Study On The Welding Process And Joint Microstructure Achieved By Narrow Gap Laser Welding With Filler Hot Wire For Q420qE Steel

As a kind of high energy beam welding method,narrow gap laser wire filling welding technology has attracted extensive attention at home and abroad due to its advantages such as less material filling,less post-welding deformation,large depth to width ratio of weld seam and narrow heat affected zone.Because the laser is used to melt both the base metal and the wire in the narrow gap laser wire filler welding,the cladding efficiency of the wire is limited.If the wire is pre-heated by hot wire equipment in the welding process,reducing the dependence on the laser heat source in the melting process of the wire,it will greatly improve the deposition efficiency and contribute to the welding process.In this paper,a study was carried out on the welding technology of narrow gap laser fillet welding for thick steel plates with low alloy and high strength for Bridges.By changing the laser power,heating current,welding speed,wire feeding speed,defocusing amount and other process parameters,the surfacing welding was carried out on the flat plate and the single-pass welding was carried out in the narrow groove,the influence law of different process parameters on the weld formation was studied,and the optimized welding process range was obtained.Q420 qE steel with a thickness of 40 mm was welded using the optimized process parameters,and the microstructure and mechanical properties of the welded joints were analyzed.High-speed video results show that with the increase of laser power,the droplet transition transition from spreading into the form of liquid bridge transition.With the increase of wire feeding speed,the form of droplet transition changes from liquid bridge transition to spreading transition.The influence of welding speed on the droplet transition is not significant.In the test,under different welding speeds,the welding wires keep in contact with the melting pool.Under the action of surface tension,the melted welding wire spreads into the melting pool to form the spreading transition.The top of the welding wire is on the test plate,and the position of inserting the welding wire into the melting pool is changed.With the increase of the height of the filament junction,the behavior of droplet transition gradually changed from the spreading liquid bridge to the side wall.When H=1mm,is the liquid bridge transition,and the droplet transition is the most stable.When the intersection height of filament is greater than 1mm,the transition form is lateral wall transition.The results show that the weld depth and weld width increase with the increase of laser power.With the increase of welding speed,the weld depth and weld width decrease.With the increase of wire feeding speed,the depth of weld increases and the width of weld decreases.With the increase of defocusing amount,the weld width increases and the weld depth decreases.When the defocusing amount is +30mm,the side wall of the weld appears undercut phenomenon.With the increase of heating current,the weld depth and weld width increase slightly.After a series of process tests,the optimized process parameters are summarized as follows: heating current 150 A,laser power 4.5kw-5.8kw,height of wire intersection 1mm,welding speed 0.36m/min-0.48m/min,wire feeding speed 6m/min-10m/min,defocusing amount +10-+20mm.Q420qE steel of 40 mm was welded with narrow gap laser fillet welding method and optimized welding parameters,and the total number of welding passes was 8.After welding,the microstructure was analyzed and observed,and the properties of the joint were analyzed through tensile,impact,bending and microhardness tests.The results showed that the welded joint of 40 mm Q420qE steel was well formed with no obvious defects.The weld center is composed of a large amount of acicular ferrite and a small amount of granular bainite.Joint tensile samples are broken in the parent metal,bend specimens 180° does not crack,the impact of the welding joint in-40? good performance;The highest value of joint hardness appears in the surface zone of heat affected zone of fine grains.