Welding stability and fatigue performance of laser welded low alloy high strength steel with 20 mm thickness

The butt joint of low alloy high strength steel with 20 mm thickness was joined by combining with high power laser welding and narrow gap hybrid laser-arc welding. For the high power laser welding, the laser power was a decisive factor of the weld formation: excessive laser power lead to unstable behavior of molten pool and key hole, while insufficient laser power resulted in the lack of penetration. For the narrow gap hybrid laser-arc welding, arc behavior was closely related to the dynamic behavior of the molten metal at tip of the wire. Unstable behavior of the molten metal at tip of the wire caused variable arcing positions, leading to the arc deflection and arc burning up. The narrow gap grooves were heated unevenly when the arc was whether deflection or burning up, leading to the formation of the sharp corner areas and lack of fusion defects. The fatigue fractures of both laser weld and hybrid weld were made up of the crack initiation areas, the crack propagation areas and the transient fracture areas. Fatigue property of the laser weld was better than that of the hybrid weld, which was thought to be strongly associated with the fine multidirectional grains within the laser weld and the precipitation of particle phases inside the hybrid weld.