Narrow Gap Scanned Laser Welding With Filling Wire For Thick High-Strength Steel

High strength steel has excellent comprehensive performance and is widely used in the manufacturing process of power generation equipment,machine tool equipment,ship manufacturing,petrochemical,Marine engineering,aerospace and other major equipment.Narrow gap scanned laser with filling wire welding has become the leading edge of the thick plate welding,the laser bead welding compared to conventional laser welding,with inhibition of pores,improve weld,enlarge the tolerance clearance,improve the stability of plasma and molten pool,and improve the joint mechanical properties etc,narrow gap welding can reduce welding groove to improve the efficiency of welding,and can be implemented under the low heat input of thick plate welding,after welding deformation is small at the same time,the residual stress is small.Therefore,this paper aimed at the field of naval ships,carried out research on Narrow gap scanned laser with filling wire vertical welding process of 120 mm thick and high-strength steel,so as to solve the low efficiency of TIG and MAG welding and the large deformation problem of heat input of submerged arc welding and develop a new process.First research on the identity of the narrow gap scanned laser with filling wire welding technology,the study found that the larger the welding heat input,solidification cracks in the weld center and upper position,because of its high weld penetration and larger than the width of weld depth,cooling speed faster,and the weld is equilibrium solidification,the center of the weld residual liquid underfill,cracking under tensile stress.Through the process optimization,the laser power can be reduced,the depth to width ratio of the weld can be improved,and the generation of solidification cracks can be effectively controlled.Then the welding technology of narrow gap laser scanned wire filling vertical welding was studied.In the studies of different scanned trajectories,the vertical scanned had better weld formation and lower porosity.With a scanned range of 2 ~ 2.5mm and a scanned frequency of 60 ~ 90 HZ,the weld was well formed and the porosity was as low as 0.8%.The effects of laser power,welding speed and wire feeding speed on the depth of the weld width layer were studied by orthogonal experiment.By combining groove design and reasonably controlling welding seam forming,the optimized welding process parameters range can be obtained as follows: The welding process parameters are laser power 3 ~ 3.5kw,welding speed 0.3 ~ 0.35m/min,wire feeding speed 3 ~ 3.5m/min.The vertical scanned trajectory is adopted,the scanned range is 2 ~ 4mm,and the scanned frequency is 60 Hz.The microstructure and properties of 120 mm high strength steel narrow gap laser scanned wire filling vertical welding joints were evaluated.Results show that laser render the weld microstructure of lath martensite,the weld microstructure of filling layer of lath martensite,hardness is higher than the underlying,microhardness in HV1:420,filling layer and hotspots of tempered martensite lath ferrite and side,cover the surface of lath martensite,cover layer heavy hotspots mainly for granular bainite,120 mm joint tensile strength an average of 875 mpa,broken in the parent metal;-50 ? impact energy for 27 j,area and shear lips there is a lot of tough fibers nest,extension area as the cleavage fracture;The porosity in the fiber area has a great influence on the impact energy at low temperature.