A small extrusion ratio synergic annealing fine-grain breakdown method for a difficult-to-deform high gamma prime phase high temperature alloy

Abstract

This invention discloses a method for fine-grained billet preparation with low extrusion ratio and synergistic annealing of difficult-to-deform high-γ′ phase superalloys, comprising the following steps: raw material purification and batching preparation – vacuum induction melting – electron beam melting pretreatment – ​​initial molten pool establishment and stabilization melting – homogenization treatment – ​​hot extrusion and annealing heat treatment. The method utilizes electron beam droplet melting directional solidification technology to prepare difficult-to-deform superalloy ingots with continuous columnar crystal structure. Taking advantage of the significantly superior dislocation storage capacity of columnar crystals compared to traditional equiaxed crystals, and combining low extrusion ratio billet preparation with subsequent precision recrystallization annealing, this method effectively avoids the problems of easy cracking, uneven microstructure, and high cost in high extrusion ratio dynamic recrystallization processes, breaking the stringent limitations of traditional processes on the lower limit of the extrusion ratio. Compared with traditional high extrusion ratio billet preparation processes, the material yield is increased from 60%–75% to 80%–90%, an increase of 15%–25%, significantly reducing the extrusion cracking scrap rate and improving the overall microstructure consistency of the bars.

Description

Technical Field

[0001] This invention belongs to the field of hot working technology, specifically relating to a method for fine-grained blanking with low extrusion ratio synergistic annealing of difficult-to-deform high γ′ phase high-temperature alloys. Background Technology

[0002] Highly alloyed wrought superalloys with high γ′ phase content are widely used in hot-end load-bearing components such as aero-engines due to their excellent high-temperature strength, creep resistance, and microstructural stability. Currently, most high-alloyed wrought superalloy ingots are prepared using duplex or triple-melting processes. However, for high-γ′ phase, difficult-to-deform superalloys, ingots obtained through these traditional melting methods generally exhibit an inhomogeneous equiaxed grain structure, with numerous triple-grain boundaries, severe interdendritic segregation, and localized weak areas. In subsequent billet preparation, to break up the coarse and inhomogeneous as-cast structure and refine the grains, a larger extrusion ratio or a larger deformation amount is usually required.

[0003] CN 104593702B discloses an extrusion method for difficult-to-deform high-temperature alloys. This extrusion method involves extruding difficult-to-process materials such as deformed high-temperature alloys and powder metallurgy high-temperature alloys. The extrusion ratio is limited to ≥4 for general difficult-to-deform high-temperature alloys and ≥8 for powder-based difficult-to-deform high-temperature alloys. The ingots prepared by this method exhibit an inhomogeneous equiaxed grain structure with a large number of triple grain boundaries between grains, accompanied by severe interdendritic segregation and local weak areas. Due to the inherent triple grain boundaries and deformation incoordination of the equiaxed grain structure, cracks are easily induced by stress concentration during billet opening at a high extrusion ratio, resulting in low billet yield, high equipment load requirements, and high production costs.

[0004] CN 112453085B discloses a continuous composite extrusion billet method for difficult-to-deform high-temperature alloy ingots. In this method, the difficult-to-deform high-temperature alloy ingot first undergoes a small-deformation diameter reduction extrusion and upsetting deformation to break up part of the casting structure, thereby improving the plastic deformation capacity. This allows the difficult-to-deform high-temperature alloy to undergo sufficiently large plastic deformation to achieve recrystallization and grain refinement. At the same time, the radial constraint effect applied to the billet by the extrusion cylinder and the diameter reduction extrusion concave cavity effectively prevents unstable deformation during the upsetting process of high-height-to-diameter high-temperature alloy ingots. Finally, through extrusion deformation with a large extrusion ratio (8:1 to 12:1), the coarse casting structure in the core is fully broken up, and uniform recrystallization behavior is generated on the surface and in the core of the bar, resulting in a uniform fine-grained high-temperature alloy bar with a grain size of 7 to 9. However, this technical solution is prone to cracking due to stress concentration because of the large extrusion ratio used in billet opening, resulting in high equipment load requirements and high production costs.

[0005] For GH4976 alloy ingot extrusion blanking, the extrusion ratio is 6, for GH4720Li alloy it is 5-7, and for GH4975 alloy it is 6. It can be seen that the existing extrusion process for difficult-to-deform high-alloy, high-γ′ phase content high-temperature alloys usually requires a large degree of deformation to achieve as-cast microstructure fragmentation and subsequent microstructure refinement, but it also easily leads to higher cracking risk and equipment load. To address this, a low extrusion ratio synergistic annealing fine-grain blanking method for difficult-to-deform high-γ′ phase high-temperature alloys is proposed. Summary of the Invention

[0006] To address the technical challenges of cracking, uneven microstructure, and high cost in dynamic recrystallization processes with large extrusion ratios, this invention provides a method for fine-grained billet preparation with low extrusion ratio synergistic annealing of difficult-to-deform superalloys. This method includes melting preparation, homogenization, low extrusion ratio deformation, and subsequent annealing. It successfully produces crack-free high-γ′ phase difficult-to-deform superalloy extruded bars, with a uniform and fine microstructure after extrusion synergistic annealing. This achieves simultaneous improvement in yield, microstructure refinement, and economic benefits in the high-γ′ phase difficult-to-deform superalloy billet preparation process.

[0007] According to one aspect of the present invention, a method for fine-grained blanking with low extrusion ratio synergistic annealing of difficult-to-deform high γ′ phase superalloys is provided, comprising the following steps:

[0008] Step 1, Raw material purification and batching preparation: The surface of the metal to be melted is purified and dried to obtain purified raw materials; Step 2: Vacuum induction melting is used to obtain the master alloy ingot; Step 3, Electron beam melting pretreatment: The master alloy ingot prepared in step 2 is pretreated to obtain an induction ingot head; Step 4, Initial molten pool establishment and stable smelting: Achieve a furnace vacuum of 5×10⁻⁶. -3 Pa, electron gun chamber vacuum reaches 3×10 -4 After Pa, preheat, connect the power supply and maintain it at 20kV, the output power of the electron gun is 3~15kW, and the induction ingot head described in step 3 is bombarded by a fixed radius ring scanning method to form an initial molten pool. Then, the electron gun power is adjusted to 10~20kW, and the variable radius ring scanning method is switched to melt and solidify to obtain the ingot. Step 5, homogenization treatment: The billet is fed into the furnace at 600~900℃, with a heating rate of 5~10℃ / min, and heated to 1250~1330℃ in 1~3h. After holding at this temperature for 10~30h, it is slowly cooled in the furnace at 0.5~10℃ / min for 5~30h to 900~1100℃, and then air-cooled out of the furnace to obtain a billet with a grain size of 1500~3000μm. Step 6: Hot extrusion and annealing heat treatment.

[0009] Based on the above technical solution, the axial reserved length of the induction spindle in step 3 shall not be less than 10cm.

[0010] The fixed radius ring scanning method described in step 4 is as follows: the electron beam spot diameter is 10 mm, the crucible inner diameter R is 40 mm, the scanning trajectory radius is 20 mm, and the scanning frequency is 20 Hz. The variable radius circular scanning method described in step 4 is as follows: the minimum radius is 0-24 mm, the maximum radius is 16-36 mm, and the scanning radius changes periodically at 5 Hz. The smelting process described in step 4 is as follows: the feeding speed is 0.36-0.59 mm / s, the ingot pulling speed is 0.36-0.59 mm / s, the ingot head rotation speed is 1-10 rpm, and the smelting is carried out by a variable radius ring scanning method. The solidification described in step 4 specifically involves scanning using a variable radius electron beam scanning method, reducing the electron gun power to 4-8 kW within 5-10 minutes, shrinking the scanning radius to within 12 mm, and reducing the power to 0 within 5-10 minutes, with a cooling time of no less than 2 hours.

[0011] Based on the above technical solution, the impurity element content at the top and bottom center positions of the billet obtained in step 4 is as follows: O≤10ppmw, N≤5ppmw, S≤5ppmw.

[0012] Based on the above technical solution, the hot extrusion in the hot extrusion and annealing heat treatment specifically involves: preheating the extrusion cylinder to 200~400℃, applying graphite emulsion lubricant to the inner wall of the extrusion cylinder, placing the pre-treated cladding assembly in a muffle furnace for heating, applying glass powder to the surface of the billet after exiting the furnace, controlling the extrusion ratio to 1~4 and the extrusion speed to 40~100mm / s for extrusion, and slow cooling to obtain the extruded high-temperature alloy workpiece; The pre-extrusion pre-treatment of the shroud assembly is obtained by machining the homogenized billet to obtain an ingot with dimensions of φ(50~80)mm×(150~500)mm, peeling, and 30° chamfering to obtain the billet to be extruded. The billet to be extruded is then shrouded and head and tail gaskets are added to form the shroud assembly, wherein the material used for the shroud is stainless steel.

[0013] Based on the above technical solution, the heating in the hot extrusion and annealing heat treatment is specifically as follows: heating to 1150~1200℃ at a heating rate of 10℃ / min and holding for 2~6 hours.

[0014] Based on the above technical solution, the grain size of the extruded high-temperature alloy workpiece is 200~500μm.

[0015] Based on the above technical solution, the annealing heat treatment in the hot extrusion and annealing heat treatment specifically involves: placing the high-temperature alloy workpiece after hot extrusion at 500~800℃ in an annealing furnace, heating it to 1150~1250℃ at a heating rate of 5~10℃ / min, holding it at that temperature for 0.5~4h, and then air cooling it.

[0016] Based on the above technical solution, the grain size after annealing heat treatment is 40~60μm.

[0017] Beneficial effects (1) The technical solution disclosed in this invention uses electron beam droplet melting directional solidification technology to successfully prepare low segregation and has <001> This process produces a difficult-to-deform high-temperature alloy ingot with a continuous columnar grain structure. Compared with traditional smelting methods, this process significantly reduces the content of O, N, and S impurities in the ingot, which is beneficial for achieving grain boundary purification. Simultaneously, the dislocation storage capacity and deformation coordination of this columnar grain structure are significantly superior to those of traditional equiaxed grains, providing a high-quality base material with both high plasticity and efficient distortion energy storage capacity for subsequent low-extrusion-ratio deformation.

[0018] (2) The technical solution disclosed in this invention abandons the traditional process route of forced dynamic recrystallization with a large extrusion ratio (6~10). By reducing the content of impurity elements through electron beam melting, the grain boundary is purified, which effectively weakens the tendency of grain boundary embrittlement and cracking in the subsequent hot working process. At the same time, by utilizing the excellent dislocation accommodation characteristics of columnar crystals and combining with a small extrusion ratio deformation strategy, the extrusion load, mold wear and equipment tonnage requirements are significantly reduced. At the same time, the plastic deformation is fully and uniformly penetrated into the columnar crystals, which effectively avoids the risk of cracking caused by insufficient thermoplasticity or stress concentration. It also accumulates high-density uniform distortion energy. Combined with precision recrystallization annealing, the uniform distortion energy stored in the small extrusion ratio deformation is used as the driving force to induce full and uniform static recrystallization, which completely transforms the coarse columnar crystal structure into a uniform and fine equiaxed fine grain structure.

[0019] (3) The technical solution disclosed in this invention breaks through the strict limitation of the lower limit of the extrusion ratio in traditional processes by controlling the melting structure and the synergistic effect of small extrusion ratio deformation annealing. It successfully prepares crack-free high γ′ phase difficult-to-deform high-temperature alloy extruded bars. After extrusion synergistic annealing, the structure is uniform and fine. While reducing the scrap rate of extrusion cracking and improving the uniformity of the structure of the bar (compared with the traditional large extrusion ratio billet process, the material yield is increased from 60% to 75% to 80% to 90%, an increase of 15% to 25%), the production cost is greatly reduced. It realizes the simultaneous improvement of the yield, fine grain structure and economic benefits of the high γ′ phase difficult-to-deform high-temperature alloy billet process. It provides a low-cost and highly reliable feasible technical path for the industrial fine grain billet of high γ′ phase difficult-to-deform high-temperature alloy. Attached Figure Description

[0020] Figure 1 These are schematic diagrams showing the macroscopic morphology and microstructure of alloy ingots prepared by electron beam droplet melting and directional solidification in Examples 1-3; Figure 2 This is a tissue diagram after extrusion in Example 1; Figure 3 This is a microstructure diagram of the annealed heat treatment in Example 1; Figure 4 This is a tissue diagram after extrusion in Example 2; Figure 5 This is a microstructure diagram of the annealed heat treatment in Example 2; Figure 6 This is a tissue diagram after extrusion in Example 3; Figure 7 This is a microstructure diagram of the annealed heat treatment in Example 3. Detailed Implementation

[0021] To make the objectives and technical solutions of this invention clearer, the following embodiments are provided for further explanation. However, the scope of protection of this invention is not limited to these embodiments; the embodiments are merely for illustrative purposes. Those skilled in the art should understand that any changes or equivalent substitutions that do not depart from the concept of this invention are included within the scope of protection of this invention.

[0022] Unless otherwise specified, all reagents and raw materials used in this invention are obtained through purchase.

[0023] The present invention provides a method for refining grains by low extrusion ratio synergistic annealing in the embodiment section of a difficult-to-deform high γ′ phase superalloy, which specifically includes the following steps: Step 1, Raw Material Purification and Batching Preparation: The various metals and intermediate alloy raw materials to be smelted are as follows: Cr granules (99.5% purity), Co flakes (99.8% purity), W powder (99.8% purity), Mo strips (99.8% purity), Al ingots (99.8% purity), Ti sponge (99.6% purity), Ta powder (99.6% purity), Nb rods (99.7% purity), high-purity graphite C (99.5% purity), B powder (99.9% purity), Hf granules (99.5% purity), and Ni plates (99.95% purity). The surfaces are polished, ultrasonically cleaned to remove oxide scale and oil, and then thoroughly dried in a vacuum drying oven to eliminate residual moisture. Precisely weigh and proportion the materials according to the nominal composition range of the target difficult-to-deform high-temperature alloy grade, and set aside.

[0024] Step 2, Vacuum Induction Melting: Clean the inner wall of the induction melting furnace crucible and add the furnace charge according to the predetermined charging sequence (following the principles of melting the matrix first, then adding refractory materials; adding inactive materials first, then adding reactive materials; adding macroelements first, then adding microelements). First, establish the molten pool with a high-purity Ni plate, then add bulk elements such as Co and Cr, followed by high-melting-point elements such as Mo, Nb, W, and Ta to ensure full melting and homogenization; then add Hf to adjust the composition, and after the melt stabilizes, add active elements such as Al and Ti. C and B are added as final adjustment elements shortly before casting. For powdered raw materials such as W powder, Ta powder, and B powder, it is advisable to pre-press or wrap them with foil to reduce losses and improve yield. Turn on the cooling water circulation system, air compressor, and main power supply of the equipment in sequence. Start the induction coil heating circuit and gradually increase the input power until the furnace charge is completely liquefied and reaches the predetermined superheat. Then, under precisely controlled casting temperature and casting rate, pour the alloy melt into the ingot mold to complete the forming. After the furnace pressure returns to atmospheric pressure, the furnace door is opened and the master alloy ingot obtained from induction melting is taken out as the raw material billet for subsequent electron beam remelting.

[0025] Step 3, Electron Beam Melting Pretreatment: Shrinkage cavities and loose areas at the top of the master alloy ingot prepared in Step 2 are removed, and the outer diameter of the ingot is machined to remove surface defects. An induction ingot head for subsequent electron beam bombardment melting is formed at the end of the master alloy ingot obtained in Step 2. The axial length of the induction ingot head is not less than 10 cm. The machined ingot head is ultrasonically cleaned sequentially with deionized water and anhydrous ethanol, and then thoroughly dried to obtain a clean and uniform ingot head (induction ingot head) ready for remelting.

[0026] Step 4, Electron beam preheating and initial molten pool establishment: Wait until the furnace vacuum reaches 5×10⁻⁶. -3 Pa, electron gun chamber vacuum reaches 3×10 -4 After achieving a vacuum level of Pa, the electron gun is started to execute the preheating program. After preheating, the electron beam current is set to zero, the high-voltage power supply is connected and maintained stably at 20kV, and the output power of the electron gun is gradually increased to 3~15kW. The induction ingot prepared in step 3 is bombarded using a ring scanning method, causing the surface of the ingot to melt completely and form an initial molten pool in the crucible. Specific parameters are as follows: electron beam spot diameter is 10mm, crucible inner diameter R is 40mm, the scanning trajectory radius inside the ingot-pulling crucible is 20mm (half of the crucible inner diameter R, i.e., R / 2), and the scanning frequency is 20Hz.

[0027] Step 5, Scanning mode switching during the stabilization melting stage: After the induction ingot prepared in Step 3 melts and forms a stable molten pool, the electron gun power is adjusted to 10~20 kW, and the scanning mode is switched from fixed radius ring scanning to variable radius ring scanning. The minimum radius is dynamically selected between 0 and 24 mm, and the maximum radius is dynamically selected between 16 and 36 mm. The scanning radius changes periodically at a frequency of 5 Hz, while the beam spot size and scanning frequency remain unchanged. Using the variable radius ring scanning method can reduce component volatilization caused by prolonged residence of electron beam energy in local areas, and also helps maintain the shallow and flat molten pool morphology, thus providing conditions for the directional growth of columnar crystals.

[0028] Step 6, Continuous Feeding and Pulling: The raw material feeding mechanism and pulling mechanism are activated according to the smelting process, continuously feeding the induction base material to be remelted from the raw material box into the molten pool area. Simultaneously, the remelted billet in the pulling crucible is pulled downwards. As smelting progresses, the mass of the base material to be melted gradually decreases, while the mass of the ingot in the pulling crucible continuously increases.

[0029] Step 7, Initiate Ingot Rotation and Composite Melting: Activate the ingot rotation function, controlling the rotation speed between 1 and 10 rpm. The feeding device guides the end of the composite stainless steel base material to the top of the molten pool. At this time, a portion of the electron beam spot, using the variable radius annular scanning method described in Step 5, simultaneously bombards the end of the base material, causing the alloy-coated portion and the stainless steel substrate to melt synchronously. Simultaneously activate the material handling action to ensure sufficient melting of the base material and stable dripping of molten droplets into the molten pool within the ingot pulling crucible. Under the continuous action of the electron beam scanning energy, the base material to be remelted maintains a stable molten state. Further initiate the ingot pulling program, matching the pulling rate with the base material melting rate. The feeding speed is 0.36–0.59 mm / s, and the ingot pulling speed is 0.36–0.59 mm / s, thereby maintaining a constant relative spatial position of the molten pool within the crucible. During this process, the mass of the base material to be melted is continuously consumed, while the mass of the induction ingot obtained in the ingot pulling crucible gradually accumulates and increases.

[0030] Step 8, Power Reduction and System Cooling at the End of Melting: After the melting task is completed, the spinning, pulling, and stacking functions are sequentially shut down, and the material return procedure is initiated, gradually moving the remaining raw material to be melted away from the area above the molten pool and back to its original position in the raw material box. During this material return process, the variable radius annular electron beam scanning method described in Step 5 is maintained, and the electron gun power is gradually reduced to 4-8 kW within 5-10 minutes. Subsequently, the scanning radius is reduced to within 12 mm, and the power is steadily reduced to zero within the next 5-10 minutes. The high voltage of the electron gun is shut off, allowing the equipment and the obtained high-temperature alloy ingot to cool naturally and fully in a vacuum environment. After the temperature of the ingot and electron gun drops to a minimum (cooling time of no less than 2 hours), the vacuum acquisition system is shut down, the furnace is opened, and the ingot is removed. The chemical composition of the ingot obtained by the above electron beam melting and directional solidification process meets the requirements of the target difficult-to-deform high-temperature alloy standard. Simultaneously, this process effectively reduces the impurity element content at the top and bottom center of the cast billet, achieving O≤10ppmw, N≤5ppmw, and S≤5ppmw, thus realizing intergranular purification. Furthermore, the ingot surface exhibits no obvious metallurgical defects, and the microstructure shows columnar crystals along... <001> It grows continuously in the direction of growth.

[0031] Step 9, Homogenization Heat Treatment: The surface of the ingot obtained in Step 8 is peeled to remove surface defects, and then the ingot is subjected to high-temperature homogenization treatment to eliminate residual micro-component segregation during solidification. Before formulating the process, the initial melting critical temperature of the alloy needs to be determined in advance through quenching tests to prevent local liquefaction of grain boundaries due to excessively high temperatures in subsequent heating stages. The ingot prepared in Step 8 is fed into the furnace at 600~900℃, with a heating rate of 5~10℃ / min, and heated to 1250~1330℃ in 1~3 hours. After holding at this temperature for 10~30 hours, it is slowly cooled in the furnace at 0.5~10℃ / min for 5~30 hours to 900~1100℃ before being air-cooled out of the furnace. The purpose of slow cooling is to allow the precipitation of large-size γ′ phase in the alloy to improve the subsequent deformation behavior of the alloy. The grain size after homogenization is 1500~3000μm.

[0032] Step 10, Pre-extrusion process: The electron beam melting billet after homogenization is machined, and peeling and chamfering are performed sequentially. The peeling process aims to remove the surface oxide scale, and the size of the ingot after processing is controlled to φ(50~80)mm×(150~500)mm; then the peeled ingot is chamfered at 30° to prepare the billet to be extruded that meets the requirements of the extrusion process.

[0033] Step 11, Pre-treatment of the sheath and gaskets: The billet to be extruded obtained in Step 10 is sheathed and fitted with head and tail gaskets to form a sheath assembly. The sheath material is stainless steel. The sheath is used to mitigate the temperature drop of the ingot during hot extrusion and reduce the risk of circumferential cracking; the head gasket guides the metal flow in the early stages of extrusion to reduce uneven deformation and stress concentration; the tail gasket improves the metal flow state at the end of extrusion to suppress the dovetail effect and improve finished product quality and yield.

[0034] Step 12, Hot Extrusion: The hot extrusion process is performed using a horizontal extrusion press. The specific operation is as follows: Preheat the extrusion cylinder to 200~400℃ and apply graphite emulsion lubricant to its inner wall; remove oxide scale from the cladding assembly obtained in Step 11, then place it in a muffle furnace for heating at a rate of 10℃ / min, holding it at 1150~1200℃ for 2~6 hours; after exiting the furnace, apply glass powder to the surface of the billet for lubrication, then quickly transfer it to the extrusion cylinder for extrusion, controlling the extrusion ratio at 1~4 and the extrusion speed at 40~100mm / s; place the extruded bar in a holding furnace for slow cooling. The extruded bar is then machined to remove the outer stainless steel cladding, exposing the internal high-temperature alloy material (the extruded high-temperature alloy workpiece has a grain size of 200~500μm).

[0035] Step 13, Annealing Heat Treatment: The extruded high-temperature alloy workpiece obtained in Step 12 undergoes recrystallization annealing to eliminate work hardening and residual stress accumulated during extrusion, and to regulate the grain structure through recrystallization to obtain a uniform and fine equiaxed grain structure. The specific annealing process is as follows: The extruded high-temperature alloy workpiece obtained in Step 12 is placed in an annealing furnace at 500~800℃. The furnace is heated with the workpiece at a controlled rate of 5~10℃ / min, and the temperature is uniformly increased to 1150~1250℃ over 1~5 hours, and held for 0.5~4 hours. If the temperature exceeds 4 hours, the internal grains of the alloy will grow excessively, resulting in abnormal grain coarsening, which will impair the subsequent processing plasticity and final service performance of the material. After holding, the workpiece is removed from the furnace and air-cooled in still air to complete the entire recrystallization annealing process. The alloy treated with this annealing process has good microstructure uniformity and adaptability to subsequent hot and cold working (grain size after annealing is 40~60μm).

[0036] Example The small extrusion ratio synergistic annealing fine-grained billet preparation method disclosed in this invention includes: raw material purification and batching preparation - vacuum induction melting - electron beam melting pretreatment - electron beam preheating and initial molten pool establishment - scanning mode switching during the stable melting stage - continuous feeding and ingot pulling - ingot head rotation and composite melting - melting end and cooling - homogenization heat treatment - pretreatment before extrusion - pretreatment of cladding and gaskets - hot extrusion - annealing heat treatment. The relevant parameters for electron beam melting pretreatment / preheating, initial molten pool establishment, and stable melting are shown in Table 1; the macroscopic morphology and microstructure of the alloy ingot prepared by electron beam droplet melting directional solidification melting are shown in Table 1. Figure 1 (Left: Macroscopic view, Right: Microstructure diagram), Parameters related to continuous feeding and ingot pulling, ingot rotation and composite melting, melting end and cooling are shown in Table 2; Parameters related to homogenization heat treatment and pre-extrusion treatment are shown in Table 3; Specific hot extrusion and yield are shown in Table 4; Parameters related to annealing heat treatment are shown in Table 5. The microstructure diagrams after extrusion and after annealing heat treatment in Example 1 are shown in Table 5. Figures 2-3 The microstructure diagrams after extrusion and after annealing heat treatment in Example 2 are shown below. Figures 4-5 The microstructure diagrams after extrusion and after annealing heat treatment in Example 3 are shown below. Figures 6-7 .

[0037] Table 1. Parameters related to electron beam melting pretreatment / preheating, initial molten pool establishment, and stable melting.

[0038] Table 2. Parameters related to continuous feeding and ingot pulling, ingot head rotation and combined melting, melting end and cooling.

[0039] Table 3. Relevant parameters for homogenization heat treatment and pre-extrusion pretreatment.

[0040] Table 4 Hot extrusion and yield

[0041] Table 5. Parameters related to annealing heat treatment

[0042] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for fine-grained billet preparation with low extrusion ratio synergistic annealing of difficult-to-deform high-γ′ phase superalloys, characterized in that, Includes the following steps: Step 1, Raw material purification and batching preparation: The surface of the metal to be melted is purified and dried to obtain purified raw materials; Step 2: Vacuum induction melting is used to obtain the master alloy ingot; Step 3, Electron beam melting pretreatment: The master alloy ingot prepared in step 2 is pretreated to obtain an induction ingot head; Step 4, Initial molten pool establishment and stable smelting: Achieve a furnace vacuum of 5×10⁻⁶. -3 Pa, electron gun chamber vacuum reaches 3×10 -4 After Pa, preheat, connect the power supply and maintain it at 20kV, the output power of the electron gun is 3~15kW, and the induction ingot head described in step 3 is bombarded by a fixed radius ring scanning method to form an initial molten pool. Then, the electron gun power is adjusted to 10~20kW, and the variable radius ring scanning method is switched to melt and solidify to obtain the ingot. Step 5, homogenization treatment: The billet is fed into the furnace at 600~900℃, with a heating rate of 5~10℃ / min, and heated to 1250~1330℃ in 1~3h. After holding at this temperature for 10~30h, it is slowly cooled in the furnace at 0.5~10℃ / min for 5~30h to 900~1100℃, and then air-cooled out of the furnace to obtain a billet with a grain size of 1500~3000μm. Step 6: Hot extrusion and annealing heat treatment.

2. The method for fine-grained billet preparation with small extrusion ratio synergistic annealing according to claim 1, characterized in that, The axial reserved length of the induction spindle head mentioned in step 3 shall not be less than 10cm.

3. The method for fine-grained billet preparation with small extrusion ratio synergistic annealing according to claim 1, characterized in that, The fixed radius ring scanning method described in step 4 is as follows: the electron beam spot diameter is 10 mm, the crucible inner diameter R is 40 mm, the scanning trajectory radius is 20 mm, and the scanning frequency is 20 Hz. The variable radius circular scanning method described in step 4 is as follows: the minimum radius is 0~24mm, the maximum radius is 16~36mm, and the scanning radius changes periodically at 5Hz.

4. The method for fine-grained billet preparation with small extrusion ratio synergistic annealing according to claim 1, characterized in that, The smelting process described in step 4 is as follows: the feeding speed is 0.36-0.59 mm / s, the ingot pulling speed is 0.36-0.59 mm / s, the ingot head rotation speed is 1-10 rpm, and the smelting is carried out by a variable radius ring scanning method. The solidification described in step 4 specifically involves scanning using a variable radius electron beam scanning method, reducing the electron gun power to 4-8 kW within 5-10 minutes, shrinking the scanning radius to within 12 mm, and reducing the power to 0 within 5-10 minutes, with a cooling time of no less than 2 hours.

5. The method for fine-grained billet preparation with small extrusion ratio synergistic annealing according to claim 1, characterized in that, The impurity element content at the top and bottom center of the billet obtained in step 4 is as follows: O≤10ppmw, N≤5ppmw, S≤5ppmw.

6. The method for fine-grained billet preparation with small extrusion ratio synergistic annealing according to claim 1, characterized in that, The hot extrusion process in the hot extrusion and annealing heat treatment is as follows: the extrusion cylinder is preheated to 200~400℃, graphite emulsion is applied to the inner wall of the extrusion cylinder for lubrication, the pre-treated cladding assembly is placed in a muffle furnace for heating, glass powder is applied to the surface of the billet after exiting the furnace, the extrusion ratio is controlled at 1~4 and the extrusion speed is 40~100mm / s for extrusion, and slow cooling is performed to obtain the extruded high-temperature alloy workpiece. The pre-extrusion pre-treatment of the shroud assembly is obtained by machining the homogenized billet to obtain an ingot with dimensions of φ(50~80)mm×(150~500)mm, peeling, and 30° chamfering to obtain the billet to be extruded. The billet to be extruded is then shrouded and head and tail gaskets are added to form the shroud assembly, wherein the material used for the shroud is stainless steel.

7. The method for fine-grained billet preparation with small extrusion ratio synergistic annealing according to claim 6, characterized in that, The heating process in the hot extrusion and annealing heat treatment is specifically as follows: heating to 1150~1200℃ at a heating rate of 10℃ / min and holding for 2~6 hours.

8. The method for fine-grained billet preparation with small extrusion ratio synergistic annealing according to claim 6, characterized in that, The grain size of the extruded high-temperature alloy workpiece is 200~500μm.

9. The method for fine-grained billet preparation with small extrusion ratio synergistic annealing according to claim 1, characterized in that, The annealing heat treatment in the hot extrusion and annealing heat treatment specifically involves placing the high-temperature alloy workpiece after hot extrusion at 500~800℃ in an annealing furnace, heating it to 1150~1250℃ at a heating rate of 5~10℃ / min, holding it at that temperature for 0.5~4h, and then air cooling it to obtain the grains after annealing heat treatment.

10. The method for fine-grained billet preparation with small extrusion ratio synergistic annealing according to claim 9, characterized in that, The grain size after annealing heat treatment is 40~60μm.

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