ACTIVATED FLUX TUNGSTEN INERT GAS WELDING OF BIMETALLIC AND TRIMETALLIC JOINTS

Abstract

In this work, activated flux tungsten inert gas (A-TIG) welding of dissimilar metal joints in bimetallic (P91 steel-P22 steel and P91 steel-AISI 316L/LN SS) and trimetallic (P91 steel- Alloy 800 and AISI 316L-Alloy 800) systems was studied. The effect of Incoloy 800 and Inconel 600 interlayers in A-TIG welding of P91 steel-AISI 316L was investigated. Moreover, a novel functionally graded weld joint between P91 steel and AISI 316L developed by A-TIG welding was studied. Additionally, a novel approach of fabricating A-TIG weld joints using external flux powder feeding was developed. Dissimilar steel weld joints between ferritic steel-ferritic steel and ferritic steelaustenitic stainless steel are commonly employed in the thermal and nuclear power plants. However, dissimilar steel weld joints developed by fusion welding techniques often suffer from the issues such as thermal expansion/contraction mismatch, carbon migration, formation of oxide notches, and martensitic layer formation, etc., due to the differences in the physical and chemical properties of the base metals. Tungsten inert gas (TIG) welding is typically used to fabricate the weld joints involving ferritic steels and austenitic stainless steels in the thermal and nuclear power plants. To improve the productivity of the conventional TIG welding process, a variant namely- activated flux tungsten inert gas (A-TIG) welding was developed many decades ago at Paton Electric Welding Institute, Ukraine. Recently, A-TIG welding process has gained a lot of attention of researchers in view of its high penetration capability. In this work, A-TIG welding of joints involved in bimetallic and trimetallic systems was performed using single component fluxes such as CuO, Cr2O3, SiO2, TiO2, and MoO3, and multi-component flux mixtures of various fluxes. A single pass autogenous welding was carried out to develop the A-TIG weld joints. Moreover, the interlayers of Incoloy 800 and Inconel 600 of 1.5 mm width were used during A-TIG welding of P91 steel-AISI 316L combination. The functionally graded weld joint between P91 steel and AISI 316L was developed by three overlapping A-TIG weld passes using interlayers of base metals of 1 mm and 5 mm width. Lastly, using an external powder feeder and TIG torch nozzle modifications, SiO2 flux powder was fed into the weld pool to develop A-TIG weld joints.