Effect of Multipass TIG and Activated TIG Welding Process on the Thermo-Mechanical Behavior of 316LN Stainless Steel Wel
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AUSTENITIC stainless steels are characterized with good physical properties even at high temperatures. Higher chromium content in the material contributes to corrosion resistance behavior. Low carbon with nitrogen addition in 316LN stainless steel reduces sensitization during its processing. This behavior makes 316LN stainless steel, suitable for the fabrication of structural components in the nuclear industry.[1] Tungsten inert gas (TIG) welding is recognized as a superior welding process as the weld pool is free from the atmosphere of an inert shielding gas. The low depth-to-width ratio of weld bead obtained during welding of thick components in a single pass is the major limitation of TIG welding. Thick components are being fabricated utilizing multipass TIG (MPTIG) welding with filler metal addition. MPTIG requires meticulous edge preparation and involves a number of welding passes which induces higher residual stress and distortion.[2] This problem can be solved by fabricating the weld joint in a single pass. It was pointed out that a novel variant of TIG welding called activated TIG (ATIG) welding engender higher depth-to-width ratio of the weld bead. It can be
K.C. GANESH, Research Scholar, and K.R. BALASUBRAMANIAN, Assistant Professor, are with the Department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli, 620015, India. Contact e-mail: [email protected] M. VASUDEVAN, P. VASANTHARAJA, and N. CHANDRASEKHAR, Scientific Officers, are with the Advanced Welding Processes and Modeling Section, Materials Technology Division, Indira Gandhi Centre for Atomic Research, Kalpakkam, 603102, India. Manuscript submitted September 23, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
employed in the welding of thick components with thickness up to 12 mm by single pass.[3] Researchers have indicated that the presence of active components like oxygen or sulfur in the activating flux controls the arc constriction and Marangoni flow during ATIG welding.[4–8] The arc constriction produces a higher current density at the weld pool center and the temperature coefficient of surface tension changes from negative to positive which reverses the Marangoni flow. These two phenomena transfer more heat to the bottom of the weld pool and increase the depth-to-width ratio of the weld bead.[8] It can be accompanied by a square butt joint, thereby eliminating the groove preparation which results in increased productivity. One of the major problems faced in the fusion welding of stainless steel is the lower thermal conductivity of material and higher heat input. Due to less heat dissipation, the distortion is considered to be high. The morphology of 316LN stainless steel-welded bead elucidates the inward weld pool flow, which induces equiaxed structure at the center of the weld zone. The columnar structure was observed in the transverse direction where there is sharp temperature gradient.[3] Few characterization studies reported that the use of oxide flux reduced the susceptibility of hot cracking, whereas the additio
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