P 973 – Welding of Steel Structures with the Laser Beam in Vacuum
The welding of heavy wall thicknesses is to date the domain of the Submerged Arc Welding (SAW) with all its process related requirements and limitations. The beam welding technologies Electron Beam Welding and Laser Beam Welding in Vacuum have a huge potential for increasing the efficiency. The combination auf a massive reduction of the welding passes and the abdication of filler material lead to a huge reduction of the cycle time and the costs.
The target of the research project is to provide an innovative and efficient welding technology for the joining of heavy wall thickness structures to the industry. The technology shall prepare the steel processing industry for the upcoming challenges in the field of the
renewable energies and in the building and construction industry.
In the first step, the welding machine for Laser Beam Welding in Vacuum was rebuild for the heavy plate thickness range of up to 60 mm. The relation between the ambient pressure, welding speed, focal position etc. on the aspect ratio and the weld seam quality for the joining of unalloyed steel with heavy wall thickness has been determined by bead on plate welding trials. The knowledge has then been transferred to connection welding of unalloyed steels. The submitted research targets (30 mm plate thickness in one welding pass and 60 mm plate thickness in two-run welding) have been exceeded. In one welding pass 50 mm plate thickness and in two-run welding 110 mm have been joined successfully. The achieved weld seam quality has been tested by metallographic methods, nondestructive testing (visual inspection following the DIN EN ISO
13919 and x-ray analysis) and determination of the mechanical technological values of the weld seam.
The extensive results, which have been achieved in the field of unalloyed steels, have been transferred to the welding of duplex stainless steel in the second part of the project. This transfer has proven to be difficult due to the different material properties (viscosity o the molten material, heat conduction) and especially due to the alloying element nitrogen. Based on an extensive process development the project targets of 10 to 30 mm plate thickness have been achieved nevertheless. The weld seam quality has also been tested by metallographic methods, nondestructive testing (visual inspection following the DIN EN ISO 13919 and x-ray analysis) and determination of the mechanical technological values of the weld seam. The microstructure of the weld metal (relation of austenite and ferrite) and the corrosion resistance have been analyzed additionally. The working hypothesis that different nitrogen partial pressure levels in the working atmosphere can reduce or prohibit the degassing of nitrogen and thereby positively affect the microstructure (nitrogen is used as alloying element to create austenite) has been proved by measurements. However, the effect is not strong enough to create a balanced proportion of austenite and ferrite in the weld seam. Therefore, it is currently not possible to achieve a balanced proportion of austenite and ferrite without filler material or a post weld heat treatment.
Only available in german language.
U. Reisgen, S. Jakobs, S. Olschok, C. Turner
FOSTA – Research Association for Steel Application