| Weld defects and its control behavior in narrow gap laser wire multilayer welding of thick high strength steel plates are mainly studied.Especially,lack of fusion and porosity in narrow gap laser welding with filler wire have been researched in the way of welding procedure.Control on the defects have been made by the research.Firstly,effects on lack of fusion with different defocus distances,laser power,feeding wire speed and welding speed have been studied.The study turned out increasing the defocus distance can improve the side wall fusion in the narrow gap and +20 mm is suitable for this study.Adjusting the ratio among the laser power,feeding wire speed and welding speed can largely remove the defects about the lack of fusion.When the welding speed is 0.42 m/min,the ratio between laser power and feeding wire speed ranging from 0.89 to 1.33 can eliminate incomplete fusion.Then,how welding parameters such as laser power,feeding wire speed and welding speed affected the porosity in the narrow gap has been studied.Pore in multilayer laser welding mainly appeared in the zone of bottom and center and it belonged to craft blowhole.Balance between the front wall of t and rear wall in the keyhole broke down by high laser power,low feeding speed and welding speed,which made keyhole unstable,causing many pores.What's more,increased depth of joint made the pore through more distances away from the joint and some of pores stayed in the weld because of long distance.Finally,thick plates with optimized parameters in the narrow gap laser wire multilayer welding have been well welded.The weld with filler wire consists of a mass of acicular ferrite and a few of granular bainite and it shows good impact toughness.The martensite mainly makes of the HAZ of weld.The highest value of hardness is obtained in the HAZ,and the value increases as the heat input increases.The fractures occur on the base metal of tensile test specimens.The weld has fine mechanical properties. |
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