Effect of laser welding parameters on fusion zone shape and solidification structure of austenitic stainless steels

Fusion zone shape and final solidification structure of different types of austenitic stainless steels with different thicknesses were evaluated as a function of laser parameters. Both bead-on-plate and autogenous butt weld joints were made using a carbon dioxide laser with a maximum output of 5 kW in the continuous wave mode. Based on the base metal thickness, the laser power, welding speed, defocusing distance and the type of shielding gas combinations should be carefully selected so that weld joints having complete penetration, minimum fusion zone size and acceptable weld profile are produced. Heat input as a function of both laser power and welding speed has almost no effect on both the type of microstructure and mechanical properties of welds. The microstructure of all laser welds was always austenite with about 2 or 3 vol% ferrite. However, the lower the laser power and/or the higher the welding speed, the finer solidification structure. Primary ferrite or mixed-mode solidification resulted in crack-free welds.