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Eingeladener Vortrag
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Laser Plasma Hybrid Welding of Austenitic Stainless Steels - Phenomena of Process Instability
(2007)
Laser plasma hybrid welding has been proved to be a very stable hybrid welding process and
welds of high quality can be produced, especially if high surface quality and low spattering is
demanded such as in welding fabrication of high alloyed austenitic stainless steels.
In particular cases, even though welds display high outer quality, X-ray examinations
revealed weld defects which may range from low porosity to blowhole-like cavities. The
phenomena and the main influencing parameters such as arc current, welding speed and
focal point position are discussed. Parameter fields will be suggested for welding plates of
different austenitic stainless steel grades with thicknesses ranging from 3 to 8 mm. The
results are based on welding experiments carried out using a 4.4 kW diode pumped Nd:YAGlaser.
Thus, also the influence of the feeding fibre diameter has been investigated and it was found
that the resulting beam shape has a major effect on the welding performance.
The results of a collaborative research project on laser beam weldability of carbon steels of
high sheet thickness are presented. That includes single and multiple pass welding of 16 mm
and 20 mm thick plates, as well as the investigation of acceptable tolerances i.e. gap
bridgeability and edge misalignment. For the welding experiments fibre lasers with 8 kW,
20 kW laser power and different MAG-techniques were used in various applications.
With the 20 kW fibre laser 16 mm plates could be welded with a single pass, 20 mm required
a seam preparation or alternatively preheating of the material. For multi pass welding with
8 kW laser power a joint preparation with a single V-butt joint with a broad root face (Ygroove)
was applied. The root pass was always welded with a hybrid process, the filler
passes with a hybrid process as well as a MAG process which produced the best results.
Anwendung der Faserlasertechnologie und Hybridtechnik zum Schweißen von dickwandigen Konstruktionen
(2008)
Single-pass solid-state laser welding of plates in the thickness range of 10 to 20 mm became
possible with the invention of the fibre laser. This new technique provides excellent beam
quality at powers as high as 20 kW or more, and has proved applicable in several industrial
applications. By replacing conventional methods with the fibre laser, it is possible to avoid
multiple-pass welding that requires time-consuming bevelling. The high energy density of the
fibre laser beam also reduces the heat input and consequently the distortion. However, the
rapid solidification and cooling associated with laser welding can cause imbalance of the
microstructure of duplex stainless steel weldments, where excessively high ferrite contents
may reduce the corrosion resistance and the ductility of the material. The solution is normally
to add nickel-based filler wire and to increase the heat input. By using a hybrid welding
process where the laser beam and the gas metal arc (GMA) process act in a common
process zone, filler metal can be added to the molten pool at higher heat input and at the
same time, higher welding speed and deeper penetration can be achieved. In this work,
13.5 mm thick 2205 (EN 1.4462, UNS S31803) was fibre laser-GMA hybrid welded in a
single-pass using 14 kW of laser power and 2209 (ISO 22 9 3 L N) as filler wire for the GMA
process. The resulting welds were free from defects, with smooth surfaces and full
penetration. The investigation examines the weld metal microstructure and the effect on
corrosion resistance and mechanical properties. The option to add nickel foil when hybrid
welding was also investigated as comparison and the effect on austenite formation was
evaluated.