Study On Laser MAG Hybrid Welding Process And Joint Properties Of Q355C

Offshore wind power,as a new renewable energy development and utilization field,has promoted the development of low-carbon economy in China with its unique advantages.Low alloy high strength steel Q355C is one of the most commonly used steels for offshore wind power tower due to its high strength,high plasticity and high toughness.Submerged arc welding and CO₂ gas shielded welding are commonly used in the welding of wind power tower tubes at home.There are some problems such as low welding efficiency and poor welding forming quality,which restrict the development of domestic offshore wind power equipment manufacturing industry.Laser arc composite welding is a new and high quality welding method,which can give full play to the advantages of laser and arc heat sources.With its higher production efficiency,excellent gap bridging performance and better process stability,it has obvious advantages in the welding of medium and thick plates.Therefore,laser arc composite welding technology has a broad application prospect in the field of offshore wind power.In this paper,the laser MAG hybrid welding technology is used to weld the 25mm thick low alloy high strength steel Q355C.The single factor variable method is used to study the influence of different welding parameters(wire spacing,wire feeding speed,defocusing amount,laser power,welding speed and heat source sequence)on the weld formation and penetration ability,and the process parameters are optimized.On the basis of the research of plate surfacing welding,the single penetration welding of 25 mm thick low alloy high strength steel Q355C plate butt welding is completed by opening“Y”groove and under the best technological parameters.The weld is well formed and free of defects.The optimum process parameters are as follows:the distance between the polished wires is 3 mm,the wire feeding speed is 11.5 m/min,the defocusing amount is-10 mm,the laser power is 23k W,and the welding speed is 0.9 m/min.The microstructure of different areas of the welded joint is observed and analyzed.The results show that the weld microstructure of arc action zone and laser action zone of laser MAG hybrid welding joint is composed of acicular ferrite and pearlite.The coarse grain zone in the arc action zone and the heat affected zone of the laser action zone is composed of coarse lath martensite.Because the arc action zone is heated and cooled slowly,the lath martensite in the coarse grain zone of the arc action zone is coarser than that in the laser action zone.The microhardness of weld zone is lower than that of heat affected zone and higher than that of base metal.The microhardness of the weld metal in the laser zone is higher than that in the arc zone due to the finer grains in the laser zone.The average tensile strength and yield strength of the composite welded joint are 522MPa and 366MPa,and the fracture of the tensile specimen occurs on the base metal.The results show that there is no crack and the bending property is good after 180°transverse bending test.The welding joint has good impact toughness under the condition of 0?.The average impact absorption work of weld,heat affected zone and base metal is 51J,46J,53J,respectively,which all meet the requirements of the standard,and the impact specimen of weld belongs to ductile fracture.The research results provide experimental and theoretical basis for laser MAG hybrid welding of tower plate in offshore wind power field.