A high-temperature titanium alloy for casting at 650°C and its investment precision casting method

Abstract

The present invention provides a high-temperature titanium alloy for casting at 650°C and a method for investment casting thereof. The titanium alloy comprises: Al: 5.5-6.5%, Sn: 2-4%, Zr: 2-8%, Hf: 4-8%, Mo: 0.5-1.5%, Nb: 0.5-1.5%, Ta: 1-2%, W: 1-2%, Y: 0.1-1%, Si: 0.2-0.4%, and Ti: the balance. The present invention uniformly mixes Y2O3 refractory powder of varying particle size distributions with a slightly alkaline binder of a silicon-yttrium composite sol, and also uniformly mixes bauxite powder, carbon fiber, and a silica sol binder to produce a mold shell surface layer and a reinforcement layer suitable for investment casting of a high-temperature titanium alloy at 650°C. Melting is performed in a suspension melting furnace, resulting in a method for melting a high-temperature titanium alloy at 650°C and a centrifugal casting process. The castings produced by this method are free of defects such as hot cracks, cold cracks, shrinkage, and pores, and the room temperature properties are: tensile strength ≥1100MPa, yield strength ≥950MPa, and elongation ≥5%; the high temperature properties at 650℃ are: tensile strength ≥650MPa, yield strength ≥580MPa, and elongation ≥8%.

Description

Technical Field

[0001] The present invention relates to the field of high-temperature titanium alloys, and in particular provides a Ti-Al-Sn-Zr-Hf-Mo-Nb-Ta-WY-Si series high-temperature titanium alloy for casting at 650°C and an investment precision casting method thereof. Background Art

[0002] High-temperature titanium alloys, due to their high specific strength, low density, excellent high-temperature performance, and superior corrosion resistance, are widely used in high-temperature components such as engines and critical structures in high-end sectors such as aerospace and weaponry. Currently, the maximum operating temperature of high-temperature titanium alloys used worldwide is 600°C. These alloys primarily adhere to the "Ti-Al-Sn-Zr-Mo-Si" system, including a few near-α-type titanium alloys such as IMI834, Ti-1100, BT36, Ti60, and Ti600. However, as service environments become increasingly harsh (increasing temperatures), higher requirements are being placed on the room-temperature and high-temperature performance of high-temperature titanium alloys. However, significant breakthroughs in the performance of high-temperature titanium alloys above 650°C have been lacking. While traditional high-temperature titanium alloys based on the "Ti-Al-Sn-Zr-Mo-Si" system still hold great potential through element and composition optimization to enhance solid solution strengthening and aging hardening, the precise determination of alloying element content remains a key challenge within the industry.

[0003] Investment casting technology is widely used in the manufacture of high-temperature titanium alloys due to the integrated, lightweight, and complex features of the formed parts. However, for high-temperature titanium alloys used above 600°C, the types and contents of alloying elements are relatively large, and the density difference is large, making it difficult to ensure the uniformity of the composition during the melting process. In addition, investment casting of high-temperature titanium alloys above 600°C is subject to defects such as hot cracking, cold cracking, shrinkage, and porosity, resulting in a low product yield. How to reduce or eliminate casting defects by adjusting the mold shell composition to improve yield and strength is a key issue that needs to be addressed for high-temperature titanium alloys above 600°C. Summary of the Invention

[0004] Aiming at the problem of insufficient mechanical properties of high-temperature titanium alloys cast at a service temperature of 650°C, the present invention provides a high-temperature titanium alloy for casting at 650°C and a precision investment casting method thereof.

[0005] The technical solutions of the present invention are as follows:

[0006] A high-temperature titanium alloy for casting at 650°C, characterized in that, in terms of mass percentage, the titanium alloy has the following composition: Al: 5.5-6.5%, Sn: 2-4%, Zr: 2-8%, Hf: 4-8%, Mo: 0.5-1.5%, Nb: 0.5-1.5%, Ta: 1-2%, W: 1-2%, Y: 0.1-1%, Si: 0.2-0.4%, and Ti: balance.

[0007] Alloy composition design is implemented based on the cluster model: Based on the cluster formula of α phase in titanium alloy, [Al-Ti 12 ]((Al,Sn)1Ti2) composition formula; Based on the cluster formula of β phase in titanium alloy, [(Si,Al)-(Ti,Zr,Hf) 14 ](Mo, Nb, Ta, W, Y, Ti)3 composition formula; the second phase precipitates from the matrix to ensure the tensile strength and yield strength at room temperature and high temperature. Therefore, the α-phase and β-phase cluster composition formulas are mixed in a special volume ratio (α:β=15:2), and the mass percentage content of elements in the Ti-Al-Sn-Zr-Hf-Mo-Nb-Ta-WY-Si high-temperature titanium alloy is determined.

[0008] The high temperature titanium alloy for casting at 650℃ of the present invention meets the requirements of 15[Al-Ti 12 ]((Al,Sn)1Ti2)+2[(Si,Al)-(Ti,Zr,Hf) 14 ](Mo,Nb,Ta,W,Y,Ti) 3-component formula.

[0009] In [(Si,Al)-(Ti,Zr,Hf) 14 ]In the (Mo, Nb, Ta, W, Y, Ti)3 composition formula, Si and Al are added in equal atomic ratios to ensure high temperature performance.

[0010] In [(Si,Al)-(Ti,Zr,Hf) 14 ](Mo, Nb, Ta, W, Y, Ti)3 In the composition formula, Mo, Ta, and W are added in equal atomic proportions to improve the strength of the alloy.

[0011] Among the currently reported Ti-Al-Sn-Zr-Mo-Si high-temperature titanium alloys, Ti65 alloy has the most alloying elements, containing 10 alloying elements (Ti, Al, Sn, Zr, Mo, Nb, Ta, W, Si, and C) with a total content of 17.35 wt.%. The alloy of the present invention contains 11 alloying elements with a total content of 23.45 wt.%, further enhancing both the room temperature and high-temperature strength of the alloy while maintaining castability.

[0012] The investment precision casting method for casting high-temperature titanium alloy at 650°C of the present invention is characterized by comprising the following steps:

[0013] (1) Preparation of the mold shell surface layer: Y2O3 refractory powder with different particle size distributions is added to a slightly alkaline binder of a silicon-yttrium composite sol at a powder-liquid mass ratio of 3:1 to 5:1, and then 0 to 0.05 wt.% of a wetting agent and 0 to 0.05 wt.% of a defoaming agent are added. The raw materials are mixed and stirred for 2 to 6 hours to prepare a surface coating; the coating is then applied to a wax mold, sanded and dried for 6 to 18 hours to obtain a surface shell; the above operation is repeated 2 to 3 times to form a surface shell of a certain thickness;

[0014] (2) Preparation of the shell reinforcement layer: bauxite powder, carbon fiber and silica sol binder are mixed evenly, and the mass ratio of the powder is controlled at 2:1 to 5:1; bauxite sand with a particle size of 20 to 100 mesh is used for sanding, and dried at an ambient temperature of 18 to 26°C and an ambient humidity of 30 to 50% for 12 to 24 hours to obtain a layer of reinforced shell; the above operation is repeated 8 to 10 times to form a reinforced shell of a certain thickness;

[0015] (3) Shell dewaxing and roasting;

[0016] (4) Melting and pouring: Use vacuum induction suspension furnace for melting. First, add titanium alloy raw materials according to the composition ratio into the copper crucible, and evacuate to 5×10 -1 When the temperature reaches 3000 Pa, a protective gas of 150 mbar is filled in; the initial melting power is 50 kW, and after the alloy raw materials are evenly heated, the melting power is gradually increased and maintained at 150 to 200 kW, and the alloy raw materials are gradually melted and mixed; after the alloy raw materials are completely melted, the melting temperature is 1600 to 2000°C, the melting time is 10 to 20 minutes, and after the melting is completed, the maximum power is maintained for 5 minutes; after three meltings, the alloy liquid is poured into the mold by a centrifugal casting process, the centrifugal speed is 200 to 500 rpm, and the mold is cooled to obtain the product.

[0017] As the preferred technical solution:

[0018] In step (1), the particle size distribution of the Y2O3 refractory powder is controlled to be: the content of coarse powder greater than 20μm and less than or equal to 60μm accounts for 60% to 90%, and the content of fine powder less than or equal to 20μm accounts for 10% to 40%. The slightly alkaline binder is a silicon yttrium composite sol, the main component of which is controlled to be SiO3 2+ :3~20wt.%Y 3+ :0.2~3wt.%, pH value:7~8.

[0019] In step (1), calcium zirconate sand with a particle size of 80 to 150 mesh is used for sanding, and the mixture is dried for 6 to 18 hours at an ambient temperature of 18 to 26° C. and an ambient humidity of 45 to 65% to obtain a surface shell; the above operation is repeated 2 to 3 times to form a surface shell of a certain thickness.

[0020] In step (2), the length of the carbon fiber is controlled to be 0.05 to 0.15 mm, the diameter is controlled to be 3 to 8 μm, and the content is controlled to be 1 to 3 wt.%.

[0021] In step (3), the shell is dewaxed and roasted: the shell is dewaxed by an infrared dewaxing process, and the heating temperature is 220-260°C; the shell roasting temperature is controlled at a rate of 100-150°C / h, and the shell is kept at 1000-1400°C for 2-4h, and the furnace is cooled to 100-200°C and taken out of the furnace for use.

[0022] The beneficial effects of the present invention are:

[0023] 1. The titanium alloy described in the present invention exhibits excellent room-temperature and high-temperature performance. Room-temperature performance indicators include: tensile strength ≥1100 MPa, yield strength ≥950 MPa, and elongation ≥5%. High-temperature performance indicators at 650°C include: tensile strength ≥650 MPa, yield strength ≥580 MPa, and elongation ≥8%. Castings produced using the method described in the present invention are free of defects such as hot cracking, cold cracking, shrinkage, and porosity.

[0024] 2. Add fine powder (≤20μm) to the original single-peak graded powder (≤60μm) to form a double-peak graded refractory powder. This scheme improves the tight stacking ability of the refractory powder, reduces the solution bound in the gaps between the powders, reduces the required amount of binder, increases the solid phase content, increases the density, and improves the surface shell strength and anti-stripping ability.

[0025] 3. The present invention solves the problem that acidic binders such as zirconium acetate and alkaline refractory materials such as Y2O3 will undergo chemical reactions and precipitation after long-term storage. The use of slightly alkaline binders effectively improves the suspension rate and stability of the coating, giving it long storage characteristics. The storage time is increased by more than 300%, achieving long-term continuous coating of large-volume slurries. In addition, the slightly alkaline binder is conducive to improving the working environment.

[0026] 4. Adding 1-3% carbon fiber to the mold reinforcement layer can improve the wet strength of the mold, reduce the room temperature dry strength and high temperature strength, improve the yieldability of the mold, and help reduce the tendency of casting defects, as well as the safety of the mold during transportation and the convenience of subsequent cleaning.

[0027] 5. Suspension melting ensures the uniformity of composition, and the casting shell is conducive to improving dimensional accuracy, surface and internal quality. The Ti-Al-Sn-Zr-Hf-Mo-Nb-Ta-WY-Si series high-temperature titanium alloy composition and its investment precision casting method are expected to be used in engines or key high-temperature resistant components for high-performance aerospace, weapons and equipment and other high-end fields, meeting the needs of casting high-temperature titanium alloy components for 650°C applications. DETAILED DESCRIPTION

[0028] Example 1

[0029] The steps to produce a high-temperature titanium alloy skeleton with a size of more than 800mm are as follows:

[0030] (1) Preparation of the shell surface layer: 70% of coarse powder (20 μm < particle size ≤ 60 μm) Y2O3 refractory powder and 30% of fine powder (particle size ≤ 20 μm) Y2O3 refractory powder are added to the silica yttrium composite sol slightly alkaline binder (SiO3 2+ :5~15wt.%Y 3+ :0.5~2.5wt.%, pH value: 7~8), the powder-liquid mass ratio is 4:1, and then 0.02wt.% wetting agent and 0.02wt.% defoaming agent are added and stirred for 6 hours to prepare a top coating; then the coating is applied to a wax mold, and sanded with calcium zirconate sand with a particle size of 100 mesh, and dried at an ambient temperature of 26℃ and an ambient humidity of 45% for 12 hours to obtain a top shell; the above operation is repeated 3 times to form a top shell;

[0031] (2) Preparation of the mold shell reinforcement layer: Bauxite powder, carbon fiber (length 0.05-0.15 mm, diameter 3-8 μm, content controlled at 2%) and silica sol binder are mixed evenly, and the mass ratio of the powder is controlled at 3:1; bauxite sand with a particle size of 80 mesh is used for sanding, and dried at an ambient temperature of 26°C and an ambient humidity of 30% for 24 hours to obtain a layer of reinforced layer mold shell; the above operation is repeated 10 times to form a reinforced layer mold shell;

[0032] (3) Mold shell dewaxing and roasting: The mold shell is dewaxed by infrared dewaxing process, and the heating temperature is 260℃; the temperature rise rate of the mold shell roasting is controlled at 100℃ / h, and the temperature is kept at 1000℃ for 4h. The furnace is cooled to 100℃ and then taken out of the furnace for use;

[0033] (4) Vacuum induction suspension furnace smelting is adopted. The smelting process is as follows: adding titanium alloy raw materials according to the composition ratio into the copper crucible, vacuuming to 5×10 -1When the pressure is 150mbar, argon is introduced as a protective gas during smelting. The initial smelting power is 50kW. After the alloy raw materials are evenly heated, the smelting power is gradually increased and maintained at 200kW, so that the alloy raw materials gradually melt and mix. During the smelting process, the coil has an electromagnetic stirring effect on the melt, which makes the melt more uniform. After the alloy raw materials are completely melted, the smelting temperature is approximately 2000℃, and the smelting time is 20min. After the smelting is completed, the maximum power is maintained for 5 minutes to make the alloy more uniform and stable. After smelting three times, the alloy liquid is poured into the casting mold using a centrifugal casting process with a centrifugal speed of 500 rpm and cooled.

[0034] Example 2

[0035] The difference from Example 1 is that, during the preparation of the mold shell reinforcement layer, bauxite powder, carbon fiber (length 0.05-0.15 mm, diameter 3-8 μm, content controlled at 1%) and silica sol binder are mixed evenly, and the powder mass ratio is controlled at 3:1; bauxite sand with a particle size of 80 mesh is used for sanding, and dried at an ambient temperature of 26°C and an ambient humidity of 30% for 24 hours to obtain a layer of reinforced layer mold shell; the above operation is repeated 10 times to form a reinforced layer mold shell.

[0036] Example 3

[0037] The difference from Example 1 is that, during the preparation of the shell surface layer, 60% of coarse powder (20 μm < particle size ≤ 60 μm) Y2O3 refractory powder and 40% of fine powder (particle size ≤ 20 μm) Y2O3 refractory powder are added to the silicon yttrium composite sol slightly alkaline binder (SiO3 2+ :3~20wt.%Y 3+ :0.2~3wt.%, pH value: 7~8), the powder-liquid mass ratio is 3:1, and the mixture is stirred for 6 hours to prepare a surface coating; then the coating is applied to a wax mold, and sanded with calcium zirconate sand with a particle size of 100 mesh, and dried at an ambient temperature of 26°C and an ambient humidity of 45% for 12 hours to obtain a surface shell; the above operation is repeated 3 times to form a surface shell.

[0038] Comparative Example 1

[0039] The steps to produce a high-temperature titanium alloy blade with a size of more than 200 mm are as follows:

[0040] (2) Preparation of the shell surface layer: 70% of coarse powder (20 μm < particle size ≤ 60 μm) Y2O3 refractory powder and 30% of fine powder (particle size ≤ 20 μm) Y2O3 refractory powder are added to the silica yttrium composite sol slightly alkaline binder (SiO3 2+ :3~20wt.%Y 3+: 0.2-3wt.%, pH value: 7-8), the powder-liquid mass ratio is 4:1, and then 0.02wt.% wetting agent and 0.02wt.% defoamer are added and stirred for 6 hours to prepare a surface coating; then the coating is applied to a wax mold, sanded with calcium zirconate sand with a particle size of 100 mesh, and dried at an ambient temperature of 26°C and an ambient humidity of 45% for 12 hours to obtain a surface shell; the above operation is repeated 3 times to form a surface shell;

[0041] (3) Preparation of the mold shell reinforcement layer: Bauxite powder, carbon fiber (length 0.05-0.15 mm, diameter 3-8 μm, content controlled at 2%) and silica sol binder are mixed evenly, and the mass ratio of the powder is controlled at 3:1; bauxite sand with a particle size of 80 mesh is used for sanding, and dried at an ambient temperature of 26°C and an ambient humidity of 30% for 24 hours to obtain a layer of reinforced layer mold shell; the above operation is repeated 10 times to form a reinforced layer mold shell;

[0042] (4) Mold shell dewaxing and roasting: The mold shell is dewaxed by infrared dewaxing process, and the heating temperature is 260℃; the temperature rise rate of the mold shell roasting is controlled at 100℃ / h, and the temperature is kept at 1000℃ for 4h. The furnace is cooled to 100℃ and then taken out of the furnace for use;

[0043] (5) Vacuum induction suspension furnace smelting is adopted. The smelting process is as follows: adding titanium alloy raw materials according to the composition ratio into the copper crucible, evacuating to 5×10 -1 When the pressure is 150mbar, argon is introduced as a protective gas during smelting. The initial smelting power is 50kW. After the alloy raw materials are evenly heated, the smelting power is gradually increased and maintained at 200kW, so that the alloy raw materials gradually melt and mix. During the smelting process, the coil has an electromagnetic stirring effect on the melt, which makes the melt more uniform. After the alloy raw materials are completely melted, the smelting temperature is approximately 2000℃, and the smelting time is 20min. After the smelting is completed, the maximum power is maintained for 5 minutes to make the alloy more uniform and stable. After smelting three times, the alloy liquid is poured into the casting mold using a centrifugal casting process with a centrifugal speed of 500 rpm and cooled.

[0044] The chemical composition of titanium alloy castings is shown in Table 1, wherein Example 1 satisfies 15[Al-Ti 12 ](Al 0.8 Sn 0.2 Ti2)+2[(Si 0.5 Al 0.5 )-Ti8Zr4Hf2](Mo 0.5 Nb1Ta 0.5 W 0.5 Y 0.5 ) composition formula; Example 2 satisfies 15[Al-Ti 12 ](Al0.8 Sn 0.2 Ti2)+2[(Si 0.5 Al 0.5 )-Ti8Zr4Hf2](Mo 0.5 Nb 0.5 Ta 0.5 W 0.5 Y 0.5 Ti 0.5 ) composition formula; Example 3 satisfies 15[Al-Ti 12 ](Al 0.8 Sn 0.2 Ti2)+2[(Si 0.5 Al 0.5 )-Ti 10 Zr2Hf2](Mo 0.5 Nb1Ta 0.5 W 0.5 Y 0.5 ) composition formula; Comparative Example 1 satisfies 15[Al-Ti 12 ](Al 0.8 Sn 0.2 Ti2)+2[(Si 0.5 Al 0.5 )-Ti 10 Zr4](Mo 0.5 Nb1Ta 0.5 W 0.5 Y 0.5 The mechanical properties of Example 1 and Comparative Example 1 after hot isostatic pressing are shown in Table 2.

[0045] It can be seen from Table 2 that after the addition of Hf element is eliminated from the chemical composition of the casting, the room temperature and high temperature strength and room temperature elongation of the casting decrease significantly.

[0046] Table 1 Titanium alloy casting composition wt.%

[0047]

[0048] Table 2 Mechanical properties of titanium alloy castings

[0049]

[0050] Matters not covered by the present invention are known technologies.

[0051] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A high-temperature titanium alloy for casting at 650°C, characterized in that: The composition of the titanium alloy is as follows: Al: 5.5-6.5%, Sn: 2-4%, Zr: 2-8%, Hf: 4-8%, Mo: 0.5-1.5%, Nb: 0.5-1.5%, Ta: 1-2%, W: 1-2%, Y: 0.1-1%, Si: 0.2-0.4%, and Ti: balance; the alloy composition is designed according to the cluster model: relying on the cluster formula of the α phase in the titanium alloy, [Al-Ti 12 ]((Al,Sn)1Ti2) composition formula; Based on the cluster formula of β phase in titanium alloy, [(Si,Al)-(Ti,Zr,Hf) 14 ](Mo, Nb, Ta, W, Y, Ti)3 composition formula; the second phase precipitates from the matrix to ensure the tensile strength and yield strength at room temperature and high temperature. Therefore, the α phase and β phase cluster composition formulas are mixed in a volume ratio of α:β=15:2, and the mass percentage content of elements in the Ti-Al-Sn-Zr-Hf-Mo-Nb-Ta-WY-Si high temperature titanium alloy is determined.

2. The high-temperature titanium alloy for casting at 650°C according to claim 1, characterized in that: In [(Si,Al)-(Ti,Zr,Hf) 14 ]In the (Mo, Nb, Ta, W, Y, Ti)3 composition formula, Si and Al are added in an equal atomic ratio.

3. The high-temperature titanium alloy for casting at 650°C according to claim 1, characterized in that: In [(Si,Al)-(Ti,Zr,Hf) 14 ]In the (Mo, Nb, Ta, W, Y, Ti)3 composition formula, Mo, Ta, and W are added in equal atomic proportions.

4. An investment casting method for casting high-temperature titanium alloy at 650°C according to claim 1, characterized in that: The following steps are involved: (1) Preparation of the mold shell surface layer: Y2O3 refractory powder with different particle size distributions is added to a silica-yttrium composite sol slightly alkaline binder with a powder-liquid mass ratio of 3:1 to 5:1, and then 0 to 0.05 wt.% of a wetting agent and 0 to 0.05 wt.% of a defoaming agent are added. The raw materials are mixed and stirred for 2 to 6 hours to prepare a surface layer coating; the coating is then applied to a wax mold, sanded and dried for 6 to 18 hours to obtain a surface layer mold shell; the above operation is repeated 2 to 3 times to form a surface layer mold shell; (2) Preparation of the mold shell reinforcement layer: bauxite powder, carbon fiber and silica sol binder are mixed evenly, wherein the mass ratio of bauxite powder to silica sol is controlled at 2:1 to 5:1, and the carbon fiber content is controlled at 1 to 3 wt.%; bauxite sand with a particle size of 20 to 100 mesh is used for sanding, and dried at an ambient temperature of 18 to 26°C and an ambient humidity of 30 to 50% for 12 to 24 hours to obtain a layer of reinforced layer mold shell; repeat the above operation 8 to 10 times to form a reinforced layer mold shell; (3) Shell dewaxing and roasting; (4) Melting and pouring: Use vacuum induction suspension furnace for melting. First, add titanium alloy raw materials according to the composition ratio into the copper crucible, and evacuate to 5×10 -1 ~9×10 -1 When the pressure is 400 Pa, a protective gas of 150 to 200 mbar is filled; the initial melting power is 20 to 50 kW, and after the alloy raw materials are evenly heated, the melting power is gradually increased and maintained at 150 to 200 kW, and the alloy raw materials are gradually melted and mixed; after the alloy raw materials are completely melted, the melting temperature is 1600 to 2000° C., the melting time is 10 to 20 minutes, and after the melting is completed, the maximum power is maintained for 5 to 10 minutes; after 3 to 5 meltings, the alloy liquid is poured into the casting mold by a centrifugal casting process, the centrifugal speed is 200 to 500 rpm, and the mold is cooled to obtain the product.

5. The investment casting method for casting high-temperature titanium alloy at 650°C according to claim 4, characterized in that: In step (1), the particle size distribution of the Y2O3 refractory powder is controlled so that the content of coarse powder greater than 20 μm and less than or equal to 60 μm accounts for 60% to 90%, and the content of fine powder less than or equal to 20 μm accounts for 10% to 40%.

6. The investment casting method for casting high-temperature titanium alloy at 650°C according to claim 4, characterized in that: In step (1), calcium zirconate sand with a particle size of 80 to 150 mesh is used for sanding, and the mixture is dried for 6 to 18 hours at an ambient temperature of 18 to 26° C. and an ambient humidity of 45 to 65% to obtain a surface shell; the above operation is repeated 2 to 3 times to form a surface shell of a certain thickness.

7. The investment casting method for casting high-temperature titanium alloy at 650°C according to claim 4, characterized in that: In step (2), the length of the carbon fiber is controlled to be 0.05 to 0.15 mm, and the diameter is controlled to be 3 to 8 μm.

8. The investment casting method for casting high-temperature titanium alloy at 650°C according to claim 4, characterized in that: In step (3), the shell is dewaxed and roasted: the shell is dewaxed by an infrared dewaxing process, and the heating temperature is 220-260°C; the shell roasting temperature is controlled at a rate of 100-150°C / h, and the shell is kept at 1000-1400°C for 2-4h, and the furnace is cooled to 100-200°C and taken out of the furnace for use.

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