Gas Pool Coupled Activating TIG (GPCA-TIG) Welding And Development Of Welding Torch

Since the1990s, A-TIG welding as activeness representatives of welding technology, has been attracted widespread attention, which uses small amounts of flux on the surface of welding plates before welding progress. It can obtain excellent welding line and significantly improve the welding efficiency compared with TIG wedling. However, its practical application promotion was hampered, because the coating process would reduce the production efficiency and not easy to ensure the stability of the process through manual coating process.As active TIG welding method research shows, the main mechanism which the weld penetration can be significantly increased for the iron series of alloy such as carbon steel, stainless steel by adding O element, is that active elements can change the welding pool surface tension temperature coefficient. In order to give full play to the advantages of active welding method, this topic through changing the way of importing active element, puts forward a new activity welding method—Gas Pool Coupled Activating welding. The method contains two layers of gas, the inner layer gas is pure inert gas(Ar or He) which would protect the welding pool and tungsten electrode; and the outer layer gas is single pure active gas(O2or CO2) or including N elements of gas(N2),or oxygen and nitrogen gas mixture (O2+N2). Oxygen or nitrogen element which is ionized through the role of the arc couples with molten pool at the surrounding of low temperature area. The function of the oxygen element is changing the Marangoni convection to obtain deep and narrow weld depth, and the performance of the weld can be improved through nitrogen element for its features of high strength and excellent toughness. This method through changing coupling of degree between outer gas and molten pool, can trace control the introduced quantity of O and N elements, and thus achieve purpose for controlling the appearance of weld and improving the quality of weld seam.This paper is mainly for GPCA-TIG welding method of developing a special welding torch and welding property. This article adopts SUS304stainless steel for welding based metal, as to the inner argon protection gas, contrast the arc welding appearance, welding surface and cross-section morphology between using the GPCA-TIG welding method and the traditional TIG welding. The results revealed the arc contracts, the penetration is deep and narrow and the depth-to-width ratio reaches1.06, in this standard the8mm thick stainless steel plate can be weld fully at one time without making a groove. In addition, the GPCA-TIG welding method can avoid the oxidation of tungsten electrode in weld process.The effects of the coupling between outer gas and welding pool, the ratio of outer gas (N2+O2), the flow of inner protection gas, and other process parameters on weld depth were researched respectively. Test results show that along with the increase of the higher level of the outer nozzle which is the coupling of degree between with the outer gas and molten pool decrease, the depth of molten become shallow. When the high level is0mm rise, the depth of molten is the deepest. So this method can control the introduction of the content of O element, and then obtain different depth of the weld penetration. With N2ratio of outer gas (0-50%) increase, the weld penetration first slightly decreased and then rise. When the proportion of N2reached above60%, the weld depth of molten became shallow. That is to say, the weld depth of molten can be increased by O element rather than N element, but N element can promote the absorption of O element. The flow of lining gas is too small or too big, can lead to the coupling between the outer gas and weld pool is too large or too small, so along with the flow of inner gas increase, the weld depth first increase and then decreases.Through the microscope, the elements of N and O were analyzed on the influence of the microstructure about GPCA-TIG welding. The results showed, weld microstructure were austenite and a small amount of ferrite composition; when outer gas added to certain proportion of N2, the weld structure was finer than outer gas as pure O2, because N element is one of austenitic form elements and has the function of fine grains. However with the increase of the proportion of N2, the weld seam organization had become thick, because the content of the ferrite decreased along with the increasing N elements of weld, which block the first austenitic organization grow up and refined the second austenite the function of the organization will abate, leading to weld austenitic coarsening of the organization. Compared to the traditional TIG welding seam organization, the grain size of weld microstructure which adopted GPCA-TIG welding method with pure O2of outer gas was smaller, the organization was refined.And the impact toughness at the room temperature and-100℃and tensile properties of GPCA-TIG welding bead were proofed by mechanical properties test. The welding line tensile fracture morphology were analysised by the scanning electron microscopy (SEM). The results showed that, whether room temperature or-100℃the impact energy was lower rather than base metal when the weld line added O element, they declined to24.79%and24.92%respectively. But when the N element was introduced into the weld, the impact energy increased, and still less than the base metal. When the N2accounted50%for outer gas, it declined to6.72%and12.14%respectively. The tensile strength is750MPa with the outer gas is pure O2, compared with base metal it had fallen by3.2%. And the tensile strength is770MPa with the N2account50%in the outer gas, quite with base metal. Weld was ductile fracture.In addition, the corrosion performance of the GPCA-TIG welding joints were tested, the result shows all the welding joints did not appear intergranular corrosion weld crack, up to the detection requirements of the national standard GB/T4334-2008"the test method about stainless steel quid of sulfuric acid—copper sulfate ". And welds according to JB4730.2-2005"of the pressure equipment nondestructive testing:the X-ray testing requirements of the" the RT (X-ray testing)100%inspection, evaluation for I level of results.Contrasted to the previous active TIG welding, this method does not need to coat with the working procedure of surfactant and precision of gas ratio, active element oxygen and nitrogen element were directly introduced by the outer gas while welding. It can significantly increase the weld penetration and improve the mechanical properties of welding seam. And for a single arc welding, the heat input and equipment investment are reduced. The welding operation is more convenient. It also has the features of high welding efficiency, stable process, strong practice, at last it can realize the automatic production. In view of the above outstanding advantages, GPCA-TIG welding has wide application prospects. This study will promote the development and application of this method, which can improve the efficiency of the traditional TIG welding.