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Evaluation of pre-determined dilution of high strength steels by the Snapshot method
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.ORCID-id: 0000-0002-8298-292x
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.ORCID-id: 0000-0003-4265-1541
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.ORCID-id: 0000-0003-2596-5303
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
Visa övriga samt affilieringar
2021 (Engelska)Ingår i: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 139, artikel-id 106512Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Dilution is an unavoidable consequence of multi-material fusion processing, i.e. welding, cladding etc. In this paper we propose a novel method for controlled dilution experiments, analyzing microstructural trends of steel filler wire diluted with steel base metal. The highlight of this method is the control of processing conditions used to melt a pre-determined dilution of two high strength steels. The materials involved are S960QL base metal machining chips and a chopped under-matched wire consumable, which is used to increase the toughness of welded joints. These materials were combined in specific mass ratios in a prepared cavity and then melted by a pulsed laser beam. A high-speed RGB camera evaluated the relative spatial temperature of the melt surface. The molten mass then solidified into a uniform nugget, confirmed by energy dispersive x-ray spectrometry (EDS) to have a homogenous chemical composition (a ‘Snapshot’ nugget). Hardness values obtained for different dilution levels were compared to a narrow gap multi-layer laser weld (NGMLW), with a decreased dilution rate yielding a decreased hardness. The Snapshot microstructures created are similar to the different regions of the NGMLW, in the weld cap and in the body of the weld. Snapshot nuggets were also evaluated for non-metallic inclusion (NMI) size distributions relating to the dilution levels (NMIs are important indicators for acicular ferrite, which has been shown to increase impact toughness).

Ort, förlag, år, upplaga, sidor
Elsevier, 2021. Vol. 139, artikel-id 106512
Nyckelord [en]
Dilution, Narrow gap multi-layer welding, Laser welding, Snapshot method, Energy dispersive x-ray spectroscopy
Nationell ämneskategori
Bearbetnings-, yt- och fogningsteknik
Forskningsämne
Produktionsutveckling
Identifikatorer
URN: urn:nbn:se:ltu:diva-82060DOI: 10.1016/j.optlaseng.2020.106512ISI: 000614093000044Scopus ID: 2-s2.0-85097904003OAI: oai:DiVA.org:ltu-82060DiVA, id: diva2:1511523
Forskningsfinansiär
Interreg Nord, 2014-2020Europeiska regionala utvecklingsfonden (ERUF), 304-15588-2015Vinnova, 2019-00781
Anmärkning

Validerad;2021;Nivå 2;2021-01-01 (johcin);

Finansiär: EC Research Fund for Coal and Steel (709954)

Tillgänglig från: 2020-12-18 Skapad: 2020-12-18 Senast uppdaterad: 2021-05-07Bibliografiskt granskad
Ingår i avhandling
1. Laser welding and laser heat treatment of high strength steels
Öppna denna publikation i ny flik eller fönster >>Laser welding and laser heat treatment of high strength steels
2021 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Alternativ titel[sv]
Laser-svetsning och värmebehandling av höghållfast stål
Abstract [en]

Laser materials processing, including thermal treatment and laser welding has been undergoing continuous growth in the manufacturing industry for decades. A laser beam offers high precision and energy transfer, capable of various processing. For many cases a Gaussian beam is applied, but lately development of more complex beam shapes has been developed, where e.g. multiple beams (beam splitting) can be used for increased tolerances during welding.

This thesis presents six papers (Papers A-F) on welding of high strength steels, laser pulse shaping, thermal treatments, and microstructural investigations. Different methods for obtaining a desirable weld were investigated through tailoring of the laser beam process. This affected the resulting temperature fields and thermal histories of the specimens. Experimental analysis was supported through various in-situ observation techniques and metallurgical studies.

Papers A-C present thermal processing and chemical manipulation to obtain the desired microstructure, by introducing and applying the here introduced Snapshot method. Paper A explores tailoring a laser pulse to mimic a hybrid welding process, Paper B elaborates the simulation to a multi-cycle process, and Paper C explores dilution. The manuscripts utilize a specialized experimental setup, optical analysis methods, and standard thermal measuring techniques. Metallographic analysis showed that thermal process optimization and/or dilution rate control during welding improved weld zone characteristics.

Improvements also include joint macrostructure characteristics, which are impacted by process stability, the theme of Papers D-F. Melt pool phenomena are studied in depth in Papers D and E. Paper D explores material ejections in a single beam welding scenario. Paper E investigates six beam shapes, from a single beam to a quad-beam arrangement. Paper F studies hybrid welding, a process that was simulated in Papers A-C but focused on the stability of the process instead of thermally guiding the microstructure. 

The studies complement each other in knowledge and methods. Welding of high strength steel is joining method-dependent, which imposes a unique thermal profile that affects the microstructures. The microstructure is also influenced by the chemical composition, an important point when multiple materials are used. The studies contribute an analysis of certain aspects of thermal and chemical effects of different laser-based processes to further optimize processing of specifically high strength steels, though the aspects can be generalized to other metals

Ort, förlag, år, upplaga, sidor
Luleå University of Technology, 2021
Serie
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Nyckelord
Laser welding, heat treatment, high strength steel, Snapshot method, microstructure
Nationell ämneskategori
Bearbetnings-, yt- och fogningsteknik
Forskningsämne
Produktionsutveckling
Identifikatorer
urn:nbn:se:ltu:diva-84181 (URN)978-91-7790-848-7 (ISBN)978-91-7790-849-4 (ISBN)
Disputation
2021-09-09, E632, Luleå, 13:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2021-05-11 Skapad: 2021-05-07 Senast uppdaterad: 2022-01-17Bibliografiskt granskad

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Robertson, StephanieFrostevarg, JanNäsström, JonasKaplan, Alexander

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Robertson, StephanieFrostevarg, JanNäsström, JonasBerndtsson, ThereseKaplan, Alexander
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Produkt- och produktionsutvecklingInstitutionen för teknikvetenskap och matematik
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Optics and lasers in engineering
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