Grain refining method of K465 high-temperature alloy and K465 high-temperature alloy

Abstract

The invention provides a grain refinement method of a K465 superalloy, and relates to the technical field of nickel-based superalloys.The grain refinement method comprises the following steps that smelting is conducted, specifically, under an external magnetic field, raw materials are subjected to smelting treatment, and alloy liquid is obtained after smelting; wherein the raw materials comprise a K465 mother alloy and WC powder; and pouring is conducted, specifically, the alloy liquid is subjected to pouring treatment, and the K465 high-temperature alloy after grain refinement is obtained. Smelting is carried out under the action of an external magnetic field, on one hand, WC can directionally move in a melt through electromagnetic force to overcome the gravity action of WC, it is ensured that WC is evenly dispersed and distributed in the melt (alloy liquid), and meanwhile due to the fact that the melting point of WC is high, dispersed and distributed WC serves as nucleation particles, and the purpose of refining grains can be achieved; and on the other hand, the electromagnetic force promotes mutual friction and collision of WC particles, coarse WC with sharp edge angles is converted into fine dispersed spherical phases or nearly spherical phases, and the spherical WC phases can avoid stress concentration in the alloy, so that loss of the mechanical property of the K465 high-temperature alloy is avoided.

Description

Technical Field

[0001] This invention belongs to the field of nickel-based superalloy technology, specifically relating to a grain refinement method for K465 superalloy and the K465 superalloy itself. Background Technology

[0002] K465 high-temperature alloy is a nickel-based high-temperature alloy with excellent high-temperature mechanical properties, and is currently widely used in important fields such as aviation, aerospace, and nuclear power. Among them, a certain type of important aerospace component is produced using investment casting technology. However, investment casting of high-temperature alloy castings faces challenges such as coarse grain size and inhomogeneous microstructure, accompanied by increased segregation and shrinkage cavities, which reduce the reliability of the casting's fatigue performance and result in dispersed mechanical property data. The key to solving these problems lies in reducing the grain size to obtain uniform, fine-grained castings. Fine-grained casting of high-temperature alloys can produce castings with fine, uniform equiaxed grains, thereby improving the casting's medium- and low-temperature low-cycle fatigue performance and significantly reducing the dispersion of mechanical property data, thus increasing the design tolerance of the casting.

[0003] Grain refinement in high-temperature alloys is typically achieved by adding grain refiners. However, traditional grain refiners are introduced through intermediate alloys, which can easily introduce impurities into the alloy, altering its chemical composition and thus affecting its performance. Existing technology proposes adding pure TiC powder to refine the grains of K4202 high-temperature alloy. Since TiC is a high-melting-point ceramic particle with good thermal stability, it forms a coherent interface with nickel-based alloys and exhibits excellent wettability with K4202. Furthermore, the introduction of TiC does not alter the chemical composition of K4202, avoiding the risks associated with introducing impurities and altering the chemical composition associated with traditional grain refiners introduced through intermediate alloys.

[0004] However, when the grains of high-temperature alloys are refined by adding pure TiC powder, TiC preferentially forms, providing heterogeneous nucleation sites for melt crystal growth. Although the matrix grains are refined, the WC in the high-temperature alloy will attach to TiC and grow due to the large amount of pure TiC powder added, which will have an adverse effect on the comprehensive mechanical properties of the high-temperature alloy, such as resulting in lower strength. Summary of the Invention

[0005] Therefore, the present invention provides a grain refinement method for K465 high-temperature alloy and K465 high-temperature alloy, so as to solve the problem that the existing grain refinement method is detrimental to the comprehensive mechanical properties of high-temperature alloy.

[0006] To address the above problems, this invention provides a method for grain refinement of K465 high-temperature alloy, comprising the following steps:

[0007] Melting: Under an external magnetic field, the raw materials are melted to obtain a liquid alloy.

[0008] The raw materials include K465 master alloy and WC powder; an external magnetic field is applied to disperse the WC powder in the alloy liquid and to cause the WC powder particles to rub and collide with each other.

[0009] Casting: The alloy liquid is cast to obtain K465 high-temperature alloy with refined grains.

[0010] Furthermore, in the smelting step: the frequency of the external magnetic field is 5 to 10 Hz, and the excitation current is 1 to 1.5 A.

[0011] Furthermore, in the raw materials, the mass of WC powder is 1% to 2.5% of the mass of the K465 master alloy.

[0012] Furthermore, in the smelting step, the smelting process includes:

[0013] The crucible containing the K465 master alloy and WC powder was placed in a vacuum melting furnace for melting.

[0014] The WC powder is wrapped in nickel paper.

[0015] Preferably, the size of the WC powder is 1.5–4 μm;

[0016] Preferably, the external magnetic field is achieved by winding an electromagnetic coil around the outside of the vacuum melting furnace;

[0017] Preferably, the vacuum degree of the vacuum melting furnace is ≤10Pa.

[0018] Furthermore, in the pouring step:

[0019] The casting process includes: placing the mold shell in a vacuum melting furnace, and then injecting the molten alloy into the mold shell under an external magnetic field;

[0020] The frequency of the applied magnetic field is 5–10 Hz, and the excitation current is 1–1.5 A.

[0021] Preferably, the pouring time is controlled to be 5-10 seconds;

[0022] Preferably, the vacuum degree of the vacuum melting furnace is ≤10Pa.

[0023] Furthermore, before placing the mold shell in the vacuum melting furnace, the process also includes: baking the mold shell at 950℃~1100℃ and then holding it at that temperature for 1.5h~3h.

[0024] Preferably, the mold shell is prepared by the following steps: preparing a shaped test rod wax model and a gating system wax model; then combining the test rod wax model and the gating system wax model to obtain the mold shell.

[0025] Furthermore, before injecting the molten alloy into the mold shell, the process includes heating the molten alloy to 1400–1450°C and then holding it at that temperature for 10–30 minutes.

[0026] Furthermore, the chemical composition of the K465 master alloy, by mass percentage, includes: C: 0.01–0.03 wt.%, S: 0.004–0.008 wt.%, P: 0.08–0.12 wt.%, Si: 0.2–0.5 wt.%, Mn: 0.2–0.5 wt.%, Cr: 15–20 wt.%, Ti: 2.2–2.5 wt.%, W: 4–4.5 wt.%, Mo: 2.8–3.2 wt.%, Al: 1–1.5 wt.%, Fe: 3.3–3.8 wt.%, with the balance being Ni and unavoidable impurities.

[0027] On the other hand, the present invention provides a method for refining the grains of a K465 superalloy, wherein the chemical composition of the K465 superalloy after grain refinement, by mass percentage, includes: C: 0.05-0.08 wt.%, S: 0.004-0.008 wt.%, P: 0.08-0.12 wt.%, Si: 0.2-0.5 wt.%, Mn: 0.2-0.5 wt.%, Cr: 15-20 wt.%, Ti: 2.2-2.5 wt.%, Mo: 2.8-3.2 wt.%, Al: 1-1.5 wt.%, Fe: 3.3-3.8 wt.%, W: 5.0-5.5 wt.%, with the balance being Ni;

[0028] Preferably, the grain size of the refined K465 high-temperature alloy is grade 6 to 9.

[0029] Furthermore, the K465 high-temperature alloy with refined grains includes a matrix phase and a WC phase. The WC phase is spherical or nearly spherical and dispersed in the matrix phase. The interface between the WC phase and the matrix phase is a coherent interface. The size of the WC phase is 1.5 to 2.5 μm. The volume fraction of the WC phase is 10% to 15%.

[0030] Preferably, at room temperature, the tensile strength of the grain-refined K465 high-temperature alloy is greater than 1000 MPa, and the yield strength is greater than 850 MPa.

[0031] Preferably, at 700°C, the tensile strength of the K465 high-temperature alloy with refined grains is greater than 820 MPa, and the yield strength is greater than 450 MPa.

[0032] Preferably, the K465 high-temperature alloy with refined grains is obtained by any of the above-described grain refinement methods.

[0033] The grain refinement method for K465 high-temperature alloy and the K465 high-temperature alloy provided by this invention have the following characteristics:

[0034] Beneficial effects:

[0035] 1. On the one hand, the present invention provides a method for refining the grain size of K465 high-temperature alloy. K465 master alloy and WC powder are used as raw materials. Under an external magnetic field, the raw materials are smelted to obtain a melted alloy. The melted alloy is then cast to obtain a K465 high-temperature alloy with refined grain size. Based on the above method, smelting is carried out under the action of an external magnetic field. On the one hand, the electromagnetic force can cause WC to move directionally within the melt, overcoming its own gravity and preventing it from sinking and accumulating at the bottom of the molten pool. This ensures that WC is uniformly dispersed in the melt (alloy liquid). Simultaneously, due to the high melting point of WC, the dispersed WC acts as nucleation sites, achieving the purpose of refining the grain size. On the other hand, the electromagnetic force causes WC particles to rub and collide with each other, transforming coarse WC with sharp edges into fine, dispersed spherical or near-spherical phases. The spherical WC phase can avoid stress concentration within the alloy, thereby preventing damage to the mechanical properties of the K465 high-temperature alloy.

[0036] 2. Furthermore, the present invention controls the frequency of the applied magnetic field to 5-10Hz and the excitation current to 1-1.5A. On the one hand, this avoids the WC from sinking due to insufficient electromagnetic force, thereby ensuring that the WC is uniformly dispersed in the melt (alloy liquid). On the other hand, it avoids the WC from being subjected to excessively large magnetic force (electromagnetic force), which would cause the WC to collide and break, resulting in smaller WC size. The smaller WC size would melt back into the alloy liquid, thus lacking nucleation points, leading to coarse grains in the K465 high-temperature alloy.

[0037] 3. On the other hand, the present invention provides a grain-refined K465 high-temperature alloy, which is obtained by the above-mentioned grain refinement method. The grain-refined K465 high-temperature alloy includes a matrix phase and a WC phase, wherein the WC phase is spherically dispersed in the matrix phase, and the size of the WC phase is 1.5 to 2.5 μm; the volume fraction of the WC phase is 10% to 15%; the spherical, fine, and dispersed WC phases act as nucleation particles, resulting in a grain size of 6 to 9 for the grain-refined K465 high-temperature alloy. At room temperature, the tensile strength of the above-mentioned grain-refined K465 high-temperature alloy is greater than 800 MPa, and the yield strength is 625 to 660 MPa; at 700°C, the tensile strength of the above-mentioned grain-refined K465 high-temperature alloy is greater than 760 MPa, and the yield strength is 510 to 560 MPa.

[0038] The grain refinement method for K465 high-temperature alloy provided by this invention differs from the traditional method of adding grain refiners. Traditional methods of adding grain refiners mostly involve intermediate alloys, while this invention directly adds pure WC powder. WC is a ceramic particle with a high melting point and good thermal stability, which has good wettability with K465 high-temperature alloy. Moreover, the introduction of WC does not change the chemical composition of K465 high-temperature alloy, thus avoiding the risk of introducing impurities and changing the chemical composition that can occur with traditional grain refiners introduced through intermediate alloys.

[0039] The K465 superalloy, after grain refinement treatment with the addition of WC powder, exhibits significantly improved high-temperature mechanical properties at 750℃ and room-temperature mechanical properties, with remarkable improvements in microstructure and properties. Furthermore, the grain refinement method for K465 superalloy provided by this invention closely aligns with the actual production process of superalloy castings in industry, is simple to operate, economical and efficient, saves energy, and has promising application prospects. Attached Figure Description

[0040] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0041] Figure 1 This is a macroscopic microstructure diagram of the K465 master alloy in Example 1;

[0042] Figure 2 This is a macroscopic microstructure diagram of the refined K465 high-temperature alloy obtained in Example 1;

[0043] Figure 3 This is a macroscopic microstructure diagram of the refined K465 high-temperature alloy obtained in Example 2;

[0044] Figure 4 The image shows the macroscopic microstructure of the refined K465 high-temperature alloy obtained in Comparative Example 1.

[0045] Figure 5 The distribution of WC at different molten pool depths in Comparative Example 2 and Example 1 is shown.

[0046] Figure 6 The images show the morphology of WC in Comparative Example 2 and Example 1.

[0047] Figure 7 A comparison diagram of the WC phase size and matrix phase grain size in the refined K465 high-temperature alloy obtained in Comparative Example 2 and Example 1.

[0048] Figure 8A comparison diagram of the mechanical properties of the refined K465 high-temperature alloy obtained in Comparative Example 3 and Example 1;

[0049] Figure 9 A comparison diagram of the WC phase size and matrix phase grain size in the refined K465 superalloy obtained in Comparative Example 4 and Example 1.

[0050] Figure 10 The microstructure morphology of the refined K465 high-temperature alloy obtained in Comparative Example 5 is shown.

[0051] Figure 11 A comparison diagram showing the grain size and tensile strength of the refined K465 high-temperature alloy obtained in Comparative Example 5 and Example 1;

[0052] Figure 12 Comparison of the microstructure of the refined K465 high-temperature alloy obtained in Comparative Example 6 and Example 1. Detailed Implementation

[0053] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0054] This invention provides a method for grain refinement of K465 high-temperature alloy, comprising the following steps:

[0055] Melting: The crucible containing K465 master alloy and WC powder is placed in a vacuum melting furnace and then melted under an external magnetic field to obtain a liquid alloy. The external magnetic field causes the WC powder to be dispersed in the liquid alloy and causes the WC powder particles to rub and collide with each other.

[0056] The applied magnetic field has a frequency of 5–10 Hz and an excitation current of 1–1.5 A; the vacuum degree of the vacuum melting furnace is ≤10 Pa; the chemical composition of the K465 master alloy, by mass percentage, includes: C: 0.01–0.03 wt.%, S: 0.004–0.008 wt.%, P: 0.08–0.12 wt.%, Si: 0.2–0.5 wt.%, Mn: 0.2–0.5 wt.%, Cr: 15–20 wt.%, Ti: 2.2–2.5 wt.% The composition of WC powder is as follows: W: 4-4.5 wt.%, Mo: 2.8-3.2 wt.%, Al: 1-1.5 wt.%, Fe: 3.3-3.8 wt.%, with the balance being Ni and unavoidable impurities. The size of the WC powder is 1.5-4 μm. The mass of the WC powder is 1%-2.5% of the mass of the K465 master alloy. The WC powder is wrapped in nickel paper. Preferably, the length of the nickel paper is 100-120 mm, the width of the nickel paper is 100-120 mm, and the thickness of the nickel paper is 0.1-0.3 mm.

[0057] Casting: The mold shell is placed in a vacuum melting furnace, and then the above alloy liquid is injected into the mold shell under an external magnetic field. After casting, K465 high-temperature alloy with refined grains is obtained.

[0058] During the casting process, an external magnetic field is applied to ensure the fluidity of the alloy liquid; preferably, the external magnetic field is achieved by winding an electromagnetic coil around the outside of the vacuum melting furnace; wherein, the frequency of the external magnetic field is 5 to 10 Hz, and the excitation current is 1 to 1.5 A; the casting time is controlled to be 5 to 10 s; preferably, the vacuum degree of the vacuum melting furnace is ≤10 Pa.

[0059] Adding pure WC powder directly to the master alloy is an option. WC is a ceramic particle with a high melting point and good thermal stability, exhibiting excellent wettability with the K465 superalloy. Furthermore, the introduction of WC does not alter the chemical composition of the K465 superalloy, avoiding the risks associated with introducing impurities and altering the chemical composition through intermediate alloys, a common practice with traditional grain refiners. However, the applicant discovered that due to WC's high density, it settles and accumulates at the bottom of the molten pool during melting, resulting in uneven distribution of WC in the alloy liquid and affecting the overall mechanical properties of the final alloy. Simultaneously, the aggregation and growth of WC within the molten pool reduces its grain refinement effect. Therefore, after adding pure WC powder, melting is carried out under the action of an external magnetic field. On the one hand, the electromagnetic force can cause WC to move in a direction within the melt to overcome its own gravity, thus preventing WC from sinking and accumulating at the bottom of the molten pool. This ensures that WC is uniformly dispersed in the melt (alloy liquid). At the same time, since WC has a high melting point, the dispersed WC acts as nucleation particles, which can achieve the purpose of refining the grains. On the other hand, the electromagnetic force causes WC particles to rub and collide with each other, transforming the coarse WC with sharp edges into fine, dispersed spherical or near-spherical phases. The spherical WC phase can avoid stress concentration inside the alloy, thus avoiding the loss of mechanical properties of K465 high-temperature alloy.

[0060] Based on the fact that the WC powder size in this invention is 1.5-4 μm, the frequency of the applied magnetic field is controlled at 5-10 Hz, and the excitation current is controlled at 1-1.5 A. If the frequency and excitation current are too low, the magnetic force on the carbide will be insufficient, the directional movement speed of the carbide will be slow, and WC will contact and aggregate to grow, thus weakening the grain refinement effect. If the frequency and excitation current are too high, the magnetic force on the WC will be too large, and the WC will collide and break, making the WC size even smaller. The smaller WC will melt back into the liquid, thus lacking nucleation points, resulting in a poor grain refinement effect of K465 high-temperature alloy.

[0061] Meanwhile, based on the aforementioned external magnetic field, the diffusion rate of large refractory atoms between WC and the matrix phase can be accelerated, and the enrichment of refractory elements near the interface can be reduced. On the one hand, this increases the antiphase boundary energy inside WC, thereby improving its ability to block dislocation movement. On the other hand, it reduces the interfacial mismatch between WC and the nickel matrix, which are both face-centered cubic structures, and improves the stability of the interfacial structure (such as forming a coherent interface between WC and the matrix). These two aspects improve the high-temperature mechanical properties of K465 alloy.

[0062] In some embodiments, before placing the mold shell in the vacuum melting furnace, the process further includes: baking the mold shell at 950°C to 1100°C and then holding it at that temperature for 1.5 to 3 hours.

[0063] Preferably, the time from when the mold shell leaves the furnace to when it is poured (i.e., the transfer time when the mold shell is transferred into the vacuum melting furnace) is controlled to be 5 to 10 minutes;

[0064] Preferably, the mold shell is prepared by the following steps: preparing a shaped test rod wax model and a gating system wax model; then combining the test rod wax model and the gating system wax model to obtain the mold shell.

[0065] The process control requirements for mold shell preparation are as follows: production environment temperature 25±2℃; process control requirements for slurry application, slurry control, and sand application: the mold assembly should be immersed in the slurry for approximately 60–75 seconds during slurry application; the slurry control time should be 2–5 minutes, during which the pouring cup should be rotated upwards; requirements for sand type and mesh size: surface layer: 80–100 mesh perlite, relative humidity: 40%–50%, drying time: 35–40 hours; second to third layers: 20–40 mesh grit sand, relative humidity: 40%–60%, drying time: 20–25 hours; fourth to sixth layers: 15–30 mesh grit sand, relative humidity: 40%–60%, drying time: 20–25 hours; seventh layer: sealing slurry, relative humidity: 25%–40%, drying time: 15–20 hours.

[0066] Furthermore, before injecting the molten alloy into the mold shell, the process includes heating the molten alloy to 1400–1450°C and then holding it at that temperature for 10–30 minutes.

[0067] On the other hand, the present invention provides a method for refining the grains of a K465 superalloy, wherein the chemical composition of the K465 superalloy after grain refinement, by mass percentage, includes: C: 0.05-0.08 wt.%, S: 0.004-0.008 wt.%, P: 0.08-0.12 wt.%, Si: 0.2-0.5 wt.%, Mn: 0.2-0.5 wt.%, Cr: 15-20 wt.%, Ti: 2.2-2.5 wt.%, Mo: 2.8-3.2 wt.%, Al: 1-1.5 wt.%, Fe: 3.3-3.8 wt.%, W: 5.0-5.5 wt.%, with the balance being Ni;

[0068] The K465 superalloy with refined grains includes a matrix phase and a WC phase. The WC phase is spherical or nearly spherical and is dispersed in the matrix phase. The size of the WC phase is 1.5 to 2.5 μm and the volume fraction of the WC phase is 10% to 15%.

[0069] Furthermore, the grain size of the refined K465 superalloy is grade 6 to 9;

[0070] At room temperature, the tensile strength of the K465 high-temperature alloy with refined grains is greater than 1000 MPa, and the yield strength is greater than 850 MPa.

[0071] At 700℃, the tensile strength of the K465 high-temperature alloy after grain refinement is greater than 820MPa and the yield strength is greater than 450MPa.

[0072] Preferably, the K465 high-temperature alloy with refined grains is obtained by any of the above-mentioned grain refinement methods.

[0073] The present invention will be further described below with reference to specific embodiments and comparative examples.

[0074] It should be noted that the K465 master alloy used in the following examples and comparative examples is K465 master alloy bar stock;

[0075] The mold shell for casting is prepared by the following steps: preparing a molded test rod wax model and a casting system wax model, finely finishing the surfaces of the molded test rod wax model and the casting system wax model, then combining the test rod wax model and the casting system wax model to obtain the mold shell, placing the mold shell in a baking furnace, baking the mold shell at 1000℃, and holding it at that temperature for 2 hours.

[0076] Example 1

[0077] This embodiment provides a method for refining the grain size of K465 high-temperature alloy, specifically including the following steps:

[0078] Melting: 8.5 kg of K465 master alloy bar and 105 g of WC powder wrapped in nickel paper were weighed as raw materials. The K465 master alloy bar was sandblasted and dried. Then the raw materials were placed in the crucible of a vacuum melting furnace and melted under a vacuum of ≤10 Pa and an external magnetic field. After melting, the alloy liquid was obtained.

[0079] The WC powder comprises approximately 1.2% of the K465 master alloy bar by mass. The K465 master alloy composition, by mass percentage, is: C: 0.02 wt.%, S: 0.006 wt.%, P: 0.01 wt.%, Si: 0.4 wt.%, Mn: 0.3 wt.%, Cr: 18 wt.%, Ti: 2.4 wt.%, W: 4.5 wt.%, Mo: 3 wt.%, Al: 1.2 wt.%, Fe: 3.5 wt.%, with the balance being Ni and unavoidable impurities. The applied magnetic field frequency is 8 Hz, and the excitation current is 1.3 A.

[0080] Casting: The molten alloy liquid was heated to 1440℃ and held for 15 minutes. Then, the mold shell in the above-mentioned calcining furnace was transferred to the casting chamber of the melting furnace for casting. After cooling, the shell was broken to obtain K465 high-temperature alloy (sample) with refined grains. The transfer time of the mold shell was 7 minutes, and the casting process took 5 seconds.

[0081] The composition of the K465 superalloy after grain refinement, by mass percentage, is as follows: C: 0.06 wt.%, S: 0.005 wt.%, P: 0.09 wt.%, Si: 0.35 wt.%, Mn: 0.35 wt.%, Cr: 18 wt.%, Ti: 2.4 wt.%, Mo: 3 wt.%, Al: 1.2 wt.%, Fe: 3.5 wt.%, W: 5.2 wt.%, with the balance being Ni.

[0082] Tensile properties of the K465 high-temperature alloy (sample) obtained in this embodiment were tested at room temperature and 700℃, and the results are shown in Table 1. The microstructures of the K465 master alloy before grain refinement and the K465 high-temperature alloy after grain refinement were obtained by tensile testing, as shown in Table 1. Figure 1 and Figure 2 As shown, the microstructure is dense and the grains are fine after WC refinement. According to the method specified in GB / T14999.7-2010 "Methods for Determination of Grain Size, Primary Dendrite Spacing and Micropores of High Temperature Alloy Castings", the grain size of the K465 high temperature alloy obtained in this embodiment is measured to be grade 6.

[0083] Example 2

[0084] This embodiment provides a method for refining the grain size of K465 high-temperature alloy, specifically including the following steps:

[0085] Melting: 8.5 kg of K465 master alloy bar and 250 g of WC powder wrapped in nickel paper were weighed as raw materials. The K465 master alloy bar was sandblasted and dried. Then the raw materials were placed in the crucible of a vacuum melting furnace and melted under a vacuum of ≤10 Pa and an external magnetic field to obtain a liquid alloy.

[0086] The WC powder accounts for approximately 2.9% of the mass of the K465 master alloy bar. The K465 master alloy composition, by mass percentage, is: C: 0.02 wt.%, S: 0.006 wt.%, P: 0.01 wt.%, Si: 0.4 wt.%, Mn: 0.3 wt.%, Cr: 18 wt.%, Ti: 2.4 wt.%, W: 4.5 wt.%, Mo: 3 wt.%, Al: 1.2 wt.%, Fe: 3.5 wt.%, with the balance being Ni and unavoidable impurities. The applied magnetic field frequency is 8 Hz, and the excitation current is 1.3 A.

[0087] Casting: The molten alloy liquid was heated to 1440℃ and held for 30 minutes. Then, the mold shell in the above-mentioned calcining furnace was transferred to the casting chamber of the melting furnace for casting. After cooling, the shell was broken to obtain K465 high-temperature alloy (sample) with refined grains. The transfer time of the mold shell was 6 minutes, and the casting process took 4 seconds.

[0088] The composition of the K465 superalloy after grain refinement, by mass percentage, is as follows: C: 0.06 wt.%, S: 0.006 wt.%, P: 0.09 wt.%, Si: 0.35 wt.%, Mn: 0.35 wt.%, Cr: 18 wt.%, Ti: 2.4 wt.%, Mo: 2.8 wt.%, Al: 1.1 wt.%, Fe: 3.4 wt.%, W: 5.2 wt.%, with the balance being Ni.

[0089] Tensile properties of the K465 superalloy (sample) obtained in this embodiment were tested at room temperature and 700℃, and the results are shown in Table 1. The macrostructure of the K465 superalloy with refined grains obtained by tensile testing is shown in Table 1. Figure 3 As shown, the K465 high-temperature alloy obtained in this embodiment has a small grain size and no obvious defects. According to the method specified in GB / T14999.7-2010 "Methods for Determination of Grain Size, Primary Dendrite Spacing and Micropores of High-Temperature Alloy Castings", the grain size of the K465 high-temperature alloy obtained in this embodiment is measured to be grade 8.

[0090] Comparative Example 1

[0091] This comparative example provides a method for refining the grain size of a K465 high-temperature alloy, specifically including the following steps:

[0092] Melting: Weigh 8.5 kg of K465 master alloy bar, 0.051 kg of pure tungsten powder and 0.051 kg of pure carbon powder as raw materials. Sandblast and dry the K465 master alloy bar. Then place the raw materials in the crucible of a vacuum melting furnace and melt them under a vacuum of ≤10 Pa and an external magnetic field. After melting, the alloy liquid is obtained.

[0093] The total mass of pure tungsten powder and pure carbon powder is approximately 1.2% of the mass of the K465 master alloy bar. The composition of the K465 master alloy, by mass percentage, is: C: 0.02 wt.%, S: 0.006 wt.%, P: 0.01 wt.%, Si: 0.4 wt.%, Mn: 0.3 wt.%, Cr: 18 wt.%, Ti: 2.4 wt.%, W: 4.5 wt.%, Mo: 3 wt.%, Al: 1.2 wt.%, Fe: 3.5 wt.%, with the balance being Ni and unavoidable impurities. The applied magnetic field frequency is 8 Hz, and the excitation current is 1.3 A.

[0094] Casting: The molten alloy liquid was heated to 1440℃ and held for 10 minutes. Then, the mold shell in the above-mentioned calcining furnace was transferred to the casting chamber of the melting furnace for casting. After cooling, the shell was broken to obtain K465 high-temperature alloy (sample). The mold shell transfer time was 6 minutes, and the casting process took 4 seconds.

[0095] The composition of the K465 superalloy after grain refinement, by mass percentage, is as follows: C: 0.05 wt.%, S: 0.0065 wt.%, P: 0.09 wt.%, Si: 0.35 wt.%, Mn: 0.354 wt.%, Cr: 17 wt.%, Ti: 2.4 wt.%, Mo: 2.7 wt.%, Al: 1.2 wt.%, Fe: 3.5 wt.%, W: 5.2 wt.%, with the balance being Ni.

[0096] Tensile properties of the K465 superalloy (sample) obtained in this comparative example were tested at room temperature and 700℃, and the results are shown in Table 1. The macrostructure of the K465 superalloy with refined grains obtained by tensile testing is shown in Table 1. Figure 4 As shown, there are many defects. The grain size of the K465 high-temperature alloy obtained in this comparative example is measured to be grade 4, indicating a large grain size. This is because pure tungsten powder and pure carbon powder were added for melting in this comparative example, and WC was synthesized in situ in the solution (alloy liquid) through W and C. However, the in-situ synthesis of WC usually involves solid-state diffusion reaction, and the reaction rate and conditions have a great influence on its morphology. For example, different temperatures and times will significantly affect the growth rate and morphology of WC. At the same time, the presence of local liquid phase causes changes in carbon concentration, which in turn affects the morphology and content of carbides. Therefore, the in-situ synthesis of WC cannot guarantee the morphology and content of WC. Irregularly shaped WC will lead to stress concentration in the high-temperature alloy, resulting in more defects and thus poor overall mechanical properties.

[0097] Comparative Example 2

[0098] This comparative example provides a method for refining the grain size of a K465 high-temperature alloy, specifically including the following steps:

[0099] Melting: Weigh 8.5 kg of K465 master alloy bar and 105 g of WC powder wrapped in nickel paper as raw materials. Sandblast and dry the K465 master alloy bar. Then place the raw materials in the crucible of a vacuum melting furnace and melt them under a vacuum of ≤10 Pa. After melting, the alloy liquid is obtained.

[0100] The WC powder accounts for approximately 1.2% of the mass of the K465 master alloy bar. The K465 master alloy composition, by mass percentage, is: C: 0.02 wt.%, S: 0.006 wt.%, P: 0.01 wt.%, Si: 0.4 wt.%, Mn: 0.3 wt.%, Cr: 18 wt.%, Ti: 2.4 wt.%, W: 4.5 wt.%, Mo: 3 wt.%, Al: 1.2 wt.%, Fe: 3.5 wt.%, with the balance being Ni and unavoidable impurities.

[0101] Casting: The molten alloy liquid was heated to 1440℃ and held for 10 minutes. Then, the mold shell in the calcining furnace was transferred to the casting chamber of the melting furnace for casting. After cooling, the shell was broken to obtain K465 high-temperature alloy (sample). The transfer time of the mold shell was 6 minutes, and the casting process took 4 seconds.

[0102] The composition of the K465 superalloy after grain refinement, by mass percentage, is: C: 0.05 wt.%, S: 0.0065 wt.%, P: 0.09 wt.%, Si: 0.34 wt.%, Mn: 0.355 wt.%, Cr: 18 wt.%, Ti: 2.4 wt.%, Mo: 2.7 wt.%, Al: 1.2 wt.%, Fe: 3.5 wt.%, W: 5.3 wt.%, with the balance being Ni.

[0103] The tensile properties of the K465 high-temperature alloy (sample) obtained in this comparative example were tested at room temperature and 700℃, and the results are shown in Table 1.

[0104] In Comparative Example 2 and Example 1, the distribution of carbides at different molten pool depths and the morphology of the carbides are as follows: Figure 5 and 6 As shown (the carbides in the figure refer only to WC), it can be seen that in Comparative Example 2, due to the lack of electromagnetic force, the carbides are larger in size and will sink to the bottom of the molten pool under their own gravity, which is not conducive to the homogenization of the structure. In contrast, the carbides in Example 1 are smaller in size and are evenly distributed at different heights in the molten pool.

[0105] Comparison of carbide and (matrix phase) grain sizes in Comparative Example 2 and Example 1 Figure 7 As shown, the WC phase size of the K465 high-temperature alloys obtained in Comparative Example 2 and Example 1 is approximately 15 μm and 2.8 μm, respectively, and the grain size is approximately 7 mm and 1 mm, respectively. Therefore, electromagnetic force can refine the carbide size and grain size. The mechanical property test results of Comparative Example 2 and Example 1 are shown in Table 1, which verifies that the mechanical properties of Comparative Example 2 are significantly lower than those of Example 1 of the present invention due to the coarse microstructure and grain size.

[0106] Comparative Example 3

[0107] This comparative example provides a method for refining the grain size of a K465 high-temperature alloy, specifically including the following steps:

[0108] Melting: 8.5 kg of K465 master alloy bar and 105 g of WC powder wrapped in nickel paper were weighed as raw materials. The K465 master alloy bar was sandblasted and dried. Then the raw materials were placed in the crucible of a vacuum melting furnace and melted under a vacuum of ≤10 Pa and an external magnetic field. After melting, the alloy liquid was obtained.

[0109] The WC powder comprises approximately 1.2% of the K465 master alloy bar by mass. The K465 master alloy composition, by mass percentage, is: C: 0.02 wt.%, S: 0.006 wt.%, P: 0.01 wt.%, Si: 0.4 wt.%, Mn: 0.3 wt.%, Cr: 18 wt.%, Ti: 2.4 wt.%, W: 4.5 wt.%, Mo: 3 wt.%, Al: 1.2 wt.%, Fe: 3.5 wt.%, with the balance being Ni and unavoidable impurities. The applied magnetic field frequency is 12 Hz, and the excitation current is 2 A.

[0110] Casting: The molten alloy liquid was heated to 1440℃ and held for 10 minutes. Then, the mold shell in the above-mentioned calcining furnace was transferred to the casting chamber of the melting furnace for casting. After cooling, the shell was broken to obtain K465 high-temperature alloy (sample) with refined grains. The transfer time of the mold shell was 7 minutes, and the casting process took 5 seconds.

[0111] The composition of the K465 superalloy after grain refinement, by mass percentage, is as follows: C: 0.06 wt.%, S: 0.005 wt.%, P: 0.09 wt.%, Si: 0.35 wt.%, Mn: 0.35 wt.%, Cr: 18 wt.%, Ti: 2.4 wt.%, Mo: 3 wt.%, Al: 1.2 wt.%, Fe: 3.5 wt.%, W: 5.2 wt.%, with the balance being Ni.

[0112] Tensile properties of the K465 high-temperature alloy (sample) obtained in this comparative example were tested at room temperature and 700°C, and the results are shown in Table 1. A comparison of the mechanical properties of the K465 high-temperature alloy obtained in this comparative example and Example 1 is provided. Figure 8As shown, the K465 high-temperature alloy obtained in this comparative example has poor mechanical properties. According to the method specified in GB / T14999.7-2010 "Determination of Grain Size, Primary Dendrite Spacing and Micropores of High-Temperature Alloy Castings", the grain size of the K465 high-temperature alloy obtained in this comparative example is grade 4. Since the magnetic field frequency and excitation current of this comparative example are higher than those of Example 1, the magnetic field force on WC in this comparative example is greater. The collision and breakage of WC results in smaller WC size. The small WC (<0.5μm) will melt back into the liquid, thus lacking nucleation points, resulting in poor grain refinement of K465 high-temperature alloy, which is not conducive to improving the mechanical properties of K465 alloy.

[0113] Comparative Example 4

[0114] This comparative example provides a method for refining the grain size of a K465 high-temperature alloy, specifically including the following steps:

[0115] Melting: 8.5 kg of K465 master alloy bar and 105 g of WC powder wrapped in nickel paper were weighed as raw materials. The K465 master alloy bar was sandblasted and dried. Then the raw materials were placed in the crucible of a vacuum melting furnace and melted under a vacuum of ≤10 Pa and an external magnetic field. After melting, the alloy liquid was obtained.

[0116] The WC powder comprises approximately 1.2% of the K465 master alloy bar mass. The K465 master alloy composition, by mass percentage, is: C: 0.02 wt.%, S: 0.006 wt.%, P: 0.01 wt.%, Si: 0.4 wt.%, Mn: 0.3 wt.%, Cr: 18 wt.%, Ti: 2.4 wt.%, W: 4.5 wt.%, Mo: 3 wt.%, Al: 1.2 wt.%, Fe: 3.5 wt.%, with the balance being Ni and unavoidable impurities. The applied magnetic field frequency is 3 Hz, and the excitation current is 0.8 A.

[0117] Casting: The molten alloy liquid was heated to 1440℃ and held for 15 minutes. Then, the mold shell in the above-mentioned calcining furnace was transferred to the casting chamber of the melting furnace for casting. After cooling, the shell was broken to obtain K465 high-temperature alloy (sample) with refined grains. The transfer time of the mold shell was 7 minutes, and the casting process took 5 seconds.

[0118] The composition of the K465 superalloy after grain refinement, by mass percentage, is as follows: C: 0.06 wt.%, S: 0.005 wt.%, P: 0.09 wt.%, Si: 0.35 wt.%, Mn: 0.35 wt.%, Cr: 18 wt.%, Ti: 2.4 wt.%, Mo: 3 wt.%, Al: 1.2 wt.%, Fe: 3.5 wt.%, W: 5.2 wt.%, with the balance being Ni.

[0119] The carbide and grain size of the K465 high-temperature alloy obtained in this comparative example and Example 1 are compared. Figure 9 As shown in Table 1, the tensile properties at room temperature and 700°C are as follows. It can be found that the magnetic field force on the carbide in this comparative example is insufficient, the directional movement speed of the carbide is slow, WC will contact and aggregate to grow, and the effect on grain refinement is weakened. Therefore, the carbide size and grain size of this comparative example are higher than those of Example 1, and the tensile strength at room temperature and high temperature is lower than that of Example 1.

[0120] Comparative Example 5

[0121] This comparative example provides a method for refining the grain size of a K465 high-temperature alloy, specifically including the following steps:

[0122] Melting: 8.5 kg of K465 master alloy bar and 105 g of TiC powder wrapped in nickel paper were weighed as raw materials. The K465 master alloy bar was sandblasted and dried. Then the raw materials were placed in the crucible of a vacuum melting furnace and melted under a vacuum of ≤10 Pa and an external magnetic field to obtain a liquid alloy.

[0123] The TiC powder comprises approximately 1.2% of the K465 master alloy bar by mass. The K465 master alloy composition, by mass percentage, is: C: 0.02 wt.%, S: 0.006 wt.%, P: 0.01 wt.%, Si: 0.4 wt.%, Mn: 0.3 wt.%, Cr: 18 wt.%, Ti: 2.4 wt.%, W: 4.5 wt.%, Mo: 3 wt.%, Al: 1.2 wt.%, Fe: 3.5 wt.%, with the balance being Ni and unavoidable impurities. The applied magnetic field frequency is 8 Hz, and the excitation current is 1.3 A.

[0124] Casting: The molten alloy liquid was heated to 1440℃ and held for 15 minutes. Then, the mold shell in the above-mentioned calcining furnace was transferred to the casting chamber of the melting furnace for casting. After cooling, the shell was broken to obtain K465 high-temperature alloy (sample) with refined grains. The transfer time of the mold shell was 7 minutes, and the casting process took 5 seconds.

[0125] The composition of the K465 superalloy after grain refinement, by mass percentage, is as follows: C: 0.06 wt.%, S: 0.005 wt.%, P: 0.09 wt.%, Si: 0.35 wt.%, Mn: 0.35 wt.%, Cr: 18 wt.%, Ti: 2.4 wt.%, Mo: 3 wt.%, Al: 1.2 wt.%, Fe: 3.5 wt.%, W: 5.2 wt.%, with the balance being Ni.

[0126] The microstructure of the K465 high-temperature alloy obtained in Comparative Example 5 is as follows: Figure 10 As shown, its grain size and room temperature tensile properties are compared with those of the K465 high-temperature alloy obtained in Example 1. Figure 11 As shown, the grain sizes of the two are not much different, but due to the brittleness of TiC, cracks are formed in the obtained K465 high-temperature alloy, resulting in poor tensile properties of the K465 alloy obtained in Comparative Example 5.

[0127] Comparative Example 6

[0128] This comparative example provides a method for refining the grain size of a K465 high-temperature alloy, specifically including the following steps:

[0129] Melting: 8.5 kg of K465 master alloy bar and 105 g of TiC powder wrapped in nickel paper were weighed as raw materials. The K465 master alloy bar was sandblasted and dried. Then the raw materials were placed in the crucible of a vacuum melting furnace and melted under a vacuum of ≤10 Pa and an external magnetic field to obtain a liquid alloy.

[0130] The TiC powder comprises approximately 1.2% of the K465 master alloy bar by mass. The K465 master alloy composition, by mass percentage, is: C: 0.02 wt.%, S: 0.006 wt.%, P: 0.01 wt.%, Si: 0.4 wt.%, Mn: 0.3 wt.%, Cr: 18 wt.%, Ti: 2.4 wt.%, W: 4.5 wt.%, Mo: 3 wt.%, Al: 1.2 wt.%, Fe: 3.5 wt.%, with the balance being Ni and unavoidable impurities. The applied magnetic field frequency is 15 Hz, and the excitation current is 2 A.

[0131] Casting: The molten alloy liquid is heated to 1440℃ and held for 15 minutes. Then, the mold shell in the above-mentioned calcining furnace is transferred to the casting chamber of the melting furnace for casting. After cooling, the shell is broken to obtain the K465 high-temperature alloy with refined grains. The transfer time of the mold shell is 7 minutes, and the casting process takes 5 seconds.

[0132] The composition of the K465 superalloy after grain refinement, by mass percentage, is as follows: C: 0.06 wt.%, S: 0.005 wt.%, P: 0.09 wt.%, Si: 0.35 wt.%, Mn: 0.35 wt.%, Cr: 18 wt.%, Ti: 2.4 wt.%, Mo: 3 wt.%, Al: 1.2 wt.%, Fe: 3.5 wt.%, W: 5.2 wt.%, with the balance being Ni.

[0133] The microstructure of the K465 high-temperature alloy obtained in this comparative example and Example 1 is as follows: Figure 12 As shown, it can be seen that an incoherent interface is formed between WC and the matrix phase in the comparative example. This is because the external magnetic field parameter of this comparative example is relatively large, which leads to a further increase in the diffusion rate of sparingly soluble elements. Elements that are far from the interface will also undergo long-range diffusion. Then, the metal atoms that diffuse into the WC phase first will hinder the uniform diffusion of subsequent atoms at the interface, which in turn leads to the enrichment of long-range diffused elements at the interface, increasing the mismatch and forming an incoherent phase interface. The lattice distortion of the incoherent phase interface is large. During high-temperature deformation, dislocations are enriched at the interface, increasing the elastic strain energy, which will lead to the formation of cracks at the interface. Therefore, the tensile strength of comparative example 6 is poor.

[0134] Table 1 Comparison of mechanical properties and grain size of K465 high-temperature alloys obtained in the examples and comparative examples.

[0135]

[0136] As can be seen from Table 1, the grain refinement method of the embodiment can obtain K465 high-temperature alloy with a grain size of 6 to 9. The K465 high-temperature alloy after grain refinement has a tensile strength greater than 800 MPa and a yield strength of 625 to 660 MPa at room temperature; a tensile strength greater than 760 MPa and a yield strength of 510 to 560 MPa at 700°C. That is, the grain refinement method of this application can ensure that the high-temperature alloy has excellent comprehensive mechanical properties while refining the grain.

[0137] It will be readily understood by those skilled in the art that, without conflict, the advantageous technical features of the above-mentioned methods can be freely combined and superimposed.

[0138] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention. The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the protection scope of the present invention.

Claims

1. A method for refining the grain size of a K465 high-temperature alloy, characterized in that, Includes the following steps: Melting: Under an external magnetic field, the raw materials are melted to obtain a liquid alloy. The raw materials include K465 master alloy and WC powder; an external magnetic field is applied to disperse the WC powder in the alloy liquid and to cause the WC powder particles to rub and collide with each other. Casting: The alloy liquid is cast to obtain K465 high-temperature alloy with refined grains.

2. The grain refinement method for K465 high-temperature alloy according to claim 1, characterized in that, In the smelting step: the frequency of the external magnetic field is 5 to 10 Hz, and the excitation current is 1 to 1.5 A.

3. The grain refinement method for K465 high-temperature alloy according to claim 1 or 2, characterized in that, In the raw materials, the mass of WC powder is 1% to 2.5% of the mass of K465 master alloy.

4. The grain refinement method for K465 high-temperature alloy according to claim 1, characterized in that, In the smelting step, the smelting process includes: The crucible containing the K465 master alloy and WC powder was placed in a vacuum melting furnace for melting. The WC powder is wrapped in nickel paper. Preferably, the size of the WC powder is 1.5–4 μm; Preferably, the external magnetic field is achieved by winding an electromagnetic coil around the outside of the vacuum melting furnace; Preferably, the vacuum degree of the vacuum melting furnace is ≤10Pa.

5. The grain refinement method for K465 high-temperature alloy according to claim 1, characterized in that, In the pouring step: The casting process includes: placing the mold shell in a vacuum melting furnace, and then injecting the molten alloy into the mold shell under an external magnetic field; The frequency of the applied magnetic field is 5–10 Hz, and the excitation current is 1–1.5 A. Preferably, the pouring time is controlled to be 5-10 seconds; Preferably, the vacuum degree of the vacuum melting furnace is ≤10Pa.

6. The grain refinement method for K465 high-temperature alloy according to claim 5, characterized in that, Before placing the mold shell in the vacuum melting furnace, the process also includes: baking the mold shell at 950℃~1100℃ and then holding it at that temperature for 1.5h~3h. Preferably, the mold shell is prepared by the following steps: preparing a shaped test rod wax model and a gating system wax model; then combining the test rod wax model and the gating system wax model to obtain the mold shell.

7. The grain refinement method for K465 high-temperature alloy according to claim 6, characterized in that, Before the step of injecting the molten alloy into the mold shell, the process also includes: heating the molten alloy to 1400-1450°C and then holding it at that temperature for 10-30 minutes.

8. The method for grain refinement of K465 high-temperature alloy according to any one of claims 1 to 7, characterized in that, The chemical composition of the K465 master alloy, by mass percentage, includes: C: 0.01–0.03 wt.%, S: 0.004–0.008 wt.%, P: 0.08–0.12 wt.%, Si: 0.2–0.5 wt.%, Mn: 0.2–0.5 wt.%, Cr: 15–20 wt.%, Ti: 2.2–2.5 wt.%, W: 4–4.5 wt.%, Mo: 2.8–3.2 wt.%, Al: 1–1.5 wt.%, Fe: 3.3–3.8 wt.%, with the balance being Ni and unavoidable impurities.

9. A K465 high-temperature alloy with refined grains, characterized in that, The chemical composition of the K465 superalloy after grain refinement, by mass percentage, includes: C: 0.05–0.08 wt.%, S: 0.004–0.008 wt.%, P: 0.08–0.12 wt.%, Si: 0.2–0.5 wt.%, Mn: 0.2–0.5 wt.%, Cr: 15–20 wt.%, Ti: 2.2–2.5 wt.%, Mo: 2.8–3.2 wt.%, Al: 1–1.5 wt.%, Fe: 3.3–3.8 wt.%, W: 5.0–5.5 wt.%, with the balance being Ni; Preferably, the grain size of the refined K465 high-temperature alloy is grade 6 to 9.

10. The K465 high-temperature alloy with refined grains according to claim 9, characterized in that, The K465 high-temperature alloy with refined grains includes a matrix phase and a WC phase. The WC phase is spherical or nearly spherical and is dispersed in the matrix phase. The interface between the WC phase and the matrix phase is a coherent interface. The size of the WC phase is 1.5 to 2.5 μm. The volume fraction of the WC phase is 10% to 15%. Preferably, at room temperature, the tensile strength of the grain-refined K465 high-temperature alloy is greater than 1000 MPa, and the yield strength is greater than 850 MPa. Preferably, at 700°C, the tensile strength of the K465 high-temperature alloy with refined grains is greater than 820 MPa, and the yield strength is greater than 450 MPa. Preferably, the K465 high-temperature alloy with refined grains is obtained by the grain refinement method described in any one of claims 1 to 8.

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