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Effects of surface and cut oxides on laser arc hybrid welding stability of high strength steels
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development. (Manufacturing Systems Engineering)ORCID iD: 0000-0002-8298-292X
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
2021 (English)In: Article in journal (Other academic) Submitted
Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2021.
Keywords [en]
Laser beam welding, high strength steels, heat treatment, microstructure, Snapshot method
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-83451OAI: oai:DiVA.org:ltu-83451DiVA, id: diva2:1553160
Available from: 2021-05-07 Created: 2021-05-07 Last updated: 2021-05-07
In thesis
1. Laser welding and laser heat treatment of high strength steels
Open this publication in new window or tab >>Laser welding and laser heat treatment of high strength steels
2021 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[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

Place, publisher, year, edition, pages
Luleå University of Technology, 2021
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keywords
Laser welding, heat treatment, high strength steel, Snapshot method, microstructure
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-84181 (URN)978-91-7790-848-7 (ISBN)978-91-7790-849-4 (ISBN)
Public defence
2021-09-09, E632, Luleå, 13:00 (English)
Opponent
Supervisors
Available from: 2021-05-11 Created: 2021-05-07 Last updated: 2022-01-17Bibliographically approved

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CiteExportLink to record
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