Abstract
The use of thin steel components that can be joined by one-layer-one-pass laser welding or laser-arc hybrid welding has been increasing with the trend of reducing the plate thickness by using higher strength steels. This has enhanced the demand for laser-arc hybrid welding of HT780 steels in the bridge and industrial machinery applications. Taking this trend into account, the authors have researched the suitable welding parameters and consumables for the hybrid welding process that combines laser and MAG arc welding for joining HT780 steel sheets. As a result the following welding parameters have been proven to be most appropriate for better root gap resistance and lower spatter: MAG arc for leading (kept at the right angle)/laser for trailing (kept at the pushing angle); laser-arc distance of 3-5 mm; laser's focus distance of ± 0 mm; and shielding gas of Ar-20%CO2. As to the welding wire for laser-arc hybrid welding of HT780 steel, the HT590-class arc welding wire of Cr-Mo-Ti type with a low amount of sol. titanium has been revealed to be suitable to obtain sufficient weld joint tensile strength and toughness. Applied plate thickness range of the most relevant wire is from 6 mm to 12 mm.
