On mechanical and morphological investigations of tungsten inert gas welded SS 304 thin pipe joints

Abstract

Tungsten inert gas welding is one of the established joining processes for stainless steel. But hitherto very little has been reported on induced residual stresses in circular thin pipe joints during tungsten inert gas welding of SS 304. This paper reports the effect of welding parameters such as welding speed, welding current and shielding gas flow rate of tungsten inert gas welding on micro-hardness, width of the heat-affected zone, residual stresses and microstructural properties of SS 304 thin pipe joints. The results indicate that the welding current and the welding speed have a significant effect on micro-hardness of weld bead and width of the heat-affected zone. Further changes in the microstructure of the joints were studied in terms of dendrite formation. It has been observed that there is proportional increase in depth/width of the heat-affected zone with the heat input during the joining process, resulting in a decrease of micro-hardness. The results are also supported by radiographic analysis and X-ray diffraction data to understand the nature of residual stresses which was observed as compressive at the weld bead and tensile along the axis of thin welded pipe joints. Finally, the process capability analysis based on Cp and Cpk values of ≥1 suggests that the process can be gainfully used for mass production.