Butt welding of SUS304 and Inconel718 tubes by using defocused laser beam

Joining stainless steel to superalloy is currently of extensive interest for applications in aviation and automotive industries. However, conventional welding is prone to encounter defects such as cracks and austenite grain coarsening in the fusion zone. In the present study, laser welding was applied to join SUS304 stainless steel and Inconel718 superalloy circular tubes due to their precise local heat input and accuracy. The effects of defocusing distance, welding speed, and laser power on welding characteristics were studied by changing the values of the mentioned parameters, which manifested that different process parameters exerted a tremendous impact on the cross section morphology and shape of the weld seam. In addition, finite element simulation software was used to simulate temperature field distribution. The results revealed that there would be a buffering region on the temperature field once the laser power gradually decreased, which remarkably reflected the effect of the laser power descending on eliminating weld craters. Therefore, the crater defects caused by laser beam accelerating and decelerating at the start and end of welding could be effectively eliminated through synchronously regulating laser power in the real welding process.