Influence of shielding gas mixtures on bead profile and microstructural characteristics of super austenitic stainless steel weldments by laser welding

A planned and orderly analysis of the microstructures and bead profiles of AISI 904 L super austenitic stainless steel bead-on-plate welds was accomplished by coupling up diffusion cooled slab 3.5 kW CO2 laser with two dissimilar shielding gaseous mixture namely 100% nitrogen (N) and 50% argon + 50% nitrogen (A + N). AISI 904 L Super Austenitic Stainless Steel (SASS) incorporates higher levels of Mo, Cr, Ni, N, and Mn under normal conditions. In heating applications, it offers a superior corrosion resistance at moderate and higher temperatures. The microstructure of SASS is exhaustively austenitic in nature, when subjected to a solution-quenched state. The objective of this study is to determine the phenomenon that follows the action of two shielding gas mixtures on microstructural and bead profiles of laser-welded 904 L SASS. The weld bead profile of laser welding depends on various parameters such as beam power; travel speed, and focal position of the laser spot, and these factors have to be chosen in an appropriate manner to obtain the desired output. The cross-sectioned area of the bead profiles like bead width and depth of penetration is measured using an optical microscope. Two different shielding gas mixtures were used to examine the microstructural changes in the weld region. Besides, the variation in the hardness of the weld region was analyzed through the Vickers hardness tester.