Model And Experimental Research On Solidification Process Of Vacuum Consumable Remelting GH984G

Vacuum consumable remelting is one of the important processes for preparing superalloys.With the global environment of energy-saving and emission reduction,700℃ ultra-supercritical power generation technology is the development direction of thermal power technology in the future.GH984G is an ideal candidate material for elbow forging in thermal power stations,and its excellent performance and high-cost performance are favored.In this paper,based on the vacuum consumable remelting process,GH984G alloy was taken as the research object.The distribution law of vacuum consumable multiphysical field,solidification structure formation processes,and comparative analysis of different ingot smelting process were studied by combining numerical simulation with experimental research.The main research contents and conclusions are as follows:The coupling characteristics and distribution of multi-physical fields(electromagnetic field,flow field,and temperature field)of vacuum consumable remelting are analyzed in detail by using the mathematical model established by Fluent software.The results show that the current flows from the electrode to the ingot,most of the current flows out of the sidewall of the mold,and a small part of the current flows from the bottom of the ingot.The maximum current density is at the center of the ingot arc contact area,with a maximum value of about 3.32×105 A·m-2.The maximum magnetic induction strength is 4.4× 10-3 A·m-1 at 1/2 radius at the top of the ingot.The maximum value of Joule heat in ingot is 1.14×105 W·m-3,which is the same as the current density.Lorentz force is distributed in the contact area between electrode and ingot,which is 9.5×102N·m-3.Based on the coupled heat transfer and solute diffusion,a three-dimensional(3D)cafe model of vacuum consumable remelting solidification process was established by using the software of ProCAST and C language.The results show that the temperature field of the ingot and the depth of the molten pool are shallow and flat at first,and then deepen to be stable at last;At the beginning of electrode melting,the molten pool is shallow,and the dendrite growth direction is vertical upward.Then the molten pool deepens,and the vertical upward columnar crystal at the bottom changes to an obliquely upward direction of about 55°.Equiaxed grains appear on the centerline of the ingot,and the equiaxed grains are embedded with columnar grains after nucleation and growth.With the increase of electrode melting rate,the depth of the molten pool becomes wider and deeper,the number of grains in the same section increases,the average area and radius of grains decrease,and the grains are refined.At the same time,the simulation results are basically consistent with the experimental results,which verifies the applicability of the model and nucleation parameters.The melting and remelting experiments of GH984G nickel base heat-resistant alloy were carried out in a laboratory-scale vacuum induction furnace and a vacuum consumable furnace.The dendrite structure changes of each position of the ingot after vacuum consumable remelting were studied.The results show that the vacuum consumable Remelting Ingot has no obvious defects,compact structure,and fine grains.The primary dendrite and secondary dendrite spacing at different positions of ingot were statistically compared.The primary dendrite and secondary dendrite spacing increased first and then decreased along the ingot radius from the center to the edge.The composition,inclusions,dendrite structure,and mechanical properties of ingots with different process routes were studied in the laboratory.The results show that:with the process optimization,the less element burning loss,the more stable the composition content,which can effectively control the nitrogen and oxygen content and keep the nitrogen and oxygen content at a low level.The inclusions in the ingot are more uniform,fine,and dispersed,and most of the inclusions are concentrated in 3 μm.The area percentage of inclusions and the number of inclusions per unit area decrease.The change of tensile strength is not obvious,but the toughness and plasticity are improved,and the overall mechanical properties are improved.Through the comparison of the four processes,it is found that the results of the two duplex processes are equivalent,and the triple process is relatively better.Therefore,it is necessary to master the influence of process route on metallurgical quality and performance,establish and develop the smelting process route for low-cost and high-quality production of iron-nickel base heat-resistant alloy ingot,so as to provide the scientific theoretical basis for the industrial preparation of GH984G.