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Laser beam welding of carbide free bainitic steel
2009 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Because of its very good mechanical properties and its relatively low costs carbide free bainitic steel has become an interest for research and development during the recent years. In this work welding tests on these steels are discussed for the first time. It is known that welding of steels with a medium or high carbon content leads to brittleness in the heat affected zone and the fusion zone because of martensite and crack formation. The steel used in this work had a carbon content of 0.54 % and a silicon content of 1.44 % to prevent carbide precipitation. It was austempered at 300 °C which lead to a carbide free bainitic microstructure with an average hardness of 442HV0.5. A ytterbium fibre laser was used for on plate bead welding and a furnace or an induction coil was used for heat treatment. The different experiments were equal in laser parameters but differed in pre- and post weld heat treatment. Unsurprisingly, the welds showed martensite and hardness values up to 796HV0.5 when welded without heat treatment. But certain heat treatment methods could lead to different microstructures and improved hardness values. The most promising results were achieved by a combination of pre- and post-weld heat treatment at 300 °C with a maximum hardness of 504HV0.5 and by a heat treatment method which was based on the quenching and partitioning concept and had a maximum hardness value of 426HV0.5.

Place, publisher, year, edition, pages
Keyword [en]
Technology, Laser beam welding, carbide free bainite, preheating, post-weld heat treatment, induction, quenching and, partitioning, fibre laser
Keyword [sv]
URN: urn:nbn:se:ltu:diva-43894ISRN: LTU-PB-EX--09/091--SELocal ID: 1b750dd9-e271-440f-8225-e02a95a73914OAI: diva2:1017136
Subject / course
Student thesis, at least 30 credits
Educational program
Materials Engineering, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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