Objective: Austenitic stainless steel is widely used during industrial production due to its excellent corrosion resistance, high temperature resistance and sound mechanical properties. Compared with traditional arc welding technology, laser welding shows great advantages in terms of high energy density, high welding speed and low heat input. So far, however, compared study about welded joints quality after the two welding methods is few to see and difference between them is still unclear. In this paper, a comparative investigation of 2mm austenitic stainless steel prepared by arc welding and laser welding was carried out to systematically evaluate the differences about as-weld quality between them, and further provide a beneficial reference for the selection of welding technologies and processes in practical engineering applications.

Method: laser welding and arc welding of 2mm SUS301L-HT stainless steel plates were performed using fiber laser device (IPG YLR-4000) and inverter arc power supply (Fronius TPS4000), respectively. After that, microstructural morphology, hardness distribution and tensile strength were obtained by optical microscope, microhardness meter and electronic universal testing machine, respectively. Moreover, fracture morphology after tensile tests was also analyzed by scanning electron microscope. According to above comparative characterization results, the differences between laser and arc welds were obtained consrdering weld forming, microstructure and mechanical properties.

Results: By comparing the weld macrostructure, microstructure and mechanical properties of 2mm SUS301L-HT stainless steel joints prepared by laser and arc welding, some obvious differences can be obtained: (1) Weld bead formation. Compared with MIG welding, laser welds showed a small deformation, a uniform shape, and a narrow width decreasing from 6.35mm to 1.64 mm. (2). Microstructure. Laser welds were composed of fine columnar austenite dendrites and interdendritic δ ferrite with a narrow heat affected zone (HAZ). Conversely, MIG welds consisted of large columnar austenite dendrites and interdendritic δ ferrite with a wide HAZ. Moreover, the vermicular ferrite dendrites were altered to strip ones, and then disappeared in coarse solid solution austenite grains of base metal (BM) with the increase of the distance from fusion line. (3) Microhardness. the hardness of laser welds was about 240 HV, in which the hardness of HAZ was slightly higher than that of fusion zone (FZ), but lower than that of BM. However, the maximum hardness of MIG weld was more than 300 HV while a relatively low hardness of only 200 HV was observed near FZ. (4) Tensile property. Laser welded joints displayed a strength of 979.1 MPa with an elongation of 48.2%. Moreover, the mechanical failure occurred in the FZ, in which there existed many dimples in the fracture surface, showing a typical ductile feature. However, the tensile strength of MIG welds were only 779.6 MPa with a 21.3% elongation. Furthermore, fracture occurred in the HAZ, in which the upper part of the fracture showed obvious tearing zones while the lower part a typical ductile feature.

Conclusion: There exist obvious differences in weld macrostructures, microstructures and mechanical properties between laser welding and arc welding of 2mm SUS301L-HT stainless steels. Due to a high energy density, high welding speed and low line energy, laser welding shows some advantages over arc welding. First, laser welds display a narrow width, a low deformation, and a uniform weld back forming. Then, laser welds also show a finer microstructure and a small HAZ. In terms of mechanical properties, laser welds possess a high tensile strength with great extensibility. In summary, compared with arc welding, laser welding shows specific advantages in weld macrostructure, microstructure and mechanical properties.