Effect of Heat Input on the Microstructure and Mechanical Properties of AISI 316 stainless steel TIG Welded tube Joints

The present work investigates the effect of heat input on the stainless steel welded tube joints using TIG welding technology. Three different heat input of 0.42 kj/mm, 0.48 kj/mm and 0.54 kj/mm have been applied on 3 mm of AISI 316 stainless steel tube to obtain the optimum weld characteristic with cost effective. Metallographic investigation carried out to study all welding regions using optical microscope. Moreover, mechanical properties in terms of hardness, tensile strength and impact were conducted to examine the joint integrity. Results showed that the tensile strength increased with increasing the welding current up to stress value of 554.5 MPa, and then start decreasing. Higher hardness of 80 HRB were observed at HAZ compared to the weld zone. The results of this work also indicated that joint welded by medium heat input of 0.48 kj/mm, exhibited highest tensile strength of 554 Mpa compared to 0.42 kj/mm with tensile strength of 502 Mpa and 0.54 kj/mm with tensile strength of 525Mpa. The absorbed energy result showed similar trend to tensile strength with highest absorbed of 270 J at medium heat input of 0.48 kj/mm. Lower absorbed energy was recorded of 150 j and 110 J for heat input of 0.42 kj/mm, 0.54 kj/mm, respectively. This could be attributed to relatively finer dendritic size and adequate amount of sigma phase and chromium carbide formation. Result showed that higher heat input led to coarsen the grain size structure and consequent impact on the mechanical properties. Consequently, a heat input of 0.48 kJ/mm was determined to be optimal, yielding high-integrity, defect-free joints with improved mechanical properties.