A method for reducing mischcrystal and recrystallization at cross-section discontinuities in nickel-based single crystal superalloys

Abstract

The present application relates to the technical field of high-temperature alloy investment casting, in particular to a method for reducing heterogeneous crystals and recrystallization at cross-section mutation of nickel-based single crystal high-temperature alloy, which comprises the following steps: (1) after wax mold pressing is completed, when the wax mold is completely cooled, low-melting-point wax is coated at the R angle of the variable cross-section adapter to expand the R angle and reduce stress concentration; (2) during shell preparation, an appropriate amount of furan resin is added to the back layer slurry, and an appropriate amount of wood chips is added to the back layer sanding material to improve the shell yielding property; (3) during casting, the pulling rate near the variable cross-section is reduced to 1.5 mm / min-2 mm / min. The present application solves the problems of recrystallization and heterogeneous crystals of variable cross-section castings with complex structure through the synergistic effect of adjusting the size of the R angle, shell preparation process and the pulling rate near the variable cross-section, and the provided preparation method of variable cross-section nickel-based single crystal high-temperature alloy castings is simple to operate, easy to implement and reduces production cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-temperature alloy investment casting, in particular to a method for reducing heterogeneous crystals and recrystallization at the cross-section mutation of a nickel-based single-crystal high-temperature alloy. BACKGROUND

[0002] Nickel-based high-temperature alloys have excellent creep properties, fatigue strength, good corrosion resistance and environmental stability, and are widely used in the manufacture of hot-end components of major power components in the fields of aviation, aerospace, ships and energy. With the increasing demand for thrust-to-weight ratio and gas efficiency of advanced aircraft engines, the key high-temperature hot-end components need to withstand the interaction of thermal stress and centrifugal force for a long time under more severe working conditions, which puts higher requirements on the temperature resistance of turbine blades. Therefore, single-crystal high-temperature alloys that eliminate the high-temperature weak structure of grain boundaries have gradually become the preferred materials for manufacturing key components of advanced aircraft engines.

[0003] With the structural complexity and large size of high-temperature components, various solidification defects such as heterogeneous crystals and recrystallization are more likely to occur during single-crystal growth, especially near the variable cross-section of the principle water-cooled disc. Due to the decrease in temperature gradient, the front of the solid-liquid interface becomes no longer horizontal, and heterogeneous crystals are easily generated when solidification occurs at the variable cross-section. In addition, in order to ensure that the shell does not occur during pouring, the high-temperature strength of the shell needs to be improved, but this will result in poor compliance, which makes it easy to occur in the variable cross-section R angle near the stress concentration during solidification, and the stress concentration is larger, which leads to the occurrence of recrystallization after subsequent heat treatment.

[0004] The occurrence of heterogeneous crystals and recrystallization affects the integrity of single-crystal castings, and cracks are easily generated at the recrystallization grain boundaries and the interface between the recrystallization layer and the base material during service, which greatly reduces the performance of the alloy and causes serious consequences. Therefore, developing a method for reducing the tendency of heterogeneous crystals and recrystallization in variable cross-section single-crystal high-temperature alloy castings is crucial for improving the performance of high-temperature alloy castings. SUMMARY

[0005] Therefore, the present application provides a method for reducing heterogeneous crystals and recrystallization at the cross-section mutation of a nickel-based single-crystal high-temperature alloy, which effectively improves the situation of easy generation of heterogeneous crystals and recrystallization in high-temperature alloy castings, and is particularly suitable for single-crystal high-temperature alloy castings with complex structure, large size and mutation interface.

[0006] To achieve the above-mentioned purpose, the present application mainly adopts the following technical solutions:

[0007] A method for reducing heterogeneous crystals and recrystallization at the cross-section mutation of a nickel-based single-crystal high-temperature alloy, the method comprising the following steps:

[0008] Step (1): wax mold preparation, wax mold pressing is carried out according to the process parameters, after the wax mold is completely cooled, the low melting point wax material is coated at the R angle transition of the variable cross section (the cross section mutation), the R angle is enlarged, and after completion, the wax mold combination is carried out;

[0009] Step (2): shell preparation, the surface layer, transition layer and back layer of the shell are prepared, and finally the slurry is dried and sealed, and during the preparation process, furan resin is added to the back layer slurry, and sawdust is added to the back layer sand material to improve the shell yielding property;

[0010] Step (3): casting pouring, using the shell prepared in step (2) to pour the casting, and lowering the pulling rate to 1.5mm / min~2mm / min at the upper and lower 20mm~30mm parts of the cross section mutation during pouring, and cooling after the casting pouring is completed;

[0011] Step (4): the cooled casting group is integrally put into the vacuum heat treatment furnace for one-time solid solution and twice aging treatment.

[0012] Step (5): the casting group after heat treatment is removed from the shell and cut, and then corroded after cutting.

[0013] Finally, the expanded R angle part is removed using professional finishing tools and R gauge.

[0014] After the wax mold pressing in step (1) is completed, the radius r is measured using the R gauge, then the low melting point wax material is coated to enlarge the R angle, and the melting point of the coated low melting point wax material is 10℃~15℃ lower than that of the wax material for the part; The radius r' of the enlarged R angle is (1.2~1.5)r; The enlarged R angle is also removed by cooperating with the R gauge in the subsequent finishing procedure. After the wax mold is cooled, the wax mold combination is carried out, and the wax mold placement time should not exceed 24h, and the casting should be completely perpendicular to the bottom plate during the combination.

[0015] The combined mold group is cleaned to facilitate the coating of the slurry.

[0016] In step (2), the surface layer and the transition layer slurry are prepared by using EC95 powder and silica sol. The composition of the surface layer slurry is EC95 powder: silica sol: wetting agent: defoaming agent = 3.5-4.0:1.0:0.003:0.01 in mass ratio. The viscosity of the surface layer slurry is 40-45 s. The surface layer sanding material is 100# corundum sand. The composition of the transition layer slurry is EC95 powder: silica sol: wetting agent: defoaming agent = 2.5-3.0:1.0:0.003:0.003 in mass ratio. The viscosity of the transition layer slurry is 30-35 s. The transition layer sanding material is 60# corundum sand. The composition of the back layer slurry is EC95 powder: silica sol: furan resin: wetting agent: defoaming agent = 1.5-2.0:1.0:0.03-0.05:0.003:0.003 in mass ratio. The viscosity of the back layer slurry is 15-20 s. When preparing the back layer slurry, the required silica sol is first added, then the furan resin is added at 3%-5% of the mass of the silica sol. The silica sol and the furan resin are stirred uniformly at a speed of 280-350 rpm. Then the EC95 powder is slowly added while stirring. After the addition of the EC95 powder is completed, the slurry is stirred thoroughly for 24-48 h. The back layer sanding material is 24# corundum sand mixed with wood chips. The amount of wood chips mixed is 0.2%-0.3% of the mass of the corundum sand. The addition of wood chips can increase the porosity of the mold shell, thereby improving the mold shell yield and reducing the stress concentration when the casting solidifies and shrinks. The addition of furan resin can improve the adhesion of the coating and ensure the close combination of the wood chips and the slurry, thereby improving the strength of the mold shell. A total of 4 layers of back layer are coated. After the last layer of back layer is completely dried, the back layer is sealed, i.e., a layer of back layer slurry is coated again, but without sanding. Finally, the final drying is performed for 48-60 h.

[0017] In step (3), after the mold shell is prepared, the casting is poured. During pouring, the pulling rate is reduced to 1.5-2 mm / min in the part between 20-30 mm below the variable cross-section and 20-30 mm above the variable cross-section, so that the solid-liquid interface front becomes horizontal, reducing the tendency of mixed crystals. The pulling rate of other parts of the casting is 3-5 mm / min. The pouring temperature is 1550℃±10℃.

[0018] In step (4), after the casting is cooled, the whole mold shell is put into a vacuum heat treatment furnace for solid solution and aging treatment, so as to avoid plastic deformation and increase the recrystallization tendency of the casting during transportation and cutting. When the casting is put into the heat treatment furnace, the pouring and gating are clamped into a special molybdenum frame for heat treatment, and the body of the part should not touch the molybdenum frame.

[0019] The heat treatment process in step (4) is one-time solid solution and two-time aging, and the heat treatment is performed by using a vacuum high-pressure gas quenching furnace, argon cooling, the solid solution temperature is 1300℃±10℃, the solid solution time is 240min±10min; the first aging treatment temperature is 1080℃±10℃, the holding time is 360min±10min; the second aging treatment temperature is 870℃±10℃, the holding time is 1440min±10min.

[0020] After the heat treatment is completed, the type shell is cleaned by using a hammer to knock the pouring riser, and the casting is cut, after the cutting is completed, corrosion treatment is performed, the conditions of the mixed crystal and the recrystallization are observed, and finally, the R angle is expanded and the expanded part is removed by using a wind mill and R gauge.

[0021] The corrosion liquid used for the corrosion treatment of the casting group in step (5) is an FeCl3 acidic solution composed of FeCl3, HCL, HNO3 and H2O, wherein the mass-volume concentration of FeCl3 is 0.11-0.13g / mL, the volume ratio of HCL, HNO3 and H2O is 20-23:1:5-6, the corrosion temperature is 60℃±5℃, and the corrosion time is 5min±1min.

[0022] The preparation method of the variable cross-section nickel-based single crystal high-temperature alloy casting provided by the application is characterized in that the structure of the stress concentration part is changed, the retreating property of the type shell is improved by adjusting the shell preparation process, so that the stress concentration tendency is reduced; further, the casting group with the shell is subjected to heat treatment, so that the tendency of plastic deformation generated in the process of transportation, shell cleaning and cutting is reduced; finally, the local pulling rate is reduced, so that the solid-liquid interface front becomes horizontal. The structure of the wax mold, the shell preparation process, the heat treatment mode and the crystal pulling speed are cooperated to solve the recrystallization and mixed crystal problems of the variable cross-section casting with complex structure, the preparation method of the variable cross-section nickel-based single crystal high-temperature alloy casting is simple to operate and easy to realize, and the production cost is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The structure schematic diagram of the nickel-based single crystal high-temperature alloy casting with the mutation cross-section prepared in Example 1.

[0024] Figure 2 The single crystal integrity condition of the casting in Example 1.

[0025] Figure 3 (a), (b) and (c) in FIG. 4 are the mixed crystal conditions of the castings in Comparative Examples 1, 2 and 3, respectively.

[0026] Figure 4 (a), (b) and (c) in FIG. 5 are the recrystallization conditions of the castings in Comparative Examples 1, 2 and 3, respectively. DETAILED DESCRIPTION

[0027] In order to further clarify the technical means and effects adopted by the present application to achieve the predetermined inventive objectives, the specific embodiments, structures, features and effects according to the present application are described in detail below in conjunction with the drawings and examples.

[0028] In the specific implementation process, the method for reducing heterogeneous crystals and recrystallization at the cross-section mutation of a nickel-based single-crystal superalloy includes the following steps:

[0029] Step (1) wax mold preparation: press the wax mold according to the process parameters, and after the wax mold is completely cooled, coat low-melting-point wax material at the R-angle transition of the variable cross-section to expand the R-angle radius, and then perform wax mold assembly.

[0030] Step (2) shell preparation: prepare the surface layer, transition layer and back layer of the shell, and finally seal and dry the slurry, and in the preparation process, add furan resin to the back layer slurry, and add an appropriate amount of sawdust to the sand material in the back layer to improve the shell yielding property.

[0031] Step (3) casting pouring: use the shell prepared in step (2) to pour the casting, and during pouring, reduce the pulling rate to 1.5 mm / min to 2 mm / min for the 20 mm to 30 mm part above and below the cross-section mutation, and then cool the casting after pouring is completed.

[0032] Step (4): put the cooled casting group into a vacuum heat treatment furnace as a whole with the shell to perform one-time solid solution and two-time aging treatment.

[0033] Step (5): perform shell removal and cutting on the casting group after heat treatment, and then perform corrosion after cutting is completed to observe the heterogeneous crystals and recrystallization.

[0034] Finally, remove the expanded R-angle part of the casting described in step (5) using professional polishing tools in cooperation with R-rules.

[0035] Next, the present application is further described in detail through examples and comparative examples.

[0036] Example 1

[0037] In this example, a nickel-based single-crystal superalloy casting with a mutation cross-section (as shown in FIG. 1) is prepared, and the preparation method adopts the method for reducing heterogeneous crystals and recrystallization at the cross-section mutation of a nickel-based single-crystal superalloy in the present application, Figure 1

[0038] ​Firstly, according to the process parameters, the wax mold is pressed, the wax material is F28 type part wax, the melting point is about 70℃, after pressing, it is cooled for 30 min, the paramelt low melting point wax material is used to expand the R angle at the variable cross-section adapter R angle, the coated paramelt low melting point wax material has a melting point of 57℃; when coating, the R gauge is used to measure the size of the R angle radius (r), after measurement, r is 3mm, after expansion, the R angle radius r' is 3.5mm; the expanded R angle is also removed in the subsequent polishing procedure by cooperating with the R gauge. After coating, the wax mold is combined, when combining, the casting is required to be completely perpendicular to the base plate, the base plate diameter is 145mm, 4 part castings are combined in each group. The combined mold group is cleaned to facilitate the coating of the slurry, the cleaning time is 5min, and it is dried for standby.

[0039] Shell preparation, the mold group is coated with slurry, sand blasted and dried to prepare the face layer, transition layer and back layer of the shell, and finally the slurry is sealed and dried to obtain the shell;

[0040] First layer face layer preparation, the mold group is immersed in the face layer slurry for coating, the composition of the face layer slurry is EC95 powder:silica sol:wetting agent:foaming agent = 3.8:1.0:0.003:0.01 in terms of mass ratio, the viscosity of the face layer slurry is 45s, then the coated mold group is placed into the sand blasting machine for sanding, the sanding material is 100# corundum sand, the face layer drying time is 4h; the drying temperature is 23±2℃; the drying humidity is 70±10%RH.

[0041] The preparation of the second layer transition layer, the mold group is immersed in the transition layer slurry for hanging slurry, the composition of the transition layer slurry is, EC95 powder: silica sol: wetting agent: defoaming agent = 3.0: 1.0: 0.003: 0.003 by mass ratio, the viscosity of the transition layer slurry is 35s, then the mold group with slurry is put into the sand spraying machine for sanding, the sanding material is 60# corundum sand, the drying time is 4h; the drying temperature is 23±2℃; the drying humidity is 70±10%RH. The preparation of the third to sixth layer back layer, the mold group is immersed in the transition layer slurry for hanging slurry, the composition of the back layer slurry is, EC95 powder: silica sol: furan resin: wetting agent: defoaming agent = 1.8: 1: 0.05: 0.003: 0.003 by mass ratio, the viscosity of the back layer slurry is 20s, then the mold group with slurry is put into the sand spraying machine for sanding, the back layer sanding material is 24# corundum sand with wood chips, the wood chip content is 0.3% of the mass content of 24# corundum sand, the particle size of the wood chip is 0.7mm, the drying time is 6h, the drying temperature is 23±2℃, and the drying humidity is 50±10%RH. The above-mentioned back layer hanging slurry, sanding and drying process is repeated for 3 times, and a total of 4 layers of back layer are coated, and after the last layer of back layer is completely dried, a sealing slurry treatment is performed, that is, a layer of back layer slurry is coated again, but without sanding, and finally, the final drying is performed, the final drying time is 48h, and after the final drying is completed, the dewaxing and baking are performed, the dewaxing temperature is 170℃, the dewaxing time is 15min, and the dewaxing pressure is 8.2bar; the baking temperature is 950℃, the baking time is 2h, and after the baking is completed, the furnace is cooled to room temperature, and the required mold shell is obtained. The prepared mold shell is subjected to a leakage test using methylene blue + alcohol solution, and a total of 5 groups are obtained, among which 1 group has slight leakage at some positions, but after repair, it does not affect pouring, and the remaining mold shells do not have leakage, and the qualified mold shells are prepared for the next pouring.

[0042] After the mold shell is prepared, a vacuum induction melting furnace is used for casting, a DD98M nickel-based single crystal superalloy is used as the mother alloy for pouring, the pouring weight is 2.7kg; the refining temperature is 1580℃; the pouring temperature is 1550℃; and during pouring, the pulling rate is reduced to 2mm / min between 25mm below the variable cross-section and 30mm above the variable cross-section, and the specific crystal pulling process is that the first section pulling rate is 5mm / min, the first section crystal pulling position is 55mm; the second section pulling rate is 3mm / min, the second section crystal pulling position is 55-200mm; and the third section pulling rate is 2mm / min, and the third section crystal pulling position is 200-255mm. By reducing the crystal pulling speed near the variable cross-section, the solid-liquid interface front becomes horizontal, and the tendency of mixed crystal is reduced.

[0043] After the pouring is completed and the castings are grouped for air cooling for 5 hours, the castings are integrally brought into a vacuum heat treatment furnace with a shell to avoid plastic deformation of the castings due to bumping during the transfer and cutting process, and to increase the recrystallization tendency. When the castings are brought into the heat treatment furnace, the pouring and feeding heads are clamped into a special molybdenum frame for heat treatment, and the body of the part should not contact the molybdenum frame. The heat treatment process is one-time solid solution plus two-time aging, and the vacuum high-pressure gas quenching furnace is used for heat treatment. The vacuum high-pressure gas quenching furnace is first evacuated to below 0.1 Pa, then heated to the solid solution temperature of 1300°C at a rate of 3°C / min, and the solid solution time is 240 min. Then, high-purity argon is used to cool to below 300°C at a rate of 50°C / min. Then, the temperature is raised to 1080°C at a rate of 3°C / min for the first aging treatment, and the holding time is 360 min. Then, high-purity argon is used to cool to below 300°C at a rate of 50°C / min. Then, the temperature is raised to 870°C at a rate of 3°C / min for the second aging treatment, and the holding time is 1440 min. Then, high-purity argon is used to cool to room temperature at a rate of 50°C / min.

[0044] After the heat treatment is completed, the pouring and feeding heads are cleaned with a hammer to clean the mold shell, and the castings are cut. After the cutting is completed, the castings are corroded using a corrosion liquid prepared by mixing 120 g of FeCl3, 750 ml of HCL, 36 ml of HNO3 and 200 ml of H2O, the corrosion liquid temperature is 60°C, the corrosion time is 5 min, and after the corrosion is completed, the recrystallization and miscellaneous crystals are observed. A total of 20 castings are poured, and no recrystallization and miscellaneous crystals are found. As shown in FIG. 1, after the detection is completed, the R is expanded and the expanded part is polished and removed to meet the size requirements. Figure 2

[0045] Comparative Example 1

[0046] This comparative example prepares a nickel-based single crystal superalloy casting with a variable cross-section which is the same as that of Example 1, and the difference between the preparation process and Example 1 lies in the following three points. First, after the wax mold is pressed, the paramelt low-melting-point wax material is not used to change the size of the variable cross-section R angle radius. Second, no furan resin is added to the back layer slurry during the mold shell preparation process, and no wood chips are added to the back layer sanding material. Third, the crystal pulling speed during the casting pouring process is 5 mm / min. The other preparation processes are the same as those of Example 1.

[0047] First, the wax mold is pressed according to the process parameters. The wax material uses F28 part wax with a melting point of about 70°C. After pressing, it is completely cooled. According to the assembly requirements, the wax mold is assembled. When assembling, the castings should be completely perpendicular to the base plate. The base plate diameter is 145 mm, and each group contains 4 part castings. The assembled mold group is cleaned to facilitate the slurry coating. The cleaning time is 5 min, and it is dried for standby.

[0048] ​The shell preparation, the mold group is hung with slurry, sand is sprayed and dried to prepare the surface layer, the transition layer and the back layer of the shell, and finally the slurry is sealed and dried to obtain the shell;

[0049] The preparation of the first layer surface layer and the second layer transition layer is completely the same as that of Example 1, the preparation of the third to sixth layer back layer, the mold group is immersed in the transition layer slurry for slurry hanging, the composition of the back layer slurry is 1.8:1:0.003:0.003 of EC95 powder:silica sol:wetting agent:foaming agent by mass ratio, the viscosity of the back layer slurry is 20 s, then the slurry-hung mold group is placed into a sand spraying machine for sand spraying, the back layer sand spraying material is 24# corundum sand, and other processes are completely the same as those of Example 1.

[0050] After the shell preparation is completed, the vacuum induction melting furnace is used for casting, the crystal pulling speed is 5 mm / min throughout the casting process, that is, the crystal pulling speed near the variable cross-section is not changed, and other processes are completely the same as those of Example 1.

[0051] The casting group heat treatment process (one solid solution and two times aging), the casting group shell removal, cutting, corrosion and casting polishing are the same as those of Example 1,

[0052] After the corrosion is completed, the recrystallization and the miscellaneous crystal are observed, a total of 20 castings are poured, the recrystallization and the miscellaneous crystal are relatively serious, see Figure 3 (a) and Figure 4 (a) in

[0053] Comparative Example 2

[0054] This comparative example prepares the same nickel-based single crystal high-temperature alloy casting with a variable cross-section as Example 1,

[0055] In the preparation process of this comparative example, only the shell preparation process (that is, the furan resin is added to the back layer slurry in the shell preparation process, and the wood chips are mixed into the back layer sand spraying material) is consistent with Example 1, and other preparation processes are consistent with Comparative Example 1.

[0056] After the corrosion test, it is found that the recrystallization problem is improved and the size is smaller, but it is not completely solved, see Figure 3 (b) and Figure 4 (b) in

[0057] Comparative Example 3

[0058] This comparative example prepares the same nickel-based single crystal high-temperature alloy casting with a variable cross-section as Example 1,

[0059] In the preparation process of this comparative example, the wax mold preparation process in step (1) is the same as that of Example 1 (that is, the paramelt low-melting-point wax material is used to enlarge the R angle, and the R angle enlargement degree is consistent with Example 1), and other preparation processes are consistent with Comparative Example 1.

[0060] Corrosion testing revealed that the recrystallized size was smaller compared to the comparative example, but the recrystallization problem was still present. (See...) Figure 3 (c) and Figure 4 (c) in the middle.

Claims

1. A method for reducing impurities and recrystallization at abrupt changes in the cross-section of a nickel-based single-crystal superalloy, characterized in that, The method includes the following steps: Step (1): Wax model preparation. Press the wax model according to the process parameters. After the wax model has completely cooled, apply low melting point wax to the R-angle of the variable cross section to expand the R-angle radius. After completion, assemble the wax model. Step (2): Shell preparation, prepare the surface layer, transition layer and back layer of the shell, and finally seal and dry. During the preparation process, furan resin is added to the back layer slurry, and wood chips are added to the back layer sanding material to improve the shell's collapsibility. Step (3): Casting. Use the mold shell prepared in step (2) to cast the part. When casting, reduce the pulling speed to 1.5mm / min to 2mm / min for 20mm to 30mm above and below the section where the cross-section changes abruptly. Cool the casting after casting is completed. Step (4): The cooled casting assembly, with its shell still attached, is placed into a vacuum heat treatment furnace for one solution treatment and two aging treatments; Step (5): After heat treatment, the casting assembly is deshelled and cut, and after cutting, it is subjected to corrosion treatment; In step (1), the melting point of the low-melting-point wax is 10°C to 15°C lower than that of the wax used for the parts. When applying the wax, the radius of the R-angle is measured using an R gauge. If the radius of the R-angle at the original variable cross-section is r, then the radius of the R-angle after expansion is r' = (1.2 to 1.5)r. Step (3) During the casting process, except for the 20mm~30mm section above and below the section where the cross-section changes abruptly, the pulling rate of other parts of the casting is 3-5mm / min, and the casting temperature is 1550℃±10℃.

2. The method according to claim 1, characterized in that, In step (2), when preparing the shell, the composition of the surface slurry is EC95 powder: silica sol: wetting agent: defoamer = 3.5~4.0:1.0:0.003:0.01 by mass. The viscosity of the surface slurry is 40s~45s. The surface sanding material is 100# corundum sand.

3. The method according to claim 1, characterized in that, In step (2), when preparing the shell, the composition of the transition layer slurry is EC95 powder: silica sol: wetting agent: defoamer = 2.5~3.0:1.0:0.003:0.003 by mass. The viscosity of the transition layer slurry is 30s~35s. The sand material for the transition layer is 60# corundum sand.

4. The method according to claim 1, characterized in that, In step (2) when preparing the shell, the composition of the back layer slurry is as follows by mass ratio: EC95 powder: silica sol: furan resin: wetting agent: defoamer = 1.5~2.0:1.0:0.03~0.05:0.003:0.003; the viscosity of the back layer slurry is 15s~20s, and the back layer sanding material is 24# corundum sand mixed with wood chips, wherein the amount of wood chips mixed is 0.2%~0.3% of the mass content of corundum sand, and the particle size of the wood chips is 0.6-0.8mm.

5. The method according to claim 1, characterized in that, In step (4), the solution treatment temperature is 1300℃±10℃ and the solution treatment time is 240min±10min; the first aging treatment temperature is 1080℃±10℃ and the holding time is 360min±10min; the second aging treatment temperature is 870℃±10℃ and the holding time is 1440min±10min.

6. The method according to claim 1, characterized in that, When loading the cooled casting assembly into the vacuum heat treatment furnace with its shell in step (4), the gating and riser should be inserted into the heat treatment molybdenum frame, and the part body should not come into contact with the molybdenum frame.

7. The method according to claim 1, characterized in that, In step (5), the etching solution used for the etching treatment of the casting group is an acidic FeCl3 solution composed of FeCl3, HCl, HNO3 and H2O. The mass-volume concentration of FeCl3 is 0.11-0.13 g / mL, the volume ratio of HCl, HNO3 and H2O is 20-23:1:5-6, the etching temperature is 60℃±5℃, and the etching time is 5min±1min.

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