| With the rapid development of industrial production,there is still a lack of a high efficiency and high quality welding method in medium thick plate connection.K-TIG welding is a welding method that adopts high current(generally higher than 300A)on the basis of traditional TIG and combines with efficient cooling effect.It greatly improves the penetration of arc and can realize the single-side welding and double-side molding of medium thick plate,making up for the shortcomings of traditional TIG welding depth.Ktig has the advantages of high welding speed,high joint strength and no need for beveling and other processes,which greatly improves the production efficiency.In addition,the low cost and easy operation of welding equipment make it have great potential in production and application.In this paper,k-tig welding method was used to weld 6mmthick 304 stainless steel plates.The spot arc voltage in the welding process was detected.The arc volt-ampere characteristic curve,weld microstructure and mechanical properties of joints were studied.The results proved that:(1)It is found by the K-TIG arc volt-ampere characteristic curve that the curve as a whole tends to rise.When the current is between 260 A and 300 A,the curve is in a gentle increase state.After the current exceeds 300 A,the voltage increases rapidly and the curve is steeper.(2)Using the K-TIG welding method,a single-sided welding of 304 stainless steel with a thickness of 6 mm was realized at a current of 380 A,and a clear goblet-like penetration was observed in the weld section.Undercutting occurs on the surface of the weld and is reduced as the current increases,but it still exists when the current is increased to 400 A.The weld penetration depth increases as the current increases,but the weld width decreases when the current reaches 340 A.(3)Due to the difference in heat input and the effect of cooling rate,there are differences in grain size in different areas of the weld and without understanding the current.The grain near the weld line is the smallest,and the grain becomes coarser as it moves toward the center of the weld.The current increases the grain size and is also coarser.Due to the influence of grain size,the microhardness of the side of the weld is higher than the microhardness of the center of the weld.The microhardness of the weld at lower current is higher than the microhardness of the weld under high current.The content of Mn and Cr in the weld decreases with the increase of current,and the Mn element cannot be detected when the current exceeds 300 A.The weld is mainly composed of austenite and skeletal or worm-like ferrite mixed structure.Due to the excessive cooling rate and element segregation,lath ferrite is formed on both sides of the weld.(4)Both the tungsten height h and the increase in the cooling water temperature C cause the arc contraction effect to be weakened,and the stiffness and penetration force are lowered.The weld bead grain refines as h and C increase,and the hardness increases as h and C increase.The tungsten height h is increased,the weld fusion line is offset,and the cross-section penetration is bowl-shaped.When the gas is protected by CO2+Ar activity,the degree of arc shrinkage increases,but the rough weld bead on the surface of the weld is curved,and the undercut phenomenon of the weld is more serious.The active protective gas weld has coarse crystal grains and a reduced hardness value.(5)It is found that the upper width of the K-TIG weld is greater than the Plasma weld,but the bottom height and the melt width are smaller.The tensile strength of the KTIG welded joint is equivalent to that of the base metal,the joint elongation is 88.3% of the base metal,and the elongation of the welded joint of the Plasma is 73.6% of the base metal.The tensile fracture of the K-TIG weld was dense and uniform,and no second phase particles were found at the bottom of the dimple,showing obvious ductile fracture. |
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