Influence of self-protective atmosphere in fiber laser welding of austenitic stainless steel

Abstract

The thermo-chemical reactions between working atmosphere and molten weld pool in fusion welding process severely affect the weld joint quality and weld metal properties. Hence, the welding atmosphere plays a significant role to decide the weld joint quality. Fiber laser source is popularly being used in recent past over Nd:YAG, CO2, and diode lasers due to characteristic advantages of compact size, high stability and reliability, and deeper penetration. In present work, the characteristic difference between a self-protective atmosphere of argon and open atmosphere have been investigated during fiber laser welding of austenitic stainless steel. A mixed mode beam power of a 2-kW ytterbium fiber laser has been used to conduct the experiments. The characteristic variation in terms of weld pool size and shape, weld bead quality, and top surface profile at various process parameters are analyzed. The experiments are conducted at 800 and 1000-W laser power and 13.33 to 18.33-mm/s laser scanning speed. The study indicates that aspect ratio as well as weld depth of penetration in a self-protective atmosphere of argon is more as compared to open atmospheric condition. The appearance of top surface profile in case of self-protective atmosphere is far better than open atmospheric conditions. Furthermore, a three-dimensional non-linear transient heat transfer model is developed to compute the weld pool dimensions using a Gaussian-distributed volumetric heat source. The result demonstrates that the numerically computed weld pool shape and size are in a fair agreement with experimentally measured macrographs.