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  • 1.
    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, p. 150-156Article 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.

  • 2.
    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, p. 573-579Article 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.

  • 3.
    Fahlström, Karl
    et al.
    Swerea KIMAB.
    Andersson, Oscar
    KTH Royal Institute of Technology.
    Todal, Urban
    Volvo Car Corporation.
    Melander, Arne
    Swerea KIMAB.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Production Engineering.
    Karlsson, Leif
    University West, Department of Engineering Science, Divison of Natural Sciences, Surveying and Mechanical Engineering.
    Distortion Analysis in Laser Welding of Ultra High Strength Steel2014In: Proceedings of the 6th International Swedish Production Symposium 2014 / [ed] Stahre, Johan, Johansson, Björn & Björkman, Mats, 2014, p. 1-9Conference paper (Refereed)
    Abstract [en]

    Due to increased demands on reduced weight in automotive industries, the use of ultra high strength steels (UHSS) has increased. When laser welding UHSS sheets, heating and cooling of the material will cause geometrical distortions and may cause low joint quality. 700 mm long U-beam structures of 1 mm thick boron steel simulating structural pillars in body-in-white constructions have been welded along the flanges with different welding speeds to investigate distortions and weld quality. The results show that final distortions appear in the range of 0-8 mm. FE simulation methods have also been presented which generally predict the distribution of welding distortions.

  • 4.
    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, p. 39-47Article 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.

  • 5.
    Harati, Ebrahim
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Dalaei, Kamellia
    ESAB AB, Gothenburg.
    The relative effects of residual stresses and weld toe geometry on fatigue life of weldments2015In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 77, p. 160-165Article in journal (Refereed)
    Abstract [en]

    The weld toe is one of the most probable fatigue crack initiation sites in welded components. In this paper, the relative influences of residual stresses and weld toe geometry on the fatigue life of cruciform welds was studied. Fatigue strength of cruciform welds produced using Low Transformation Temperature (LTT) filler material has been compared to that of welds produced with a conventional filler material. LTT welds had higher fatigue strength than conventional welds. 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. It was concluded that residual stress had a relatively larger influence than the weld toe geometry on fatigue strength.

  • 6.
    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, p. 1-14, article id 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.

  • 7.
    Harati, Ebrahim
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Ottosson, Mattias
    University West, Department of Engineering Science, Division of Automation Systems.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Non-destructive measurement of weld toe radius using Weld Impression Analysis, Laser Scanning Profiling and Structured Light Projection methods2014In: Proceedings of First International Conference on Welding and Non Destructive Testing (ICWNDT2014), 2014, p. 1-8Conference paper (Refereed)
  • 8.
    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, p. 64-74Article 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.

  • 9.
    Harati, Ebrahim
    et al.
    University West, Department of Engineering Science, Division of Production Engineering.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    The measurement of weld toe radius using three non-destructive techniques2014In: Proceedings of The 6th International Swedish Production Symposium 201416-18 September 2014 / [ed] Johan Stahre, Björn Johansson,Mats Björkman, 2014, p. 1-8Conference paper (Refereed)
    Abstract [en]

    The three non-destructive methods Weld Impression Analysis, Laser Scanning Profiling and Structured Light Projection were employed to measure the weld toe radius of fillet welds. All three methods could be used succesfully but results are dependent on evaluation procedure. The results show that the weld toe geometry cannot be considered uniform and varies along the weld. It was also found that the measured weld toe radii do not vary significantly with minor variations ofthe surface profile orientation.

  • 10.
    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 Integrety, Vol. 2, p. 3483-3490Article in journal (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.

  • 11.
    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, p. 96-106Article 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.

  • 12.
    Hosseini, Vahid A.
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes. Innovatum AB, Trollhättan, Sweden.
    Valiente Bermejo, María Asunción
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Gårdstam, Johannes
    Swerea KIMAB AB, Kista, Sweden.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Influence of multiple thermal cycles on microstructure of heat-affected zone in TIG-welded super duplex stainless steel2016In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 60, no 2, p. 233-245Article in journal (Refereed)
    Abstract [en]

    The influence of heat input and multiple welding cycles on the microstructure of the heat-affected zone in autogenously TIG-welded 6 mm 2507 type super duplex stainless steel plates was investigated. In order to produce multiple thermal cycles, one to four pass bead-on-plate welds were made with arc energies of 0.47 and 1.08 kJ/mm, corresponding to heat inputs of 0.37 and 0.87 kJ/mm. Several thermocouples were attached to record thermal cycles on the front and back sides of the plates. Finite element modelling was successfully done to map and correlate measured and calculated peak temperatures. Only minor changes were seen in the ferrite content at 1 and 2 mm from the fusion boundary. Nitrides formed in all passes of the low heat input samples in a region next to the fusion boundary, but only after the third and fourth passes of the high heat input samples. Sigma phase precipitated only in a zone heated to a peak temperature in the range of approximately 828 to 1028 °C. Multiple reheating was found to promote precipitation of sigma phase relatively more than slower cooling. A precipitation free zone was observed between the nitride and sigma phase bands. The precipitation behaviour could be understood from equilibrium phase diagrams, evaluation of local thermal cycles and by correlating results from the modelling and measurements of peak temperatures. It is suggested that the peak temperature, the accumulated time in the critical temperature range between approximately 828 and 1028 °C, and the number of thermal cycles are the most relevant criteria when evaluating the risk of sigma phase formation.

  • 13.
    Hosseini, Vahid A.
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Wessman, Sten
    University West, Department of Engineering Science, Division of Manufacturing Processes. Swerea KIMAB AB, Kista, Sweden.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Nitrogen loss and effects on microstructure in multipass TIG welding of a super duplex stainless steel2016In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 98, no May, p. 88-97Article in journal (Refereed)
    Abstract [en]

    Nitrogen loss is an important phenomenon in welding of super duplex stainless steels. In this study, a super duplex stainless steel was autogenously TIG-welded with one to four bead-on-plate passes with low or high heat inputs using pure argon shielding gas. The goal was to monitor nitrogen content and microstructure for each weld pass. Nitrogen content, measured by wavelength dispersive X-ray spectrometry, was after four passes reduced from 0.28 wt% in the base metal to 0.17 wt% and 0.10 wt% in low and high heat input samples, respectively. Nitrogen loss resulted in a more ferritic structure with larger grains and nitride precipitates. The ferrite grain width markedly increased with increasing number of passes and heat input. Ferrite content increased from 55% in base metal to 75% at low and 79% at high heat inputs after four passes. An increasing amount of nitrides were seen with increasing number of weld passes. An equation was suggested for calculation of the final nitrogen content of the weld metal as functions of initial nitrogen content and arc energy. Acceptable ferrite contents were seen for one or two passes. The recommendation is to use nitrogen in shielding gas and proper filler metals.

  • 14.
    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, p. 405-415Article 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.

  • 15.
    Hosseini, Vahid
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Multipass Autogenous TIG Welding of Super Duplex Stainless2015In: 16th national conference of welding and inspection, Yazd, Iran: Proceedings, Yazd, 2015Conference paper (Refereed)
    Abstract [en]

    Multipass welding of super duplex stainless steels (SDSS) needs further characterization due to their growing applications inpetrochemical and offshore industries. This study, as a result, is aimed at investigating the effects of the number of passesand the arc energy on the microstructure and properties of 2507-type SDSS (UNS S32750). From one to four TIG weldpasses were autogenously applied on a plate using two different arc energies and with pure argon gas as the shielding gas.Chemical analysis showed increasing nitrogen loss with an increasing number of passes and increasing arc energy.Microstructural analyses revealed formation of nitrides in the weld metal and heat affected zone, and sigma phase at somedistance from the fusion boundary. Thermal cycle analysis in combination with Thermo-Calc calculations indicated thatexcessive reheating cause degradation of corrosion properties of multipass weldments, by reducing the pitting resistanceequivalent number of austenite to less than 40. Multipass welding resulted in a more ferritic weld metal microstructure and anincreased hardness.Recommendations, based on the present study, are as follows: 1) Corrosion attack can occur not only in the weld zone andnext to the fusion boundary, but also in a location at some distance from the fusion zone due to reheating in the sigma phaseformation temperature range. This should be considered in inspection procedures 2) Nitrogen loss degrades the mechanicaland corrosion properties of weldments even when welding with a low heat input. Using filler metals with higher nickelcontents and nitrogen containing shielding gases are therefore recommended. 3) It is often recommended to use a heat inputin the lower end of the recommended 0.3-1.5 kJ/mm range in multipass welding of super duplex stainless steels. However,welding with a higher heat input and fewer passes, in some cases, can decrease the risk of formation of secondary phases.

  • 16.
    Hosseini, Vahid
    et al.
    University West, Department of Engineering Science, Division of Welding Technology. Innovatum AB., Trollhättan, Trollhättan, Sweden.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Engelberg, D.
    University of Manchester, School of Materials, M13 9PL, Manchester, United Kingdom.
    Wessman, Sten
    University West, Department of Engineering Science, Division of Welding Technology.
    Correction to: Time-temperature-precipitation and property diagrams for super duplex stainless steel weld metals (Welding in the World, (2018), 62, 3, (517-533), 10.1007/s40194-018-0548-z)2018In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 62, no 4, p. 893-Article in journal (Refereed)
    Abstract [en]

    Unfortunately due to typesetting mistakes, Tables 4-€“6 have been displayed erroneously in the article. © 2018, International Institute of Welding.

  • 17.
    Hosseini, Vahid
    et al.
    University West, Department of Engineering Science, Division of Welding Technology. Innovatum AB.,Trollhättan, Trollhättan, Sweden.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Engelberg, Dirk
    The University of Manchester, School of Materials,Manchester,UK.
    Wessman, Sten
    University West, Department of Engineering Science, Division of Welding Technology.
    Time-temperature-precipitation and property diagrams for super duplex stainless steel weld metals2018In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 62, no 3, p. 517-533Article in journal (Refereed)
    Abstract [en]

    Super duplex stainless steel (SDSS) weld metal microstructures, covering the complete temperature range from ambient to liquidus, were produced by arc heat treatment for 1 and 10 min. Temperature modeling and thermodynamic calculations complemented microstructural studies, hardness mapping and sensitization testing. After 1 min, intermetallics such as sigma and chi phase had precipitated, resulting in moderate sensitization at 720–840 °C. After 10 min, larger amounts of intermetallics resulted in hardness up to 400 HV0.5 and more severe sensitization at 580–920 °C. Coarse and fine secondary austenite precipitated at high and low temperatures, respectively: The finer secondary austenite was more detrimental to corrosion resistance due to its lower content of Cr, Mo, and N as predicted by thermodynamic calculations. Increased hardness and etching response suggest that 475 °C embrittlement had occurred after 10 min. Results are summarized as time-temperature-precipitation and property diagrams for hardness and sensitization.

  • 18.
    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, p. 11-23Article 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.

  • 19.
    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.
    Wessman, Sten
    University West, Department of Engineering Science, Division of Welding Technology. Swerea KIMAB AB, P.O. Box 7047, Kista, Sweden.
    Fuertes, Nuria
    Swerea KIMAB AB, P.O. Box 7047, Kista, Sweden.
    Effect of sigma phase morphology on the degradation of properties in a super duplex stainless steel2018In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 11, no 6, article id 933Article in journal (Refereed)
    Abstract [en]

    Sigma phase is commonly considered to be the most deleterious secondary phase precipitating in duplex stainless steels, as it results in an extreme reduction of corrosion resistance and toughness. Previous studies have mainly focused on the kinetics of sigma phase precipitation and influences on properties and only a few works have studied the morphology of sigma phase and its influences on material properties. Therefore, the influence of sigma phase morphology on the degradation of corrosion resistance and mechanical properties of 2507 super duplex stainless steel (SDSS) was studied after 10 h of arc heat treatment using optical and scanning electron microscopy, electron backscattered diffraction analysis, corrosion testing, and thermodynamic calculations. A stationary arc was applied on the 2507 SDSS disc mounted on a water-cooled chamber, producing a steady-state temperature gradient covering the entire temperature range from room temperature to the melting point. Sigma phase was the major intermetallic precipitating between 630 °C and 1010 °C and its morphology changed from blocky to fine coral-shaped with decreasing aging temperature. At the same time, the average thickness of the precipitates decreased from 2.9 Όm to 0.5 Όm. The chemical composition of sigma was similar to that predicted by thermodynamic calculations when formed at 800-900 °C, but deviated at higher and lower temperatures. The formation of blocky sigma phase introduced local strain in the bulk of the primary austenite grains. However, the local strain was most pronounced in the secondary austenite grains next to the coral-shaped sigma phase precipitating at lower temperatures. Microstructures with blocky and coral-shaped sigma phase particles were prone to develop microscale cracks and local corrosion, respectively. Local corrosion occurred primarily in ferrite and in secondary austenite, which was predicted by thermodynamic calculations to have a low pitting resistance equivalent. To conclude, the influence of sigma phase morphology on the degradation of properties was summarized in two diagrams as functions of the level of static load and the severity of the corrosive environment. © 2018 by the authors.

  • 20.
    Hosseini, Vahid
    et al.
    University West, Department of Engineering Science, Division of Welding Technology. Innovatum AB., Trollhättan, Trollhättan, Sweden.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Örnek, Cem
    KTH Royal Institute of Technology, Department of Chemical Science and Engineering, Division of Surface and Corrosion Science, Stockholm, Sweden, Department of Corrosion in Energy and Processing Industry, Swerea KIMAB AB, P.O. Box 7047, Kista, Sweden.
    Reccagni, Pierfranco
    The University of Manchester, School of Materials, Manchester, United Kingdom.
    Wessman, Sten
    University West, Department of Engineering Science, Division of Welding Technology.
    Engelberg, Dirk
    The University of Manchester, School of Materials, Manchester, United Kingdom.
    Microstructure and functionality of a uniquely graded super duplex stainless steel designed by a novel arc heat treatment method2018In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 139, p. 390-400Article in journal (Refereed)
    Abstract [en]

    A novel arc heat treatment technique was applied to design a uniquely graded super duplex stainless steel (SDSS), by subjecting a single sample to a steady state temperature gradient for 10 h. A new experimental approach was used to map precipitation in microstructure, covering aging temperatures of up to 1430 °C. The microstructure was characterized and functionality was evaluated via hardness mapping. Nitrogen depletion adjacent to the fusion boundary depressed the upper temperature limit for austenite formation and influenced the phase balance above 980 °C. Austenite/ferrite boundaries deviating from Kurdjumov–Sachs orientation relationship (OR) were preferred locations for precipitation of σ at 630–1000 °C, χ at 560–1000 °C, Cr2N at 600–900 °C and R between 550 °C and 700 °C. Precipitate morphology changed with decreasing temperature; from blocky to coral-shaped for σ, from discrete blocky to elongated particles for χ, and from polygonal to disc-shaped for R. Thermodynamic calculations of phase equilibria largely agreed with observations above 750 °C when considering nitrogen loss. Formation of intermetallic phases and 475 °C-embrittlement resulted in increased hardness. A schematic diagram, correlating information about phase contents, morphologies and hardness, as a function of exposure temperature, is introduced for evaluation of functionality of microstructures. © 2018 The Authors

  • 21.
    Hosseini, Vahid
    et al.
    University West, Department of Engineering Science, Division of Welding Technology. Innovatum AB Trollhättan,Trollhättan,Sweden.
    Thuvander, Mattias
    Chalmers University of Technology, Department of Physics, Gothenburg,Sweden.
    Wessman, Sten
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Spinodal Decomposition in Functionally Graded Super Duplex Stainless Steel and Weld Metal2018In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 49A, no 7, p. 2803-2816Article in journal (Refereed)
    Abstract [en]

    Low-temperature phase separations (T < 500 °C), resulting in changes in mechanical and corrosion properties, of super duplex stainless steel (SDSS) base and weld metals were investigated for short heat treatment times (0.5 to 600 minutes). A novel heat treatment technique, where a stationary arc produces a steady state temperature gradient for selected times, was employed to fabricate functionally graded materials. Three different initial material conditions including 2507 SDSS, remelted 2507 SDSS, and 2509 SDSS weld metal were investigated. Selective etching of ferrite significantly decreased in regions heat treated at 435 °C to 480 °C already after 3 minutes due to rapid phase separations. Atom probe tomography results revealed spinodal decomposition of ferrite and precipitation of Cu particles. Microhardness mapping showed that as-welded microstructure and/or higher Ni content accelerated decomposition. The arc heat treatment technique combined with microhardness mapping and electrolytical etching was found to be a successful approach to evaluate kinetics of low-temperature phase separations in SDSS, particularly at its earlier stages. A time-temperature transformation diagram was proposed showing the kinetics of 475 °C-embrittlement in 2507 SDSS.

  • 22.
    Karlsson, Leif
    et al.
    University West, Department of Engineering Science, Divison of Natural Sciences, Surveying and Mechanical Engineering.
    Börjesson, J.
    ESAB AB, PO Box 8004, Göteborg.
    Orientation relationships of intragranular austenite in duplex stainless steel weld metals2014In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, Vol. 19, no 4, p. 318-323Article in journal (Refereed)
    Abstract [en]

    Formation and characteristics of fine intragranular austenite were studied for low energy input duplex stainless steel welds. Microstructures were largely ferritic with some allotriomorphic grain boundary austenite, Widmanstätten type austenite, fine intragranular austenite and nitrides. Electron backscattered diffraction analysis revealed that grain boundary austenite had a random orientation relationship (OR) with one of the adjacent ferrite grains and was close to Kurdjumov-Sachs (KS) with the other, whereas Widmanstätten austenite always showed an OR near KS. The finest intragranular austenite was mainly randomly oriented, whereas coarser austenite more often was close to KS. It is argued that the OR of intragranular austenite with the ferritic matrix is governed by a combination of composition, determining driving force for nucleation at temperature, cooling rate and the availability of nitrides acting as nucleation sites. A random OR is most likely for higher cooling rates and compositions promoting nucleation at lower temperatures. © 2014 Institute of Materials, Minerals and Mining.

  • 23.
    Karlsson, Leif
    et al.
    University West, Department of Engineering Science, Divison of Natural Sciences, Surveying and Mechanical Engineering.
    Hurtig, Kjell
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Production Engineering.
    Influence of dilution on properties of high strength steel weld metals2014In: Biuletyn Instytutu Spawalnictwa W Gliwicach: Rocznik 58, 2014, p. 65-71Conference paper (Refereed)
  • 24.
    Karlsson, Leif
    et al.
    University West, Department of Engineering Science, Divison of Natural Sciences, Surveying and Mechanical Engineering.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Production Engineering.
    Hurtig, Kjell
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Efficient welding of high strength steel2014In: Proceedings of the 6th International Swedish Production Symposium 2014 / [ed] Stahre, Johan, Johansson, Björn & Björkman, Mats, 2014, p. 1-8Conference paper (Refereed)
    Abstract [en]

     Producing welds with properties matching those of the steel is a challenge at high strength levels. The present study investigated how cooling rates and dilution affects strength and toughness when welding steels with yield strengths of 777 MPa and 1193 MPa. Overmatching weld metal strength was achieved for the less strong steel and weld strengths >1000 MPa were recorded for the stronger steel. Fracture in transverse tensile testing was always located in base material or HAZ. Low dilution, rapid cooling and single pass welding contributed to higher strength. Impact toughness was higher for lower strength and low dilution.

  • 25.
    Lahti, K.
    et al.
    Lappeenranta University of Technology, Finland.
    Hiltunen, E.
    Lappeenranta University of Technology, Finland.
    Pirinen, M.
    Lappeenranta University of Technology, Finland.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Submerged Arc Welding of High Strength Steel for Shipbuilding Applications2015In: Proceedings of JOM 18 International conference on joining materials, Helsingör, Danmark, april 26-29 2015, JOM-institute , 2015, p. 1-8Conference paper (Refereed)
    Abstract [en]

    In most cases primary purpose for use of high strength steels is weight reduction with resulting benefits in product lifecycle costs. However, as the operating environments vary, it is important to take consideration to the specific requirements for the product in concern. In this study, high strength steel F40SW (YS 460 MPA, UTS 550 MPa) for use in arctic conditions, e.g., icebreakers, are welded with submerged arc welding (SAW) and resulting welds are analyzed for mechanical and metallurgical properties. Submerged arc welding (SAW) is preferred joining process for thick steel plates in shipbuilding.However, as the mechanical properties of steel are improved, restrictions in heat input are often set thus limiting effective use of SAW, and probably therefore Manual Metal Arc (MMA) welding and manual Gas Metal Arc (GMA) welding are typically the processes mainly referenced in literature when welding steels with higher strength levels are studied. In this study, submerged arc welds on F40SW steel were made with overmatching tubular and solid welding wire at heat input levels above the normally recommended maximum of approximately 2,0 kJ/mm. Resulting welds were tested for mechanical properties with focus on toughness properties at low temperatures.Impact toughness KV 150 / 7,5 at -60°C was above 27J for both tested wires in the weld and at the heat affected zone (HAZ). Tested yield and tensile strength of the joints matched unwelded base material and all of the samples were broken at the base material far from the weld and HAZ area. Also the 180° bending tests for both surface- and rootside were passed without remarks. Based on the findings in this study, no obvious limitations for use of submerged arc welding in joining of arctic grade steel F40SW were observed. This encourages for increased use of SAW as economical and environmentally sound joining process for this kind of steel.

  • 26.
    Lahti, K.
    et al.
    Lappeenranta University of Technology, Finland.
    Hiltunen, E.
    Lappeenranta University of Technology, Finland.
    Pirinen, M.
    Lappeenranta University of Technology, Finland.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Martikainen, J.
    Lappeenranta University of Technology, Finland.
    Productivity Aspects in Submerged Arc Welding of Thick High-Strength Steels2015In: Proceedings of IIW International Conference, High-Strength Materials: Challenges and Applications, 2-3 July 2015, Helsinki, Finland, Helsingfors, 2015, Helsingfors, 2015, Vol. 0904, p. 1-6-Conference paper (Refereed)
    Abstract [en]

    A series of welding tests were made on 35 mm thick F500W high strength steel. This specific steel grade is developed for use in arctic conditions, especially in shipbuilding, and it has excellent impact toughness at temperatures down to -60°C. Submerged arc welding tests were performed using solid and flux-cored welding wire keeping the heat-input at levels typically recommended for thermo mechanically processed highstrengthsteels. Process improvement trials were even made using electrode extension (EE) allowing for higher melt-on rates without any increase in the heat input.However, as the chemical composition of F500W allows for higher heat input without risk for excessive grain growth, tests at higher heat inputs were also made as reference for additional ways to increase productivity. Three fundamental means for improving productivity were analyzed in this study: 1) use of solid or flux-cored wire, 2) effect of groove preparation, and 3) use ofelectrode extension. These all can be introduced without changes in heat input, and hence implementation to existing production systems is easy, economical and quick. Highest increase in productivity is gained by using electrode extension with optimized groove geometry. In the studied thickness of 35 mm, the number of runs was decrease by 60 % from 22 to 9 without increase in the heat input and with approved mechanical properties for this specific steel. Based on the outcome of this study, submerged arc welding can successfully be used for joining of this high strength steel with approved mechanical properties and high productivity.

  • 27.
    Li, Peigang
    et al.
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Markocsan, Nicolaie
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Karlsson, Leif
    University West, Department of Engineering Science.
    Cold laps - micro-lack of fusion defects in steel arc welds: a reviewManuscript (preprint) (Other academic)
  • 28.
    Mraz, Lubos
    et al.
    Welding Research Institute - Industrial Institute SR, Račianska 71, 83259 Bratislava, Slovakia .
    Karlsson, Leif
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Mikula, Pavol
    Nuclear Physics Institute ASCR v.v.i., 250 68 Řež, Czech Republic .
    Vrana, Miroslav
    Nuclear Physics Institute ASCR v.v.i., 250 68 Řež, Czech Republic .
    Identification of Weld Residual Stresses Using Diffraction Methods andtheir Effect on Fatigue Strength of High Strength Steels Welds2014In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 768-769, p. 668-674Article in journal (Refereed)
    Abstract [en]

    It is well known that fatigue strength of welded joints does not depend on steel strength. Better fatigue strength of welded joints, e.g. longer life time of fatigue loaded weld structures, can be achieved with a smooth transition between the weld and the base material to minimize stress concentration. It has also been recognized that residual stresses play a critical role in the fatigue behaviour of welds. In the last decade an extensive research has been performed in order to increase the fatigue strength of high strength steel weldments. The martensite and bainite transformation start temperatures of weld metals have been shown to have a large effect on fatigue life time of high strength steel welds. This is of particular importance if the full potential of high strength steels is to be used in fatigue loaded constructions. A detailed investigation of the effect of phase transformation temperature on residual stress distribution in the vicinity high strength steel welds and its effect on fatigue life time has been performed. The transformation temperature of the weld metal was varied by changing the chemical composition of the filler material. Residual stress distributions have been measured by neutron as well as by X-ray diffraction and fatigue tests have been performed on the fillet welds. A strong effect of weld metal phase transformation temperature on residual stress level was observed. Fatigue strength increased approximately three times when an optimised low transformation temperature filler material was used in comparison to the application of conventional filler material

  • 29.
    Mraz, Lubos
    et al.
    Welding Research Institute - Industrial Institute SR, 832 59 Bratislava, Slovakia.
    Karlsson, Leif
    University West, Department of Engineering Science, Divison of Natural Sciences, Surveying and Mechanical Engineering.
    Vrana, Miroslav
    Nuclear Physics Institute ASCR, v.v.i, 25068 Rez, Czech Republic .
    Mikula, Pavol
    Nuclear Physics Institute ASCR, v.v.i, 25068 Rez, Czech Republic .
    Residual stress distributions at high strength steel welds prepared by low transformation temperature (LTT) and conventional welding consumables2014In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 777, p. 40-45Article in journal (Refereed)
    Abstract [en]

    Residual stress distributions in fillet welds in 8 mm 900 MPa steel have been mapped perpendicular and parallel to the weld line and also through the thickness in the vicinity of weld toe position. Measurements were carried out on four welds when two of them were performed with conventional and two with the so called LTT (low transformation temperature) filler materials. Both neutron and X-ray diffractions were used for determination of the residual stress distribution. Fatigue properties have also been evaluated for all test welds. Neutron diffraction measurements showed that the stress profiles perpendicular to the weld toe qualitatively did not depend on filler material type although the absolute stress levels differed. Trends were similar for positions 2, 4 and 6 millimetres below the surface for all three stress components; σx (direction perpendicular to the weld), σy (parallel to the weld) and σz (through the thickness). X-ray diffraction showed difference in residual stress level at the weld toe. Lower residual stress levels have been identified for LTT filler material when compared to the conventional consumable compositions. The effect of residual stress is discussed in relation to fatigue properties of all four welds. Remarkable higher fatigue strength has been measured for welds prepared by the LTT filler materials. © (2014) Trans Tech Publications, Switzerland.

  • 30.
    Mráz, Lubos
    et al.
    Welding Reseach Insitute - Industrial Insitute of SR, Racinska 71, 832 59 Bratislava, Slovak Republic.
    Karlsson, Leif
    University West, Department of Engineering Science, Divison of Natural Sciences, Surveying and Mechanical Engineering.
    Vrána, Miroslav
    Nuclear Physics Institute AS CR, v.v.i., Řež 130, Czech Republic ..
    Neutron Diffraction Studies of Residual Stress Distribution in the Vicinity of the Single Pass Fillet Steel Welds2015In: Applied Mechanics and Materials, ISSN 1660-9336, E-ISSN 1662-7482, Vol. 732, p. 13-19Article in journal (Refereed)
    Abstract [en]

    In this contribution the results of residual strain/stress measurements performed on several single pass fillet steel welds, which were carried out at different welding conditions, namely, with different filler materials are presented.

  • 31.
    Mráz, Lubos
    et al.
    Welding Research Institute, Industrial Institute SR, Bratislava, Slovakia .
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Vrána, Miroslav
    Nuclear Physics Institute AS CR, v.v.i., Řež 130, Czech Republic .
    Mikula, Pavol
    Nuclear Physics Institute AS CR, v.v.i., Řež 130, Czech Republic .
    Residual stress distribution measurement by neutron diffraction of the single pass fillet steel welds2014In: 52nd International Scientific Conference on Experimental Stress Analysis (EAN 2014): Proceedings of a meeting held 2-5 June 2014, Marianske Lazne, Czech Republic., Czech Society for Mechanics ( CSM ) , 2014Conference paper (Refereed)
    Abstract [en]

    In this contribution the results of residual strain/stress measurements performed on several single pass fillet steel welds which were carried out at different welding conditions, namely, with different filler materials are presented.

  • 32.
    Ramjaun, T.
    et al.
    University of Cambridge.
    Stone, H. J.
    Unversity of Cambridge.
    Karlsson, Leif
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Gharghouri, M.A.
    Canadian Neutron Beam Centre, Chalk River Laboratories, Chalk River, Ont. K0J 1J0, Canada.
    Dalaei, K
    ESAB AB, Lindholmsalln 9, 417 55 Göteborg.
    Moat, R..J
    Materials Engineering, The Open University, Milton Keynes MK7 6AA, UK.
    Bhadeshia, H.K.D.H.
    University of Cambridge.
    Surface residual stresses in multipass welds produced using low transformation temperature filler alloys2014In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, ISSN 1362-1718, Vol. 19, no 7, p. 623-630Article in journal (Refereed)
    Abstract [en]

    Tensile residual stresses at the surface of welded components are known to compromise fatigue resistance through the accelerated initiation of microcracks, especially at the weld toe. Inducement of compression in these regions is a common technique employed to enhance fatigue performance. Transformation plasticity has been established as a viable method to generate such compressive residual stresses in steel welds and exploits the phase transformation in welding filler alloys that transform at low temperature to compensate for accumulated thermal contraction strains. Neutron and X-ray diffraction have been used to determine the stress profiles that exist across the surface of plates welded with low transformation temperature welding alloys, with a particular focus on the stress at the weld toe. For the first time, near surface neutron diffraction data have shown the extent of local stress variation at the critical, fusion boundary location. Compression was evident for the three measurement orientations at the fusion boundaries. Compressive longitudinal residual stresses and tensile transverse stresses were measured in the weld metal.

  • 33.
    Ramjaun, T.
    et al.
    University of Cambridge.
    Stone, H. J.
    Unversity of Cambridge.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Kelleher, J.
    ISIS Facility, Rutherford Appleton Laboratory.
    Moat, R. J.
    The Open University.
    Kornmeier, J. R.
    Forschungs-Neutronenquelle Heinz Maier-Leibnitz.
    Kemellia, Dalaei
    ESAB AB, Lindholmsalln 9, 417 55 Göteborg.
    Bhadeshia, H.K.D.H.
    University of Cambridge.
    Effect of interpass temperature on residual stresses in multipass welds produced using low transformation temperature filler alloy2014In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, ISSN 1362-1718, Vol. 19, no 1, p. 44-51Article in journal (Refereed)
    Abstract [en]

    Weld filler alloys that exploit transformation plasticity through low austenite to martensite transformation temperatures offer an effective method of reducing residual stresses in strong steel welds. However, in multipass welds, the heat input from later weld passes may be insufficient to retransform prior welding passes, leading to the accumulation of thermally induced strains and elevated residual stresses. In this work, the residual stress distributions produced around arc welds fabricated with a martensitic weld filler alloy that transforms at a low temperature have been studied as a function of the number of passes deposited and the interpass temperature. It is found that when the interpass temperature is above the transformation temperature of the weld metal, the entire multipass weld transforms as a single entity, thus permitting the optimum exploitation of the transformation plasticity. In contrast, the deposition of new metal with a relatively low interpass temperature leads to increased residual stresses in the underlying layers, reducing or eliminating the beneficial stress states previously created.

  • 34.
    Ramjaun, T.
    et al.
    University of Cambridge.
    Stone, H. J.
    Unversity of Cambridge.
    Karlsson, Leif
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Kelleher, J.
    ISIS Facility, Rutherford Appleton Laboratory.
    Ooi, S.W.
    University of Cambridge.
    Dalaei, K
    ESAB AB, Lindholmsalln 9, 417 55 Göteborg.
    Kornmeier, J. R.
    Forschungs-Neutronenquelle Heinz Maier-Leibnitz.
    Bhadeshia, H.K.D.H.
    University of Cambridge.
    Effects of dilution and baseplate strength on stress distributions in multipass welds deposited using low transformation temperature filler alloys2014In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, ISSN 1362-1718, Vol. 19, no 6, p. 461-467Article in journal (Refereed)
    Abstract [en]

    Transformation plasticity can be utilised to control residual stresses in steel welds. This requires special filler alloys that transform at a sufficiently low temperature to compensate for accumulated thermal contraction strains. However, the welding parameters needed to optimise the effect in multipass joints have yet to be established. This topic has been investigated by characterising the residual stress distribution in multipass welds fabricated with different welding alloys and baseplates using neutron diffraction to assess the effects of dilution and baseplate strength. While the use of richly alloyed weld metal does enhance fatigue performance in single pass joints, the extent of stress relief that can be derived from transformation plasticity is reduced due to incomplete martensitic transformation when further layers are deposited. For all cases studied, compressive stresses were measured in the weld metal with balancing tensile stress in the heat affected zone of the plate. The magnitude of the tension was observed to be a function of the strength of the baseplate. Recommendations are also presented for the combination of welding and material parameters that lead to the optimum exploitation of transformation plasticity as a method for boosting the fatigue performance of multipass welded joints.

  • 35.
    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, p. 1609-1618Article 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.

  • 36.
    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, p. 1-10Conference 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.

  • 37.
    Rehan, Arbab
    et al.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Medvedeva, Anna
    Uddeholms AB, S-68385 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.
    Retained Austenite Transformation during Heat Treatment of a 5 Wt Pct Cr Cold Work Tool Steel2017In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 48A, no 11, p. 5233-5243Article in journal (Refereed)
    Abstract [en]

    Retained austenite transformation was studied for a 5 wt pct Cr cold work tool steel tempered at 798 K and 873 K (525 degrees C and 600 degrees C) followed by cooling to room temperature. Tempering cycles with variations in holding times were conducted to observe the mechanisms involved. Phase transformations were studied with dilatometry, and the resulting microstructures were characterized with X-ray diffraction and scanning electron microscopy. Tempering treatments at 798 K (525 degrees C) resulted in retained austenite transformation to martensite on cooling. The martensite start (M-s) and martensite finish (M-f) temperatures increased with longer holding times at tempering temperature. At the same time, the lattice parameter of retained austenite decreased. Calculations from the Ms temperatures and lattice parameters suggested that there was a decrease in carbon content of retained austenite as a result of precipitation of carbides prior to transformation. This was in agreement with the resulting microstructure and the contraction of the specimen during tempering, as observed by dilatometry. Tempering at 873 K (600 degrees C) resulted in precipitation of carbides in retained austenite followed by transformation to ferrite and carbides. This was further supported by the initial contraction and later expansion of the dilatometry specimen, the resulting microstructure, and the absence of any phase transformation on cooling from the tempering treatment. It was concluded that there are two mechanisms of retained austenite transformation occurring depending on tempering temperature and time. This was found useful in understanding the standard tempering treatment, and suggestions regarding alternative tempering treatments are discussed. (C) The Author(s) 2017.

  • 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.
    Svensson, Lars-Erik
    et al.
    University West, Department of Engineering Science, Division of Production Engineering.
    Karlsson, Leif
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Harati, Ebrahim
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Increasing fatigue life using Low Transformation Temperature (LTT) welding consumables,2013In: 2nd Swedish conference on design and fabrication of welded structures: Conference proceedings / [ed] Zuheir Barsoum, Stockholm, 2013, p. 49-64Conference paper (Other academic)
  • 40.
    Svensson, Lars-Erik
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Ohlsson, A. R.
    SSAB AB, Oxelösund, Sweden.
    Stemne, D.
    SSAB AB, Oxelösund, Sweden.
    Gustafsson, M.
    ESAB AB, Göteborg, Sweden.
    Bengtsson, P.
    AGA Gas AB, Stockholm, Sweden.
    Strength and Impact Toughness of High Strength Steel Weld Metals: Influence of Welding Method, Dilution and Cooling Rate2015In: Proceedings of IIW International Conference, High-Strength Materials: Challenges and Applications, 2-3 July 2015, Helsinki, Finland, Helsingfors, 2015, p. 1-9Conference paper (Refereed)
    Abstract [en]

    Producing welds with properties matching those of the steel is a challenge at high strength levels. The present study has investigated how the choice of welding method affects weld metal mechanical properties through effects on dilution and cooling rate. Butt welds were produced in 12 mm plates in 777 MPa and 1193 MPa yield strength steels. Conventional arc welding methods including manual metal arc, gas metal arc welding, rapid arc welding and submerged arc welding were used as well as laser-gas metal arc hybrid welding. Filler materials with nominal yield strengths between 810 and 1000 MPa were used. Cooling times between 800 C and 500 C were varied between 5s and 15s and measured by insertion of thermocouples into the weld pool.High quality welds were produced efficiently with all welding methods even though dilution varied between 3%, for manual metal arc welding, to 73% for laser-hybrid welding. Low dilution, rapid cooling and single pass welding contributed to higher strength. Overmatching weld metal strength was achieved for the less strong steel and weld yield strengths of >1000 MPa were recorded for the stronger steel. Fracture in transverse tensile testing was always located in base material or HAZ. Impact toughness was higher for lower strength and low dilution. Results are discussed relating choice of welding method and cooling rate to weld metal properties for different steel strength levels.

  • 41.
    Svensson, Lars-Erik
    et al.
    University West, Department of Engineering Science, Division of Production Engineering.
    Karlsson, Leif
    University West, Department of Engineering Science, Divison of Natural Sciences, Surveying and Mechanical Engineering.
    Soder, R.
    Department of Chassis & Vehicle Dynamics, Volvo Group Trucks Technology, SE-40508, Göteborg, Sweden.
    Welding enabling light weight design of heavy vehicle chassis2015In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, Vol. 20, no 6, p. 473-482Article in journal (Refereed)
    Abstract [en]

    Development of lightweight cars for saving fuel and reducing emission has been a priority for more than a decade. A similar trend is now seen for heavy vehicles. Here, however, the chassis rather than the cab is in focus, since this is by far the heaviest part of the vehicle. Using welding fabrication has many advantages like larger freedom in choice of material and more compact design. However, there are also factors like fatigue strength, residual stresses and geometric distortion, which must be addressed. There are large potentials to save weight in heavy vehicles by utilising high strength steels or aluminium alloys. In general, existing joining methods can be used, but new filler materials or recently developed post-weld treatments may be necessary to fulfil the demands on the components. In this paper, two examples are given, showing possible weight reduction solutions. In both cases, welding plays a central role.

  • 42.
    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, p. 1-5Conference 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.

  • 43.
    Valiente Bermejo, María Asunción
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    DebRoy, Tarasankar
    University Park, Department of Materials Science and Engineering, The Pennsylvania State University, State College PA 16801, USA.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    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.
    Towards a Map of Solidification Cracking Risk in Laser Welding of Austenitic Stainless Steels2015In: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 78, p. 230-239Article in journal (Refereed)
    Abstract [en]

    In this work, two series of specimens with Hammar and Svensson's Cr- and Ni-equivalents (Creq+Nieq) = 35 and 45 wt% were used to cover a wide range of austenitic grades. These were laser welded with different energy inputs achieving cooling rates in the range of 103 °C/s to 104 °C/s. As high cooling rates and rapid solidification conditions could favour fully austenitic solidification and therefore raise susceptibility to solidification cracking, the solidification modes of the laser welded specimens were compared to the ones experienced by the same alloys under arc welding conditions. It was found that high cooling rates experienced in laser welding promoted fully austenitic solidification for a wider range of compositions, for example specimens with (Creq+Nieq) = 35% under arc welding cooling conditions at 10 °C/s showed fully austenitic solidification up to Creq/Nieq = 1.30, whilst the same specimens laser cooled at 103 °C/s showed fully austenitic solidification up to Creq/Nieq = 1.50 and those cooled at 104 °C/s showed it up to Creq/Nieq = 1.68. Therefore, high cooling rates extended the solidification cracking risk to a wider range of Creq/Nieq values. This work also compares the cooling rates experimentally determined by thermocouples to the computed cooling rates calculated by a highly-advanced computational model. The distance between the thermocouple's wires and the thermal resistance of thermocouples together with the small size of the weld pools proved to be practical limitations in the experimental determination of cooling rates. However, an excellent agreement was found between computed and experimental solidus isotherms at high energy input settings. For low energy input settings cooling rate was in the order of magnitude of 104 °C/s, whilst for high energy input settings cooling rate was found to be in the order of magnitude of 103 °C/s.

  • 44.
    Valiente Bermejo, María Asunción
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    DebRoy, Tarasankar
    Pennsylvania State University.
    Influence of low energy laser welding on solidification and microstructure of austenitic stainless steel welds2013In: 14th NOLAMP Conference: The 14th Nordic Laser Materials Processing Conference, August 26th – 28th 2013, Gothenburg, Sweden / [ed] Alexander Kaplan, Hans Engström, Luleå: Luleå University of Technology, 2013, p. 3-14Conference paper (Refereed)
    Abstract [en]

    Primary austenitic solidification is related to increased hot cracking susceptibility in welding of austenitic stainless steels. It is also recognised that high cooling rates and rapid solidification conditions, like those achieved in laser beam welding (LBW), increase the stability of austenite versus ferrite as the primary solidification phase. Knowledge about the solidification mode under LBW conditions is therefore of utmost importance. A series of austenitic stainless steel alloys were prepared using an electric arc furnace and cooled at a rate of 10 ºC/s. The overall alloying composition was kept constant at [Cr eq+Nieq] = 40 wt% while changing the Cr eq/Nieq ratio from 1.52 to 1.84. These alloys were then laser welded using a continuous wave ytterbium fibre laser at two different energy input levels. Cooling rates were experimentally determined to be in the range of 10 3 ºC/s to 104 ºC/s and the values were confirmed by computational modelling. The compositional border between primary austenitic and primary ferritic solidification was found to shift to higher Cr eq/Nieq values at higher cooling rates. However, all the alloys showed coexistence of regions of primary austenitic and primary ferritic solidification for both laser settings although ustenite tended to more abundant at higher cooling rates. Austenite content and refinement of microstructure is discussed in terms of effects of cooling rate on solidification behaviour and solid state transformations.

  • 45.
    Valiente Bermejo, María Asunción
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Optimising Quality and Productivity in Welding of Duplex and Superduplex Stainless Steels2014In: Proceedings of the 6th International Swedish Production Symposium 2014 / [ed] Stahre, Johan, Johansson, Björn & Björkman, Mats, 2014, p. 1-7Conference paper (Refereed)
    Abstract [en]

    The aim of this work was to study the influence of shielding gases and welding positions on properties of duplex and superduplex stainless steel circumferential pipe welds. Corrosion resistance, microstructural features and weld defects were assessed and related to the welding procedures. Horizontal and vertical upward welding positions produced high quality welds. However, welding in the overhead position resulted in less good results in terms of porosity and corrosion resistance. Shielding gases containing 30% helium showed best results, whilst using a mixture Ar+2%CO2 resulted in undercuts and porosity in all welding positions.

  • 46.
    Valiente Bermejo, María Asunción
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Hurtig, Kjell
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Rasmuson, H.
    ESAB AB, Göteborg, Sweden.
    Frodigh, M.
    Sandvik Materials Technology, Sandviken, Sweden.
    Bengtsson, P.
    AGA Gas AB, Lidingö, Sweden.
    Effect of shielding gas on welding performance and properties of duplex and superduplex stainless steel welds2015In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 59, no 2, p. 239-249Article in journal (Refereed)
    Abstract [en]

    The influence of shielding gases on welding performanceand on properties of duplex and superduplex stainlesssteel welds was studied. Using argon as the reference gas,helium, nitrogen and carbon dioxide were added and fivemixtures evaluated. Bead-on-plate welds and circumferentialpipe welds were produced using mechanisedGMAwelding inthe downhand position. Welding performance, corrosion resistance,mechanical properties, microstructural features andweld imperfections were assessed and related to the shieldinggas. Shielding gases containing 30 % helium showed excellentresults; whilst pure argon showed unstable arc and poorweld pool fluidity and Ar+2 %CO2 resulted in underfill andporosity. Mixtures containing helium resulted in higher ductilitywelds and higher impact toughness values than weldsproduced with Ar+2 %CO2. Sound and balanced duplexmicrostructures free from intermetallics were found with suitableferrite contents for all the shielding gases studied. All theduplex pipe welds passed the corrosion test regardless of theshielding gas used, and the best results in the corrosion test forsuperduplex pipe welds were found when using Ar+30 %He+0.5 %CO2+1.8 %N2 as shielding gas.

  • 47.
    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, p. 635-650Article 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.

  • 48.
    Valiente Bermejo, María Asunción
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Karlsson, Leif
    University West, Department of Engineering Science, Divison of Natural Sciences, Surveying and Mechanical Engineering.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Rasmuson, Helene
    ESAB AB, Göteborg, Sweden.
    Frodigh, Mette
    Sandvik Materials Technology, Sandviken, Sweden .
    Bengtsson, Per
    AGA Gas AB, Lidingö, Sweden.
    Effect of welding position on properties of duplex and superduplex stainless steel circumferential welds2015In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 59, no 5, p. 693-703Article in journal (Refereed)
    Abstract [en]

    The influence of welding position on properties ofduplex and superduplex stainless steel welds was studied. Circumferential pipe welds were produced using mechanised gasmetal arc welding in flat position, vertical up position and overhead position. Dilution, corrosion resistance, mechanical properties, microstructural features and weld imperfections were assessed and related to the welding position. Welds produced in flat and vertical up positions were less likely to produce porosity than those welded in overhead position, whilst underfill was not observed in overhead position welds. All the duplex pipe welds passed the corrosion test regardless of the welding position and showed sound microstructures. Under fixed arc energy conditions, welds produced in vertical up position showed the lowest dilution values whilst welds in flat position showed the highest. Excellent impact toughness values and cross tensile values were found regardless of the welding positions. Whenever possible, flat position is recommended as welds showed less proneness to porosity. Vertical up position is recommended as the second best choice.

  • 49.
    Zachrisson, Jan
    et al.
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Börjesson, J
    ESAB AB.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Role of inclusions in formation of high strength steel weld metal microstructures2013In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, Vol. 18, no 7, p. 603-609Article in journal (Refereed)
    Abstract [en]

    A series of high strength weld metals with varying Al content are studied. The inclusions are characterised using energy dispersive X-ray analysis and electron diffraction. The tendency for alignment of the microstructure is characterised quantitatively using electron backscatter diffraction and a recently developed post-processing technique. Correlation is found between the inclusion phases present and the amount of aligned neighbouring grains in the microstructure. It is shown that amorphous Si-Al oxides form at low Al weld metal contents and an Mg-Al spinel at higher contents. The former is associated with less alignment of the microstructure and therefore higher impact toughness. The effect of these inclusions on the formation of the microstructure is discussed.

  • 50.
    Zachrisson, Jan
    et al.
    University West, Department of Engineering Science, Research Environment Production Technology West.
    Börjesson, Johan
    ESAB AB, Lindholmsallén 9, Box 8004, SE-40277 Gothenburg.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    A new EBSD based methodology for the quantitative characterisation of microstructures formed by displacive fcc–bcc transformations2013In: Micron, ISSN 0968-4328, E-ISSN 1878-4291, Vol. 45, no February, p. 45-54Article in journal (Refereed)
    Abstract [en]

    This work is concerned with a new methodology that can be used to quantify the degree to which grains in the microstructure are aligned in the form of packets. The methodology is based on a crystallographic definition of the term packet which is used to deduce the theoretically ideal misorientations of intra-packet grain boundaries. A misorientation distribution obtained from extensive EBSD mapping can thus be split into intra- and inter-packet misorientations and the corresponding fractions can be determined by integration. The theoretical framework of the methodology is explained and a step-by-step description of the procedure is given. Results from a trace analysis are provided to justify the assumptions made regarding habit plane and examples are included showing how the grain boundary network can be split into two separate parts, one for lath boundaries and the other for packet boundaries. Moreover, example weld metal microstructures along with the corresponding misorientation distributions as well as quantitative values of the microstructures are presented.

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