| 309S stainless steel has a good heat resistance, corrosion resistance and good weldability. Due to the current capacity of tungsten and the distribution of the electric arc heat source, the conventional TIG welding has low penetration in a single weld and low productivity. Moreover, because of the small coefficient of thermal conductivity, joint of stainless steel apt to appearing coarse grain in the weld pool, which reduce the impact toughness and tensile strength of the weld joint. Meanwhile, a great linear expansion coefficient of austenitic stainless steel leads to welding stress and deformation when the welding interlayer with a ladge temperature difference. The activated flux TIG ?A-TIG? welding process increase the weld penetration by coating a layer of flux on the welding materials surface. As a kind of welding method with high efficiency, good quality, energy saving and environmental protection, A-TIG welding is widely used in the welding of stainless steel, aluminum, titanium and low alloy steel welding. However, the research of activating flux on the depth-to-width radio that related to the arc shape and temperature also to be rare. In addition, some welding defect as pool distortion and adhesion of slag occurred in activated TIG welding on account of the dispersion of activated flux.According to the related problems in the TIG welding process of stainless steel, this paper selected three kinds of activated flux as TiO2, CaF2 and ZrO2 and welded 309S stainless steel with different mass percentage in single component, two component and three component. The morphology of activated flux, arc voltage, surface tension, profile of weld pool, temperature in HAZ, phase composition and diffusion of activated atom were tested and analyzed combined with the microhardness, bending and impact strength after A-TIG welding.The results show that single-component activated flux coating is porous lamellar structure. The porosity increased with mass percentage and kinds of activated flux increased in multicomponent. In the A-TIG welding process, Calcium fluoride has the greatest effect in the shrinkage characteristics of welding arc and the voltage increased 16 V because of arc contraction. But the Titanium dioxide led to the greater weld depth-to-width ratio and the maximum D/W ratio is 0.8. With the mass percentage increased, weld depth to width ratio increased and the biggest deep wide ratio is 3 times more than it in conventional TIG welding.Compared with the conventional TIG welding, the titanium dioxide has biggest effect on the temperature on the surface of weld puddle and the temperature which was welded with activated flux rose of up to 195?. Element analysis found that the content of activated atom is high width direction, but there is rare in penetration position. It is shown that the main factors which decided to the shape of molten pool in A-TIG welding process is surface tension gradient and Marangoni convection. Subsequently, the arc voltage increased to 79 V when welded with two-component activated flux of 309S stainless steel in TIG welding, maximum arc voltage increased 17 V. It was found that the arc has a secondary shrinkage with three components activated flux in TIG welding. The temperature on A-TIG weld pool surface increased with the mass persentage of calcium fluoride increased and large change of temperature is 110?.In A-TIG welding, temperature was related to the content of calcium fluoride, when calcium fluoride was lower than the other two components, the temperature on surface of the molten pool decreased or increased when calcium fluoride was higher than the other two components in A-TIG welding. There was a few activated atoms in width direction and mainly component was austenitic organization with C, Cr, Mn, Fe, Ni and a small amount of intermetallic compounds as Fex?Ni,Ti?y in the molten pool. |
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