Process Investigation And Temperature Field Simulation On Deep Penetration TIG Welding Of Mid-thickness Steel

Deep penetration TIG(DP-TIG)welding process is based on Keyhole TIG(K-TIG)welding.Compared with K-TIG,DP-TIG welding torch is special designed to strengthen the cooling effect on tungsten electrode.Therefore the arc jet diameter is restricted,the force and energy density of the welding arc are hence improved.A keyhole forms inside the weld pool.The free-burning arc can heat the bottom workpiece metal,greatly improving the penetration ability.Mid-thickness workpieces can be joined by DP-TIG welding in a single pass at a relatively high welding speed.Groove preparation is unnecessary and additional filler wire is saved.The main content in this paper is as follows:316L plates were jointed using DP-TIG welding process.The effects of welding parameters on fusion zone profile were investigated.The weld properties,including mechanical properties,microstructure,and corrosion resistance,were analyzed.Q345 low alloy steel plates,which have a high thermal conductivity,were welded using DP-TIG welding process by adding water-cooling at the back side of workpiece.The weld properties were analyzed.The welding temperature field with water-cooling was simulated using ANSYS software and was compared with that in traditional air environment.The reasons why water-cooling improved the DP-TIG welding process of Q345 were analyzed.The following conclusions are drawn from the results of these studies.1.Single-pass DP-TIG welding can be applied to 10-mm-thick AISI 316 L stainless steels without filler wire addition or edge preparation and hot cracks were avoided.The strength of the weld reached 96.64% of the base metal,while the elongation of the weld was 88.02% of the base metal.The impact property of the weld was 92.20% of the base metal.The corrosion current density of the weld was 69.78% of base metal and corrosion speed was 69.81% of base metal.The corrosion resistance of weld was even better than that of the base metal.Overall,the weld quality of DP-TIG was perfect.2.Single-pass DP-TIG welding can be applied to 8-mm-thick Q345 low alloy steels by adding water-cooling at the back side of workpiece.Cold weld cracks and pores were avoided.The specimen fractured at the location of base metal during tensile tests,indicating the strength and ductile of the weld were good.The tensile strength of joint was 560 MPa and was even same with the base metal.Impact properties of the weld decreased a lot and was only 48.21% of base metal,but the impact energy of HAZ decreased only slightly and reached 82.14% compared to the base metal.Overall,the quality of the weld was relatively good.3.The welding temperature field with water-cooling was simulated using ANSYS software.A combination of double ellipsoid heat source on the upper half and the cylinder heat source on the lower half was used and simulation results with agreement of experimental results were obtained.The welding temperature field with water-cooling was compared with that in air environment.The improvement theory of the water-cooling was confirmed.First,the volume of welding pool decreased when adding water-cooling.The area of full penetration weld in air environment was 91mm~2,which was 2.12 times than that with water-cooling.Second,the temperature of fusion metal decreased rapidly,thus the surface tension of the root liquid metal increased rapidly beneficial for the forming and maintenance of the welding keyhole.With water-cooling,the times from the highest temperature to 400? was 2.7s of root fusion metal.But for the root fusion metal in the air environment,the temperature was still higher than 1600? even the cooling time reached 10 s.