Research On Microstructure And Properties Of MIG Welded Joints For GH4169 Nickel-based Superalloy

GH4169 nickel-based superalloy has good comprehensive mechanical properties in a wide range of temperature and can be used in many industries.The welding process directly affects the macroscopic temperature field distribution of welding structure and has a profound impact on the microstructure and mechanical properties of welded joints,which finally determines the quality of welding products.In this paper,the orthogonal experiments of MIG welding for GH4169 nickel-based superalloy thin plates are carried out.The three-dimensional simulation of welding temperature field and the two-dimensional microstructure simulation of the solidification process of weld pool are completed.The microstructure and mechanical properties of welded joints are studied,and the welding process parameters are optimized.Firstly,based on the MIG welding process of GH4169 nickel-based superalloy,a three-dimensional finite element model is established to simulate the macroscopic temperature field.The variation over time and the distribution along welding direction,vertical weld direction and thickness direction of the welding temperature field are analyzed.The influence of welding current and welding speed on the temperature field distribution is studied.Secondly,in view of the solidification process of weld pool for GH4169 nickel-based superalloy,a two-dimensional dendrite growth model is set up using the cellular automaton method,based on the dendrite nucleation and growth kinetics and the solute diffusion equations,and allowing for the randomness of nucleation position and crystallographic orientation.The influence factors of the crystallization morphology of weld pool and the distribution of crystallization microstructure of weld seam are studied.The equiaxed dendrite growth in the center of weld pool and the columnar dendrite growth at the edge of weld pool are simulated respectively.The evolution of dendrite morphology and solute concentration distribution is obtained.The distribution of solute concentration along the center line of equiaxed dendrite is analyzed.Then,aimed at the welded joints for GH4169 nickel-based superalloy,the macro morphology of weld seams under different welding process parameters is analyzed.The microstructure of welded joints is observed by means of the metallographic test.The microstructure of base metal is mainly composed of?matrix,??phase,??phase,?phase and carbide.The equiaxed dendrite zone with fine grain size is in the center of weld seam and the columnar dendrite zone with large grain size and obvious growth direction is at the edge of weld seam.The heat affected zone is coarse-grained,narrow in range and indistinct in regional division.The content distribution of joints is studied through the scanning electron microscopy(SEM)and the energy dispersive spectrum(EDS)analysis.The tensile strength,elongation after fracture and microhardness of welded joints are tested by the tensile and microhardness tests.The effects of welding heat input,welding current,arc voltage and welding speed on the mechanical properties of joints are analyzed.Finally,according to the influence of welding process parameters on the temperature field distribution and the mechanical properties of welded joints,the optimized welding parameters are acquired,namely,welding current is 55 A,arc voltage is 18 V,welding speed is 0.30 m/min,and welding heat input is 1.98×10~3 J/cm.