Authors:
Greger Wiklund
Department of Applied Sciences and Mathematics, Luleå University of Technology, SE-971 87 Luleå, Sweden

Odd Akselsen
SINTEF Materials and Chemistry, P. O. Box 4760 Sluppen, NO-7465 Trondheim, Norway

Arve J. So&slash;rgjerd
Kvaerner Verdal AS, Material Department, Hamnevegen 7, NO-7650 Verdal, Norway

Alexander F. H. Kaplan
Department of Applied Sciences and Mathematics, Luleå University of Technology, SE-971 87 Luleå, Sweden

Hot cracks were frequently found in double sided laser-arc hybrid welding thick section (20 mm) low carbon steel. Other research has usually investigated the metallurgical resolidification mechanisms of the welded metal alloy, but here possible relationships between the hot cracks and geometrical aspects of their surrounding weld and heat-affected zone cross sections were studied. The motivation behind this research was to identify guidelines for laser-arc hybrid welding to avoid hot cracks. Weld cross sections were used to analyze hot cracking because they are rather easy to prepare and straightforward to alter through the process parameters. In this study, hot cracks were found in a preferred geometrical window, namely, in the middle of the narrow deep region of the weld which was generated by the laser beam. From the cross section analysis, a first indicator was that a more inclined, converging shape of the lower part of the weld cross section can avoid hot cracks, associated with different energy input and resolidification front geometry. Significant reduction of the welding speed has avoided hot cracks, being a second indicator.