A Study on Micro Tig Tube Welding of Thin Extra Aisi 321 Austenitic Stainless Steel Sheets

Abstract

Exhaustgas recirculation tubes were used for this study. To make bellows shape fromTIG (Tungsten Inert Gas) welded extra thin tubes hydraulic forming method isused in industry. For this study, 0.2 mm thick AISI 321 austenitic sheets werecombined by using micro TIG welding method and 11.80 mm in diameter pipes wereproduced. For the TIG welding process of thin sheet tubes shaped by liquidpressure precise welding parameter adjustment is required. With the micro TIGarc welding technique, healthy weld seams were obtained in three differentpower parameters. The effects of this differences on the mechanical propertiesand microstructure of the weld joints were experimentally investigated. Thewelding speed was kept constant and three different welding current and voltagevalues were selected. The images of the weld zone of the samples were taken byan optical microscope. The microstructures formed in the weld zone wereexamined. Micro hardness values of the base metal, HAZ (Heat Affected Zone) andweld zone were evaluated. Tensile tests of the samples were carried out forthree different parameters. Strength of welding seams is very important in thehydroforming process. In order to evaluate the strength of the joint, thewelded tube elastomer expansion test was applied. The effect of the expandingtube wall on the welded joint was evaluated by the expansion test. As aconsequence of the study, the optimum power parameters of the welded joint wasdetermined by destructive and non-destructive tests.