Product Code: ICAL06_105

Avoiding Hot Cracking by Induction Based Change of Thermal Strains during Laser Welding
Berndt Brenner, Fraunhofer IWS Dresden; Dresden Germany
Gunther Goebel, Fraunhofer IWS Dresden; Dresden Germany
Presented at ICALEO 2006

Hot cracking in welding is still an unresolved problem for a wide range of materials. Restricting the chemical composition usually helps to reduce this problem, e.g. limiting the sulphur content on steels to very low levels. But for industrial applications such additional restrictions on the material norm are hardly applicable. Furthermore some steels grades like free cutting steels contain additional sulphur which counteracts this approach. Therefore a new effective technology was developed to reduce the cracks without regard to the composition: The thermo-mechanical reason for the hot cracks, the thermal stresses in the weld are counteracted. Volumes next to the weld are directly and effectively heated by induction in such a way that their thermal expansion reduces the weld strain during the critical stages of the solidification. This technology was successfully tested on strongly hot cracking sensitive free cutting steel plates with thicknesses up to 6 mm. It will be shown that this technology enables fully crack free laser welding of hardenable steels with sulphur content up to 0,2 % S and carbon content up to 0,45% C. Possibilities and limits of this approach were evaluated in regard to metallurgical and mechanical factors by varying both material composition and geometry as well as induction parameters.

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