protective tribofilm which is able to form on the blasted surface, but not on the brushed surface.

  • 65.
    Eriksson, Jenny
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Galling and wear characteristics of some commercial PVD coatings as evaluated by tribological testing2009In: International conferens on metallurgical coatings and thin films (ICMCTF), San Diego, 2009Conference paper (Other academic)
  • 66.
    Eriksson, Jenny
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Galling resistance of some selected tool steel/high strength steel sheet materials as evaluated under lubricated sliding conditions using pin-on-disc testing2009In: Wear of Materials, Las Vegas, 2009Conference paper (Other academic)
  • 67.
    Eriksson, Jenny
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Ranking the performance of lubricants, tool steels and PVD coatings for the forming of high strength steel using pin-on-disc testing2009In: Tool 09, Aachen, 2009Conference paper (Other academic)
  • 68.
    Eriksson, Jenny
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Tribological testing of commercial CrN, (Ti,Al)N and CrC/C PVD coatings: evaluation of galling and wear characteristics against different high strength steels2011In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 205, no 16, p. 4045-4051Article in journal (Refereed)
    Abstract [en]

    The increasing use of high strength steels in a variety of mechanical engineering applications has illuminated problems associated with galling in sheet metal forming operations. Galling is a tribological phenomenon associated with transfer of material from the steel sheet to the tool surface during forming resulting in seizure of the tool/steel sheet contact and extensive scratching of the steel sheet surface. As a result, a number of concepts have been developed in order to reduce the tendency of galling in sheet metal forming, including the development of new dry lubricants, new forming tool steel grades and improved surface engineering treatments such as the deposition of low friction CVD- and PVD-coatings. In the present study the potential performance of three commercial PVD coatings, including CrN, (Ti,Al)N and a CrC/C DLC-based coating, in the forming of hot and cold rolled high strength steel as well as electro and hot-dip galvanized high strength steel has been evaluated using pin-on-disc testing under lubricated contact conditions. Post-test examination of the tribosurfaces using FEG-SEM and EDS analyses was performed in order to evaluate the mechanisms controlling the tendency to material transfer and wear. The results show that in contact with the hot and cold rolled steel the material pick-up tendency of the PVD coatings tend to increase in the order CrC/C–CrN–(Ti,Al)N while in contact with the two galvanized steel sheets, the CrC/C and the (Ti,Al)N coating show a significantly lower material pick-up tendency as compared with the CrN coating. Further, the substrate hardness has a strong influence on the wear of the PVD coatings and consequently on the friction characteristics and galling tendency of the coating/substrate composite. Low substrate hardness, resulting in a low load bearing capacity, increases the tendency to cracking and subsequently chipping of the brittle coating.

  • 69.
    Eriksson, Malin
    Dalarna University, School of Technology and Business Studies, Material Science.
    Kartläggning av härdsprickor vid induktionslinjenpå stålsorterna Ovako 327A och 356D2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The thesis work investigates the steel grades Ovako 327A and Ovako 356D. Thepurpose of the investigation is to examine the origin of the hardening crackscreated during the induction hardening process. In an earlier investigation done bythe company it was shown that carbon segregations can be the cause of theproblem. Two other causes have also been examined within this project. Thesecauses are end cracks from the cold shear process and rolling defects. The methodsof the examination are hardness testing, segregation testing and visual inspectionof the bars. The result shows increased carbon content in the centre of the bars insteel grade Ovako 327A. Steel grade Ovako 356D shows a normal carbon content.The hardness testing on steel grade Ovako 327A shows a higher hardness in thecentre compared to the surface hardness on the samples containing carbonsegregation. Discovered rolling defects have not created hardening cracks in theinduction line. The effects from end cracks could not be investigated sincediscovered end cracks had to be removed because the study was made on customermaterial. The conclusion from this thesis work is that more material from the topof the ingot in steel grade Ovako 327A should be cropped in the primary rollingmill in Hofors to remove carbon segregations. The steel grade Ovako 356D showsno sign of hardening cracks in this study.

  • 70.
    Eriksson, Mia
    Dalarna University, School of Technology and Business Studies, Material Science.
    Modellering och styrning av arbetsvalsarnas termiska expansion och förslitning i ett steckelverk: Modelling and controlling the thermal expansion and wear in a steckel rolling mill2006Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [sv]

    Vid genomfört examensarbete har undersökning och simulering av den termiska expansionen av arbetsvalsarna i steckelverket för varmvalsning av band på Sandvik Materials Technology gjorts. Syftet med detta arbete var att undersöka om det är den termiska expansionen som gör att målprofilen med en relativ bandkrona på 1 % ej nås i verket. Vidare har valstrycket mellan stödvals och arbetsvals i steckelverket simulerats för att undersöka om valstryckspikar uppstår under valsning. Dessutom har en kartläggning av arbetsvalsarnas slitage i verkets förpar påbörjats. Resultaten visar att temperaturen och den termiska expansionen är olika för den övre och den undre arbetsvalsen i steckelverket, vilket tillsammans med det faktum att slitaget ser olika ut för övre respektive undre arbetsvals innebär att ett osymmetriskt valsgap fås under valsning. Profilavvikelsen på grund av den termiska expansionen är i samma storleksordning som den profilavvikelse som arbetsvalsens slipade form ger, vilket förklarar varför styrsystemet ej klarar att kompensera för den termiska expansionen. Med en valskylning som minskar den termiska expansionen och utjämnar temperaturskillnaderna mellan övre och undre arbetsvals skulle ett symmetriskt valsgap erhållas. Det slitage som fås på stödvalsarna indikerar lokalt höga valstryck mellan stödvals och arbetsvals i steckelverket. Simulering av detta tryck visar att med befintlig avfasning på stödvals erhålles valstryckspikar vid stora förskjutningar. Vidare visar simuleringarna att en optimering av stödvalsens avfasning skulle eliminera valstryckspikarna. Den påbörjade kartläggningen av arbetsvalsarnas slitage i förparet visar att detta är större än förväntat samt att den termiska påverkan, främst i form av termisk utmattning på valsarna är stor. I takt med att produktionstakten ökar måste valsarna svarvas om oftare.

  • 71.
    Fallqvist, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Flerstegstegsformning av DP-stål: Sequential forming of DP-steel2006Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [sv]

    SSAB Tunnplåt Borlänge tillverkar tunnplåt i tjockleksintervallet 0,4-16 mm. För att undersöka materialens formningsegenskaper utförs olika formningsoperationer, däribland djupdragning. Syftet med examensarbetet är att undersöka möjligheten att forma DP-stål i flera steg samt möjligheten att simulera processen. Materialen som undersöks är DPstålen 600 DL, 1000 DP, det martensitiska stålet 1200 M samt det mikrolegerade stålet 500 YP. Djupdragningen sker i tre steg. Töjningarna mäts med ett kamerasystem och för 600 DL jämförs de med simulerade töjningar i första och andra steget. Ännu en geometri pressas och ett antal mätpunkter på detaljen väljs. Denna geometri simuleras och materialparametrarna i det valda konstitutiva sambandet ändras så att bästa passning erhålls. Resultaten används för att kalibrera de konstitutiva samband som används vid undersökningen av flerstegsformningen, så kallad invers simulering. Undersökningen visar att materialen 600 DL, 1000 DP och 500 YP är möjliga att forma i flera steg, och dessutom får bättre formbarhet än vid ett steg. 1200 M är möjligt att forma i två steg i aktuell undersökning, men inte i tre. Vid simulering av djupdragningen stämmer resultatet relativt väl överens med de praktiska försöken medan de stämmer väl överens vid ubockningen. Den inversa simuleringen kalibrerar de konstitutiva sambanden väl.

  • 72.
    Fallqvist, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    The role of surface defects on the surface fatigue and tribological characteristics of VxN-PVD coatings in sliding contacts2010In: 14th Nordtrib Conference, Storforsen, 2010Conference paper (Other academic)
    Abstract [en]

    The influence of surface defects in arc-evaporated VxN PVD coatings on the adhesion, surface fatigue resistance, friction and wear characteristics has been investigated in a scratching contact using a diamond stylus and a sliding contact using a stainless steel pin. Post-test characterisation using scanning electron microscopy and 3D optical interferometric surface profilometry was performed in order to investigate the mechanical and tribological response of the coatings. The results show that surface defects such as droplets and craters show a strong influence on the tribological behaviour of the coatings causing abrasive wear of the counter surface and material pick-up on the coating surface. In contrast, the influence on the mechanical properties of the coatings, i.e. cracking behaviour, fatigue resistance, etc, was found to be relatively small and cracking seems to be restricted to larger droplets showing a low interfacial bonding to the adjacent coating matrix.

  • 73.
    Fallqvist, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Andersson, Jon
    Msauobi, Rachid
    The influence of surface topography on the formation of build-up layers and wear of CVD-Al2O3 coatings2009In: Wear of Materials, Las Vegas, 2009Conference paper (Other academic)
    Abstract [en]

    During the last years it has become more and more obvious that the surface topography and surface texture strongly influences the performance of CVD and PVD coated cutting tools. As a result the interest for different types of pre- and post-surface treatments of the substrates and the deposited coatings has increased. In the present study the friction and wear characteristics of CVD a-Al2O3 coated cemented carbide exposed to different post-surface treatments, including grinding, wet and dry micro-blasting and polishing, have been investigated using modified scratch testing and pin-on-disc testing using , AISI 304 stainless steel, AISI A2 tool and steel reinforcing iron as counter materials. The influence of the coating surface topography/texture on the resulting friction characteristics, tendency to build up layer formation and prevailing wear mechanisms were identified by optical profilometry, FEG-SEM and EDX analysis. Based on the results obtained, the potential of pin-on-disc testing in the tribological characterisation of CVD coatings for cutting tool applications is discussed.

  • 74.
    Fallqvist, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Ruppi, Sakari
    Abrasive wear of multilayer kappa-Al2O3-Ti(C,N) CVD coatings on cemented carbide2007In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 263, no 1-6, p. 74-80Article in journal (Refereed)
    Abstract [en]

    In the present study the wear resistance of kappa-Al2O3–Ti(C,N) multilayer CVD coatings with different multilayer structures (8, 15, 32 layers of kappa-Al2O3 separated by thin Ti(C,N) layers) have been investigated using a micro-abrasion and a cutting test. The results show that the wear rate of the kappa-Al2O3 multilayer coatings tend to decrease with decreasing layer thickness in the micro-abrasion test and decrease with increasing layer thickness in the cutting tests. The reason for this is mainly due to the difference in wear behaviour depending on temperature. The results obtained are discussed in relation to the dominant wear mechanisms of the coatings which have been identified using scanning electron microscopy and energy dispersive X-ray spectroscopy. The potential of the micro-abrasion test in the characterisation of thin CVD coatings for cutting tool applications is discussed.

  • 75. Filipovic, Mirjana
    et al.
    Jonsson, Stefan
    Dalarna University, School of Technology and Business Studies, Material Science.
    Experimental and numerical study of the evolution of artificial inner defects in stainless steel rolled in a wire rod block2009Manuscript (preprint) (Other academic)
    Abstract [en]

    The evolution of a central longitudinal defect was investigated for an austenitic stainless steel of type AISI 304L by preparing 12.5 mm round bars with a 4 mm round hole of length 100 mm. The evolution was monitored by taking out bars, rolled 1, 1+2, 1+2+3 passes and so on, from a wire rod block operated at a final exiting speed of 60 m/s. Cross sections of the rolled bars through the central defect were investigated with respect to geometrical changes and microstructure. The rolling process of the first 4 passes were analysed with FEM. The results show good agreement between simulations and experiments. In general, the defect is reduced quicker in size than predicted by a pure geometrical scaling. The analyses show that the round passes are more effective in reducing the defect size than the ovals. The velocity changes imposed by the central defect closing and reopening is analysed.

  • 76. Fisk, Martin
    et al.
    Hansson, Sofia
    Dalarna University, School of Technology and Business Studies, Material Science.
    FE-Simulation of combined induction heating and extrusion in manufacturing of stainless steel tubes2009In: Computational Plasticity (COMPLAS) X: Fundamentals and Applications: proceedings of the tenth International Conference on Computational Plasticity held in Barcelona, Spain, 2th-4th September 2009 / [ed] E. O˜nate and D.R.J. Owen, Barcelona: International Center for Numerical Methods , 2009Conference paper (Refereed)
    Abstract [en]

    The manufacturing process chain for extrusion of AISI 316L tubes is simulatedusing the finite element method. Models of induction heating and expansion is included and thetemperature field in the billet before extrusion is calculated. It is shown that a correct initialtemperature of the billet is needed in order to predict the extrusion force curve in the initialstage of the process.

  • 77. Friedlein, R
    et al.
    Sorensen, S.L
    Baev, A
    Gel'mukhanov, F
    Birgerson, Jonas
    Dalarna University, School of Technology and Business Studies, Material Science.
    Crispin, A
    Jong, M.P d.
    Osikowicz, W
    Murphy, C
    Ågren, H
    Salaneck, W.R
    Role of electronic localization and charge-vibrational coupling in resonant photoelectron spectra of polymers: Application to poly-(para-phenylenevinylene)2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 69Article in journal (Refereed)
  • 78.
    Frödebrink, John
    Dalarna University, School of Technology and Business Studies, Material Science.
    Materialundersökning på ESR-material map processtartsrelaterade egenskaps- och analysvariationer2006Independent thesis Basic level (degree of Bachelor)Student thesis
  • 79.
    Gatu, Stefan
    Dalarna University, School of Technology and Business Studies, Material Science.
    Modell för att prediktera när tertiära glödskalsproblem uppstår2005Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [sv]

    SSAB Tunnplåt har i Borlänge en produktionsanläggning innehållande varmvalsverk, kallvalsverk, normaliseringsanläggning, betsträckor, spaltsträckor, klippsträckor och ytbeläggningslinjer m.m. Genom hela varmvalsningsprocessen bildas oxid på den varma stålytan s.k. glödskal. Under pågående processer avlägsnas glödskalet för att ej påverka slutproduktens ytfinish och materialegenskaper. Fastän ytan spolas ren från glödskal före varje valsning händer det att det finns glödskalsproblem i form av grov yta på de färdiga banden. Anledningen till detta är att det hinner bildas glödskal i början av färdigverket efter att den sista glödskalsrensningen gjorts. Denna glödskalsbildning beror på en rad olika faktorer och troligen kombinationer av olika faktorer. En nyligen installerad ytsyningsanläggning detekterar återbildat (tertiärt) glödskal, detta presenteras som area fraktion av defekter per band. Detta mått används som resultat parameter när man med hjälp av ett verktyg för multivariatdataanalys analyserar ett stort antal valsningsparametrar som kan ha påverkan på det återbildade glödskalet. Analysen utförs med ett verktyg för multivariatdataanalys som heter Simca. Resultatet från analysen skall ses som ett hjälpmedel för att tala om inom vilka gränser valsverket skall köras för att undvika problemen med återbildat glödskal.

  • 80.
    GILLGREN, LENA
    Dalarna University, School of Technology and Business Studies, Material Science.
    Optimering av stickserie för mellanvalsning av ett kromstål vid Sandvik Materials Technology: Pass schedule optimization for intermediate rolling of a chromium steel at Sandvik Materials Technology2007Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [sv]

    Vid Sandvik Materials Technology finns ett antal kallvalsverk för valsning av band. Både vid mellanvalsningen och färdigvalsningen används reversibla valsverk, vilket innebär att bandet förs fram och tillbaks mellan samma valspar tills det nått önskad tjocklek. Den reversibla processen gör att produktiviteten starkt kommer att styras av bandens genomloppstid vilket gör optimerade stickserier extremt viktigt. Detta examensarbete behandlar hur optimering av stickserier för kallvalsning av band kan utföras med bibehållen produktkvalitet. Rapporten berör även tillförlitligheten för olika materialoch valskraftsmodeller. Materialets flytspänning har beräknats vid olika töjningar med hjälp av inversmetoden utifrån Ekelunds valskraftsmodell samt uppmätta valskrafter från tidigare utförda valsningar. Ludwik- Hollomons ekvation samt en ekvation där hänsyn tas till både töjning och töjningshastighet, anpassades till flytspänningarna. För prediktering av valskrafter användes dels Ekelunds valskraftsmodell, dels Von Karmans differentialekvation. Stickserieutformningen har styrts av valsverkets motoreffekt samt begränsningen av den givna maximala valskraften och valsningshastigheten. Fullskaleförsök utfördes för utvärdering av stickserier samt valskraftsberäkningsmetoder. Valsningsförsöken visade att valskrafterna för alla stick, i de framtagna stickserierna, understiger valsverkets begränsning. Försöken tyder även på att ingen försämring av bandens planhet kommer att ske med tillämpning av de nya stickserierna. Det framkom dock att utveckling av ställdonen för planhet måste utföras för att undvika kantsprickor och bandbrott vid valsning med stor reduktionsgrad. Den kortaste genomloppstiden och därmed även den högsta produktiviteten gav serierna med minst antal stick. Vad gäller metoder för valskraftsberäkning gav både Ekelunds och Von Karmans modeller tillförlitliga predikteringar.

  • 81.
    Granbom, Ylva
    Dalarna University, School of Technology and Business Studies, Material Science.
    Structure and mechanical properties of dual phase steels: An experimental and theoretical analysis2010Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The key to the understanding of the mechanical behavior of dual phase (DP) steels is to a large extent to be found in the microstructure. The microstructure is in its turn a result of the chemical composition and the process parameters during its production. In this thesis the connection between microstructure and mechanical properties is studied, with focus on the microstructure development during annealing in a continuous annealing line. In-line trials as well as the lab simulations have been carried out in order to investigate the impact of alloying elements and process parameters on the microstructure. Further, a dislocation model has been developed in order to analyze the work hardening behavior of DP steels during plastic deformation. From the in-line trials it was concluded that there is an inheritance from the hot rolling process both on the microstructure and properties of the cold rolled and annealed product. Despite large cold rolling reductions, recrystallization and phase transformations, the final dual phase steel is still effected by process parameters far back in the production chain, such as the coiling temperature following the hot rolling. Lab simulations showed that the microstructure and consequently the mechanical properties are impacted not only by the chemical composition of the steel but also by a large number of process parameters such as soaking temperature, cooling rate prior to quenching, quench and temper annealing temperature. Studying the behavior of DP steels under deformation it was observed that the plastic deformation proceeds inhomogeneously. This was taken into account when developing a dislocation model accurately describing the work hardening behavior for this type of steel. By fitting the dislocation model to experimental stress-strain data it is possible to obtain information about the material’s behavior, e.g. it was observed that only a fraction of the ferrite phase takes part in the initial plastic deformation, which explains the high initial deformation hardening rate in DP steels. Another finding was that the flow stress ferrite grain size sensitivity in DP steels is much larger than that in ferritic steels. Further, the deformation hardening part of the flow stress experiences a ferrite grain size dependence, which is in glaring contrast to that found for ferritic steels.

  • 82.
    Granbom, Ylva
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Ryde, Lena
    Jeppsson, Johan
    Simulation of the soaking and gas jet cooling in a continuous annealing line using dilatometry2010In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 81, no 2Article in journal (Refereed)
    Abstract [en]

    The present study concerns the simulation of a continuous annealing line (CAL), using dilatometry. Simulations of CAL have been performed on four commercial steel grades with different chemical compositions in order to investigate how the alloying elements C, Mn, Si and B affect the microstructure and hardness of dual phase (DP) and martensitic steels. Three annealing cycles corresponding to those used in a CAL have been applied. When annealing intercritically, as is the case in DP-steel production, the materials do not reach equilibrium during soaking. Mn and C increase the austenite content and consequently the hardness of the materials. Higher levels of Si (0.4?wt %) are required to retard the formation of new ferrite during cooling in the gas jet section, prior to quenching. B increases hardenability effectively when annealing in the austenite region but is not as efficient during intercritical annealing, which implies that boron restrains ferrite nucleation rather than impeding ferrite growth. Results from DICTRA calculations show that it is possible to simulate the phase transformations during soaking, gasjet cooling and quenching.

  • 83.
    Grehk, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Berger, Robert
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Material Science.
    Investigation of the drying process of linseed oil using FTIR and ToF-SIMS2008In: Proceedings of the 17th International Vacuum Congress/13th International Conference on Surface Science/Internatinal Conference on Nanoscience and Technology, Stockholm, 2008, Vol. 100Conference paper (Refereed)
    Abstract [en]

    The drying process of linseed oil, oxidized at 80 oC, has been investigated with rheology measurements, Fourier transformation infrared spectroscopy (FTIR), and time of flight secondary ion mass spectrometry (ToF-SIMS). The drying process can be divided into three main steps: initiation, propagation and termination. ToF-SIMS spectra show that the oxidation is initiated at the linolenic (three double bonds) and linoleic fatty acids (two double bonds). ToF-SIMS spectra reveal peaks that can be assigned to ketones, alcohols and hydroperoxides. In this article it is shown that FTIR in combination with ToF-SIMS are well suited tools for investigations of various fatty acid components and reaction products of linseed oil.

  • 84.
    Grehk, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Engkvist, Josefin
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Material Science.
    Richter, Jan H
    Karlsson, Patrik G
    Sandell, Anders
    Initial stages of metal-organic chemical-vapor deposition of ZrO2 on a FeCrAl alloy2007In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 516, no 6, p. 875-879Article in journal (Refereed)
    Abstract [en]

    The initial stages of metal-organic chemical-vapor deposition of ZrO2 on a model FeCrAl alloy was investigated using synchrotron radiation photoelectron spectroscopy, X-ray absorption spectroscopy, scanning Auger microprobe, and time of flight secondary mass spectrometry. The coatings were grown in ultra-high vacuum at 400 °C and 800 °C using the single source precursor zirconium tetra-tert-butoxide. At 400 °C the coatings mainly consist of tetragonal ZrO2 and at 800 °C amixed ZrO2/Al2O3 layer is formed. The Almetal diffuses from the FeCrAl bulk to themetal/coating interface at 400 °C and to the surface of the coating at 800 °C. The result indicates that the reactionmechanism of the growth process is different at the two investigated temperatures.

  • 85.
    Grehk, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Göthelid, Mats
    Björkqvist, Magnus
    Le Lay, Guy
    Karlsson, Ulf
    Li-induced phase transition from the Ge(111)3x1:Li surface reconstruction to the Ge(111)rot3xrot3:Li lithium germanid2000In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 61, no 7, p. 4963-4967Article in journal (Refereed)
    Abstract [en]

    We have investigated the Li-induced phase transition from the Ge(111)3×1:Li to the Ge(111)sqrt[3]×sqrt[3]:Li reconstruction with photoemission. The Ge(111)3×1:Li reconstruction can be described as parallel rows of Ge atoms separated by single rows of Li atoms. The Ge(111)sqrt[3]×sqrt[3]:Li reconstruction, on the other hands, has to be described in terms of a Li-germanide phase extending over at least two atomic layers.

  • 86.
    Grenmyr, Gustav
    Dalarna University, School of Technology and Business Studies, Material Science.
    Undersökning av rekristallisationsglödgning av det rostfria stålet 7C27Mo2 (AISI 420);: Study on recrystallization annealing of the stainless steel 7C27Mo2 (AISI 420)2006Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [sv]

    En undersökning av rekristallisationsglödgning av det rostfria stålet 7C27Mo2 (AISI 420) har utförts. Prov med olika reduktionsgrad har glödgats under korta tider för att efterlikna kontinuerlig glödgning. Rekristallisationsgraden mättes med ”electron backscatter diffraction” (EBSD) av korrosions- och metallforskningsinstitutet (KIMAB). Resultatet användes för att skapa modeller för att kunna förutsäga hur kallvalsning och glödgningsparametrar påverkar rekristallisationsgraden och därmed inverkar på materialets mekaniska egenskaper. Andelen rekristalliserad struktur påverkades starkt av kallreduktionsgraden och glödgningstemperaturen. Störst inverkan på de mekaniska egenskaperna hade temperaturen. Parallellt med EBSD-analysen utvärderades olika etsmetoder med hjälp av såväl ljusoptisk mikroskopi som i svepelektronmikroskopi (SEM). Genom att överetsa proverna och analysera dessa i SEM gick det att synliggöra kornstrukturen och därmed borde det vara möjligt att utveckla en alternativ metod till EBSD för att mäta rekristallisationsgraden. En annan del av arbetet bestod av att ta fram en metod för att indirekt kontrollera rekristallisationsgraden. Genom mätning av mekaniska egenskaper för materialet i kallvalsat och glödgat tillstånd kunde rekristallisationsgraden bestämmas mycket bra. Utöver detta har ett försök gjorts för att relatera materialets magnetiska egenskaper till rekristalliserad andel. Resultatet av dessa försök visar att korrelationen mellan remanens och rekristallisationsgrad är mycket svag.

  • 87.
    HAAG, MARIA
    Dalarna University, School of Technology and Business Studies, Material Science.
    Problematiken kring fasomvandlingar i kylsträckan och rekristallisation i Bredbandverket på SSAB: Problems concerning phase transformation in the cooling line and recrystallization in the Hot Strip Mill at SSAB2007Independent thesis Basic level (degree of Bachelor)Student thesis
    Abstract [sv]

    Syftet med examensarbetet var att belysa problematiken kring kylsträckan. För att kunna avgöra vilka kvaliteter man bör lägga in extra resurser på, är det viktigt att veta det totala antalet band som gjorts. Diagrammet jag fått fram visar ett totalt sammantaget resultat av de mest felkylda banden i antal. Jag har infört de egna beteckningarna absolut-% och relativ-%, eftersom det inte räcker med att man vet hur stor del av alla kylfel ett visst stål står för. Absolut-% visar hur mycket av en viss stålsort som blir fel. Relativ-% är hur stor del av alla kylfel som är just av den aktuella kvaliteten. Vilka av kvaliteterna man bör rikta in sig på är främst en ekonomisk fråga. Om den absoluta frekvensen är så hög som 17,3% kanske hela vinsten på sortiment uteblir och man bör låta bli att tillverka dessa. Det kanske är bättre att gå in för att jobba med de som har hög relativ felfrekvens, eftersom de är så vanligt förekommande och står för en större kostnadsbesparing. Stålkvaliteten ÄS 63039 har visat en mycket varierande långtidsadaption (LTAD) under 2005. Detta behöver inte vara konstigt, eftersom varje ÄS innehåller flera tjockleksgrupper. Att tjockare band kräver mer vatten än tunnare band är lätt att förstå, men i detalj är sambandet inte helt utrett. Vattenmängden som används har också ett nära samband med temperaturen på kylvattnet och tenderar tyvärr till att vara säsongsberoende. Syres löslighet i vatten är ett mått på kylförmågan, om man ser detta ur termodynamisk synvinkel. Den undersökning jag gjorde var en interpolation av de värden jag hade i tabell för syres löslighet i vatten. Slutsatsen man kan dra är att SMS-koefficienterna och testet mot syres löslighet i vatten av olika temperaturer stämmer väl överens, vilket tyder på att det hela är korrekt kompenserat. En förutsättning för rätt kylförmåga är dock att det finns tillräckligt med vatten i tanken. Ett försök med Schaeffler diagram gjordes då detta skulle kunna kontrollera relevansen av olika ekvivalenter, som används av SSAB för att beskriva likartade kvaliteter och få ner antalet adaptionsgrupper. Skillnaden i molybdenhalten antogs ha stor betydelse. Försöket visade dock inget förutom att de två stålkvaliteter vi jämförde mot varandra hamnade nära varandra i diagrammet, fast i ”felaktigt” martensistiskt område. Via Termo Calc har två fasdiagram för ekvivalenterna tagits fram och analyserats. Där ser de ekvivalenta ut. Ett speciellt försök gjordes slutligen som gick ut på att ta reda på hur mycket molybdenhalten påverkar härdbarheten för ÄS:en. ÄS 63046 har en härdbarhetsfaktor som är nästan 30% högre än ÄS 63039. Så stor skillnad borde innebära att dessa ÄS inte är ekvivalenta, utan bör kylas olika.

  • 88.
    Hansson, Sofia
    Dalarna University, School of Technology and Business Studies, Material Science.
    A three-dimensional finite element simulation of stainless steel tube extrusion using a physically based material model2006Conference paper (Refereed)
  • 89.
    Hansson, Sofia
    Dalarna University, School of Technology and Business Studies, Material Science.
    Modeling of the Stainless Steel Tube Extrusion Process2010Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Seamless tubes of stainless steel can be extruded using glass as a lubricant in the Ugine-Sejournet process. The process is performed at high temperature and is associated with large deformations and high strain rates. The use of finite element modeling (FEM) in the analysis and design of extrusion and other metal forming processes is constantly increasing. Computer models that with adequate accuracy can describe the material behavior during extrusion can be very useful for product and process development. The process development in industrial extrusion today is, to a great extent, based on trial and error. This often involves full size experiments which are expensive, time consuming and interfere with the production. It would be of great value if these experiments could be performed in a computer. In this work, FE models of the stainless steel tube extrusion process were developed and used. Simulations were carried out for different tube dimensions and three different materials: two austenitic stainless steels and one duplex (austenitic/ferritic) stainless steel. The models were validated by comparing the predicted values of extrusion force with measurements from production presses. A large number of input parameters are used in a FE analysis of extrusion. This includes boundary conditions, initial conditions and parameters that describe the mechanical and thermal properties of the material. The accuracy of the extrusion simulation depends, to a large extent, on the accuracy of these parameters. Experimental work, both in the form of material testing and production trials, was performed in order to give an accurate description of the input parameters in these extrusion models. A sensitivity analysis was performed for one of the models and the results showed that the initial billet temperature is the parameter that has the strongest impact on the extrusion force. In order to study the temperature evolution in the billet during manufacturing, the entire process chain at extrusion of stainless steel tubes was simulated using FEM. This process flow model includes sub-models of induction heating, expansion and extrusion. The work includes the use of a dislocation density-based material model for the AISI type 316L stainless steel. It is expected that this physically based model can be extrapolated to a wider range of strains, strain rates and temperatures than an empirical model, provided that the correct physical processes are described by the model and that no new phenomena occur. This is of interest for steel extrusion simulations since this process is carried out at higher strains and strain rates than what are normally used in mechanical laboratory tests. The developed models have given important contributions to the understanding of different phenomena that occur during extrusion of stainless steel tubes, and can be used to analyze how different process parameters affect the extrusion process.

  • 90.
    Hansson, Sofia
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Domkin, Konstantin
    Physically based material model in finite element simulation of extrusion of stainless steel tubes2005Conference paper (Refereed)
  • 91.
    Hansson, Sofia
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science. Sandvik Mat Technol, R&D Ctr, Sandviken.
    Fisk, Martin
    Simulations and measurements of combined induction heating and extrusion processes2010In: Finite elements in analysis and design (Print), ISSN 0168-874X, E-ISSN 1872-6925, Vol. 46, no 10, p. 905-915Article in journal (Refereed)
    Abstract [en]

    The manufacturing process chain at glass-lubricated extrusion of stainless steel tubing is simulated using the finite element method. The developed model includes sub-models of induction heating, expansion and extrusion. An in-house mapping tool is used to transfer the temperature fields between the electromagnetic-thermal and thermo-mechanical analyses. Using the combined model it is possible to study the influence of different process parameters on the temperature distribution in the billet, and how this affects the final extrusion properties. In this study, the model is applied to two cases of tube extrusion, one using an austenitic stainless steel and one using a duplex, austenitic/ferritic, stainless steel. It is shown that the induction heating model successfully predicts the temperatures obtained experimentally from thermocouples placed in the steel billets during heating. The agreement between models and experiments regarding extrusion force and expansion force is satisfactory.

  • 92.
    Hansson, Sofia
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science. Sandvik Mat Technol, R&D Ctr, SE-81181 Sandviken.
    Jansson, Tomas
    Sensitivity analysis of a finite element model for the simulation of stainless steel tube extrusion2010In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 210, no 10, p. 1386-1396Article in journal (Refereed)
    Abstract [en]

    In this work, a sensitivity analysis has been performed on a finite element model of glass-lubricated extrusion of stainless steel tubes. Fifteen model parameters, including ram speed, billet and tool temperatures, friction coefficients and heat transfer coefficients, were considered. The aim of the study was to determine the parameters that are most important for the response of the extrusion force. The relationship between the model parameters and the responses was analyzed by a calculation of two different regression models: one linear polynomial model and one model that includes interaction terms. Additional simulations were then carried out to validate the regression models. The results show that the initial billet temperature is the factor that has the strongest impact on the extrusion force within the parameter ranges studied in this work. The goodness of prediction and goodness of fit are very good for both regression models.

  • 93.
    Harlin, Peter
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Carlsson, Per
    Dalarna University, School of Technology and Business Studies, Material Science.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Material Science.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Influence of surface roughness of PVD coatings on tribological performance in sliding contacts2006In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 201, no 7, p. 4253-4259Article in journal (Refereed)
    Abstract [en]

    The influence of surface roughness on the tribological performance, i.e. friction, wear and material pick-up tendency, of two different commercial PVD coatings, TiN and WC/C, in sliding contact with ball bearing steel has been evaluated using two different types of sliding wear laboratory tests. Post-test characterisation using SEM/EDS, AES, ToF-SIMS and XPS was used to evaluate the prevailing friction and wear. The results show that the surface roughness of the coating is of importance in order to control the initial material pick-up tendency and thus the friction characteristics in a sliding contact. Once initiated, the material pick-up tendency will increase, generating a tribofilm at the sliding interface. For steel–TiN sliding couples a FeO-based tribofilm is generated on the two surfaces and FeO/FeO becomes the sliding interface (interfilm sliding) resulting in a high friction coefficient. For steel–WC/C sliding couples the WC/C displays a pronounced running-in behaviour which generates a WO3-based tribofilm on the steel surface while a carbon rich surface layer is formed on the WC/C surface, i.e. WO3/C becomes the sliding interface (interface sliding) resulting in a low friction coefficient.

  • 94.
    Harlin, Peter
    et al.
    Sandvik Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Abrasive wear resistance of starch consolidated and sintered high speed steel2009In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 267, no 9-10, p. 1482-1489Article in journal (Refereed)
    Abstract [en]

    The abrasive wear resistance of starch consolidated (SC) and super solidus liquid phase sintered (SLPS) M3/2 high speed steel (HSS) samples have been evaluated by a two-body micro-abrasion test (low stress abrasion), using 6 µm diamond abrasive particles, and a three-body abrasion test (high stress abrasion), using significantly larger abrasive particles of blast furnace slag (600 HV) and silicon carbide (2400 HV), respectively. In the tests a commercial powder metallurgical (PM) HSS was used as a reference material. The results show that the microstructure of the SC and SLPS HSS samples is strongly dependent on the sintering temperature used. With increasing temperature the microstructure ranges from a porous (5% porosity) relatively fine grained low temperature sintered microstructure to a fully dense relatively coarse grained high temperature sintered microstructure with eutectic carbides/carbide networks. However, despite the pronounced microstructural differences displayed by the as-sintered HSS microstructures these show a relatively high abrasive wear resistance, comparable with that of a HIPed HSS reference, both under low and high stress abrasion contact conditions. The characteristic features of the low and high temperature sintered microstructures, i.e. the pores and coarse eutectic carbides/carbide networks, only show a limited impact on the wear rate and the wear mode (dominant wear mechanism). The results obtained imply that near net shaped components manufactured by starch consolidation and super solidus liquid phase sintering might be of interest in tribological applications.

  • 95.
    Harlin, Peter
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Starch consolidation of M3/2 high speed steel - Influence of sintering temperature on mechanical properties2007In: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 50, no 3, p. 232-238Article in journal (Refereed)
  • 96.
    Harlin, Peter
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Starch consolidation of M3/2 high speed steel powder: influence of process parameters on resulting microstructure2007In: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 50, no 4, p. 345-353Article in journal (Refereed)
    Abstract [en]

    The possibility to produce near net shape high speed steel components with an adequate microstructure by the combination of starch consolidation (SC) and super solidus liquid phase sintering (SLPS) has been evaluated using a gas atomised M3/2 high speed steel (HSS) powder. Characterisation of the green body and as sintered microstructures using light optical microscopy (LOM), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX) reveals that both the SC and SLPS processes strongly influence the resulting microstructure and thus the properties of the high speed steel material. The results obtained show that the morphology and distribution of starch to a high extent affect the green body surface strength and that the large pores remaining after sintering originates from entrapped air introduced in the fabrication process of the green body. The results illuminate the possibility to combine SC and SLPS to produce HSS components with fully dense microstructures and retained green body geometry from a powder with particle size distribution 50 - 150 mu m.

  • 97.
    Harr, Thomas
    Dalarna University, School of Technology and Business Studies, Material Science.
    Minskning av ändeffekter vid valsning i fristående trimvalsverk2005Independent thesis Advanced level (degree of Master (Two Years))Student thesis
  • 98. Heinrichs, J.
    et al.
    Gerth, J.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Material Science.
    Larsson, M.
    Wiklund, U.
    Influence from surface roughness on steel transfer to PVD tool coatings in continuous and intermittent sliding contacts2012In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 56, p. 9-18Article in journal (Refereed)
    Abstract [en]

    A sliding test is used in order to evaluate the influence of tool surface roughness on the material transfer in intermittent and continuous sliding of PVD coated HSS against case hardening steel (20NiCrMo2). Two cutting tool coatings, TiN and AlCrN, and three different surface roughnesses are tested. For polished surfaces the same types of material transfer are obtained irrespective of sliding mode and coating type. If the surfaces are too rough, the tribofilms do not grow thick enough to separate the surfaces and the work material is abrasively worn in both sliding modes. With increased sliding distance, cracking of the TiN coating occurs while the AlCrN coating remains intact. (C) 2012 Elsevier Ltd. All rights reserved.

  • 99. Heinrichs, Jannica
    et al.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Jacobson, Staffan
    Mechanisms of material transfer studied in situ in the SEM: explanations to the success of DLC coated tools in aluminium forming2012In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 292, p. 49-60Article in journal (Refereed)
    Abstract [en]

    Metal forming constitutes a group of industrially important processes to form metallic components to net shape. When forming aluminium and other materials that tend to stick to the tools, problems occur. The transferred work material increases the friction, which increases the forming forces. Additionally, the transferred work material becomes hardened and then scratches the softer work material in subsequent forming. This process, known as galling, compromises the surface finish of the next pieces to be formed. This paper employs a newly developed technique to investigate the initial stages of transfer at high resolution in situ in the SEM. We show that the complex microscale processes involved can be distinguished into three classes: primary transfer, secondary transfer and damage activated transfer. The damage activated transfer constitutes a new fundamental tribological phenomenon, involving the activation and healing of a soft metal in sliding contact with a harder surface. Damage activation leads to transfer onto surfaces such as the polished DLC in this investigation, which would otherwise not see any transfer. These processes are important when forming aluminium, but are expected to be of general tribological significance, in sliding involving non-perfect lubricant films, especially for soft metals with protective surface oxides. (C) 2012 Elsevier B.V. All rights reserved.

  • 100. Heinrichs, Jannica
    et al.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Jacobson, Staffan
    New understanding of the initiation of material transfer and transfer layer build-up in metal forming: in situ studies in the SEM2012In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 292, p. 61-73Article in journal (Refereed)
    Abstract [en]

    The tribological mechanisms behind the initiation of material transfer and build-up of transfer layers in aluminium forming have been studied in situ in the SEM where a tip of aluminium is put into contact with a tool steel surface under controlled sliding contact conditions. By combining in situ observations with post-test high resolution FEG-SEM studies of the contacting surfaces we have shown that aluminium is immediately transferred onto the fine polished tool steel. It was also confirmed that the initial transfer occurs on a very fine scale and is localised to the surface irregularities presented by the slightly protruding carbonitrides. In contrast, the less protruding M6C carbides, as well as the martensitic steel matrix exhibit very little initial transfer. Intentionally made scratches (roughly 5 mu m wide and 2 mu m deep) across the tool surface immediately result in larger scale transfer, which grows upon further passages of work material causing a high coefficient of friction. The study illuminates the extreme value of combining the in situ technique with high-resolution scanning electron microscopy using low acceleration voltage as a mean to detect the very thin initial transfer layers. With the higher acceleration voltages normally used, the transferred aluminium becomes transparent and can hardly be detected. (C) 2012 Elsevier B.V. All rights reserved.

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