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  • 1.
    Andersson, Oscar
    et al.
    KTH Royal Institute of Technology, Sweden.
    Budak, Nesrin
    KTH Royal Institute of Technology, Sweden.
    Melander, Arne
    RISE - Research Institutes of Sweden, Swerea, Swerea KIMAB. KTH Royal Institute of Technology, Sweden.
    Palmquist, Niclas
    Volvo Car Corporation, Sweden.
    Experimental measurements and numerical simulations of distortions of overlap laser-welded thin sheet steel beam structures2017In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 61, no 5, p. 927-934Article in journal (Refereed)
    Abstract [en]

    Distortions of mild steel structures caused by laser welding were analyzed. One thousand-millimeter U-beam structures were welded as overlap joints with different process parameters and thickness configurations. Final vertical and transverse distortions after cooling were measured along the U-beam. Significant factors, which affect distortions, were identified. Heat input per unit length, weld length, and sheet thickness showed a significant effect on welding distortions. Furthermore, the welding distortions were modeled using FE simulations. A simplified and computationally efficient simulation method was used. It describes the effect of shrinkage of the weld zone during cooling. The simulations show reasonable computation times and good agreement with experiments.

  • 2.
    Hedegård, Joakim
    et al.
    RISE, Swerea, Swerea KIMAB.
    Nerman, Peter
    RISE, Swerea, Swerea KIMAB.
    Wahlsten, Joakim
    RISE, Swerea, Swerea KIMAB.
    Randelius, Mats
    RISE, Swerea, Swerea KIMAB.
    Larsson, Mats
    RISE, Swerea, Swerea KIMAB.
    Influence of internal microfissures on fatigue life2009In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 53, p. R209-R220Article in journal (Refereed)
    Abstract [en]

    The influence of microfissures on the fatigue strength of submerged arc weids in two high-alloyed, austenitic stainless steels has been studied. It was shown that internal microfissures in the weld metal can have a significant influence on the fatigue strength of the joint when the weld geometry is omitted (machined flat).. Still, all test series showed good fatigue performance and reached better results than expected. Three of the four fatigue series reached a loading capacity close to Rp0.2 for the base metal and one of the series reached levels close to Rp0.2 for the weld metal.

  • 3.
    Hosseini, Vahid
    et al.
    University West, Sweden; Innovatum AB, Sweden.
    Hurtig, Kjell
    University West, Sweden.
    Eyzop, Daniel
    Outokumpu Stainless AB, Sweden.
    Östberg, Agneta
    Sandvik Materials Technology, Sweden.
    Janiak, Paul
    RISE - Research Institutes of Sweden, Materials and Production, KIMAB.
    Karlsson, Leif
    University West, Sweden.
    Ferrite content measurement in super duplex stainless steel welds2019In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 63, no 2, p. 551-563Article in journal (Refereed)
    Abstract [en]

    Approaches to determining ferrite fraction (%) and ferrite number (FN) were examined for super duplex stainless steel (SDSS) welds. A reference sample was produced by bead-on-plate gas–tungsten arc welding of a type-2507 SDSS plate. By comparing different etchants and measurement practices, it was realized that etching with modified Beraha followed by computerized image analysis (IA) was the most accurate and quickest technique to measure ferrite fraction, which determined the same ferrite fraction (68.0 ± 2.6%) as that measured by electron diffraction backscattered analysis (67.6 ± 2.3%). A Round Robin test was performed on a reference sample at University West, Swerea KIMAB, Outokumpu Stainless, and Sandvik Materials Technology to investigate the repeatability of the technique. The ferrite fraction measurements performed at different laboratories showed very small variations, which were in the range of those seen when changing microscope in the same laboratory. After verification of the technique, the relationship between ferrite fraction and ferrite number (measured with FERITSCOPE®) was determined using 14 single (root) pass welds, including butt, corner, and T-, V-, and double V-joint geometries. The best-fit equation found in this study was ferrite number (FN) = 1.1 × ferrite fraction (%). To conclude, the ferrite fraction technique suggested in the present paper was accurate and repeatable, which made it possible to determine a ferrite fraction–ferrite number formula for SDSS single-pass welds.

  • 4.
    Larsson, J.K.
    et al.
    Volvo Car Corporation.
    Lundgren, J.
    Volvo Car Corporation.
    Asbjörnsson, Einar
    RISE, Swerea, Swerea IVF.
    Andersson, H.
    Gestamp HardTech AB.
    Extensive introduction of ultra high strength steels sets new standards for welding in the body shop2009In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 53, p. s.4-14Article in journal (Refereed)
    Abstract [en]

    In order to meet upcoming legislative demands regarding acceptable levels of C02 emissions and to contribute to the fight against global warming, while also meeting customer expectations of reduced fuel consumption, all automotive OEMs are today focusing on lightweight engineering. Some of them, mainly low volume premium brands, have chosen to introduce fairly expensive lightweight materials such as aluminium and magnesium to meet these targets, whereas the main portion of high volume producers are trying to optimize the classic steel concept by introducing different grades of advanced high strength steels. Volvo Cars has decided upon a unique utilization of hot-formed, press-hardened, ultra high strength steel components featuring tensile strength levels in the order of 1 500 MPa, but on the other hand, producing these parts in very thin gauges for weight saving reasons. The first product launched according to this ultra high strength steel intensive concept was the 2008YM version of the Volvo V70 and its sibling, the cross-country version XC70, both built on the EuCD platform. The body contains several parts manufactured by hot-forming and press-hardening. The extensive use of this type of Boron alloyed steel challenged all welding methods commonly used in car body manufacturing, not least, traditional resistance spot welding. This paper will address the following topics: overview of the V70 body structure and utilization of materials, a brief description of the hot-forming, press-hardening process, the procedure for validating weldability before going into series production, lessons learnt from resistance spot welding trials of material combinations involving one or more boron alloyed steel parts, and recommendations for default welding data, influence on the manufacturing system, introducing electro-servo welding guns, adaptive weld timers and ultrasonic non-destructive weld quality checking, necessary revisions of existing spot weld requirements. The presentation will end with a glimpse at perspectives for future welding challenges in Volvo body shops, as the need for further weight saving will promote a considerable introduction of various new grades of advanced high strength steels.

  • 5.
    Stenberg, Thomas
    et al.
    KTH Royal Institute of Technology, Sweden.
    Barsoum, Zuheir
    KTH Royal Institute of Technology, Sweden.
    Åstrand, Eric A
    Volvo Construction Equipment AB, Sweden.
    Öberg, Anna Ericsson
    Volvo Construction Equipment AB, Sweden.
    Schneider, C.
    RISE - Research Institutes of Sweden, Swerea, Swerea KIMAB.
    Hedegård, Joakim
    RISE - Research Institutes of Sweden, Swerea, Swerea KIMAB.
    Quality control and assurance in fabrication of welded structures subjected to fatigue loading2017In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 61, no 5, p. 1003-1015Article in journal (Refereed)
    Abstract [en]

    The current paper presents a comprehensive overview of weld quality control and assurance of welded structures where the major failure prevention is due to fatigue loading. It gives the drawbacks and limitation of quality control systems, international weld quality standards, and guidelines used in today’s weld production. Furthermore, in recent development in quality control and assurance of welded structures, a new online method is presented. The main target is to enable a complete, online evaluation of large quantities of welds in an accurate and repeatable fashion. Information gathered will not only be used for determining the weld quality level with respect to the fatigue strength but also to be evaluated for use in improved process control, in welding power sources, and robot control systems. It is verified that the new online method, a new laser scanning technology, and algorithms can successfully be used as modern tools for automated unbiased geometrical weld quality assurance and implemented in weld production environment.

  • 6.
    Wessman, Sten
    et al.
    RISE, Swerea, Swerea KIMAB.
    Karlsson, L.
    ESAB AB.
    Pettersson, R.
    Outokumpu Stainless AB.
    Östberg, A.
    AB Sandvik Materials Technology.
    Computational thermodynamics study of the influence of tungsten in superduplex stainless weld metal2012In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 56, p. 79-87Article, review/survey (Refereed)
    Abstract [en]

    Tungsten is used by some duplex stainless steel producers for partial substitution of molybdenum, both elements enhancing the corrosion resistance of duplex stainless steel. The negative aspect of both molybdenum and tungsten alloying is that they increase the tendency to precipitate intermetallic phases, which may have a detrimental effect on corrosion and mechanical properties. The temperature region for intermetallic phase precipitation is about 700-1000 C, depending on alloy composition, and the time for precipitation is within minutes for superduplex steels.There has been scientific discussion on the relative effects of Mo alone or Mo-W on intermetallic precipitation behaviour in superduplex steels for the past two decades. While the base material response to ageing and precipitation of intermetallic phases has been satisfactorily assessed, weld metal has proved more of a challenge. The main reason for this is that welding is a very complex process introducing many parameters to the assessment which not have to be considered in studies of base material. For example superduplex weld metal typically solidify fully ferritic but may in case excessive nitrogen is added solidify as a mixture of ferrite and austenite. The solidification mode may vary also between weld passes as a consequence of minor variations in composition. Ferritic solidification is the preferred mode, giving the well known Widmanstätten austenite, which forms in the solid state during cooling. Mixed mode solidification gives a vermicular appearance, which is known to increases the tendency to intermetallic formation. A comprehensive study using computational thermodynamics was done to investigate this matter. This study included equilibrium calculations, Scheil-Gulliver solidification simulations, and calculations of the driving force for intermetallic phase precipitation and further a study of diffusion of Mo and W in these alloy systems. The different approaches were applied on model superduplex weld metals with nominal compositions matching commercial superduplex fillers available today. The principal conclusion is that all thermodynamic calculations clearly indicates the W containing filler to show a more pronounced sensitivity to heat treatments by precipitation of intermetallic phases. © 2012 International Institute of Welding.

  • 7.
    Wessman, Sten
    et al.
    RISE, Swerea, Swerea KIMAB.
    Selleby, M.
    KTH Royal Institute of Technology.
    Evaluation of austenite reformation in duplex stainless steel weld metal using computational thermodynamics2014In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 58, no 2, p. 217-224Article in journal (Refereed)
    Abstract [en]

    This paper provides a theoretical study of austenite reformation during cooling of duplex stainless weld metal using computational thermodynamics and kinetics. Model alloys of the superduplex 2509 weld metal and 2205 base material were used for the study and austenite reformation was calculated at equilibrium conditions and at cooling rates from 0.01 to 2,000 K/s. The calculations also provided the possibility to study the distribution of the alloying elements at ferrite and austenite phase boundaries. The importance of nitrogen for austenite reformation at rapid cooling was studied by comparing with simulations for a low-nitrogen alloy. The results were also compared with experimental and model results from the literature providing good correlation and the unique possibility to study the distribution of alloying elements between the growing austenite and the shrinking ferrite. © 2013 International Institute of Welding.

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