Application of LBW and LAHW for fillet welds of 12 and 15 mm structural steel

Laser beam welding (LBW) and laser-arc hybrid welding (LAHW) are attractive joining methods of medium thickness (10-20 mm) plates in a single pass welding technique. Both utilize high energy process in order to achieve high penetration depth and high welding speeds offering substantial increase in productivity. Deep and narrow welds were produced by LBW and LAHW suffered from high hardness (> 350 HV), primarily in the coarse-grained heat affected zone in joined 12 mm and 15 mm thick plates. In addition, weld imperfections like porosity, cracks, undercuts, or humping may occur. Mainly bainite and lath martensite were formed in LBW joints. By contrast, LAHW provided high volume fraction of acicular ferrite in the upper area. Filler wire was not transported to the root zone in fillet welds with flat position since standard arc mode caused unstable weld pool formation. A numerical model was developed to predict cooling rates and correlated to hardness and microstructure evolution. (C) 2019 The Authors. Published by Elsevier B.V.