Process Study Of Q345 Multi-layer Laser Welding With Wire Filling In Narrow Gap

This paper has mainly studied the multilayer laser welding technology,and its applicability in shipbuilding industry has been discussed.The Q345 steel plate with 18mm thick was welded by the multilayer laser welding with filler wire,the narrow gap groove,a wire guiding device and a gas guiding device were designed,which were suitable for the welding of thick plate.To ensure the stability of welding process,the wire feeding and the protective gas must be sent into the internal groove normally.To meet the requirements of single factor variables,the blunt edge laser welding and the laser welding with filler wire was carried out layer by layer in the same kind of narrow gap groove.After it,the welding quality and the influence of welding parameters was analyzed,and the groove design and the parameters were optimized.In the optimization design for butt joint groove size,the depth of the blunt edge is 3mm,the width of the gap groove is 2 mm,and the angle of side wall is 0 degrees.When the laser power is 3 kW,the welding speed is 0.3 m/min,the wire feeding speed is 10 m/min,the focal shift is 5 mm,and the flow of protective gas is 15 L/min,the welding quality is best,and the average layer bead height is 5.07 mm.After the design and improvement of welding groove size,the 18 mm thick ship steel joint has been welded,the microstructure of the weld zone is mainly composed of granular bainite and martensite.HAZ is mainly presented in the form of lath martensite,the size of the coarse grain zone is large,but the fine grain area is in a small size,which contains a small amount of granular bainite.The two-phase area contains a great deal of martensite and sorbite,compared with the weld zone,the remelting region has a slightly larger size,which is mainly composed of bainite and tempered martensite.The results of the hardness test of the weld joint is shown as follow:The weld zone in the joint with blunt edge laser welding has a significantly higher hardness than that of the groove laser welding with filler wire.But instead,the hardness of the heat affected zone in the joint with filler wire welding is much more higher.The middle layer of the joint is remelted,and the weld microstructure of remelting zone has been involved in the calendar tempering process,which causes a higher hardness.The tensile test results show that:The tensile samples were all broken in the base metal,indicating that the strength of the joint is higher than that of the base metal.Considering the average hardness of the parent material is the lowest,it shows that the mechanical properties of the parent material is the weakest.