Thick Plate CO₂-Laser Based Hybrid Welding of Structural Steels

Abstract

Laser and hybrid laser-arc welding are after two decades of intensive work now well-established processes in the welding of structural steels as well as other materials. Many results have been reported over the years and many advantages in comparison with traditional welding processes have been obtained. Very thick part laser welding using penetration depth in excess of approximately 12 mm in structural steel does however continue to be a serious challenge. This is partly due to limitations in the achievable welding depth because the penetration as a function of laser power shows a very non-linear behaviour, and partly to the large molten volume that must be controlled. Although fibre- and disc-lasers today are being developed to high powers, CO₂-lasers sources are still dominating larger penetration welding. In the present investigation the potential and limitations of hybrid CO₂-laser/MAG welding of thick plate structural steels have been investigated. Welds in excess of 12 mm thickness of structural steels are presented together with achieved mechanical properties as e.g. hardness, toughness and fatigue. The investigations were made using structural steels of the grades S235, S355 and S690QL.