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Session Chair: Prof. Michael Rethmeier, Bundesanstalt für Materialforschung und -prüfung (BAM), Germany
Location:Room 1 ICM
10:00am - 10:15am
High-power joining of duplex steels using laser beam-submerged arc hybrid welding
Rabi Lahdo1, Sarah Nothdurft1, Jörg Hermsdorf1, Patrick Urbanek2, Markus Puschmann2, Frank Riedel2, Stefan Kaierle1, Ludger Overmeyer1
1Laser Zentrum Hannover e.V., Germany; 2Fraunhofer-Institut für Werkzeugmaschinen und Umformtechnik IWU, Germany
Duplex steels are used in many application fields due to their outstanding performance in respect to strength, toughness and corrosion resistance. These properties result from a microstructure of delta ferrite and at least 30 % of austenite. Hitherto, duplex steels are welded using multi-pass arc welding characterized by a low efficiency. Beam welding has not been successful due to the low ratio of austenite formed. Aim of this study is the development of a reliable and efficient laser beam-submerged arc hybrid welding process for duplex steel 1.4462 (t= 15 mm) with a high proportion of austenite using a disc laser beam source (PL= 16 kW). The influence of the process parameters on the stability of the process are investigated by cross-section and visual inspection. As a result, a stable and efficient one-layer hybrid process was archived. Furthermore, a higher ratio of austenite compared to laser beam welded seams forms.
10:15am - 10:30am
Joining ultra-high strength steels by edge welds
Christoph Wendt1, Martin Dahmen2, Viktoria Olfert3, Alexander Sagel1
1Scansonic MI, Schwarze-Pumpe-Weg 16, 12681 Berlin, Germany; 2Fraunhofer Institute for Laser Technology, Steinbachstrasse 15, 52074 Aachen, Germany; 3Laboratory for Material and Joining Technology, Paderborn University.Pohlweg 47-49, 33098 Paderborn, Germany
An advantage of edge welding is the possible reduction in the required flange length compared to conventionally welded lap joints. As part of a pilot study, this method has been applied to welding of a press hardened martensitic chromium steel in similar and dissimilar joints to current high and ultra-high strength steels. A dedicated optical set-up was used to implement these welds. High-frequency beam oscillation was used to ensure mixing of the different materials and to prevent crack formation which appeared mainly in the combination with the ferritic-pearlitic grade. The welding results are evaluated using micrographs, hardness tests and tensile tests. For the tensile testing, an adapted LWF-KS2-sample geometry was designed to generate for the first time reliable comparative results compared to conventionally overlap-welded laser welds.
10:30am - 10:45am
Joining technology and mechanical properties of laser-beam welded joints with martensitic chromium steels
Martin Dahmen1, Jörg Baumgartner4, Benjamin Möller2, Viktoria Olfert3, Rainer Wagener2
1Fraunhofer Institute for Laser Technology, Germany; 2Fraunhofer Institute for Structural Durability and System Reliability, Bartningstrasse 47, 64289 Darmstadt, Germany; 3Laboratory for Material and Joining Technology, Paderborn University.Pohlweg 47-49, 33098 Paderborn, Germany; 4Technical University of Darmstadt, Mechanical Engineering Department, Research Group SAM, Otto-Berndt-Strasse 2, 64287 Darmstadt, Germany
Investigations were undertaken on welding of press-hardened martensitic stainless steels in similar joints as well as in combination with state-of-the-art and modern steel grades. Parameter development was conducted for square-butt and lap joint configuration aiming at the production of defect-free welds. In order to homogenise the mechanical properties of the weld area, a heat treatment has been developed and applied successfully. Tests on load capacity of lap joints have been carried out under quasi-static and dynamic loading using the LWF-KS2 concept. Emphasis is laid on the investigation of contour welds. Especially for the chromium steel a strong dependence on the load angle was detected. Heat treatment led to a significant improvement of strength and ductility. Independent of heat treatment and seam weld shape, uni-directional fatigue testing of lap joints shows similar endurable load amplitudes. The critical location of failure is the intersection of the fused zone with the joint plane.
10:45am - 11:00am
Impact of sulphur content on spattering and weld seam shape in steel specimens using modified side-gas application technique
Goran Jovic1,4, Axel Bormann1, Johannes Proell2, Thomas Niendorf3, Stefan Boehm4
1Robert Bosch GmbH, Manufacturing Center of Competence Laser Welding, Am Börstig 2, 96052 Bamberg, Germany; 2Robert Bosch GmbH, BaP/TEF1.2 – Laser Material Processing and Joining Technology, Am Börstig 2, 96052 Bamberg, Germany; 3Institute of Materials Engineering – Metallic Alloys, University of Kassel, Mönchebergstr. 3, 34125 Kassel, Germany; 4Department for Cutting and Joining Manufacturing Processes, University of Kassel, Kurt-Wolters-Str. 3, 34125 Kassel, Germany
Laser welding experiments have been carried out using stainless steel specimens (1.4003/1.4005) with different sulphur contents (S1:10ppm, S2:210ppm, S3:2770ppm). A parameter for spatter control, the capillary widening ratio mainly affected by the side-gas jet is considered. This value can be controlled by welding speed, laser power and side-gas pressure. Decreasing the sulphur content resulted in (1) a shift of the humping threshold to higher side-gas pressure and (2) an increase in weld seam bulge while decreasing spatter quantity at the same time. For S1 and S2, aspect ratios of R≥3 were achieved while spattering could not be detected by high speed imaging at 2000 fps. By increasing the welding speed from 1.5m/min to 3.0m/min and a simultaneous adaption of laser power, differences in spattering and weld seam shape between S1 and S2 were minor, indicating that higher melt pool velocities acting in welding direction dominate the surface tension driven effects.