Study on laser welding of austenitic stainless steel by varying incident angle of pulsed laser beam

Abstract

In the present work, AISI 304 stainless steel sheets are laser welded in butt joint configuration using a robotic control 600W pulsed Nd:YAG laser system. The objective of the work is of twofold. Firstly, the study aims to find out the effect of incident angle on the weld pool geometry, microstructure and tensile property of the welded joints. Secondly, a set of experiments are conducted, according to response surface design, to investigate the effects of process parameters, namely, incident angle of laser beam, laser power and welding speed, on ultimate tensile strength by developing a second order polynomial equation. Study with three different incident angle of laser beam 89.7deg, 85.5deg and 83deghas been presented in this work. It is observed that the weld pool geometry has been significantly altered with the deviation in incident angle. The weld pool shape at the top surface has been altered from semispherical or nearly spherical shape to tear drop shape with decrease in incident angle. Simultaneously, planer, fine columnar dendritic and coarse columnar dendritic structures have been observed at 89.7deg, 85.5deg and 83deg incident angle respectively. Weld metals with 85.5deg incident angle has higher fraction of carbide and δ-ferrite precipitation in the austenitic matrix compared to other weld conditions. Hence, weld metal of 85.5deg incident angle achieved higher micro-hardness of ∼280HV and tensile strength of 579.26MPa followed by 89.7deg and 83deg incident angle welds. Furthermore, the predicted maximum value of ultimate tensile strength of 580.50MPahas been achieved for 85.95deg incident angle using the developed equation where other two optimum parameter settings have been obtained as laser power of 455.52W and welding speed of 4.95mm/s. This observation has been satisfactorily validated by three confirmatory tests.