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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, 11-23 p.Article 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, 39-47 p.Article 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, 150-156 p.Article 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, 405-415 p.Article 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, 64-74 p.Article 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, 573-579 p.Article 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, 1-14 p., 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, 5233-5243 p.Article 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
Rehan, A., Medvedeva, A., Högman, B., Svensson, L.-E. & Karlsson, L. (2016). Effect of Austenitization and Tempering on the Microstructure and Mechanical Properties of a 5 wt% Cr Cold Work Tool Steel. Steel Research International, 12(1 December), 1609-1618.
Open this publication in new window or tab >>Effect of Austenitization and Tempering on the Microstructure and Mechanical Properties of a 5 wt% Cr Cold Work Tool Steel
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2016 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 12, no 1 December, 1609-1618 p.Article in journal (Refereed) Published
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.

Keyword
Cold work, tool steel, austenitization, tempering, retained austenite, impact toughness
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-9689 (URN)10.1002/srin.201600012 (DOI)000392632900005 ()2-s2.0-84971330355 (Scopus ID)
Available from: 2016-12-16 Created: 2016-08-10 Last updated: 2017-04-24Bibliographically approved
Harati, E., Svensson, L.-E., Karlsson, L. & Hurtig, K. (2016). Effect of HFMI treatment procedure on weld toe geometry and fatigue properties of high strength steel welds. In: Procedia Structural Integrity: . Paper presented at 21st European Conference on Fracture, ECF21, 20-24 June 2016, Catania, Italy (pp. 3483-3490). , 2.
Open this publication in new window or tab >>Effect of HFMI treatment procedure on weld toe geometry and fatigue properties of high strength steel welds
2016 (English)In: Procedia Structural Integrity, 2016, Vol. 2, 3483-3490 p.Conference paper, Published paper (Refereed)
Abstract [en]

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

Keyword
Fatigue strength, high frequency mechanical impact treatment, high strength steel, weld toe
National Category
Mechanical Engineering
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-9598 (URN)10.1016/j.prostr.2016.06.434 (DOI)
Conference
21st European Conference on Fracture, ECF21, 20-24 June 2016, Catania, Italy
Available from: 2016-07-24 Created: 2016-07-24 Last updated: 2017-08-23Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-8822-2705

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