Test material The test material is prepared by vacuum induction + vacuum consumable smelting process Φ240mm GH710 alloy billet, the free-forging one-way forging Φ210mm forging rod, see the chemical composition of raw materials. The microstructure of the raw materials is compact and has no other metallurgical defects visible to the naked eye. However, the grain structure is rather coarse, and the residual dendrites and microstructures exist in some large grains. GH710 alloying due to a high degree of ingot prone to elemental segregation, as-cast dendrite serious interdendritic rich in primary γ 'and MC phase, making ingot hot deformation performance is poor, when the billet extremely easy Forging cracks. Bar coarse tissue and residual dendrite existence, mainly due to forging billet deformation is not enough.
Test Method The isothermal forging experiment of alloy is carried out on a 6300kN hydraulic press. The mold material is cast superalloy, and the billet heating temperature is 1100 ℃. Isothermal forging turbine disk forgings after air cooling standard heat treatment: 1170 ℃ × 4h, air cooling +1080 ℃ × 4h, air cooling +845 ℃ × 24h, air cooling +760 ℃ × 16h, air cooling. Metallographic samples were prepared according to a conventional procedure with etchant of 50 ml hydrofluoric acid + 20 ml hydrochloric acid + 10 ml hydrogen peroxide.
Effect of forging process on microstructure and propertiesIn order to effectively eliminate the coarse microstructure and residual dendrite in GH710 alloy bar and make the alloy have good formability, the deformation experiment of alloy was carried out by isothermal forging process, and the temperature of billet heating was 1100 ℃, the deformation of 50% and 70% respectively.
GH710 alloy has good plasticity during isothermal forging deformation. When the primary deformation reaches 50% and 70%, the integrity of the cake billets is good and no forging cracks occur. After isothermal forging deformation of the alloy, the microstructure has been significantly improved, the coarse grain in the bar was effectively broken, the alloy to achieve complete recrystallization. All parts of cake billet deformation uniform, no deformation dead zone. Its microstructure.
Isothermal forging cake billets after the standard four-stage heat treatment, cut the sample, the room temperature tensile, smooth and lasting 980 ℃ performance, 815 ℃ notch durability performance were tested. After the GH710 alloy with low-fold coarse grain is isothermal forging deformation, the cake billet forging has good room temperature strength and high-temperature durability performance, and the performance of the forging parts is very uniform and the dispersion of performance results is very small.
Isothermal forging GH710 alloy microstructure, low magnification and microstructure detection analysis found no more than 1mm coarse grains; 815 ℃ notch life of 114h did not pull off, much higher than the standard ≥ 30h technical requirements; 980 ℃ smooth and durable life of 80h above, but also much higher than the standard technical requirements ≥ 30h.
In order to verify the rationality of isothermal forging process for manufacturing GH710 alloy turbine disk, isothermal forging process was studied. Isothermal forging process was successfully applied to the development of GH710 alloy turbine disk forging. Trial appearance of a good appearance GH710 alloy Φ240mm turbine disk isothermal forging die forgings, and forgings for testing the performance of the organization.
GH710 alloy isothermal forging turbine disk forgings, small grains, uniform forgings of various parts of the forging streamline continuous distribution of contour along the forging, there is no deformation dead zone, forgings low magnification organization as shown. Turbine wheel forging pieces of wheels, spokes and rims of the various parts of the grain size uniformity, the grain boundary γ 'phase precipitation, forgings of various parts of the microstructure as shown.
Isothermal forging turbine disk mechanical properties GH710 alloy isothermal forging turbine disk forgings after four sections of standard heat treatment, according to the literature <5> requirements of the test specimen to test its mechanical properties, isothermal forging turbine disk forgings mechanical properties results fully meet the literature <6> Technical requirements. Its tensile properties at room temperature σb up to 1200MPa, 890MPa higher than the standard requirements of more than 300MPa; 815 ℃ notch life of 64150h gap has not yet pulled off the sample; and 980 ℃ smooth lasting performance is beyond the technical standards in the life of ≥ 30h, According to the experimental site conditions, increase the test stress will force the sample pulled off. See also.
Conclusion (1) Isothermal forging process can effectively improve the deformation properties of GH710 alloy, refine the grain structure and improve the mechanical properties. (2) isothermal forging can be obtained by isothermal forging process, which has the advantages of complete appearance, small grains and uniform microstructure. (3) Isothermal forging process is the ideal forming process for preparing GH710 alloy fine grain turbine disk.
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