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  • 1.
    Asala, G.
    et al.
    University of Manitoba, Department of Mechanical Engineering, Winnipeg, Canada.
    Khan, A. K.
    University of Manitoba, Department of Mechanical Engineering, Winnipeg, Canada.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Mechanical Engineering. University West, Department of Engineering Science, Division of Welding Technology.
    Ojo, O. A.
    University of Manitoba, Department of Mechanical Engineering, Winnipeg, Canada.
    Microstructural Analyses of ATI 718Plus® Produced by Wire-ARC Additive Manufacturing Process2017In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 48A, no 9, 4211-4228 p.Article in journal (Refereed)
    Abstract [en]

    A detailed microstructural study of ATI 718Plus superalloy produced by the wire-arc additive manufacturing (WAAM) process was performed through the use of scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron probe micro-analysis (EPMA), and electron backscatter diffraction (EBSD). Extensive formation of eutectic solidification microconstituents including Laves and MC-type carbide phases, induced by micro-segregation, are observed in the build of the alloy in the as-deposited condition. Notwithstanding the significant segregation of niobium (Nb), which has been reported to promote the formation of the delta-phase in ATI 718Plus, only eta-phase particles are observed in the deposit. Excessive precipitation of eta-phase particles is found to be linked to Laves phase particles that are partially dissolved in the deposit after post-deposition heat treatment (PDHT). The EBSD analysis shows a high textured build in the aOE (c) 100 > directions with only a few misoriented grains at the substrate-deposit boundary and the top of the deposit. Investigation on the hardness of the build of the alloy, in the as-deposited condition, showed a softened zone about 2 mm wide at the deposited metal heat affected zone (DMHAZ), which has not been previously reported and potentially damaging to the mechanical properties. An extensive analysis with the use of both microstructural characterization tools and theoretical calculations shows that the DMHAZ has the lowest volume fraction of strengthening precipitates (gamma’ and gamma aEuro(3)) in terms of their number density, which therefore induces the observed softness. Delayed re-precipitation kinetics and the extent of the precipitation of gamma’ and gamma aEuro(3) in the DMHAZ which is related to the diffusion of segregated solute elements from the interdendritic regions are attributed to this phenomenon. The microstructural analyses discussed in this work are vital to adequate understanding of properties of ATI 718Plus produced by the additive manufacturing process technique.

  • 2.
    Babu, Bijish
    et al.
    Mechanics of Sold Materials, Luleå University of Technology, SE-971 87, Luleå, Sweden.
    Charles Murgau, Corinne
    University West, Department of Engineering Science, Avdelningen för svetsteknologi (SV).
    Lindgren, Lars-Erik
    Mechanics of Sold Materials, Luleå University of Technology, SE-971 87, Luleå, Sweden.
    Physically Based Constitutive Model of Ti-6Al-4V for Arbitrary Phase CompositionArticle in journal (Other academic)
    Abstract [en]

    The main challenge in producing aerospace components using Ti-6Al-4V alloy is to employ the optimum process window of deformation rate and temperature in order to achieve desired material properties. Understanding the microstructure property relationship qualitatively is not enough to achieve this goal. Developing advanced material models to be used in manufacturing process simulation is the key to iteratively computeand optimize the process. The focus in this work is on physically based flow stress models coupled with microstructure evolution models. Such a model can be used to simulate processes involving complex and cyclic thermo-mechanical loading

  • 3.
    Charles Murgau, Corinne
    University West, Department of Engineering Science, Avdelningen för svetsteknologi (SV).
    Microstructure model for Ti-6Al-4V used in simulation of additive manufacturing2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is devoted to microstructure modelling of Ti-6Al-4V. The microstructure and the mechanical properties of titanium alloys are highly dependent on the temperature history experienced by the material. The developed microstructure model accounts for thermaldriving forces and is applicable for general temperature histories. It has been applied to study wire feed additive manufacturing processes that induce repetitive heating and cooling cycles.The microstructure model adopts internal state variables to represent the microstructure through microstructure constituents' fractions in finite element simulation. This makes it possible to apply the model efficiently for large computational models of general thermomechanical processes. The model is calibrated and validated versus literature data. It is applied to Gas Tungsten Arc Welding -also known as Tungsten Inert Gas welding-wire feed additive manufacturing process.Four quantities are calculated in the model: the volume fraction of phase, consisting of Widmanstätten, grain boundary, and martensite. The phase transformations during cooling are modelled based on diffusional theory described by a Johnson-Mehl-Avrami-Kolmogorov formulation, except for diffusionless martensite formation where the Koistinen-Marburger equation is used. A parabolic growth rate equation is used for the to transformation upon heating. An added variable, structure size indicator of Widmanstätten, has also been implemented and calibrated. It is written in a simple Arrhenius format.The microstructure model is applied to in finite element simulation of wire feed additive manufacturing. Finally, coupling with a physically based constitutive model enables a comprehensive and predictive model of the properties that evolve during processing.

  • 4.
    Charles Murgau, Corinne
    et al.
    University West, Department of Engineering Science, Avdelningen för svetsteknologi (SV).
    Lundbäck, Andreas
    Division of Mechanics of Solid Materials, Luleå University of Technology, 971 81 Luleå, Sweden .
    Åkerfeldt, Pia
    Division of Materials Science, Luleå University of Technology, 971 81 Luleå, Sweden .
    Pederson, Robert
    GKN Aerospace Engine Systems, 461 81 Trollhättan, Sweden .
    Temperature and microstructure evolution in Gas Tungsten Arc Welding wire feed additive manufacturing of Ti-6Al-4VArticle in journal (Other academic)
    Abstract [en]

    The Finite Element Method (FEM) is used to solve temperature field and microstructure evolution during GTAW wire feed additive manufacturing process.The microstructure of titanium alloy Ti-6Al-4V is computed based on the temperature evolution in a point-wise logic. The methodology concerning the microstructural modeling is presented. A model to predict the thickness of the Į lath morphology is also implemented. The results from simulations are presented togethe rwith qualitative and quantitative microstructure analysis.

  • 5.
    Chazelas, Christophe
    et al.
    European Ceramic Center, SPCTS CNRS UMR 7315, University of Limoges, Limoges, France.
    Trelles, Juan Pablo
    Mechanical Engineering, University of Massachusetts Lowell, Lowell, USA.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Vardelle, Armelle
    European Ceramic Center, SPCTS CNRS UMR 7315, University of Limoges, Limoges, France.
    Main issues for a fully predictive plasma spray torch model and numerical considerations2017In: Plasma chemistry and plasma processing, ISSN 0272-4324, E-ISSN 1572-8986, Vol. 37, no 3, 627-651 p.Article in journal (Refereed)
    Abstract [en]

    Plasma spray is one of the most versatile and established techniques for the deposition of thick coatings that provide functional surfaces to protect or improve the performance of the substrate material. However, a greater understanding of plasma spray torch operation will result in improved control of process and coating properties and in the development of novel plasma spray processes and applications. The operation of plasma torches is controlled by coupled dynamic, thermal, chemical, electromagnetic, and acoustic phenomena that take place at different time and space scales. Computational modeling makes it possible to gain important insight into torch characteristics that are not practically accessible to experimental observations, such as the dynamics of the arc inside the plasma torch. This article describes the current main issues in carrying out plasma spray torch numerical simulations at a high level of fidelity. These issues encompass the use of non-chemical and non-thermodynamic equilibrium models, incorporation of electrodes with sheath models in the computational domain, and resolution of rapid transient events, including the so-called arc reattachment process. Practical considerations regarding model implementation are also discussed, particularly the need for the model to naturally reproduce the observed torch operation modes in terms of voltage and pressure fluctuations.

  • 6.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Gas tungsten arc models including the physics of the cathode layer: remaining issues2017In: Welding in the World, ISSN 0043-2288, 1-20 p.Article in journal (Refereed)
    Abstract [en]

    A recent review pointed out that the existing models for gas tungsten arc coupling the electrode (a cathode) and the plasma are not yet complete enough. Their strength is to predict with good accuracy either the electric potential or the temperature field in the region delimited by the electrode and the workpiece. Their weakness is their poor ability to predict with good accuracy these two fields at once. However, both of these fields are important since they govern the heat flux to the workpiece through current density and temperature gradient. New developments have been made since then. They mainly concern the approaches addressing the electrode sheath (or space charge layer) that suffered from an underestimation of the arc temperature. These new developments are summarized and discussed, the modelling assumptions are examined, and important modelling issues that remain unexplored are underlined.

  • 7.
    Choquet, Isabelle
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Javidi Shirvan, Alireza
    University West, Department of Engineering Science, Division of Welding Technology.
    Nilsson, Håkan
    Chalmers University of Technology, Department of Applied Mechanics, Gothenburg, Sweden.
    A predictive model for gas tungsten arc heat source2016In: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings: 25th – 27th of October 2016, Lund: Swedish Production Academy , 2016, 1-10 p.Conference paper (Refereed)
    Abstract [en]

    Gas tungsten arcs are used as heat sources in production processes such as welding and metal deposition.However, the most advanced of the existing gas tungsten arc models still lack predicting the arc temperature observed experimentally, unless imposing a priori the extent of the cathode arc attachment.Possible causes of this problem were investigated. It was concluded that the physical state of the arcing gas tungsten cathode was too simplified by the existing models. This oversimplification results in an overestimation of the cathode arc attachment area and an underestimation of the arc temperature field.An improved model was developed based only on physical criteria. It was tested by comparison with experimental measurements available in the literature. Good agreement with the temperature measured on the cathode surface and within the arc were obtained.

  • 8. Davies, P.
    et al.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Welding Technology. Institute of Structural Materials, College of Engineering, Swansea University, Bay Campus, Fabian Way, Swansea SA1 8EN, United Kingdom.
    Coleman, M.
    Institute of Structural Materials, College of Engineering, Swansea University, Bay Campus, Fabian Way, Swansea SA1 8EN, United Kingdom.
    Birosca, S.
    Institute of Structural Materials, College of Engineering, Swansea University, Bay Campus, Fabian Way, Swansea SA1 8EN, United Kingdom.
    The hierarchy of microstructure parameters affecting the tensile ductility in centrifugally cast and forged Ti-834 alloy during high temperature exposure in air2016In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 117, 51-67 p.Article in journal (Refereed)
    Abstract [en]

    Ductility regression is the main concern in using Ti-834 titanium alloy at temperatures above 500 °C for aerospace applications. The reduction of ductility in titanium alloys at high temperatures is strongly correlated to the exposure time. In the current study the effect of prolonged exposure at 500 °C on the tensile ductility of two differently processed Ti-834 alloys was investigated. In order to simulate actual Ti-834 processing routes, forged and centrifugally cast materials were used. The tensile tests were conducted on various specimens exposed at 500 °C for 100, 200 and 500 h to observe microstructure feature changes. Moreover, the effect of microstructure, microtexture, α-case, α2 and silicide precipitate coarsening during high temperature exposure was studied thoroughly. The cast alloy was found to have a minimum ductility and failed at 1.8% strain after exposure at 500 °C/500 h when the α-case layer was retained during testing, whilst, the ductility of the forged alloy was unaffected. The effects of individual microstructural parameters on the ductility regression in Ti-834 alloy were quantified. The results showed that 7.1% strain differences between the cast and forged alloy are related to microstructural variations including; morphology, lath widths, grain size and shape, grain orientations and microtexture. A total of 9.6% strain loss was observed in centrifugally cast Ti-834 after aging at 500°C/500 h and quantified as follow; 3.6% due to α-case formation during high temperature exposure, 0.2% due to α2-precipitates coarsening, 4.4% due to further silicide formation and coarsening, 1.4% due to additional microstructure changes during high temperature exposure. Furthermore, silicide coarsening on α/β phase boundaries caused large void formation around the precipitates. A theoretical model supported by experimental observations for silicide precipitation in fully colony and duplex microstructures was established. The element partitioning during exposure caused Al and Ti depletion in the vicinity of the β phase in the lamellae, i.e., αs area. This resulted in lowering the strength of the alloy and facilitated the formation of Ti3(SiZr)2 precipitates. The Al depletion and nano-scale partitioning observed at the αs/β boundaries resulted in easy crack initiation and promoted propagation in the centrifugally cast colony microstructure and reduced the basal slip τcrss. Furthermore, silicides were not formed in αp (high Al, Ti and low Zr areas) in the forged duplex microstructure that promoted superior mechanical performance and ductility over the cast alloy.

    Graphical abstract

  • 9.
    de Souza Amaral, Thiago
    et al.
    CBMM, Araxá, MG, Brasil.
    Carboneri Carboni, Marcelo
    CBMM, São Paulo, SP, Brasil.
    Scotti, Americo
    University West, Department of Engineering Science, Division of Welding Technology. Universidade Federal de Uberlândia – UFU, Uberlândia, MG, Bras.
    Avaliação da Aplicação de um Atlas de Soldagem de um Aço Bainítico Microligado ao Nióbio: Application Assessment of a Welding Atlas of a Niobium Microalloyed Bainitic Steel2017In: Soldagem & Inspeção, ISSN 0104-9224, E-ISSN 1980-6973, Vol. 22, no 2, 163-173 p.Article in journal (Refereed)
    Abstract [en]

    Niobium microalloyed steels have shown to be an excellent solution for fabrication of structural beams, employing concepts already developed for the oil and gas industry. However, the definition of the actual welding related needs of this family of bainite steels is not well described in the welding standards mostly used in the structural construction sector. This paper demonstrates the construction and assessment of a Welding Atlas, built from using physical simulations (Gleeble and dilatrometry) and mechanical tests of the simulated specimens. The objective is to have the Atlas as a guiding tool to improve the parametrization for welding this class of steels. The proposal methodology was applied to a HSLA bainitic steel class 65 ksi. It was possible to determine with more accuracy the recommended energy range of the weld, including the need or not of preheating, and show that they were comparable with actual welds. The methodology shows benefits including a safer parametrization and cost savings resulting from unnecessary preheating elimination.

  • 10.
    Edberg, J.
    et al.
    Luleå University of Technology, 971 87 Luleå, Sweden.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Use of Indicators for Hot and Warm Cracking in Welded Structures2017In: Procedia Manufacturing, ISSN 2351-9789, Vol. 7, 145-150 p.Article in journal (Refereed)
    Abstract [en]

    Weight reduction of mechanical components is becoming increasingly important as a way to provide more environment friendly production and operation of different equipment. This is true in almost any manufacturing industry, but is especially important to the aerospace industry. Casting has often been replaced by hot and cold metal working operations and welding, usually including an additional heat treatment. This gives components better material properties and provides components with less weight and cost but with increased strength and efficiency. This may even be true for rotating Ni- based superalloy components, and is enabled by welding methods. However, weld cracking of precipitation hardening Ni-based superalloys is a serious problem, both in manufacturing and overhaul since it endangers component life if cracks are allowed to propagate. Cracks can appear in a weld and in it’s surroundings. The triggering mechanisms depend on its location and when it is nucleated. Generally saying, weld cracking in precipitation hardening Ni-based superalloys consists of two different types of cracking, hot cracking and warm cracking which may be further divided into heat affected zone (HAZ) liquation cracking, solidification cracking and strain age cracking, respectively. Finite element simulations of welding and heat treatment processes started in the seventies for small laboratory set-up cases and have today matured, and are now used on large-scale structures like aerospace components. But FE-based crack criteria that can predict the risk of cracking due to welding or heat treatments are rare. In a recent study both hot cracking and warm cracking have been investigated in Ni-based superalloys, and two FE-based indicators showing the risk of hot and warm cracks have been proposed. The objective of the investigation presented in this paper is to compare results from FE-simulations with experimental results from weldability tests, like the Varestraint test and the high temperature mechanical Gleeble test. © 2016

  • 11.
    Edberg, Jonas
    et al.
    Luleå University of Technology, Sweden.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Use of indicators for hot and warm cracking in welded structures2016In: Procedia Manufacturing, ISSN 1873-6580, E-ISSN 2212-0173, Vol. 7, 145-150 p.Article in journal (Refereed)
    Abstract [en]

    Weight reduction of mechanical components is becoming increasingly important as a way to provide more environment friendly production and operation of different equipment. This is true in almost any manufacturing industry, but is especially important to the aerospace industry. Casting has often been replaced by hot and cold metal working operations and welding, usually including an additional heat treatment. This gives components better material properties and provides components with less weight and cost but with increased strength and efficiency. This may even be true for rotating Ni- based superalloy components, and is enabled by welding methods. However, weld cracking of precipitation hardening Ni-based superalloys is a serious problem, both in manufacturing and overhaul since it endangers component life if cracks are allowed to propagate.

    Cracks can appear in a weld and in it's surroundings. The triggering mechanisms depend on its location and when it is nucleated. Generally saying, weld cracking in precipitation hardening Ni-based superalloys consists of two different types of cracking, hot cracking and warm cracking which may be further divided into heat affected zone (HAZ) liquation cracking, solidification cracking and strain age cracking, respectively.

    Finite element simulations of welding and heat treatment processes started in the seventies for small laboratory set-up cases and have today matured, and are now used on large-scale structures like aerospace components. But FE-based crack criteria that can predict the risk of cracking due to welding or heat treatments are rare. In a recent study both hot cracking and warm cracking have been investigated in Ni-based superalloys, and two FE-based indicators showing the risk of hot and warm cracks have been proposed. The objective of the investigation presented in this paper is to compare results from FE-simulations with experimental results from weldability tests, like the Varestraint test and the high temperature mechanical Gleeble test.

  • 12.
    Fahlström, Karl
    et al.
    University West, Department of Engineering Science, Research Enviroment Production Technology West. Swerea KIMAB in Kista.
    Andersson, O.
    Volvo Cars in Torslanda & KTH in Stockholm, Sweden.
    Melander, A.
    Swerea KIMAB in Kista, Sweden.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Correlation between laser welding sequence and distortions for thin sheet structures2017In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, Vol. 22, no 2, 150-156 p.Article in journal (Refereed)
    Abstract [en]

    Thin ultra-high strength steel shaped as 700 mm long U-beams have been laser welded in overlap configuration to study the influence of welding sequence on distortions. Three different welding directions, three different energy inputs as well as stitch welding have been evaluated, using resistance spot welding (RSW) as a reference. Transverse widening at the ends and narrowing at the centre of the beam were measured. A clear correlation was found between the weld metal volume and distortion. For continuous welds there was also a nearly linear relationship between the energy input and distortion. However, the amount of distortion was not affected by a change in welding direction. Stitching and RSW reduced distortion significantly compared to continuous laser welding.

  • 13.
    Fahlström, Karl
    et al.
    University West, Department of Engineering Science, Research Enviroment Production Technology West. University West, Department of Engineering Science, Research Environment Production Technology West.
    Andersson, Oscar
    Volvo Cars, Torslanda, Sweden.
    Karlsson, Leif
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Production Engineering. University West, Department of Engineering Science, Division of Welding Technology.
    Metallurgical effects and distortions in laser welding of thin sheet steels with variations in strength2017In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, Vol. 22, no 7, 573-579 p.Article in journal (Refereed)
    Abstract [en]

    Geometrical distortions occur while welding, but the understanding of how and why they occur and how to control them is limited. The relation between the weld width, weld metal volume, total energy input, width of hard zone and distortions when laser welding three different thin sheet steels with varying strength has therefore been studied. Weld metal volume and total energy input show a good correlation with distortion for one steel at a time. The best correlation with the when including all three steel grades was the width of the hard zone composed of weld metal and the martensitic area in the heat affected zone. © 2017 Institute of Materials, Minerals and Mining. Published by Taylor & Francis on behalf of the Institute.

  • 14.
    Hanning, Fabian
    et al.
    Chalmers University of Technology, Department of Materials and Manufacturing Technology, Gothenburg, Sweden.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    A Review of Strain Age Cracking in Nickel Based Superalloys2016In: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings: 25th – 27th of October 2016, Lund: Swedish Production Academy , 2016, 1-7 p.Conference paper (Refereed)
    Abstract [en]

    This paper reviews the literature with emphasis on strain age cracking, a cracking phenomenon that can occur during welding or heat treatment of precipitation hardening superalloys. The influence of chemical composition in terms of e.g. hardening elements and impurities, microstructure of base material and weld zone, precipitation-induced stress development, welding heat input, restraint and post weld heat treatment (PWHT) conditions is discussed and related to the cracking susceptibility of different nickel based superalloys. Furthermore, an overview on available testing methods is presented and scrutinized. As of now, neither a standardized nor universally applicable procedure is available where the now existing tests generally can be divided into two groups; procedures representing actual welds usually providing qualitative comparisons under specified conditions, and simulative tests like those based on the Gleeble® system which can provide fundamental insight into the ongoing mechanisms.

  • 15.
    Harati, Ebrahim
    University West, Department of Engineering Science, Division of Welding Technology.
    Improving fatigue properties of welded high strength steels2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In recent years a strong interest has been expressed to produce lighter structures.One possible solution to reduce the weight is to utilize high strength steels and use welding as the joining method. Many components experience fatigue loadingduring all or part of their life time and welded connections are often the prime location of fatigue failure. This becomes more critical in welded high strength steels as fatigue strength of welds does not increase by increasing the steel strength. A possible solution to overcome this issue is to use fatigue improvement methods.The main objectives of this project are, therefore, to increase understanding of the factors that control fatigue life and to investigate how the fatigue strength improvement methods; high frequency mechanical impact (HFMI) treatment and use of Low Transformation Temperature (LTT) consumables will affect fatigue properties of welds in high strength steels. In this regard, Gas Metal Arc Welding(GMAW) was used to produce butt and fillet welds using LTT or conventional fillers in steels with yield strengths ranging from 650-1021 MPa and T-joint weldsin a steel with 1300 MPa yield strength. The effect of HFMI on fatigue strength of the welds in 1300 MPa yield strength steels was also investigated. Butt and fillet welds in 650-1021 MPa steels were fatigue tested under constant amplitude tensile loading with a stress ratio of 0.1 while T-joints were fatigue tested under constant amplitude fully reversed bending load with a stress ratio of -1. The nominal stress approach was used for fatigue strength evaluation of butt and fillet welds whereas the effective notch stress approach was used in case of T-joints. Relative effectsof the main parameters such as residual stress and weld toe geometry influencing fatigue strength of welds were evaluated. Residual stresses were measured using X-ray diffraction for as-welded and HFMI treated welds. Neutron diffraction was additionally used to investigate the near surface residual stress distribution in 1300 MPa LTT welds.Results showed that use of LTT consumables increased fatigue strength of welds in steels with yield strengths ranging from 650-1021 MPa. For butt welds, the vii characteristic fatigue strength (FAT) of LTT welds at 2 million cycles was up to46% higher when compared to corresponding welds made with conventional fillermaterials. In fillet welds, a maximum improvement of 132% was achieved when using LTT wires. The increase in fatigue strength was attributed to the lower tensile residual stresses or even compressive stresses produced close to the weldtoe in LTT welds. Weld metals with martensite transformation start temperatures around 200 °C produced the highest fatigue strength. In 1300 MPa yield strength steel, similar FAT of 287 MPa was observed for LTT welds and 306 MPa for conventional welds, both much higher than the IIW FATvalue of 225 MPa. The relative transformation temperatures of the base and weldmetals, specimen geometry and loading type are possible reasons why the fatigue strength was not improved by use of LTT wires. Neutron diffraction showed that the LTT consumable was capable of inducing near surface compressive residual stresses in all directions at the weld toe. It was additionally found that there arevery steep stress gradients both transverse to the weld toe line and in the depth direction, at the weld toe. Due to difficulties to accurately measure residual stresses locally at the weld toe most often in the literature and recommendations residual stresses a few millimetre away from the weld toe are related to fatigue properties. However, this research shows that caution must be used when relating these to fatigue strength, in particular for LTT welds, as stress in the base materiala few millimetre from the weld toe can be very different from the stress locally at the weld toe.HFMI increased the mean fatigue strength of conventional welds in 1300 MPa steels about 26% and of LTT welds by 13%. It increased the weld toe radius slightly but produced a more uniform geometry along the treated weld toes. Large compressive residual stresses, especially in the longitudinal direction, were introduced adjacent to the weld toe for both LTT and conventional treated welds. It was concluded that the increase in fatigue strength by HFMI treatment is due to the combined effect of weld toe geometry modification, increase in surface hardness and introduction of compressive residual stresses in the treated region.It was concluded that the residual stress has a relatively larger influence than the weld toe geometry on fatigue strength of welds. This is based on the observation that a moderate decrease in residual stress of about 15% at the 300 MPa stress level had the same effect on fatigue strength as increasing the weld toe radius by approximately 85% from 1.4 mm to 2.6 mm, in fillet welds. Also, a higher fatigue strength was observed for HFMI treated conventional welds compared to as welded samples having similar weld toe radii but with different residual stresses.

  • 16.
    Harati, Ebrahim
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Dalaei, Kamellia
    ESAB AB, Lindholmsallen 9, 40227 Gothenburg.
    Applicability of Low Transformation Temperature welding consumables to increase fatigue strength of welded high strength steels2017In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 97, 39-47 p.Article in journal (Refereed)
    Abstract [en]

    Application of Low Transformation Temperature (LTT) consumables in welding is a recent approach to increase the fatigue strength of welds. In this paper high strength steels with yield strengths ranging from 650-1021 MPa were fillet and butt welded using different LTT and conventional consumables. The effects of weld metal chemical composition on phase transformation temperatures, residual stresses and fatigue strength were investigated. Lower transformation start temperatures and hence lower tensile or even compressive residual stresses were obtained close to the weld toe for LTT welds. Fatigue testing showed very good results for all combinations of LTT consumables and high strength steels with varying strength levels. For butt welds, the characteristic fatigue strength (FAT) of LTT welds at 2 million cycles was up to 46% higher when compared to corresponding welds made with conventional filler materials. In fillet welds, a minimum FAT improvement of 34% and a maximum improvement of 132% was achieved when using LTT wires. It is concluded that different LTT consumables can successfully be employed to increase fatigue strength of welds in high strength steels with yield strength up to 1021 MPa. Weld metals with martensite transformation start temperatures close to 200°C result in the highest fatigue strengths.

  • 17.
    Harati, Ebrahim
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Pirling, Thilo
    Institut Max von Laue-Paul Langevin, 6 rue Jules Horowitz, BP156, F-38042 Grenoble, France.
    Dalaei, Kamellia
    ESAB AB, Lindholmsallen 9, 40227 Gothenburg, Sweden.
    Neutron Diffraction Evaluation of Near Surface Residual Stresses at Welds in 1300 MPa Yield Strength Steel2017In: Materials, E-ISSN 1996-1944, Vol. 10, no 6, 1-14 p., E593Article in journal (Refereed)
    Abstract [en]

    Evaluation of residual stress in the weld toe region is of critical importance. In this paper, the residual stress distribution both near the surface and in depth around the weld toe was investigated using neutron diffraction, complemented with X-ray diffraction. Measurements were done on a 1300 MPa yield strength steel welded using a Low Transformation Temperature (LTT) consumable. Near surface residual stresses, as close as 39 µm below the surface, were measured using neutron diffraction and evaluated by applying a near surface data correction technique. Very steep surface stress gradients within 0.5 mm of the surface were found both at the weld toe and 2 mm into the heat affected zone (HAZ). Neutron results showed that the LTT consumable was capable of inducing near surface compressive residual stresses in all directions at the weld toe. It is concluded that there are very steep stress gradients both transverse to the weld toe line and in the depth direction, at the weld toe in LTT welds. Residual stress in the base material a few millimeters from the weld toe can be very different from the stress at the weld toe. Care must, therefore, be exercised when relating the residual stress to fatigue strength in LTT welds.

  • 18.
    Harati, Ebrahim
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Improving fatigue strength of welded 1300 MPa yield strength steel using HFMI treatment or LTT fillers2017In: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 79, no September, 64-74 p.Article in journal (Refereed)
    Abstract [en]

    Fatigue improvement techniques are widely used to increase fatigue strength of welded high strength steels. In this paper high frequency mechanical impact (HFMI) and a Low Transformation Temperature (LTT) filler material were employed to investigate the effect on fatigue strength of welded 1300 MPa yield strength steel. Fatigue testing was done under fully reversed, constant amplitude bending load on T-joint samples. Fatigue strength of LTT welds was the same as for welds produced using a conventional filler material. However, HFMI treatment increased the mean fatigue strength of conventional welds about 26% and of LTT welds about 13%. Similar distributions of residual stresses and almost the same weld toe radii were observed for welds produced using LTT and conventional consumables. HFMI increased the weld toe radius slightly and produced a more uniform geometry along the treated weld toes. Relatively large compressive residual stresses, adjacent to the weld toe were produced and the surface hardness was increased in the treated region for conventional welds after HFMI. For this specific combination of weld geometry, steel strength and loading conditions HFMI treatment gave higher fatigue strength than LTT consumables.

  • 19.
    Harati, Ebrahim
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Welding Technology.
    Effect of HFMI treatment procedure on weld toe geometry and fatigue properties of high strength steel welds2016In: Procedia Structural Integrity, 2016, Vol. 2, 3483-3490 p.Conference paper (Refereed)
    Abstract [en]

    The effects of high frequency mechanical impact (HFMI) treatment procedure on the weld toe geometry and fatigue strength in 1300 MPa yield strength steel welds were investigated. In this regard first the effect of three or six run treatments on the weld toe geometry was evaluated. The fatigue strength and weld toe geometry of as-welded and HFMI treated samples was then compared. Fatigue testing was done under fully reversed, constant amplitude bending load. When increasing the number of treatment runs from three to six, the weld toe radius and width of treatment remained almost constant. However, a slightly smaller depth of treatment in the base metal and a somewhat larger depth of treatment in the weld metal was observed. HFMI treatment increased the fatigue strength by 26%. The treatment did not increase the weld toe radius significantly, but resulted in a more uniform weld toe geometry along the weld. A depth of treatment in the base metal in the range of 0.15-0.19 mm and a width of treatment in the range of 2.5-3 mm, were achieved. It is concluded that the three run treatment would be a more economical option than the six run treatment providing a similar or even more favourable geometry modification.

  • 20.
    Harati, Ebrahim
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Widmark, Mattias
    Material Technology, Volvo Group Trucks Technology, Gothenburg, Sweden.
    Effect of high frequency mechanical impact treatment on fatigue strength of welded 1300 MPa yield strength steel2016In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 92, 96-106 p.Article in journal (Refereed)
    Abstract [en]

    High frequency mechanical impact (HFMI) is a recent post weld treatment method which can be employed to increase the fatigue strength of welded components. In this paper the fatigue strength of as-welded and HFMI treated fillet welds in a 1300 MPa yield strength steel was compared. Fatigue testing was done under fully reversed, constant amplitude bending load. Finite element analysis was used to calculate the stress distribution in the weld toe region to permit evaluation of the fatigue data with the effective notch stress approach. As-welded samples showed a mean fatigue strength of 353 MPa and a characteristic fatigue strength of 306 MPa. HFMI treatment increased the mean fatigue strength by 26% and the characteristic fatigue strengths by 3%. The weld toe radii in as-welded condition were large. HFMI only increased the weld toe radii slightly but resulted in a more uniform weld toe geometry along the weld. A depth of indentation in the base metal in the range of 0.15–0.19 mm and a width of indentation in the range of 2.5–3 mm, were achieved. Maximum compressive residual stresses of about 800 MPa in the longitudinal and 250 MPa in the transverse direction were introduced by HFMI treatment, adjacent to the weld toe. The surface hardness was increased in the entire HFMI treated region. It is concluded that the increase in fatigue strength is due to the combined effects of the weld toe geometry modification, increase in surface hardness and creation of compressive residual stresses in the treated region.

  • 21.
    Hosseini, Vahid
    University West, Department of Engineering Science, Division of Welding Technology.
    Influence of multiple welding cycles on microstructure and corrosion resistance of a super duplex stainless steel2016Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Super duplex stainless steel (SDSS) has found a wide use in demanding applications such as offshore, chemical and petrochemical industries thanks to its excellent combination of mechanical properties and corrosion resistance. Welding of SDSS, however, is associated with the risk of precipitation of secondary phases and formation of excessive amounts of ferrite in the weld metal and heat affected zone. The present study was therefore aimed at gaining knowledge about the effect of multiple welding thermal cycles on the microstructure and possible sensitization to corrosion of welds in SDSS.Controlled and repeatable thermal cycles were produced by robotic welding. Oneto four autogenous TIG-remelting passes were applied on 2507 type SDSS plates using low or high heat inputs with pure argon as shielding gas. Thermal cycles were recorded using several thermocouples attached to the plates. Thermodynamic calculations and temperature field modelling were performed in order to understand the microstructural development and to predict the pitting corrosion resistance. Etching revealed the formation of different zones with characteristic microstructures: the fused weld zone (WZ) and the heat affected zone composed of the fusion boundary zone (FBZ), next to the fusion boundary, and further out Zone 1 (Z1) and Zone 2 (Z2). The WZ had a high content of ferrite and often nitrides which increased with increasing number of passes and decreasing heati nput. Nitrogen content of the WZ decreased from 0.28 wt.% to 0.17 wt.% after four passes of low heat input and to 0.10 wt.% after four passes of high heatinput. The FBZ was reheated to high peak temperatures (near melting point) and contained equiaxed ferrite grains with austenite and nitrides. Zone 1 was free from precipitates and the ferrite content was similar to that of the unaffected base material. Sigma phase precipitated only in zone 2, which was heated to peak temperatures in the range of approximately 828°C to 1028°C. The content of sigma phase increased with the number of passes and increasing heat input. 

    All locations, except Z1, were susceptible to local corrosion after multiplere heating. Thermodynamic calculations predicted that a post weld heat treatment could restore the corrosion resistance of the FBZ and Z2. However, the pitting resistance of the WZ cannot be improved significantly due to the nitrogen loss. Steady state and linear fitting approaches were therefore employed to predict nitrogen loss in autogenous TIG welding with argon as shielding gas. Two practical formulas were derived giving nitrogen loss as functions of initial nitrogen content and arc energy both predicting a larger loss for higher heat input and higher base material nitrogen content. A practical recommendation based on the present study is that it is beneficial to perform welding with a minimum number of passes even if this results in a higherheat input as multiple reheating strongly promotes formation of deleterious phases.

  • 22.
    Hosseini, Vahid
    et al.
    University West, Department of Engineering Science, Division of Welding Technology. Innovatum AB, Trollhättan, Sweden.
    Aashuri, H.
    Sharif Univ Technol, Mat Sci & Engn Dept, Azadi Ave, Tehran, Iran.
    Kokabi, A. H.
    Sharif Univ Technol, Mat Sci & Engn Dept, Azadi Ave, Tehran, Iran.
    Effect of welding parameters on semisolid stir welding of Mg-9Al-1Zn magnesium alloy2016In: Transactions of Nonferrous Metals Society of China, ISSN 1003-6326, E-ISSN 2210-3384, Vol. 26, no 10, 2586-2594 p.Article in journal (Refereed)
    Abstract [en]

    Semisolid stir welding of AZ91 was investigated with focus on the joining temperature and rotational speed. An Mg-25% Zn interlayer was located between two AZ91 pieces and the system was heated up to the semisolid state of base metal and interlayer. The weld seam was stirred using a drill-tip at different joining temperatures and rotational speeds. Optical and scanning electron microscopes were employed to study microstructure, cavity formation, and segregation. Hardness profile and shear punch test were also employed to rank the welds based on their quality and homogeneity. Results showed that the lowest cavity content (2.1%) with the maximum ultimate shear strength (about 188 MPa) was obtained in weld with the joining temperature of 530 degrees C and the rotational speed of 1600 r/min. Low quality welds and a reduction of ultimate shear strength were observed at very high or low rotational speeds and joining temperatures. The process, in conclusion, produced close mechanical properties to those of the base metal and homogenous quality throughout the joint, when the intermediate temperature and rotational speeds were employed.

  • 23.
    Hosseini, Vahid
    et al.
    University West, Department of Engineering Science, Division of Welding Technology. Hogskolan Vast.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Effect of multipass TIG welding on the corrosion resistance and microstructure of a super duplex stainless steel2017In: Materials and corrosion - Werkstoffe und Korrosion, ISSN 0947-5117, E-ISSN 1521-4176, Vol. 68, no 4, 405-415 p.Article in journal (Refereed)
    Abstract [en]

    This is a study of the effect of repetitive TIG (tungsten inert gas) welding passes, melting and remelting the same material volume on microstructure and corrosion resistance of 2507 (EN 1.4410) super duplex stainless steel. One to four weld passes were autogenously (no filler added) applied on a plate using two different arc energies and with pure argon shielding gas. Sensitization testing showed that multipass remelting resulted in significant loss of corrosion resistance of the weld metal, in base material next to the fusion boundary, and in a zone 1 to 4 mm from the fusion boundary. Metallography revealed the main reasons for sensitization to be a ferrite-rich weld metal and precipitation of nitrides in the weld metal, and adjacent heat affected zone together with sigma phase formation at some distance from the fusion boundary. Corrosion properties cannot be significantly restored by a post weld heat treatment. Using filler metals with higher nickel contents and nitrogen containing shielding gases, are therefore, recommended. Welding with a higher heat input and fewer passes, in some cases, can also decrease the risk of formation of secondary phases and possible corrosion attack.

  • 24.
    Hosseini, Vahid
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Welding Technology.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Engelberg, Dirk
    The University of Manchester, School of Materials, Manchester M13 9PL, UK.
    Roy, Matthew J.
    The University of Manchester, School of Mechanical, Aerospace and Civil Engineering,Manchester M13 9PL, UK.
    Kumara, Chamara
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    A novel arc heat treatment technique for producing graded microstructures through controlled temperature gradients2017In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 121, no May, 11-23 p.Article in journal (Refereed)
    Abstract [en]

    This paper introduces a novel arc heat treatment technique to produce samples with graded microstructures through the application of controlled temperature gradients. Steady state temperature distributions within the sample can be achieved and maintained, for times ranging from a few seconds to several hours. The technique reduces the number of samples needed to characterize the response of a material to thermal treatments, and can consequently be used as a physical simulator for materials processing. The technique is suitable for conventional heat treatment analogues, welding simulations, multi-step heat treatments, and heat treatments with controlled heating and cooling rates. To demonstrate this technique, a super duplex stainless steel was treated with a stationary TIG arc, to confirm the relationship between generated steady-state temperature fields, microstructure development, hardness, and sensitization to corrosion. Metallographic imaging and hardness mapping provided information about graded microstructures, confirming the formation of secondary phases and microstructure sensitization in the temperature range 850–950 °C. Modelling of temperature distributions and thermodynamic calculations of phase stabilities were used to simulate microstructure development and associated welding cycles.

  • 25.
    Jacobsson, J
    et al.
    Department of Materials and Manufacturing Technology, Chalmers University of Technology, Gothenburg, Sweden; Research and Technology Department, GKN Aerospace Engine Systems, Trollhättan, Sweden.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Brederholm, Anssi
    Aalto University School of Engineering, Helsinki, Finland.
    Hänninen, Hannu
    Aalto University School of Engineering, Helsinki, Finland.
    Weldability of Ni-Based Superalloys Waspaloy® and Haynes® 282®: A Study Performed with Varestraint Testing2016In: Research & Reviews: Journal of Material Sciences, ISSN 2321-6212, Vol. 4, no 4Article in journal (Refereed)
    Abstract [en]

    There is a need for materials with high strength, oxidation resistance, thermal stability and adequate weldability in order to facilitate the production of large structural jet engine components. Therefore, the weldability of Waspaloy® and Haynes® 282® have been evaluated using the Varestraint weldability test. The experiments reveal that Waspaloy® has a higher susceptibility to hot cracking compared to Haynes® 282®. This conclusion is supported by increased total crack length (10 mm or more) and larger brittle temperature range (approx. 65°C) for Waspaloy® when compared to Haynes® 282® in Varestraint and Gleeble hot ductility tests, respectively. The cracking in Haynes® 282® seems to be connected with a secondary phase which presumably can be associated with Ti-Mo based MC-type carbide observed in the fusion zone. Also, a surrounding segregated area is present near this secondary phase as well as along the grain boundaries. Furthermore, micro-Vickers hardness results revealed more or less the same weld metal hardness (260- 280 HV) but a difference in the base metal hardness. The weld metal hardness of Waspaloy® was lower than that of the base metal hardness, while Haynes® 282® had a higher hardness in comparison.

  • 26.
    Jacobsson, Jonny
    et al.
    Department of Materials and Manufacturing Technology, Chalmers University of Technology, Gothenburg, Sweden / Research and Technology Department, GKN Aerospace Engine Systems, Trollhättan, Sweden.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Brederholm, Anssi
    Aalto University School of Engineering, Helsinki, Finland.
    Hänninen, Hannu
    Aalto University School of Engineering, Helsinki, Finland.
    Weldability Study of Superalloys Waspaloy® and Haynes® 282®2016In: 10th International Conference on Trends in Welding Research & 9th International Welding Symposium of Japan Welding Society (9WS), October 11-14, 2016, Tokyo, Japan: Proceedings, 2016, 325-328 p.Conference paper (Other academic)
    Abstract [en]

    The weldability of Waspaloy® and Haynes® 282® have been evaluated using the Varestraint weldability test. The experiments reveal that Waspaloy® has a higher susceptibility to hot cracking compared to Haynes® 282®. This conclusion is supported by increased total crack length (10 mm or more) for Waspaloy® when compared to Haynes® 282® in Varestraint test. The cracking in Haynes® 282® seems to be connected with a secondary phase which presumably can be associated with Ti-Mo based MC-type carbide observed in the fusion zone. Also, a surrounding segregated area is present near this secondary phase as well as along the grain boundaries. Furthermore, micro-Vickers hardness results revealed more or less the same weld metal hardness (260-280 HV) but a difference in the base metal hardness. The weld metal hardness of Waspaloy® was lower than that of the base metal hardness, while Haynes® 282® had a higher hardness in comparison.

  • 27.
    Javidi Shirvan, Alireza
    University West, Department of Engineering Science, Avdelningen för svetsteknologi (SV).
    Modelling of cathode-plasma interaction in short high-intensity electric arc: Application to Gas Tungsten Arc Welding2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In arc welding the quality of the weld is strongly influenced by the thermal history of the workpiece which is itself governed by the electric arc heat source. The models for predicting weld properties thus need a good evaluation of the distribution of the heat input from thearc to the workpiece. To have a predictive model of arc heat source it is necessary to take into account the cathode and its coupling with the plasma. The coupling allows to calculate the temperature and current density distributions along the cathode surface rather than prescribing them. This thesis focuses on the arc-cathode coupling for a plasma assumed to be in local thermal equilibrium. A self-consistent coupling boundary model for high-intensity electric arc on a refractory cathode (thoriated tungsten) was developed accounting for the physics of the sub-layers of the cathode layer and the non-uniformity of the cathode surface physical state. The cathode layer model accounts for the non-equilibria in the cathode layer. It was tested in one-dimensional calculations and then extended to a cathode-plasma coupling boundary condition for gas tungsten arc implemented in OpenFOAM. Different modelling assumptions commonly used for developing the model were questioned and investigated. It was checked that the secondary electron emission is negligible compared to the effect of emitted electrons and ions. It was verified that it is justified to neglect the space charge of emitted electron when calculating the cathode surface electric field. It was verified that Richardson-Dushman electron emission law supplemented with Schottky correction is used within its domain of validity in GTA applications even for low work function emitters. It was shown that the radiative absorption of the cathode surface is not negligible compared to the radiative emission. The cathode layer model was also further developed to take into account the in homogeneity of the cathode material. It was shown that the cathode in homogeneityhas a significant effect on the size of the arc attachment and consequently on the cathode surface and the plasma temperature. Good agreement was obtained with the measured cathode surface and plasma temperatures without imposing any adjustable parameters. The results showed that the proposed model, which is only based on physical principles, is ableto predict the trends observed experimentally.

  • 28.
    Javidi Shirvan, Alireza
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Nilsson, Håkan
    Chalmers University of Technology.
    Effect of cathode model on arc attachment for short high-intensity arc on a refractory cathode2016In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 49, no 3 November 2016, 1-17 p., 485201Article in journal (Other academic)
    Abstract [en]

    Various models coupling the refractory cathode, the cathode sheath and the arc at atmospheric pressure exist. They assume a homogeneous cathode with a uniform physical state, and differ by the cathode layer and the plasma arc model. However even the most advanced of these models still fail in predicting the extent of the arc attachment when applied to short high-intensity arcs such as gas tungsten arcs. Cathodes operating in these conditions present a non-uniform physical state. A model taking into account the first level of this non-homogeneity is proposed based on physical criteria. Calculations are done for 5 mm argon arcs with a thoriated tungsten cathode. The results obtained show that radiative heating and cooling of the cathode surface are of the same order. They also show that cathode inhomogeneity has a significant effect on the arc attachment, the arc temperature and pressure. When changing the arc current (100 A, 200 A) the proposed model allows predicting trends observed experimentally that cannot be captured by the homogeneous cathode model unless restricting a priori the size of the arc attachment. The cathode physics is thus an important element to include to obtain a comprehensive and predictive arc model

  • 29.
    Javidi Shirvan, Alireza
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Nilsson, Håkan
    Chalmers University of Technology, 412 96 Gothenburg, Sweden.
    Jasak, Hrvoje
    University of Zagreb, Faculty of Mechanical Engineering and Naval Architecture, 10 000 Zagreb, Croatia.
    Coupling boundary condition for high-intensity electric arc attached on a non-homogeneous refractory cathode2017In: Computer Physics Communications, ISSN 0010-4655Article in journal (Refereed)
    Abstract [en]

    The boundarycoupling high-intensity electricarc and refractory cathode is characterized bythree sub- layers: the cathode sheath,the Knudsen layerand the pre-sheath. A self-consistent coupling boundarycondition accounting for these three sub-layers is presented; its novel propertyis to take into account a non-uniform distribution of electronemitters on the surface of the refractory cathode. This non- uniformity is due to cathode non-homogeneity induced by arcing.The computational model is appliedto a one-dimensional test case to evaluate the validity of different modelingassumptions. It is also applied coupling a thoriated tungstencathode with an argon plasma(assumed to be in local thermal equilibrium) to compare the calculation results with uniform and non-uniform distribution of the electron emitters to experimental measurements. The resultsshow that the non-uniformity of the electronemitters’ distribution has a significant effect on the calculated properties. It leads to good agreementwith the cathode surfacetemperature, and with the plasmatemperature in the hottest region.Some differences are observedin colder plasmaregions, where deviation from local thermalequilibrium is known to occur.

  • 30.
    Javidi Shirvan, Alireza
    et al.
    University West, Department of Engineering Science, Avdelningen för svetsteknologi (SV).
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Nilsson, Håkan
    Chalmers University of Technology.
    Jasak, Hrvoje
    Chalmers University of Technology.
    Coupling boundary condition for high-intensity electricarc attached on a non-homogeneous refractory cathode2016Article in journal (Other academic)
  • 31.
    Neikter, Magnus
    et al.
    Luleå University of Technology, Division of Materials Science, Luleå.
    Åkerfeldt, P
    Luleå University of Technology, Division of Materials Science, Luleå.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Welding Technology.
    Antti, M-L
    Luleå University of Technology, Division of Materials Science, Luleå.
    Microstructure characterisation of Ti-6Al-4V from different additive manufacturing processes2017In: IOP Conference Series: Materials Science and Engineering, IOP Science , 2017, Vol. 258, 012007Conference paper (Refereed)
    Abstract [en]

    The focus of this work has been microstructure characterisation of Ti-6Al-4V manufactured by five different additive manufacturing (AM) processes. The microstructure features being characterised are the prior β size, grain boundary α and α lath thickness. It was found that material manufactured with powder bed fusion processes has smaller prior β grains than the material from directed energy deposition processes. The AM processes with fast cooling rate render in thinner α laths and also thinner, and in some cases discontinuous, grain boundary α. Furthermore, it has been observed that material manufactured with the directed energy deposition processes has parallel bands, except for one condition when the parameters were changed, while the powder bed fusion processes do not have any parallel bands.

  • 32.
    Panwisawas, C.
    et al.
    University of Birmingham, School of Metallurgy and Materials, UK.
    Sovani, Y.
    University of Birmingham, School of Metallurgy and Materials, UK.
    Anderson, M.J.
    University of Birmingham, School of Metallurgy and Materials, UK.
    Turner, R.
    University of Birmingham, School of Metallurgy and Materials, UK.
    Palumbo, N. M.
    Rolls-Royce plc, Derby, UK.
    Saunders, B. C.
    Rolls-Royce plc, Derby, UK.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Brooks, J.W.
    University of Birmingham, School of Metallurgy and Materials, UK.
    Basoalto, H.C.
    University of Birmingham, School of Metallurgy and Materials, UK.
    A Multi-scale Multi-physics Approach to Modelling of Additive Manufacturing in Nickel-based Superalloys2016In: Superalloys 2016: Proceedings of the 13th International Symposium on Superalloys / [ed] M. Hardy, E. Huron, U. Glatzel, B. Griffin, B. Lewis, C. Rae, V. Seetharaman och S. Tin, Minerals, Metals & Materials Society, 2016, 1021-1030 p.Conference paper (Refereed)
    Abstract [en]

    A multi-scale, multi-physics modelling framework of selective laser melting (SLM) in the nickel-based superalloy IN718 is presented. Representative powder-bed particle distribution is simulated using the measured size distribution from experiment. Thermal fluid dynamics calculations are then used to predict melting behaviour, sub-surface morphology, and porosity development during a single pass scanning of the SLM process. The results suggest that the pores and uneven surface structure are exacerbated by increasing powder layer thicknesses. Predicted porosity volume fraction is up to 12% of the single track when 5 statistical powder distributions are simulated for each powder layer thickness. Processing-induced microstructure is predicted by linking cellular automatons – finite element calculations indicate further that the cooling rate is about 4400 o C/s and grain growth strongly follows the thermal gradient giving rise to a columnar grain morphology if homogeneous nucleation is assumed. Random texture is likely for as-fabricated SLM single pass with approximately 8 Pm and 6 Pm grain size for 20 Pm and 100 Pm powder layer thickness fabrication. Use has been made of the cooling history to predict more detailed microstructure using a γ" precipitation model. With the short time scale of solidification and rapid cooling, it becomes less likely that γ" precipitation will be observed in the condition investigated unless a prolonged hold at temperature is carried out. Future work on extension of the proposed multiscale modelling approach on microstructure predictions in SLM to mechanical properties will be discussed.

  • 33.
    Panwisawas, Chinnapat
    et al.
    School of Metallurgy and Materials, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
    Sovani, Yogesh
    School of Metallurgy and Materials, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
    Turner, Richard P.
    School of Metallurgy and Materials, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
    Brooks, Jeffery W.
    School of Metallurgy and Materials, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
    Basoalto, Hector C.
    School of Metallurgy and Materials, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Modelling of thermal fluid dynamics for fusion welding2017In: Journal of Materials Processing Technology, ISSN 0924-0136, Vol. 252, no February, 176-182 p.Article in journal (Refereed)
    Abstract [en]

    A fluid dynamics approach to modelling of fusion welding in titanium alloys is proposed. The model considers the temporal and spatial evolution of liquid metal/gas interface to capture the transient physical effects during the heat source–material interaction of a fusion welding process. Melting and vaporisation have been considered through simulation of all interfacial phenomena such as surface tension, Marangoni force and recoil pressure. The evolution of the metallic (solid and liquid) and gaseous phases which are induced by the process enables the formation of the keyhole, keyhole dynamics, and the fully developed weld pool geometry. This enables the likelihood of fluid flow-induced porosity to be predicted. These features are all a function of process parameters and formulated as time-dependent phenomena. The proposed modelling framework can be utilised as a simulation tool to further develop understanding of defect formation such as weld-induced porosity for a particular fusion welding application. The modelling results are qualitatively compared with available experimental information.

  • 34.
    Raza, Tahira
    University West, Department of Engineering Science, Division of Welding Technology.
    A review of selective laser melting: Process parameters and its influence on microstructure, defects and strength in superalloy Alloy 718.2016Conference paper (Other academic)
  • 35.
    Raza, Tahira
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, L. E.
    University West, Department of Engineering Science, Division of Welding Technology.
    A review of the effect of selective laser melting process parameters and its influence on microstructure, defects and strength in the iron-nickel based superalloy Alloy 7182016In: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings: 25th – 27th of October 2016, Lund: Swedish Production Academy , 2016, 1-8 p.Conference paper (Refereed)
    Abstract [en]

    This review presents a basic insight into the powder-bed fusion process selective laser melting (SLM), with focus on the microstructure and mechanical properties of the iron-nickel based superalloy Alloy 718. The microstructures and mechanical properties of SLM components are highly affected by the process parameters. Laser power, scanning speed, powder layer thickness and hatch distance, are the primary process parameters which can be adjusted in order to influence the microstructure and minimize potential defects. SLM-manufactured Alloy 718 generally produce a columnar microstructure which is a result of epitaxial formation and dendritic grain growth in the build direction (perpendicular to the substrate). Gas porosity, lack of fusion and residual stresses are process induced problems observed in SLM-manufactured Alloy 718. The microstructure of the as-manufactured Alloy 718 is susceptible to microsegregation of Nb and Mo as well as to subsequent non-equilibrium phase transformation. A post-process heat treatment of as-manufactured Alloy 718 is required in order to improve general mechanical properties and to relieve the residual stresses. The tensile strength, yield strength and hardness of heat treated SLM-manufactured Alloy 718 are comparable to that of wrought material.

  • 36.
    Rehan, Arbab
    et al.
    University West, Department of Engineering Science, Research Enviroment Production Technology West. Uddeholms AB, Hagfors, Sweden.
    Medvedeva, Anna
    Uddeholms AB, Hagfors, Sweden.
    Högman, Berne
    Uddeholms AB, Hagfors, Sweden.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Effect of Austenitization and Tempering on the Microstructure and Mechanical Properties of a 5 wt% Cr Cold Work Tool Steel2016In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 12, no 1 December, 1609-1618 p.Article in journal (Refereed)
    Abstract [en]

    The effects of austenitization and tempering temperatures for a 5 wt% Cr cold work tool steel are studied with an aim of understanding the influence on microstructure and mechanical properties. Microstructures are characterized with scanning electron microscopy and light optical microscopy. Retained austenite contents and martensite start temperatures are measured by X-ray diffraction and dilatometry, respectively. Hardness, impact toughness, and compressive yield strength are also determined. When the austenitization temperature is increased from 1020 or 1050 to 1075 °C, followed by tempering at 525 °C, significant hardness is gained while there is no increase in compressive yield strength. Higher austenitization temperatures also produce larger amounts of retained austenite. At the same time, the impact toughness is reduced due to coarsening of the martensitic microstructure. When the steel is tempered at 200 °C, a higher impact toughness and a higher volume fraction of retained austenite are observed. Retained austenite is not found after tempering at temperatures of 525 °C or above. It is concluded that the best combination of mechanical properties is achieved by austenitization at 1020 or 1050 °C followed by tempering at 525 °C.

  • 37.
    Rehan, Arbab
    et al.
    University West, Department of Engineering Science, Research Enviroment Production Technology West. Uddeholms AB, SE-683 85, Hagfors, Sweden.
    Medvedeva, Anna
    Uddeholms AB, SE-683 85, Hagfors, Sweden. .
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Effects of Austenitisation Temperature and Multiple Tempering on the Microstructure and Impact Toughness of a 5 wt. % Cr Cold Work Tool Steel2016In: 10th TOOL Conference, Tool, conference proceedings, 10th TOOL Conference , 2016, 1-10 p.Conference paper (Other academic)
    Abstract [en]

    The microstructure and properties of a 5 wt.% Cr cold work tool steel were studied after austenitisation at 1020°C, 1050°C or 1075°C followed by single, double and triple tempering treatments at 525°C. The microstructures were investigated with scanning electron microscopy and X-ray diffraction and phase transformations were studied by dilatometry. Furthermore, hardness and Charpy un-notched and V-notched impact toughness testing was performed and results were correlated to observed microstructures. With higher austenitisation temperature, the martensite and bainite start temperatures were lowered resulting in microstructures containing a higher volume fraction of retained austenite. Retained austenite transformed into martensite on cooling from the tempering temperature. Specimens that were austenitised at 1050°C or 1075°C and tempered twice contained fresh martensite. Applying a third tempering was therefore required to guarantee a fully tempered microstructure. The second tempering resulted in an increase of the un-notched impact energy while the third tempering did not have a pronounced effect. A triple tempering procedure could be preferable when austenitising at high temperatures to avoid undesirable fresh martensite in the tool microstructure.

  • 38.
    Rehan, Arbab
    et al.
    University West, Department of Engineering Science, Research Enviroment Production Technology West. Dept. of Material Technology, Uddeholms AB, Hagfors, Sweden.
    Medvedeva, Anna
    Uddeholms AB.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Retained austenite transformation during heat treatment of a 5wt.% Cr cold work tool steelManuscript (preprint) (Other academic)
  • 39.
    Segerstark, Andreas
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, L. E.
    University West, Department of Engineering Science, Division of Welding Technology.
    Influence of Heat Input on Grain Structure in Thin-Wall Deposits using Laser Metal Powder Deposition2016In: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings: 25th – 27th of October 2016, Lund: Swedish Production Academy , 2016, -7 p.Conference paper (Refereed)
    Abstract [en]

    Laser metal deposition (LMD) is an additive manufacturing method which is used to deposit material directly onto a metal surface layer upon layer until a final component is achieved. The material used in this study is the nickel iron based superalloy Alloy 718. There is a strong thermal gradient associated with this method which generally produces columnar grains growing in the build-up direction. The preferred solidification orientation of the FCC matrix is in the (001) direction which makes it possible to build directionally solidified structures with epitaxial grains growing through the layers. In this study LMD with powder as additive has been used to build thin walled samples, multiple layers high. The main objectives of this research are to assess the influence of the heat input on the grain structure in LMD builds and evaluate how the morphology and texture of the grains are affected by the changes in process parameters. Two different parameter sets are compared where a high and a low heat input have been used. The two samples with different heat inputs have been evaluated using a scanning electron microscope coupled to an electron back scatter diffraction detector in order to obtain quantitative grains size measurements as well as crystallographic information. It was shown that the grain structure was considerably affected by the heat input where the high heat input produced a strong texture with columnar grains growing in the build-up direction. With a low heat input the grains became finer and, although elongated, the grains became more equiaxed.

  • 40.
    Segerstark, Andreas
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Investigation of laser metal deposited Alloy 718 onto an EN 1.4401 stainless steel substrate2017In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 97, no Supplement C, 144-153 p.Article in journal (Refereed)
    Abstract [en]

    This paper focuses on how process parameters affect the deposition of Alloy 718 onto an EN 1.4401 stainless steel substrate in terms of secondary phase formation, dilution and hardness. A columnar solidification structure with elongated grains growing in the direction normal to the substrate was observed for all parameters. In the interdendritic regions, phases with a high content of Niobium were identified. Scanning Electron Microscopy imaging and Energy Dispersive Spectroscopy measurements revealed these phases to most likely be Laves phase and Nb-carbides. Temperature measurements indicated no significant aging in the deposits. Considerable enrichment of iron was found in the initially deposited layers due to dilution from the substrate. The increased content of iron seemed to aid in forming constituents rich in niobium which, in turn, influenced the hardness. The highest mean hardness was noted in the sample with the lowest area fraction of Nb-rich constituents.

  • 41.
    Singh, Sukhdeep
    et al.
    Chalmers University of Technology, Department of Materials and Manufacturing Technology, Gothenburg, Sweden.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Review of Hot Cracking Phenomena in Austenitic Stainless Steels2016In: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings: 25th – 27th of October 2016, Lund: Swedish Production Academy , 2016, 1-7 p.Conference paper (Refereed)
    Abstract [en]

    Hot cracking is a phenomenon occurring during welding. Hot cracks that form in the fusion zone are named solidification cracking while cracking that takes place in the heat affected zone is referred to as liquation cracking. This paper reviews the hot cracking phenomena specifically of relevance to austenitic stainless steels. The currently existing main theories explaining solidification and liquation cracking are considered together with the influence of main parameters in relation to susceptibility towards hot cracking. Important factors are the base metal microstructure, primary solidification mode, solidification rate, distribution of delta ferrite, amount of nitrogen, level of impurities and minor elements.

  • 42.
    Skhabovskyi, Iaroslav
    et al.
    Laprosolda – Center for Research and Development of Welding Processes, Faculty of Mechanical Engineering, Universidade Federal de Uberlândia (UFU), Uberlândia, Brazil.
    Batista, Natassia Lona
    Materials and Technology Department, School of Engineering, Universidade Estadual Paulista (UNESP), Guaratinguetá, Brazil.
    Damato, Cesar Augusto
    ALLTEC Materiais Compostos, São José dos Campos, Brazil.
    Reis, Ruham Pablo
    Laprosolda – Center for Research and Development of Welding Processes, Faculty of Mechanical Engineering, Universidade Federal de Uberlândia (UFU), Uberlândia, Brazil.
    Botelho, Edson Cocchieri
    Materials and Technology Department, School of Engineering, Universidade Estadual Paulista (UNESP), Guaratinguetá, Brazil.
    Scotti, Americo
    University West, Department of Engineering Science, Division of Welding Technology. Laprosolda – Center for Research and Development of Welding Processes, Faculty of Mechanical Engineering, Universidade Federal de Uberlândia (UFU), Uberlândia, Brazil.
    Appraisal of fiber-metal laminate panels reinforced with metal pins deposited by CMT welding2017In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 180, no Supplement C, 263-275 p.Article in journal (Refereed)
  • 43.
    Steffenburg-Nordenström, Joachim
    et al.
    University West, Department of Engineering Science, Research Enviroment Production Technology West. GKN Aerospace Sweden.
    Pérez Caro, Lluís
    IUC, Olofström, Sweden.
    Odenberger, Eva-Lis
    IUC, Olofström, Sweden.
    Oldenburg, Mats
    Luleå University of technology, Luleå, Sweden.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Comparison of forming, welding and heat treatment simulations in LS-DYNA and MSC Marc2016In: Proceedings of 10th International Conference on Trends in  Welding Research & 9th International Welding Symposium of Japan Welding, American Welding Society (AWS) & Japan Welding Society (JWS) , 2016, 660-663 p.Conference paper (Refereed)
    Abstract [en]

    The manufacturing of components for aero engine structures from a flat sheet to the final shape usually requires several steps that may introduce residual stresses and shape distortions in the part. Depending on the magnitude, sign and distribution with respect to the stresses induced by the service load, the remaining stresses may affect the service life of a component, especially when submitted to cyclic loading. Nowadays, several types of software that have the ability to predict the residual stresses and the final shape of a component subjected to various process steps are available. However, literature shows a lack of comparison studies among different software tools for multi-step simulations of a manufacturing process. In this study, the manufacturing process chain of an aerospace component including forming, welding and heat treatment in the nickel-based superalloy 718 is modelled and simulated using the two finite element software codes LS-DYNA and MSC.Marc. The results from the displacement of the blank in the punch stroke direction, the equivalent plastic strain and the von Mises stress are compared between both FE codes. The displacement of the blank after forming is slightly higher in LS-DYNA compared to MSC.Marc, as well as the equivalent plastic strain and the von Mises stress values. This tendency is also observed after trimming and welding. It can also be noted that the distribution of both strains and stresses on the trimmed and welded parts varies between the two compared codes, presumably due to the choice of different solver options, explicit and implicit.

  • 44.
    Steffenburg-Nordenström, Joachim
    et al.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Simulation and validation of forming, edge milling, welding and heat treatment of an alloy 718 componentManuscript (preprint) (Other academic)
    Abstract [en]

    This paper describes finite element simulations of a manufacturing process chain consisting of forming, weld preparation by milling, laser welding and stress relief heat treatment of an alloy718 aero-engine part. The work also includes experimental validation with optical measurements of the part after each process step. Approximation and discretization errors were avoided by keeping the same mesh and constitutive model. The results show that the remaining stresses affect the subsequent manufacturing process step and therefore, simulation of the process chain is essential. The accuracy with respect to the geometry showed relatively good agreement between measurement and simulation.

  • 45.
    Steffenburg-Nordenström, Joachim
    et al.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Simulation and Validation of Forming, Milling, Welding and Heat Treatmentof an Alloy 718 Component2017In: International Journal of Materials Forming and Machining Processes IJMFMP), ISSN 2334-4563, Vol. 4, no 2, 15-28 p.Article in journal (Refereed)
    Abstract [en]

    This paper describes finite element simulations of a manufacturing process chain consisting of

    forming, weld preparation by milling, laser welding and stress relief heat treatment of an alloy 718

    aero-engine part. The work also includes experimental validation with optical measurements of the

    part after each process step. Approximation and discretization errors were avoided by keeping the

    same mesh and constitutive model. The results show that the remaining stresses affect the subsequent

    manufacturing process step and therefore, simulation of the process chain is essential. The accuracy

    with respect to the geometry showed relatively good agreement between measurement and simulation.

  • 46.
    Svenungsson, Josefine
    University West, Department of Engineering Science, Division of Welding Technology.
    Keyhole laser process for welding Titanium alloy: modelling and experiment2016Conference paper (Other academic)
  • 47.
    Valiente Bermejo, Maria Asuncion
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Welding Technology.
    Hosseini, Vahid
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Monitoring Thermal Cycles in Multi-pass Welding2016In: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings: 25th – 27th of October 2016, Swedish Production Academy , 2016, 1-5 p.Conference paper (Refereed)
    Abstract [sv]

    Differently from any previous investigation in welding, this research work presents a novel development that allows temperature to be measured and recorded simultaneously with up to 32 thermocouples indifferent locations of a welding joint. Four experiments were designed to optimise the measurement technique by comparing the performance of three types of thermocouples (K, N, C) insulated with different materials and varying the insertion technique of the thermocouples in the joint. Results showed that type-K thermocouple had the best performance and proved that glass fibre insulation provided better protection than Inconel. The optimised measurement procedure developed in this work enables to monitor the thermal cycles in multi-pass welds. That information is essential in multi-pass welding of materials such as super duplex stainless steels, carbon steels or nickel alloys, as heating them repeatedly makes them susceptible to the formation of brittle phases and in turn it influences their mechanical and corrosion properties. This technique could be really important for future applications such as temperature modellingor prediction of mechanical properties and microstructure in relation to the thermal cycle experienced by alloys susceptible to the formation of undesirable phases.

  • 48.
    Valiente Bermejo, María Asunción
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Welding Technology.
    Rasmuson, H.
    ESAB AB, Goteborg Svezia, Sweden.
    Frodigh, M.
    Sandvik Materials Technology, Sandviken, Svezia, Sweden.
    Bengtsson, P.
    AG A Gas AB, Germany .
    Influenza del gas di protezione sul comportamento e le proprietà  di giunti sa dati di acciai duplex e superduplex: Effect of shielding gas on welding performance and properties of duplex and superduplex stainless steel welds2016In: Rivista Italiana della Saldatura, ISSN 0035-6794, Vol. 68, no 5, 635-650 p.Article in journal (Other academic)
    Abstract [en]

    The influence of shielding gases on welding performance and on properties of duplex and superduplex stainless steel welds was studied. Using argon as the reference gas, helium, nitrogen and carbon dioxide were added and five mixtures evaluated. Bead-on-plate welds and circumferential pipe welds were produced using mechanised GMA welding in the downhand position. Welding performance, corrosion resistance, mechanical properties, microstructural features and weld imperfections were assessed and related to the shielding gas. Shielding gases containing 30% helium showed excellent results; whilst pure argon showed unstable arc and poor weld pool fluidity and Ar + 2% CO2resulted in underfill and porosity. Mixtures containing helium resulted in higher ductility welds and higher impact toughness values than welds produced with Ar + 2% CO2. Sound and balanced duplex microstructures free from intermetallics were found with suitable ferrite contents for all the shielding gases studied. All the duplex pipe welds passed the corrosion test regardless of the shielding gas used, and the best results in the corrosion test for superduplex pipe welds were found when using Ar + 30%He + 0.5% CO2+ 1.8% N2as shielding gas.

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