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Evaluation of laser weldability of 1800 and 1900 MPa boron steels
RISE, Swerea, KIMAB. RISE - Research Institutes of Sweden, Materials and Production, KIMAB.ORCID iD: 0000-0001-8933-6720
RISE, Swerea, KIMAB.
Volvo Cars, Sweden.
Gestamp, Spain.
2016 (English)In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 28, no 2, article id 022426Article in journal (Refereed) Published
Abstract [en]

Ultrahigh strength steels are frequently used within the automotive industry. The driving force for use of these materials is to exchange thicker gauges to thinner and lighter structures. To get excellent strength and beneficial crash performance, the steel is microalloyed with boron which contributes to the 1500 MPa tensile strength. Increasing the carbon content will give superior tensile strength up to 2000 MPa. Welding of these components is traditionally done by resistance spot welding, but to get further productivity and increased stiffness of the structure, laser welding can be introduced. Welding of boron alloyed high strength steel is in general a stable and controlled process, but if increasing the carbon content quality issues such as cracking could possibly be a problem. In the present study, weldability of two different hardened boron steels with tensile strengths of 1800 and 1900 MPa, respectively, has been evaluated. Laser welding has been done in a lap joint configuration with 3.8-4.7 kW and varying welding speed between 3.5 and 5.5 m/min. As reference, results from more conventional 1500 MPa boron steel have been compared to 1800 and 1900 MPa boron steels to show the influence of the carbon content. Metallographic investigation, hot crack test, cold crack test, shear tensile, and cross-tension strength tests have been done. The results show that a weld quality similar to that for conventional boron steel can be achieved. Cracking and other defects can be avoided. As expected when welding martensitic steels, the failure mode in tensile testing is brittle. No weld defects have been found that influence strength. The sheet interface weld width, which together with stack-up thickness correlates with strength of the joint, could be increased by increasing the heat input and defocusing the laser beam. The effect of increased carbon content on weldability will be discussed more in detail, as well as the risk of cracking.

Place, publisher, year, edition, pages
Laser Institute of America , 2016. Vol. 28, no 2, article id 022426
Keywords [en]
Automotive industry, Boron, Cracks, Defects, High strength steel, Laser beam welding, Laser beams, Martensitic steel, Quality control, Resistance welding, Spot welding, Tensile testing, Weldability, Welding, Welds, Carbon content, Controlled process, Crash performance, Driving forces, Laser weldability, Resistance spot welding, Tension strength, Ultra high strength steel, Tensile strength
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:ri:diva-41210DOI: 10.2351/1.4944102Scopus ID: 2-s2.0-84963582700OAI: oai:DiVA.org:ri-41210DiVA, id: diva2:1377352
Available from: 2019-12-11 Created: 2019-12-11 Last updated: 2019-12-11Bibliographically approved

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Fahlström, Karl

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