Research On Non-axisymmetric Rotating Tungsten Narrow Gap GTAW Technology Of 316LN Thick Plate For Fusion

The development and utilization of nuclear power can solve the problem of global energy shortage,and the advantages of nuclear fusion,such as unlimited resources and no generation of nuclear waste,make it a hope to solve the energy crisis.Thick plate 316 LN stainless steel is widely used as a key material for nuclear fusion reactor equipment.The overall welding performance of 316 LN stainless steel is good,but there are still problems such as intergranular corrosion,embrittlement,thermal cracking,surface oxidation and stress corrosion in welded joints.Controlling heat input during welding of thick plates is the key to solving this problem.In order to solve this problem,the new non-axisymmetric rotating tungsten electrode narrow gap GTAW welding equipment independently designed by our research group.The non-axisymmetric tip of the tungsten electrode is connected to the built-in motor,and its speed is controlled by an external motor control box.The rotation of the tungsten electrode drives the arc with a certain degree of stiffness to rotate.The periodic rotation of the arc in the narrow gap groove causes the bottom and side walls of the narrow gap to be alternately heated and melted,which solves the problem that the side walls of the narrow gap welding are not fused.The visual acquisition and electrical signal acquisition systems are set up to collect and analyze the physical process and electrical signals in the narrow gap welding process of rotating arc.With the increase of arc rotation frequency,droplet transition frequency is accelerated.Due to the periodic rotation of the arc,the welding wire is not evenly heated.Only when the arc is rotated to the end of the wire,the wire will melt and the material transfer process take place.The arc rotation can apply the applied mechanical force to the droplet transition process and make the droplet swing violently,which is conducive to get rid of the surface tension between the end of the wire and the droplet and accelerate the droplet transition behavior.The shape of the non-axisymmetric tip can obviously change the shape of the rotating arc.By adding a platform to the tip,the position of the arc initiation can be effectively restrained and the cross-sectional area of the arc colμmn can be prevented from growing up due to the increase of the current.The behavior of the tracer particles in the molten pool was visually detected by a high-speed camera system.The positions of the tracer particles at different moments in the molten pool can clearly reflect the flow behavior of the liquid metal.Compared with traditional static tungsten,the liquid metal layer on the surface of the molten pool fluctuates greatly under the influence of rotating non-axisymmetric tungsten.The main reasons for the flow and shape change of the molten pool are the mechanical external force of the rotating arc and the inertial centrifugal force caused by the molten pool rotation.The rapid flow turbulence in the molten pool accelerates the heat and mass transfer.The periodic rotation of arc can obviously improve the flow mode of the molten pool,enlarge the edge of the plate molten pool and increase the molten pool area.The vortex at the edge of the molten pool enhances the scouring of the side wall and promotes the fusion of the sidewalls with narrow gap.Narrow gap welding experiments were carried out on 316 LN stainless steel.After optimizing the welding parameters,the heat input for base welding,fill welding and cover welding was 9.9 KJ/cm,14.2 KJ/cm and 11.4 KJ/cm,respectively,and the linear heat input was significantly reduced.XRD tests were carried out on the weld zone,the base metal zone and the heat-affected zone,and the phase composition remained unchanged.EBSD tests were carried out on the three regions respectively.The phase distribution changed to some extent,but the phase content was basically the same.The optimized parameters were welded,and the mechanical properties of the whole welding part were tested,and the mechanical properties were excellent.DL-EPR was used to test the intergranular corrosion performance in the weld zone,the base metal zone and the heat affected zone.The corrosion resistance of the weld zone was much higher than that of the base metal and the heat affected zone,while the corrosion resistance of the heat affected zone was slightly lower than that of the base metal with little difference.