Optimizing the mechanical properties of weld joint in laser welding of GTD-111 superalloy and AISI 4340 steel

•Application of Nd:YAG pulsed laser welding for joint of GTD-111 superalloy and AISI 4340 steel.•Investigating the influence of laser power, pulse frequency and welding speed on the microstructure and mechanical properties of the weld joint.•Optimization of the mechanical properties of weld joint in laser welding of GTD-111 superalloy and AISI 4340 steel. The present research pertains to the optimization of the mechanical properties of weld joint between GTD-111 superalloy and 4340 steel through Nd:YAG pulsed laser welding process. For this purpose, the response surface methodology in combination with desirability function technique were employed to optimize the laser welding parameters. The parameters of laser power (1500, 2000, 2500 W), welding speed (0.5, 1, 1.5 mm/s) and pulse frequency (5, 10, 15 Hz) were considered to improve the responses of tensile strength, elongation, hardness and weld penetration, simultaneously. The microstructure characteristics of the weld joint were examined using optical and scanning electron microscopy. The results indicated that an increase in the laser power up to 2500 W decreased the tensile strength (from 1017 to 705 MPa) and hardness (from 460 to 375 kgf) due to formation of the Laves phase and nucleation of solidification cracks, arising from segregation of Nb, Ti, Mo, W and Ta elements. The increase of welding speed decreased the amount of Laves particles due to lower heat input, which resulted in an improvement in the tensile strength and hardness up to 911 MPa and 417 kgf, respectively. However, an increase of welding speed reduced the elongation and weld penetration to 12.7 % and 1147 μm, respectively. Concurrent increase of the laser power and pulse frequency associated with the formation of shrinkage voids in HAZ of 4340 steel side and the nucleation of liquation cracks in HAZ of GTD-111 superalloy side. The optimal values of parameters were found to be a laser power of 1812 W, pulse frequency of 15 Hz and welding speed of 1.3 mm/s. Under the optimal conditions, the following values of responses have been obtained: tensile properties = 1013 MPa, elongation = 16.9 %, hardness = 416 kgf and weld penetration = 1165 μm.