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Fatigue strength of laserhybridwelded high strength steel
2008 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Welding is a process that is used to join two or more components, usually for metallic material. The welding process is of great importance and is used when complex shapes or very big structures are needed. Instead of making one big part, it is possible to join smaller parts which facilitates i.e. transportation and production. The disadvantage of welded material is that its mechanical properties deteriorate which restricts its usability more than unwelded material. The restriction is mainly dependent on, except the material used what kind of welding process that is used. There are many different welding processes but in this master thesis conventional MAG-welding and a relatively new welding process called laserhybridwelding is used. Duroc Rail AB in Luleå has developed a laserhybridmethod that is used to weld 4 mm thick DOMEX 650 MC steel sheet for production of ore wagons. Since little studies about the fatigue strength of laserhybridwelded material have been made, I was given the task to do a research in this field. In the current study a high strength steel sheet called DOMEX 700 MC with a thickness of 5 mm was used. This report contains: • Fatigue strength results for one and two string MAG-welded DOMEX 700 MC steel sheet • Fatigue strength results for transverse- and longitudinal tested laserhybridwelded DOMEX 700 MC steel sheet • Comparisons of the fatigue results for the different welding methods • HAZ- and microstructure investigation • Hardness measurements • Impact toughness results for laserhybridwelded DOMEX 700 MC steel sheet The main objective of this master thesis was to investigate how effective the laserhybridwelding process is and make a comparison to conventional MAG- welding. There will also be a theoretical part highlighting the compensation of fatigue strength for butt welded structures and the importance of various factors that contribute to the fatigue failure of welded material. It has been shown in this study that the laserhybrid method is a better method to join high strength steel (DOMEX 700 MC) and has many advantages. A C-value of 192 MPa was obtained for the transverse tested laserhybrid method, which is approximately two times higher than the conventional MAG- welding used in this study. The hardness and impact toughness were almost the same as for the two string MAG-weld. Also, the HAZ was smaller for the laserhybridwelded specimens.

Place, publisher, year, edition, pages
Keyword [en]
Technology, Laserhybrid
Keyword [sv]
URN: urn:nbn:se:ltu:diva-43024ISRN: LTU-EX--08/033--SELocal ID: 0f279861-61d3-4998-b95a-55a2eda3e4bfOAI: diva2:1016251
Subject / course
Student thesis, at least 30 credits
Educational program
Engineering Physics, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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