Objective At present, the Inconel690 nickel-based alloy and SUS304 stainless steel are widely used in nuclear power, aerospace, and petrochemical fields owing to their excellent performance in thermal strength, corrosion resistance, and specific strength. Compared with traditional welding methods, laser welding is characterized by higher energy density, smaller welding deformation, and a narrower heat- affected zone. Compared with laser welding, laser welding with filler wire achieves the purpose of changing the metal composition of weld seams and thereby improving the mechanical properties of the welded joints. Different materials have different laser absorptivity, linear expansion coefficients, specific heat capacity, thermal conductivity, and microstructure evolution during solidification. These factors further affect the performance of the welded joints of dissimilar materials. The current research on stainless steel and nickel-based superalloys mainly focuses on the mechanical properties of the welded joints under the influence of precipitates. In this study, laser welding and laser welding with filler wire are carried out under different heat inputs, and mechanical properties are investigated. Methods The thickness of the SUS304 and Inconel690 used in this experiment is 4. 5 mm. Inconel ERNiCrFe-7A is used as the filler wire. The welding equipment used in this study is a 10 kW TRUMPF lasers TruDisk 10002. In addition, 99. 99% pure argon gas is used as the shielding gas with a gas flow rate of 25 L/ min. After welding, the ZEISS Axio Observer A1m metallurgical microscope is used to observe the surface morphology, and energy dispersive spectroscopy is employed to test the precipitates in the weld seams. The CMT4303 electronic universal testing machine is applied to test the tensile strength of the welded joints. The HVS-30 Vickers hardness tester is utilized to test the microhardness of the welded joints. Results and Discussions The cross-sections of the welded joints are in the typical goblet shape with no crack defects. In the weld zone S2 ( 1. 5 kJ/cm), many white particles are observed near the grain boundary, and they can be further confirmed as a titanium-containing phase. After the ERNiCrFe-7A filler wire is added, an irregularly shaped white precipitated phase is observed in the weld seam, and it can be determined as a chromium-rich phase. The X- ray diffraction (XRD) results suggest that this chromium- rich phase is Cr0. 19Fe0. 7Ni0. 11 phase. The tensile strength of S2 (1. 5 kJ/ cm) is 9. 7% higher than that of S1 (2. 6 kJ/ cm). After the filler wire is added, the tensile strength of S3 (1. 5 kJ/ cm) is 683 MPa, which is 16. 2% higher than that of S1 (2. 6 kJ/ cm). Owing to the decrease in heat input, the grain size in the weld seam becomes smaller, which improves the plastic toughness and average hardness of the weld seam. When the heat input are 2. 6 kJ/cm and 1. 5 kJ/cm, the average hardness of the weld seam are 176. 8 HV and 190. 4 HV, respectively. After the filler wire is added, the average hardness of the weld seam in weld zone S1 (2. 6 kJ/ cm) is 216. 7 HV. Conclusions In this study, laser butt welding of Inconel690 nickel-based alloy and SUS304 stainless steel is carried out. The influences of heat input and filler metal on the microstructure and mechanical properties of joints are studied. The results indicate that the cross-section of the weld seam is in the classical goblet shape after laser welding. The weld width of S1 (2. 6 kJ/cm) is larger than that of S2 ( 1. 5 kJ/ cm). As the heat input increases, the grain size in the weld seam becomes larger. A titanium- containing phase is diffusively distributed in the weld seams of all welded joints. After the ERNiCrFe-7A filler wire is added, a chromium-rich phase appears, and it is speculated to be Cr0. 19Fe0. 7Ni0. 11 phase according to the XRD results. The grain size of S2 (1. 5 kJ/cm) is 40% smaller than that of S1 ( 2. 6 kJ/ cm), and the mechanical properties of the joints are improved.
