High-strength and high-toughness cast nickel-based alloy and sand mold casting method thereof

Abstract

The application discloses a high-strength and high-toughness cast nickel-based alloy, which comprises the following components in percentage by weight: C 0.008-0.02%, Si <=0.8%, Mn <=1.0%, P <=0.025%, S <=0.02%, Cr 20.0-22.5%, Mo 12.5-14.5%, Fe 2.0-6.0%, V <=0.35%, W 2.5-3.5%, Nb 0.02-0.05%, Te 0.05-0.3%, and the balance of Ni and inevitable impurities; in the preparation process of the cast nickel-based alloy, Fe and Te are added in the form of Fe-Te intermediate alloy. The Cr and Mo element contents are controlled, Fe, W and Te elements are added at the same time, the three elements are coupled, the castings are refined, and the structure is homogenized, so that the problems of coarse grains in the sand mold castings in the casting process, many inclusion defects under the condition of no protection, low strength of the castings, poor corrosion resistance and toughness are fundamentally solved, the cast product yield is improved, and the production cost is greatly reduced.

Description

Technical Field

[0001] This invention belongs to the field of nickel-based corrosion-resistant alloy technology, specifically relating to a high-strength and high-toughness cast nickel-based alloy and its sand casting preparation method. Background Technology

[0002] Currently, the petrochemical, pharmaceutical, metallurgical, and defense industries are developing rapidly. In particular, the emergence of cutting-edge technologies such as fourth-generation nuclear power and nuclear fusion has placed more stringent and comprehensive performance requirements on corrosion-resistant metal materials, including high temperature resistance, pressure resistance (impact resistance), strong corrosion resistance, and high radiation resistance. Nickel-based corrosion-resistant alloys containing Ni, Cr, and Mo (such as Hastelloy C22 and GH3535 alloys) have become key materials in the fields of corrosion resistance and high temperature resistance due to their excellent resistance to "oxidation-reduction" composite media.

[0003] Thorium-based molten salt reactors are representative of my country's fourth-generation advanced nuclear energy systems. Utilizing a flowing molten salt medium at extremely high temperatures (approximately 700°C), they are highly efficient and versatile, and have achieved complete domestic production. In this system, seawater or water is used as the heat transfer medium to cool the light water in the third loop. The pump systems or heat exchangers (including pump bodies, valves, impellers, heat exchanger components, etc.) are characterized by their large size and complex shapes, making them difficult to manufacture or strengthen through forging or machining. Therefore, casting is typically used to achieve integral molding. Sand casting is particularly suitable for the production of large and complex components, offering advantages such as low machining allowance, low cost, and good economic efficiency. Furthermore, due to the strong corrosiveness of seawater and fluoride salts, the pumps and heat exchange systems must withstand fluid corrosion, high-temperature and high-pressure impacts, etc. Therefore, the materials for pump bodies, heat exchangers, and other related components must possess high strength, high ductility and toughness, be free of casting defects, and have excellent resistance to chloride and fluoride corrosion as well as resistance to fluid erosion corrosion. Therefore, developing high-strength, high-toughness, corrosion-resistant nickel-based casting alloys and their preparation methods suitable for sand casting has become a key bottleneck.

[0004] Achieving both high strength and high toughness simultaneously in nickel-based alloys is challenging because these two properties are inherently contradictory. High strength can be achieved by adding more alloying elements (such as Cr and Mo) to the nickel matrix to enhance solid solution strengthening. Further strength improvements require grain refinement through forging and the precipitation of uniform, fine-grained phases through aging treatment. However, while solid solution strengthening and precipitation strengthening significantly increase strength, they often noticeably impair toughness and corrosion resistance. Currently, grain refinement and microstructure homogenization are the main effective strategies for simultaneously achieving high strength and high toughness. However, casting requires heating and melting the nickel-based alloy before pouring it into a mold to form a monolithic part. Sand casting, especially for large, complex-shaped parts, is difficult to perform under vacuum protection, easily leading to casting defects such as shrinkage porosity, gas porosity, and oxide inclusions. Furthermore, the coarse grains in the casting result in low strength and toughness. The integral casting process is extremely difficult, with a rejection rate of 70% to 90% or higher for large sand castings.

[0005] For example, patent CN116179896A uses vacuum melting to produce a Ni-W (26%~28%)-Cr (6%~8%) alloy, and achieves high mid-temperature strength and plasticity through hot working (forging or hot rolling). Its tensile strength is only 578 MPa, and its elongation is 36.5%, but room-temperature impact toughness is not reported, and this alloy composition is not suitable for sand casting. Patent CN117265332B also uses vacuum melting and casting to prepare a Ni-Cr-Co-W-Mo alloy. By adding various trace elements such as Sr and Nd to refine the grains and increase precipitates, its room-temperature tensile strength can reach 1240 MPa, but its plasticity is only 14.5%, and room-temperature impact toughness is also not reported.

[0006] In summary, to improve the strength and toughness of nickel-based alloy sand castings and increase the yield of large castings, it is urgent to develop nickel-based alloys suitable for sand casting and their supporting preparation methods. Summary of the Invention

[0007] The purpose of this application is to overcome the above-mentioned deficiencies of the prior art and provide a high-strength and high-toughness cast nickel-based alloy and a method for preparing the same casting. This method is not only applicable to sand casting, reducing casting defects in large castings and lowering production costs, but also simultaneously improves the strength, ductility, toughness, and corrosion resistance of the castings.

[0008] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows: A high-strength and high-toughness cast nickel-based alloy comprises, by weight percentage: C 0.008~0.02%, Si ≤0.8%, Mn ≤1.0%, P ≤0.025%, S ≤0.02%, Cr 20.0~22.5%, Mo 12.5~14.5%, Fe 2.0~6.0%, V ≤0.35%, W 2.5~3.5%, Nb 0.02~0.05%, Te 0.05~0.3%, with the balance being Ni and unavoidable impurities; during the preparation of the cast nickel-based alloy, Fe and Te are added in the form of Fe-Te master alloy.

[0009] Ni-based alloys have excellent toughness. This invention refines the microstructure of sand castings under simple argon protection by designing key elements and solidifying trace alloying elements such as Te, W, V, and Nb. At the same time, it enhances the strength of the matrix.

[0010] Nickel, as the matrix element of Ni-based alloys, possesses excellent properties: its crystal structure is face-centered cubic, and it undergoes no allotropic transformation from the room-temperature γ phase to high-temperature phases, ensuring structural stability. Pure nickel typically exhibits good plasticity and excellent corrosion resistance, but its strength is low, necessitating the addition of alloying elements to achieve solid solution strengthening and enhance the matrix strength.

[0011] Chromium is an important element in Ni-based alloys. Cr mainly enters the γ phase, playing a role in solid solution strengthening. It can also resist high-temperature oxidation and improve high-temperature strength. In addition, Cr is also a major element for resisting corrosion in oxidizing media. Therefore, the Cr content in Ni-based alloys is generally greater than 15%. However, Cr is also a topologically close-packed σ phase (TCP) forming element. The appearance of σ phase leads to increased brittleness and decreased toughness in Ni-based alloys. Therefore, the Cr content needs to be controlled within a reasonable range. In this invention, the chromium content is controlled at 20.0-22.5%.

[0012] Mo and W primarily enter the matrix γ phase and simultaneously dissolve in the strengthening γ' precipitates, thus playing a solid solution strengthening role. Mo is a key element for resisting corrosion in reducing media; to ensure good corrosion resistance in Ni-based alloys, the Mo content is generally greater than 10%. The addition of W can further enhance the corrosion resistance of Mo and increase the number of strengthening phases in the alloy. Furthermore, W and Mo are carbide-forming elements in Ni-based alloys, primarily forming M6C-type carbides, which improve strength. However, excessive or unevenly distributed precipitates can easily lead to decreased toughness. Therefore, this invention controls the molybdenum content at 12.5–14.5% and the W content at 2.5–3.5%.

[0013] V and Nb are commonly used grain-refining and microalloying strengthening elements that can improve the toughness and cracking tendency of castings. However, V and Nb have high melting points and easily form carbides with carbon, becoming inclusions, so their content cannot be too high. This invention designs the V and Nb composition to be at a low level, with V ≤0.35% and Nb 0.02~0.05%.

[0014] Fe is a cost-controlling element in Ni-based alloys; too much Fe reduces the corrosion resistance and high-temperature resistance of Ni-based alloys. This invention designs the Fe content to be controlled between 2.0% and 6.0%, while simultaneously controlling the addition of W to not exceed the Fe content to prevent excessive precipitates. Another important objective is to form an intermediate alloy with Te, because Te is not solid-soluble with other alloying elements (except Fe) and tends to segregate at grain boundaries, causing embrittlement. To ensure uniform distribution of Te in the Ni-based alloy matrix, the addition of Te needs to form an intermediate alloy with Fe before being added to the Ni-based alloy matrix.

[0015] Most importantly, the addition of Te in this invention improves the corrosion resistance, strength, wear resistance, and high-temperature oxidation resistance of cast Ni-based alloys, and refines the casting microstructure, resulting in a denser oxide film. This is mainly due to the formation of the high-melting-point Fe3TeO8 phase with Fe. Crucially, Te first forms an intermediate alloy with Fe and is uniformly distributed within the Ni-based alloy matrix. Therefore, the purpose of adding Te is to effectively refine the microstructure of the cast alloy and improve the impact toughness of the Ni-based alloy. However, Te can also cause intergranular cracking in Ni-based alloys, increasing the risk of brittleness. This can be effectively suppressed by increasing the Cr content (Cr content greater than 15%), but the Te content needs to be strictly controlled. In this invention, the Te content is controlled at 0.05–0.3%, and it is added in the form of an Fe-Te intermediate alloy.

[0016] Preferably, the mass ratio of Fe to Te is 100:(2~5), and the mass ratio of Fe to W is 1:(0.5~1). When the mass ratio of Fe to Te is 100:(2~5), the resulting microstructure is characterized by α-Fe and a small amount of FeTe eutectic, with a eutectic temperature of approximately 1200℃ and a relatively high melting temperature.

[0017] Preferably, the cast nickel-based alloy has a grain size of 300-500 μm, is composed of a single γ phase, and has no other precipitated phases. This grain structure exhibits excellent high-temperature creep strength, good microstructural stability, excellent thermal fatigue resistance, and good corrosion and oxidation resistance.

[0018] This invention also provides a method for preparing sand castings of high-strength and high-toughness cast nickel-based alloys, specifically including the following steps: S1. The raw materials of the cast nickel-based alloy are melted in a VIM refining electric furnace to obtain a high-temperature alloy liquid. The alloy composition of the high-temperature alloy liquid is detected by a spectrometer, and adjustments are made according to the detection results until the alloy composition meets the design requirements. S2. The high-temperature alloy liquid is purified by a medium-frequency induction furnace, and the furnace bottom and furnace surface are protected by argon gas. S3. Pour the high-temperature alloy liquid into an argon-protected sand mold, air cool it in the sand mold for 15-30 minutes, then hot open the mold to remove the sand, water cool it to room temperature, cut off the gating system, and take out the casting. S4. Transfer the casting to a heat treatment furnace for homogenization treatment; S5. After homogenization, remove from the furnace and quickly cool to room temperature with water.

[0019] The above preparation method includes steps such as VIM refining and preliminary melting, medium-frequency induction refining, argon protection, casting, homogenization treatment, and water cooling. VIM refining ensures ultimate purity from the source; medium-frequency induction refining is not just remelting, but also a homogenization process to ensure high uniformity; the casting process is the last time the molten metal comes into contact with the outside world, so argon protection is crucial; the heat treatment after casting is the key step to give the casting its final properties, eliminating microsegregation, followed by water quenching to obtain the ideal microstructure.

[0020] Preferably, in step S1, the melting temperature is 1650–1680°C, and Fe and Te elements are added in the form of an Fe-Te master alloy. The higher melting temperature prolongs the melt holding time, allowing Te to fully homogenize through diffusion. During the melting process, the Fe-Te master alloy locally forms Fe-rich microregions, which have a small density difference with the matrix, making them less prone to gravity segregation. Compared to directly adding pure Te or Te-containing compounds, the master alloy route significantly reduces both macroscopic and microscopic segregation.

[0021] Preferably, in step S2, the gas parameters include a gas supply intensity of 0.5~1.0 m³ / s. 3 / ton·min, Ar gas purity ≥99.99%, gas source pressure ≥0.8 MPa. In step S2, the purification treatment is set at a temperature of 1580~1650℃ for 20~40 minutes; and during the purification treatment, the surface of the high-temperature alloy liquid is covered with a layer of special refining slag.

[0022] Under the premise of protecting the melt from secondary contamination, the physicochemical synergy of strong argon stirring and active slag layer is used to remove gas, non-metallic inclusions and harmful impurity elements to the maximum extent, so as to obtain a melt with high purity and high consistency, and provide high-quality mother liquor for subsequent casting of single-phase structure.

[0023] Preferably, in step S3, the casting temperature is 1510–1560°C. This casting temperature setting is beneficial for obtaining high-purity, uniformly structured nickel-based alloy castings to meet stringent performance requirements such as high-temperature creep life and structural stability.

[0024] Preferably, in step S4, the homogenization treatment includes: placing the casting into a heat treatment furnace at a temperature of 1205~1250℃ and holding it at that temperature for 3~5 hours, followed by water cooling to room temperature. The high temperature of 1205~1250℃ promotes the rapid diffusion of elements such as W, Mo, and Te, and the dendritic segregation is eliminated after 3~5 hours, significantly improving the compositional uniformity. Then, rapid water cooling is used to suppress the formation of any precipitated phases during the cooling process, ultimately obtaining a cast nickel-based alloy casting with uniform composition and pure grain boundaries.

[0025] Preferably, in step S5, the water cooling method is circulating water cooling, wherein the circulating water temperature is ≤80℃.

[0026] Compared with the prior art, this application has the following technical effects: 1. The present invention controls the content of Cr and Mo elements in Ni-based casting alloy, and adds Fe, W and Te elements. In particular, Fe and Te are added in the form of Fe-Te master alloy. Through the coupling effect of these three elements, the microstructure of the casting can be refined and homogenized, which fundamentally solves the problems of coarse grains, many inclusion defects without protection, low strength and poor toughness of sand castings during the casting process. The casting yield is improved and the production cost is significantly reduced.

[0027] 2. The Ni-based casting alloy of the present invention can be cast and formed in sand casting under non-vacuum protection, which can obtain fine grains and uniformly distributed structure, significantly improving the strength, room temperature plasticity, impact toughness and corrosion resistance of the casting. Its room temperature tensile strength is as high as 580 MPa or more, while its room temperature elongation is as high as 65% or more, and its room temperature average impact toughness is as high as 200 J or more. Attached Figure Description

[0028] Figure 1 The metallographic structure of the casting after cooling in the sand casting of Embodiment 1 of the present invention; Figure 2 This is an X-ray diffraction pattern of the casting after cooling in Example 1 of the present invention. Figure 3 The scanning electron microstructure of the casting after cooling in Example 1 of this invention; Figure 4 The metallographic structure of the casting after sand casting and cooling in Embodiment 2 of the present invention; Figure 5 This is an X-ray diffraction pattern of the casting after cooling in the sand casting process of Embodiment 2 of the present invention. Detailed Implementation

[0029] To enable those skilled in the art to better understand the present invention, the present invention will now be further described in conjunction with specific embodiments.

[0030] In the following description, the embodiments of this application are for illustrative purposes and not for limiting purposes, so as to provide a thorough understanding of the embodiments. However, those skilled in the art will understand that the embodiments of this application can also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known preparation methods have been omitted so as not to obscure the description of the embodiments of this application with unnecessary details. Unless otherwise specified, the raw materials used in the following embodiments are all commercially available.

[0031] It should also be understood that the terms "comprising," "including," "having," and their variations all mean "including but not limited to," unless otherwise specifically emphasized. Only content related to the inventive points is described here; other details can be obtained from related technologies and will not be elaborated further here. The following embodiments merely illustrate several implementations of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

[0032] The specific implementation method is as follows: Example 1 A method for preparing a sand casting includes the following steps: S1. The raw materials for casting nickel-based alloys are melted in a VIM refining electric furnace at 1680℃ to obtain a high-temperature alloy liquid. The alloy composition of the high-temperature alloy liquid is detected by a spectrometer, and adjustments are made according to the test results until the alloy composition meets the design requirements. Chemical composition requirements: C 0.008~0.02%, Si ≤0.8%, Mn ≤1.0%, P ≤0.025%, S ≤0.02%, Cr 21%, Mo 13.5%, Fe 4.4%, V 0.14%, W 3%, Nb 0.04%, Te 0.22%, with the balance being Ni and unavoidable impurities. The basic raw materials are prepared according to the chemical composition requirements, with Fe and Te added as an intermediate alloy (Fe:Te weight ratio of 100:5).

[0033] S2. The high-temperature alloy liquid is purified using a medium-frequency induction furnace, with argon protection at the furnace bottom and surface. Gas parameters include a gas supply intensity of 0.8 m³ / s. 3 / ton·min, Ar gas purity ≥99.99%, gas source pressure ≥0.8 MPa. Temperature set at 1600℃, time 30 minutes.

[0034] S3. The temperature of the high-temperature alloy liquid was lowered to 1547℃ and poured into an argon-protected sand mold. The high-temperature alloy liquid was air-cooled for 20 minutes, then the mold was opened and the sand was removed. After water cooling to room temperature, the gating system was cut off and the casting was taken out. The casting was observed to have no macroscopic large cracks or microscopic cracks, and the surface was dense. A small sample was cut from the casting, and the alloy composition was analyzed using a spectrometer. The results are shown in Table 1, and the composition meets the design requirements.

[0035] S4. Place the casting into a heat treatment furnace at a temperature of 1230℃ and hold for 3.5 hours.

[0036] S5. After heat treatment, the furnace is cooled by water. The water cooling is a circulating water cooling system with a water temperature ≤ 80℃.

[0037] The produced castings have a dense microstructure and, after penetrant testing, meet the requirements of ASME VIII, DIV.1, and APP.7. Small samples were cut from the large castings for metallographic observation (after electrolysis with 5% oxalic acid). Figure 1 As shown, its grain size is 300~500μm, and the microstructure is uniform. Its microstructure consists of a single γ phase; no other precipitated phases were observed. Figure 2 As shown. Observed using a scanning electron microscope (e.g.) Figure 3 As shown in the figure, its microstructure contains a small number of spherical inclusions with a size of about 1-2 μm.

[0038] Mechanical properties of the sample were tested according to ASTM A370 method. The yield strength was 355 MPa, the tensile strength was 584 MPa, and the elongation was 66.5%. The room temperature (25℃) impact resistance was 266 AKV / J, demonstrating excellent mechanical properties and exhibiting high strength and toughness. A 24-hour crevice corrosion test was conducted according to ASTM G48-3A method in a 6% FeCl3 solution at 50℃. The weight loss was 0.0011 g, and no pitting corrosion was observed, indicating excellent corrosion resistance.

[0039] Example 2 A method for preparing a sand casting includes the following steps: S1. The raw materials for casting nickel-based alloys are melted in a VIM refining electric furnace at 1650℃ to obtain a high-temperature alloy liquid. The alloy composition of the high-temperature alloy liquid is detected by a spectrometer, and adjustments are made according to the test results until the alloy composition meets the design requirements. Chemical composition requirements: C 0.008~0.02%, Si ≤0.8%, Mn ≤1.0%, P ≤0.025%, S ≤0.02%, Cr 20.1%, Mo 13.9%, Fe 4.48%, V 0.14%, W 3.23%, Nb 0.03%, Te 0.12%, with the balance being Ni and unavoidable impurities. The basic raw materials are prepared according to the chemical composition requirements, with Fe and Te added as an intermediate alloy (Fe:Te weight ratio of 100:2.7).

[0040] S2. The high-temperature alloy liquid is purified using a medium-frequency induction furnace, with argon protection at the furnace bottom and surface. Gas parameters include a gas supply intensity of 0.8 m³ / s. 3 / ton·min, Ar gas purity ≥99.99%, gas source pressure ≥0.8 MPa. Temperature set at 1600℃, time 30 minutes.

[0041] S3. Cool the high-temperature alloy liquid to 1518℃ and pour it into an argon-protected sand mold. Air-cool the high-temperature alloy liquid for 30 minutes, then hot-open the mold and remove the sand. Water-cool to room temperature, disconnect the gating system, and remove the casting. Observe the casting; there are no large macroscopic cracks or microscopic cracks, and the surface is dense. Cut a small sample from the casting and analyze the alloy composition using a spectrometer. The results are shown in Table 1, and the composition meets the design requirements.

[0042] S4. Place the casting into a heat treatment furnace at a temperature of 1205℃ and hold for 5 hours.

[0043] S5. After heat treatment, the furnace is cooled by water. The water cooling is a circulating water cooling system with a water temperature ≤ 80℃.

[0044] The produced castings have a dense structure and mechanical properties as shown in Table 2, exhibiting good strength, toughness, and excellent corrosion resistance.

[0045] Comparative Example 1 A method for preparing a sand casting includes the following steps: S1. Melt all raw materials for the cast nickel-based alloy at 1680℃ using a VIM refining electric furnace to obtain a high-temperature alloy liquid. Analyze the alloy composition of the high-temperature alloy liquid using a spectrometer and adjust it according to the results until the alloy composition meets the designed requirements. Chemical composition requirements: C 0.008~0.02%, Si ≤0.8%, Mn ≤1.0%, P ≤0.025%, S ≤0.02%, Cr 21.1%, Mo 13.8%, Fe 4.16%, V 0.13%, W 3.02%, Nb 0.04%, balance being Ni and unavoidable impurities. Prepare the basic raw materials according to the chemical composition requirements.

[0046] S2. The high-temperature alloy liquid is purified using a medium-frequency induction furnace, with argon protection at the furnace bottom and surface. Gas parameters include a gas supply intensity of 0.8 m³ / s. 3 / ton·min, Ar gas purity ≥99.99%, gas source pressure ≥0.8 MPa. Temperature set at 1600℃, time 30 minutes.

[0047] S3. Cool the high-temperature alloy liquid to 1550℃ and pour it into an argon-protected sand mold. Air-cool the high-temperature alloy liquid for 20 minutes, then hot-open the mold and remove the sand. Water-cool to room temperature, disconnect the gating system, and remove the casting. Observe the casting; there are no large macroscopic cracks or microscopic cracks, and the surface is dense. Cut a small sample from the casting and analyze the alloy composition using a spectrometer. The results are shown in Table 1, and the composition meets the design requirements.

[0048] S4. Place the casting into a heat treatment furnace at a temperature of 1230℃ and hold for 4 hours.

[0049] S5. After heat treatment, the furnace is cooled by water. The water cooling is a circulating water cooling system with a water temperature ≤ 80℃.

[0050] Small samples were cut from the large casting for metallographic observation (after electrolysis with 5% oxalic acid). Figure 4 As shown, the grain size is 1000~1500μm, and it is difficult to observe a complete grain in the field of view. Many irregular corrosion pits are observed within a single grain, indicating segregation of its microstructure. Its microstructure consists of a single γ phase; no other precipitated phases were observed. Figure 5 As shown, it has a distinct (200) crystal plane texture, which also indicates that the sample has coarse grains. The mechanical properties of the sample were also tested according to the ASTM A370 method. As shown in Table 2, its yield strength is 351 MPa, its tensile strength is only 468 MPa, and its elongation is reduced to 27%. The key point is that its impact resistance at room temperature (25℃) is only 32AKV / J, and its strength and toughness are very poor.

[0051] Comparative Example 2 A method for preparing a sand casting includes the following steps: S1. Melt all raw materials for the cast nickel-based alloy at 1680℃ using a VIM refining electric furnace to obtain a high-temperature alloy liquid. Analyze the alloy composition of the high-temperature alloy liquid using a spectrometer and adjust it according to the results until the alloy composition meets the designed requirements. Chemical composition requirements: C 0.008~0.02%, Si ≤0.8%, Mn ≤1.0%, P ≤0.025%, S ≤0.02%, Cr 20.8%, Mo 13.2%, Fe 4.09%, V 0.18%, W 3.04%, Nb 0.03%, balance being Ni and unavoidable impurities. Prepare the basic raw materials according to the chemical composition requirements.

[0052] S2. The high-temperature alloy liquid is purified using a medium-frequency induction furnace, with argon protection at the furnace bottom and surface. Gas parameters include a gas supply intensity of 0.8 m³ / s. 3 / ton·min, Ar gas purity ≥99.99%, gas source pressure ≥0.8 MPa. Temperature set at 1600℃, time 30 minutes.

[0053] S3. Cool the high-temperature alloy liquid to 1527℃ and pour it into an argon-protected sand mold. Air-cool the high-temperature alloy liquid for 20 minutes, then hot-open the mold and remove the sand. Water-cool to room temperature, disconnect the gating system, and remove the casting. Observe the casting; there are no large macroscopic cracks or microscopic cracks, and the surface is dense. Cut a small sample from the casting and analyze the alloy composition using a spectrometer. The results are shown in Table 1, and the composition meets the design requirements.

[0054] S4. Place the casting into a heat treatment furnace at a temperature of 1230℃ and hold for 3.5 hours.

[0055] S5. After heat treatment, the furnace is cooled by water. The water cooling is a circulating water cooling system with a water temperature ≤ 80℃.

[0056] The produced castings have a dense structure and mechanical properties as shown in Table 2, but exhibit poor strength and toughness.

[0057] Comparative Example 3 A method for preparing a sand casting includes the following steps: S1. Melt all raw materials for the cast nickel-based alloy at 1680℃ using a VIM refining electric furnace to obtain a high-temperature alloy liquid. Analyze the alloy composition of the high-temperature alloy liquid using a spectrometer and adjust it according to the results until the alloy composition meets the designed requirements. Chemical composition requirements: C 0.008~0.02%, Si ≤0.8%, Mn ≤1.0%, P ≤0.025%, S ≤0.02%, Cr 21%, Mo 13.8%, Fe 4.6%, V 0.14%, W 3.28%, Nb 0.04%, Te 0.23%, with the balance being Ni and unavoidable impurities. Prepare the basic raw materials according to the chemical composition requirements, noting that Fe and Te are not added as intermediate alloys but added separately.

[0058] S2. The high-temperature alloy liquid is purified using a medium-frequency induction furnace, with argon protection at the furnace bottom and surface. Gas parameters include a gas supply intensity of 0.8 m³ / s. 3 / ton·min, Ar gas purity ≥99.99%, gas source pressure ≥0.8 MPa. Temperature set at 1600℃, time 30 minutes.

[0059] S3. The temperature of the high-temperature alloy liquid was lowered to 1537℃ and poured into an argon-protected sand mold. The high-temperature alloy liquid was air-cooled for 20 minutes, then the mold was opened and the sand removed. It was then water-cooled to room temperature, the gating system was cut off, and the casting was removed. The casting was observed to have no large macroscopic cracks or microscopic cracks, and the surface was dense. Small samples were cut from the casting, and the alloy composition was analyzed using a spectrometer. The results are shown in Table 1, and the composition meets the design requirements.

[0060] S4. Place the casting into a heat treatment furnace at a temperature of 1230℃ and hold for 4 hours.

[0061] S5. After heat treatment, the furnace is cooled by water. The water cooling is a circulating water cooling system with a water temperature ≤ 80℃.

[0062] The produced castings have a dense structure and mechanical properties as shown in Table 2. Their toughness is significantly improved compared to Comparative Examples 1 and 2, but their strength and elongation are not significantly improved compared to Comparative Examples 1 and 2. Compared to Examples 1 and 2, their strength and toughness are poor.

[0063] Table 1. Casting composition (mass percentage) of the examples and comparative examples Table 2 Performance Comparison of Examples and Comparative Examples Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A high-strength, high-toughness cast nickel-based alloy, characterized in that, The alloy comprises, by weight percentage: C 0.008~0.02%, Si ≤0.8%, Mn ≤1.0%, P ≤0.025%, S ≤0.02%, Cr 20.0~22.5%, Mo 12.5~14.5%, Fe 2.0~6.0%, V ≤0.35%, W 2.5~3.5%, Nb 0.02~0.05%, Te 0.05~0.3%, with the balance being Ni and unavoidable impurities; during the preparation of the cast nickel-based alloy, Fe and Te are added in the form of Fe-Te master alloy.

2. The high-strength, high-toughness cast nickel-based alloy as described in claim 1, characterized in that, The mass ratio of Fe to Te is 100:(2~5), and the mass ratio of Fe to W is 1:(0.5~1).

3. The high-strength, high-toughness cast nickel-based alloy as described in claim 1, characterized in that, The cast nickel-based alloy has a grain size of 300~500μm, is composed of a single γ phase, and has no other precipitated phases.

4. A method for preparing sand castings, characterized in that, The metal raw material used is the high-strength and high-toughness cast nickel-based alloy as described in any one of claims 1 to 3, and the process specifically includes the following steps: S1. The raw materials of the cast nickel-based alloy are melted in a VIM refining electric furnace to obtain a high-temperature alloy liquid. The alloy composition of the high-temperature alloy liquid is detected by a spectrometer, and adjustments are made according to the detection results until the alloy composition meets the design requirements. S2. The high-temperature alloy liquid is purified by a medium-frequency induction furnace, and the furnace bottom and furnace surface are protected by argon gas. S3. Pour the high-temperature alloy liquid into an argon-protected sand mold, air cool it in the sand mold for 15-30 minutes, then hot open the mold to remove the sand, water cool it to room temperature, cut off the gating system, and take out the casting. S4. Transfer the casting to a heat treatment furnace for homogenization treatment; S5. After homogenization, remove from the furnace and quickly cool to room temperature with water.

5. The method for preparing sand castings as described in claim 4, characterized in that, In step S1, the melting temperature is 1650–1680 °C, and Fe and Te elements are added in the form of Fe-Te master alloy.

6. The method for preparing sand castings as described in claim 4, characterized in that, In step S2, the gas parameters include a gas supply intensity of 0.5~1.0 m³ / s. 3 / ton·min, Ar purity ≥99.99%, gas source pressure ≥0.8 MPa.

7. The method for preparing sand castings as described in claim 4, characterized in that, In step S3, the casting temperature is 1510–1560℃.

8. The method for preparing sand castings as described in claim 4, characterized in that, In step S4, the homogenization process includes: placing the casting into a heat treatment furnace at a temperature of 1205~1250℃, holding it at that temperature for 3~5 hours, and then water-cooling it to room temperature.

9. The method for preparing sand castings as described in claim 4, characterized in that, In step S5, the water cooling method is circulating water cooling, wherein the circulating water temperature is ≤80℃.

10. The method for preparing sand castings as described in claim 4, characterized in that, In step S2, the purification treatment is set at a temperature of 1580–1650°C for 20–40 minutes; and during the purification treatment, the surface of the high-temperature alloy liquid is covered with a layer of special refining slag.

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