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Hosseini, V., Karlsson, L., Örnek, C., Reccagni, P., Wessman, S. & Engelberg, D. (2018). Microstructure and functionality of a uniquely graded super duplex stainless steel designed by a novel arc heat treatment method. Materials Characterization, 139, 390-400
Open this publication in new window or tab >>Microstructure and functionality of a uniquely graded super duplex stainless steel designed by a novel arc heat treatment method
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2018 (English)In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 139, p. 390-400Article in journal (Refereed) Published
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

Place, publisher, year, edition, pages
Elsevier Inc., 2018
Keyword
Austenite; Chromium compounds; Cold rolling; Embrittlement; Hardness; Heat treatment; Microstructure; Nitrogen; Nitrogen compounds; Phase equilibria; Schematic diagrams; Stainless steel, Chi phase; Functionally graded microstructures; Nitrogen loss; R phase; Sigma phase, Temperature
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-12235 (URN)10.1016/j.matchar.2018.03.024 (DOI)2-s2.0-85044113030 (Scopus ID)
Note

Available online 19 March 2018

Available from: 2018-04-03 Created: 2018-04-03 Last updated: 2018-04-04Bibliographically approved
Hosseini, V., Karlsson, L., Engelberg, D. & Wessman, S. (2018). Time-temperature-precipitation and property diagrams for super duplex stainless steel weld metals. Welding in the World
Open this publication in new window or tab >>Time-temperature-precipitation and property diagrams for super duplex stainless steel weld metals
2018 (English)In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669Article in journal (Refereed) Epub ahead of print
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.

Keyword
Super duplex stainless steel, Weld metal, Time-temperature-precipitation diagram, Sensitization, Hardness, Sigma phase, Stationary arc, Heat treatment, Secondary austenite
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-12054 (URN)10.1007/s40194-018-0548-z (DOI)
Note

First Online: 17 January 2018

Available from: 2018-02-07 Created: 2018-02-07 Last updated: 2018-02-07Bibliographically approved
Hosseini, V., Karlsson, L., Hurtig, K., Choquet, I., Engelberg, D., Roy, M. J. & Kumara, C. (2017). A novel arc heat treatment technique for producing graded microstructures through controlled temperature gradients. Materials & design, 121(May), 11-23
Open this publication in new window or tab >>A novel arc heat treatment technique for producing graded microstructures through controlled temperature gradients
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2017 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 121, no May, p. 11-23Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Reigate, Surrey: Scientific and technical P., 2017
Keyword
Stationary arc, Heat treatment, Graded microstructure, Super duplex stainless steels, Physical simulation, Welding
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-10760 (URN)10.1016/j.matdes.2017.02.042 (DOI)000399625000002 ()2-s2.0-85013031461 (Scopus ID)
Available from: 2017-02-28 Created: 2017-02-28 Last updated: 2017-12-18Bibliographically approved
Harati, E., Karlsson, L., Svensson, L.-E. & Dalaei, K. (2017). Applicability of Low Transformation Temperature welding consumables to increase fatigue strength of welded high strength steels. International Journal of Fatigue, 97, 39-47
Open this publication in new window or tab >>Applicability of Low Transformation Temperature welding consumables to increase fatigue strength of welded high strength steels
2017 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 97, p. 39-47Article in journal (Refereed) Published
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.

Keyword
Low Transformation Temperature Welding Consumables, Fatigue Strength, Residual Stress, Martensite Start Temperature
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-10212 (URN)10.1016/j.ijfatigue.2016.12.007 (DOI)000393631300005 ()2-s2.0-85007154275 (Scopus ID)
Available from: 2016-12-05 Created: 2016-12-05 Last updated: 2017-08-23Bibliographically approved
Fahlström, K., Andersson, O., Melander, A., Karlsson, L. & Svensson, L.-E. (2017). Correlation between laser welding sequence and distortions for thin sheet structures. Science and technology of welding and joining, 22(2), 150-156
Open this publication in new window or tab >>Correlation between laser welding sequence and distortions for thin sheet structures
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2017 (English)In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, Vol. 22, no 2, p. 150-156Article in journal (Refereed) Published
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.

Keyword
Automotive, Distortion, High strength steel, Laser welding, Welding sequence
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-9678 (URN)10.1080/13621718.2016.1207046 (DOI)2-s2.0-84978705979 (Scopus ID)
Available from: 2016-12-16 Created: 2016-08-10 Last updated: 2017-11-29Bibliographically approved
Hosseini, V., Hurtig, K. & Karlsson, L. (2017). Effect of multipass TIG welding on the corrosion resistance and microstructure of a super duplex stainless steel. Materials and corrosion - Werkstoffe und Korrosion, 68(4), 405-415
Open this publication in new window or tab >>Effect of multipass TIG welding on the corrosion resistance and microstructure of a super duplex stainless steel
2017 (English)In: Materials and corrosion - Werkstoffe und Korrosion, ISSN 0947-5117, E-ISSN 1521-4176, Vol. 68, no 4, p. 405-415Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2017
Keyword
Welding, corrosion, resistance
National Category
Metallurgy and Metallic Materials
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-9885 (URN)10.1002/maco.201609102 (DOI)000398581800002 ()2-s2.0-84986268706 (Scopus ID)
Available from: 2016-09-13 Created: 2016-09-13 Last updated: 2017-12-18Bibliographically approved
Harati, E., Svensson, L.-E. & Karlsson, L. (2017). Improving fatigue strength of welded 1300 MPa yield strength steel using HFMI treatment or LTT fillers. Engineering Failure Analysis, 79(September), 64-74
Open this publication in new window or tab >>Improving fatigue strength of welded 1300 MPa yield strength steel using HFMI treatment or LTT fillers
2017 (English)In: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 79, no September, p. 64-74Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Oxford: Pergamon Press, 2017
Keyword
Fatigue strength; Low transformation temperature welding consumable; High frequency mechanical impact treatment; High strength steel; Residual stress
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-10923 (URN)10.1016/j.engfailanal.2017.04.024 (DOI)000405538800006 ()2-s2.0-85018745969 (Scopus ID)
Available from: 2017-04-27 Created: 2017-04-27 Last updated: 2017-12-11Bibliographically approved
Fahlström, K., Andersson, O., Karlsson, L. & Svensson, L.-E. (2017). Metallurgical effects and distortions in laser welding of thin sheet steels with variations in strength. Science and technology of welding and joining, 22(7), 573-579
Open this publication in new window or tab >>Metallurgical effects and distortions in laser welding of thin sheet steels with variations in strength
2017 (English)In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, Vol. 22, no 7, p. 573-579Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Taylor and Francis Ltd., 2017
Keyword
Distortion (waves); Hardness; Heat affected zone; High strength steel; Laser beam welding; Martensitic steel; Metallurgy; Metals; Sheet metal; Welding; Welds, automotive; Geometrical distortion; Good correlations; Steel grades; Thin sheet; Total energy; Weld metal; Weld widths, Steel metallurgy
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-10936 (URN)10.1080/13621718.2016.1275483 (DOI)000406522500004 ()2-s2.0-85009275116 (Scopus ID)
Note

Published online: 12 Jan 2017

Available from: 2017-08-25 Created: 2017-08-25 Last updated: 2017-08-25Bibliographically approved
Harati, E., Karlsson, L., Svensson, L.-E., Pirling, T. & Dalaei, K. (2017). Neutron Diffraction Evaluation of Near Surface Residual Stresses at Welds in 1300 MPa Yield Strength Steel. Materials, 10(6), 1-14, Article ID E593.
Open this publication in new window or tab >>Neutron Diffraction Evaluation of Near Surface Residual Stresses at Welds in 1300 MPa Yield Strength Steel
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2017 (English)In: Materials, E-ISSN 1996-1944, Vol. 10, no 6, p. 1-14, article id E593Article in journal (Refereed) Published
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.

Keyword
Residual stress; high strength steel; neutron diffraction; weld toe; low transformation temperature welding consumable
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-11065 (URN)10.3390/ma10060593 (DOI)000404415000027 ()28772953 (PubMedID)2-s2.0-85020406713 (Scopus ID)
Available from: 2017-06-29 Created: 2017-06-29 Last updated: 2017-12-05Bibliographically approved
Rehan, A., Medvedeva, A., Svensson, L.-E. & Karlsson, L. (2017). Retained Austenite Transformation during Heat Treatment of a 5 Wt Pct Cr Cold Work Tool Steel. Metallurgical and Materials Transactions. A, 48A(11), 5233-5243
Open this publication in new window or tab >>Retained Austenite Transformation during Heat Treatment of a 5 Wt Pct Cr Cold Work Tool Steel
2017 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 48A, no 11, p. 5233-5243Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
SPRINGER, 2017
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-11884 (URN)10.1007/s11661-017-4232-5 (DOI)000412849400010 ()2-s2.0-85029581719 (Scopus ID)
Available from: 2017-12-05 Created: 2017-12-05 Last updated: 2017-12-13Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0001-8822-2705

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