Welding thick-walled steel sheets with established joining processes such as gas metal arc welding and submerged arc welding is often associated with very long production times and high-energy input due to the low welding depth and welding speed. Laser beam welding in vacuum enables efficient joining of thick-walled components with only one weld seam at moderate working pressure of 0.2 mbar. This paper demonstrates the extension of the known limits of laser beam welding in vacuum using up to 40 kW laser power.