Welding of thick stainless steel plates up to 50mm with high brightness lasers

Thick-section stainless steels are widely used in the components and structures for nuclear power plant. Laser welding is being considered as a high-efficiency method instead of arc welding for some components, so as to improve the production efficiency and reduce the residual stresses of the heat-affected zone. In this paper, multi-passes narrow gap welding of 50mm thick Type 316L plates with an 8 kW disk laser was firstly investigated. The effect of welding conditions on the weld bead geometry and welding defects was studied. It shows that lack-of-fusion could be prevented by optimizing the relationship between laser power intensity and the deposited metal volume. Butt joint of 50mm thick plates with narrow gap could be performed with 8-layers welding at laser power of 6 kW and welding speed of 0.4 m/min. In order to reduce the weld passes further, gas jet assisted laser welding was tried to weld thick Type 316L plates with a 10 kW fiber laser. The result shows that butt-joint welding of 40 mm plated without filler wire could be performed at 0.3 m/min welding speed without porosity and other welding defects. As for 50 mm thick plate, good weld bead could be obtained with bead-on-plate welding from both sides at 0.2 m/min welding speed.