A coreless solidification forming method and device for a large-thickness high-temperature alloy hollow pipe

Abstract

The application discloses a coreless solidification forming method and device for a large-wall-thickness high-temperature alloy hollow pipe, forms a high-temperature melt zone at the lower part of a crystallizer and a low-temperature melt zone at the upper part of the crystallizer, utilizes a temperature gradient and a traction to generate a vertical directional hot piston flow along the inner wall, realizes melt replacement of the inner wall solidification front and high-low temperature circulation flow, forms a horizontal rotary shearing flow through low-frequency electromagnetic stirring, and couples the hot piston flow to form a composite three-dimensional strong shearing flow field, so that the melt is uniformly and rapidly solidified, and a large-wall-thickness high-temperature alloy hollow pipe blank is obtained. The application forms an up-down temperature gradient through medium-frequency heating at the lower part of the crystallizer and cooling at the upper part of the crystallizer, generates a vertical directional hot piston flow and builds a high-low temperature melt closed circulation, can continuously deliver the high-temperature clean melt to the inner wall solidification front, replaces the low-temperature melt rich in solute, cooperates with the low-frequency electromagnetic stirring, reduces the inner wall paste zone, improves the inner wall surface quality, reduces macrosegregation of alloy elements, and makes the pipe blank full-wall-thickness structure and composition more uniform.

Description

Technical Field

[0001] This invention relates to a coreless solidification forming method and apparatus for thick-walled high-temperature alloy hollow tubes. Background Technology

[0002] High-temperature alloy hollow tubes are key structural components for hot-end parts of aero-engines and gas turbines, as well as high-end chemical equipment. Their service environment is harsh, requiring materials to possess excellent high-temperature creep resistance, thermal fatigue resistance, and oxidation corrosion resistance. Strict requirements are placed on the uniformity of the tube's microstructure, compositional segregation, internal surface quality, and density.

[0003] Vertical upward continuous casting can achieve near-net-shape forming, reduce machining workload, and avoid secondary oxidation of the melt, giving it significant advantages in the preparation of high-performance hollow components. However, this process still faces insurmountable technical bottlenecks when applied to thick-walled high-temperature alloy pipes with a wall thickness of not less than 20 mm.

[0004] When using coreless continuous casting, the inner wall of high-temperature alloy pipes relies on the autonomous solidification of the melt. High-temperature alloys have a wide solidification range and a high viscosity in the mushy region. The melt dissipates heat slowly from the inner wall, resulting in a small temperature gradient. The solidification front remains in a semi-solid state for a long time, easily leading to coarse microstructure, a rough inner wall surface, and significant positive segregation at the center, reducing mechanical properties and increasing the risk of hot cracking. Increased wall thickness further exacerbates heat dissipation difficulties and insufficient feeding, making the inner wall prone to defects such as shrinkage cavities and porosity.

[0005] While traditional low-frequency electromagnetic stirring can refine grains and homogenize composition and temperature, its effectiveness is limited when used for thick-walled hollow billets. Its flow field is unevenly distributed radially and axially, resulting in a weak effect on the inner wall region; it lacks a stable axial driving force, making it difficult to achieve directional transport and renewal of the melt; and it cannot fundamentally improve the unfavorable temperature gradient near the inner wall.

[0006] Therefore, a solidification forming method and apparatus for thick-walled high-temperature alloy hollow tubes that can control the solidification process of the inner wall and effectively solve problems such as coarse inner wall structure, high roughness, and severe segregation are proposed. Summary of the Invention

[0007] The main objective of this invention is to provide a coreless solidification forming method and apparatus for thick-walled high-temperature alloy hollow tubes, in order to solve the problems mentioned in the background above.

[0008] The objective of this invention can be achieved by adopting the following technical solution:

[0009] A method for coreless solidification forming of thick-walled high-temperature alloy hollow tubes includes the following steps:

[0010] Step S1: After melting the high-temperature alloy, pour it into the crystallizer;

[0011] Step S2: The lower part of the crystallizer is heated by medium-frequency electromagnetic induction to make the melt superheated to form a high-temperature melt zone, and the upper part of the crystallizer is cooled to form a low-temperature melt zone.

[0012] Step S3: After observing the melt at the crystallizer outlet begins to solidify, the traction and pulling process begins. The melt in the high-temperature melt zone forms a stable, upward, vertically directional hot piston flow along the inner wall of the crystallizer and flows towards the solidification front of the inner wall of the high-temperature alloy tube blank, replacing the low-temperature melt at that location.

[0013] Step S4: The low-temperature melt after displacement flows downward back to the high-temperature melt zone, and after being heated, it forms a hot piston flow that flows upward again, forming a circulation flow of high and low temperature melts;

[0014] Step S5: Apply low-frequency electromagnetic stirring to the melt inside the crystallizer to form a horizontal rotating shear flow, which is superimposed and coupled with the vertical directional hot piston flow to form a composite three-dimensional strong shear flow field.

[0015] Step S6: The high-temperature alloy melt achieves uniform and rapid solidification under the action of a composite three-dimensional strong shear flow field, and a high-temperature alloy hollow tube blank is obtained by continuous traction drawing.

[0016] Preferably, in step S1, the high-temperature alloy is an iron-based, nickel-based, or cobalt-based high-temperature alloy.

[0017] Preferably, in step S1, the melting of the high-temperature alloy is carried out in a protective atmosphere or vacuum environment.

[0018] Preferably, in step S2, the melt temperature in the lower high-temperature melt zone of the crystallizer is 150°C-250°C higher than the liquidus temperature of the high-temperature alloy, and the melt temperature in the upper low-temperature melt zone of the crystallizer forms a radial temperature gradient, with the center temperature higher than the liquidus temperature of the high-temperature alloy and the edge temperature lower than the liquidus temperature of the high-temperature alloy, and the temperature difference is higher than 150°C.

[0019] Preferably, in step S2, the crystallizer is heated from bottom to top in an area with a height of 1 / 5 to 1 / 3 of the working height of the crystallizer to form a high-temperature melt zone.

[0020] Preferably, in step S3, the density of the high-temperature melt zone is lower than that of the low-temperature melt zone, and the vertical directional hot piston flow is formed by the combined action of the density difference between the high-temperature melt zone and the low-temperature melt zone and the upward drag force generated by traction.

[0021] Preferably, in step S4, the displaced cryogenic melt flows downward under the influence of gravity, the driving force of the hot piston flow, and the entrainment effect of the horizontal rotating shear flow.

[0022] Preferably, in step S5, the vertically oriented thermal piston flow provides an axial flow core for the horizontally rotating shear flow, forming a composite three-dimensional strong shear flow field.

[0023] Preferably, the wall thickness of the high-temperature alloy hollow tube blank is ≥20mm.

[0024] A solidification forming apparatus for thick-walled high-temperature alloy hollow tubes includes:

[0025] A crystallizer is used to contain molten high-temperature alloys.

[0026] A medium-frequency electromagnetic induction heating device is installed on the lower outer periphery of the crystallizer to heat the lower region of the crystallizer to form a high-temperature melt zone;

[0027] A cooling device is provided on the upper outer periphery of the crystallizer to cool the upper region of the crystallizer to form a low-temperature melt zone;

[0028] A low-frequency electromagnetic stirring device is disposed on the outer periphery of the cooling device to apply low-frequency electromagnetic stirring to the melt inside the crystallizer to form a horizontal rotating shear flow.

[0029] A traction device is located above the crystallizer and is used to continuously draw high-temperature alloy hollow tube blanks.

[0030] Compared with the prior art, the beneficial technical effects of the present invention are:

[0031] 1. This invention creates a temperature gradient by using medium-frequency heating at the bottom and cooling at the top of the crystallizer. This generates a vertically directional hot piston flow and constructs a closed loop of high and low temperature melts. The high-temperature clean melt is continuously transported to the solidification front of the inner wall, replacing the solute-rich low-temperature melt. Combined with low-frequency electromagnetic stirring, the high-temperature melt flowing upwards from the crystallizer is subjected to rotational electromagnetic stirring, creating annular disturbances that scour the inner wall of the pipe. This achieves the solidification and scour of one layer of melt inside the pipe, followed by the scour of another layer, ultimately realizing the continuous solidification and scour of high-temperature melt layer by layer. This reduces the mushy area on the inner wall, improves the surface quality of the inner wall, and simultaneously homogenizes the melt temperature and composition distribution, reduces macroscopic segregation of alloying elements, and makes the microstructure and composition of the billet more uniform throughout its entire wall thickness.

[0032] 2. This invention constructs a composite three-dimensional strong shear flow field through the coupling of a vertically directional hot piston flow and a horizontally rotating shear flow. This forcefully drives the melt movement, effectively homogenizing the melt temperature distribution, suppressing local undercooling, and significantly improving circumferential and radial temperature uniformity. Simultaneously, it breaks up dendrites formed in the early stages of solidification, which then act as nucleation sites for equiaxed crystals, helping to stabilize the solidification front, resulting in a smooth and uniform solidification interface, inhibiting the growth of coarse columnar crystals, and promoting the formation of a uniform and fine equiaxed crystal structure. The stable and orderly melt flow significantly improves the solidification uniformity of thick-walled high-temperature alloy hollow tube billets, reduces internal defects, and increases the density of the cast billet.

[0033] 3. The solidification process of the present invention is optimized, and the solidified shell is more uniform and firm, which can improve the drawing speed to a certain extent, thereby improving production efficiency. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the solidification forming apparatus according to an embodiment of the present invention.

[0035] In the diagram: 1. Crystallizer; 2. Medium-frequency electromagnetic induction heating device; 3. Cooling device; 4. Low-frequency electromagnetic stirring device; 5. Traction device.

[0036] Note: The arrows indicate the direction of high and low temperature melt circulation. Detailed Implementation

[0037] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0038] Please see Figure 1 An embodiment of the coreless solidification forming method for thick-walled high-temperature alloy hollow tubes provided by the present invention:

[0039] A method for coreless solidification forming of thick-walled high-temperature alloy hollow tubes includes the following steps:

[0040] Step S1: After melting the high-temperature alloy, pour it into crystallizer 1;

[0041] Step S2: The lower part of the crystallizer 1 is heated by medium frequency electromagnetic induction to make the melt superheated to form a high temperature melt zone, and the upper part of the crystallizer 1 is cooled to form a low temperature melt zone.

[0042] Step S3: After observing the melt at the outlet of crystallizer 1 begins to solidify, the traction and pulling are started. The melt in the high-temperature melt zone forms a stable upward vertical directional hot piston flow along the inner wall of crystallizer 1 and flows to the solidification front of the inner wall of the high-temperature alloy tube blank, replacing the low-temperature melt at that point.

[0043] Step S4: The low-temperature melt after displacement flows downward back to the high-temperature melt zone, and after being heated, it forms a hot piston flow that flows upward again, forming a circulation flow of high and low temperature melts;

[0044] Step S5: Apply low-frequency electromagnetic stirring to the melt inside crystallizer 1 to form a horizontal rotating shear flow, which is superimposed and coupled with the vertical directional hot piston flow to form a composite three-dimensional strong shear flow field.

[0045] Step S6: The high-temperature alloy melt achieves uniform and rapid solidification under the action of a composite three-dimensional strong shear flow field, and a high-temperature alloy hollow tube blank is obtained by continuous traction drawing.

[0046] Due to the rapid increase in temperature, the density of the melt in the high-temperature melt zone decreases significantly, becoming lower than that in the low-temperature melt zone. This generates a strong Archimedes' buoyancy in the gravitational field. This buoyancy drives the high-temperature melt to form a strong, stable, and continuous upward flow along the inner wall of crystallizer 1. With the assistance of traction, a thermal piston flow is formed, which is an enhanced type of thermal natural convection.

[0047] The hot piston flow rushes vertically towards the solidification front of the hollow billet's inner wall at a high velocity, which is the interface between the mushy and liquid regions. This continuous upward flow performs two key functions: first, thermal displacement, directly transporting a large amount of superheated heat to the solidification front, significantly increasing the local temperature in this region and narrowing or even eliminating the mushy region; second, mass displacement, replacing the lower-temperature melt at the solidification front, which has accumulated a high concentration of solute elements due to solute discharge, with a high-temperature melt and low solute concentration.

[0048] The solute-rich, lower-temperature melt, displaced from the inner wall solidification front, flows downwards under the influence of gravity, the main flow, and the entrainment effect of the rotating flow field generated by low-frequency electromagnetic stirring, re-entering the high-temperature melt zone at the bottom of crystallizer 1. Under the action of the medium-frequency electromagnetic induction heating device 2, this re-flowing melt is rapidly reheated and homogenized, becoming a high-temperature, pure melt again, thus completing a closed vertical cycle from the inner wall solidification front to the lower high-temperature zone and back to the inner wall solidification front. This cycle continues, ensuring that the inner wall solidification front is always in contact with high-quality melt.

[0049] The low-frequency electromagnetic stirring device 4 induces a strong electromagnetic volume force inside the melt, driving the melt to undergo intense horizontal rotation and three-dimensional turbulent motion, forming a forced convection of rotating machinery, namely, a horizontal rotating shear flow. This horizontal rotating shear flow provides the entire melt with powerful shear force and macroscopic mixing, greatly refining equiaxed crystals and homogenizing the overall composition. The hot piston flow generated by the medium-frequency electromagnetic induction heating not only forms a high-low temperature melt circulation but also injects a forced and stable axial flow core into the horizontal rotating shear flow, providing stable axial guidance and making the overall melt flow more stable and orderly, avoiding turbulence and fluctuations in the rotating flow field.

[0050] The combined effect of these two forces creates a three-dimensional high-shear flow field that integrates mechanical forced convection and thermal natural convection. This flow field possesses both powerful overall stirring capability and precise axial mass transport capability, resulting in a more uniform and stable melt temperature, flow state, and solute distribution within the solidification region of the hollow billet. Under the action of this composite flow field, the mushy region on the inner wall is effectively suppressed, the solidification front is smooth and stable, and the solidification structure transforms from coarse columnar crystals to uniform and fine equiaxed crystals, ultimately enabling the billet to achieve uniform and rapid solidification from the outer wall to the inner wall along the axial height direction.

[0051] The medium-frequency heating frequency used in this embodiment is 1kHz-10kHz, and the low-frequency stirring frequency is 10Hz-30Hz.

[0052] Furthermore, in step S1, the high-temperature alloy is an iron-based, nickel-based, or cobalt-based high-temperature alloy. This is suitable for alloys with a narrow solid-liquid two-phase region, especially alloys with a solid-liquid two-phase temperature below 100°C. The narrower the solid-liquid two-phase region, the easier it is to rapidly transform from a liquid to a solid state, and the easier it is to achieve continuous increases in wall thickness.

[0053] Furthermore, in step S1, the melting of the high-temperature alloy is carried out under a protective atmosphere or vacuum environment.

[0054] Furthermore, in step S2, the melt temperature in the high-temperature melt zone at the bottom of the crystallizer 1 is 150℃-250℃ higher than the liquidus of the high-temperature alloy. This ensures good melt fluidity and prevents the volatilization of a large number of strengthening elements in the alloy. The high-temperature alloy contains various strengthening elements such as Al, Ti, Nb, Ta, W, and Mo, with significant density differences between the elements (e.g., W and Mo have much higher densities than the matrix), and elements such as Nb and Ta have high melting points. By maintaining a sufficiently high superheat, the specific gravity segregation caused by density differences can be effectively suppressed, preventing high-density elements from depositing at the bottom of the molten pool when the temperature is insufficient, thereby eliminating macroscopic segregation defects.

[0055] The melt temperature in the upper low-temperature melt zone of crystallizer 1 forms a radial temperature gradient, with the center temperature higher than the liquidus temperature of the high-temperature alloy and the edge temperature lower than the liquidus temperature of the high-temperature alloy, and the temperature difference is higher than 150℃. This creates a sufficiently high temperature gradient between the molten metal and the solidified shell, ensuring good fluidity in the core while ensuring rapid solidification of the edge into a billet shell.

[0056] Furthermore, in step S2, the area of ​​crystallizer 1 from bottom to top, with a height of 1 / 5 to 1 / 3 of the working height of crystallizer 1, is heated to form a high-temperature melt zone. This creates a stable and significant temperature gradient and melt density difference within crystallizer 1, providing sufficient buoyancy to drive the vertically oriented hot piston flow and ensuring a strong, stable, and directional upward flow of the melt. Simultaneously, it avoids an excessively large heating area that weakens the upper cooling effect, creating a clear functional zone between upper cooling and lower heating, further improving flow field stability and solidification uniformity.

[0057] Furthermore, the wall thickness of the high-temperature alloy hollow tube blank is ≥20mm.

[0058] A solidification forming apparatus for thick-walled high-temperature alloy hollow tubes includes:

[0059] Crystallizer 1 is used to contain high-temperature alloy melt;

[0060] The medium-frequency electromagnetic induction heating device 2 is installed on the lower outer periphery of the crystallizer 1 to heat the lower region of the crystallizer to form a high-temperature melt zone.

[0061] Cooling device 3 is installed on the upper outer periphery of crystallizer 1 to cool the upper region of crystallizer to form a low-temperature melt zone;

[0062] The low-frequency electromagnetic stirring device 4 is set on the outer periphery of the cooling device 3 and is used to apply low-frequency electromagnetic stirring to the melt inside the crystallizer 1 to form a horizontal rotating shear flow.

[0063] The traction device 5 is located above the crystallizer 1 and is used to continuously draw high-temperature alloy hollow tube blanks.

[0064] By using medium-frequency electromagnetic induction heating below the crystallizer 1, the melt entering the crystallizer 1 through the flow channel is heated to 150-250°C above the liquidus, ensuring the fluidity of the melt. By pulling the billet upwards, the melt near the inner wall of the billet generates an upward drag force, causing an exchange between the lower heated melt and the upper cooled melt, fully ensuring the superheat of the melt on the inner wall of the crystallizer 1. Combined with the effect of low-frequency electromagnetic stirring, the high-temperature melt continuously scours the inside of the pipe, thereby improving the uniformity of the melt temperature during the solidification process of the inner wall of the pipe. The higher temperature melt scours the inner wall of the pipe while solidifying, which is beneficial for producing metal pipes with good inner wall smoothness, fine and uniform structure and consistent composition.

[0065] Example 1

[0066] Hollow tube blanks of Inconel 625 nickel-based superalloy with an outer diameter of 150 mm and a wall thickness of 25 mm were prepared. The liquidus temperature of Inconel 625 nickel-based superalloy is 1350℃.

[0067] The composition is as follows (mass fraction): Nickel (Ni) 61.5%, Chromium (Cr) 21.5%, Molybdenum (Mo) 9.0%, Niobium (Nb) 3.6%, Iron (Fe) 2.5%, Cobalt (Co) 0.5%, Aluminum (Al) 0.20%, Titanium (Ti) 0.20%, Carbon (C) 0.05%, Manganese (Mn) 0.25%, Silicon (Si) 0.25%, Phosphorus (P) 0.008%, Sulfur (S) 0.005%.

[0068] A crystallizer 1 with an inner diameter of 150 mm and a cavity wall thickness of 25 mm is selected, and a medium-frequency electromagnetic induction heating device 2 is installed at the lower part of the crystallizer 1 with a coverage height of 200 mm.

[0069] Under argon protection, refined Inconel 625 melt at 1450℃ is injected into the cavity of crystallizer 1. The medium-frequency electromagnetic induction heating device 2 and cooling device 3 are activated, rapidly heating the high-temperature melt zone at the bottom of crystallizer 1 to 1550℃, cooling the low-temperature melt at the upper edge of crystallizer 1 to 1000℃, and reaching a center temperature of 1400℃ at the top. The melt density in the high-temperature melt zone is much lower than that in the low-temperature melt zone, generating buoyancy and forming a vertically directional hot piston flow that rises rapidly along the inner wall of crystallizer 1. This causes the superheated melt at the bottom of crystallizer 1 to flow towards the solidification front on the inner wall, displacing the low-temperature melt there. The displaced low-temperature melt then flows downwards back to the high-temperature melt zone, where it is reheated and forms a hot piston flow upwards again, creating a circulation of high and low temperature melts. Simultaneously, the low-frequency electromagnetic stirring device 4 is activated, causing the melt in the upper low-temperature melt zone of crystallizer 1 to generate a horizontal rotating shear flow. The vertical directional hot piston flow and the horizontal rotating shear flow are superimposed and coupled to form a composite three-dimensional strong shear flow field. Under the action of the composite three-dimensional strong shear flow field, the Inconel 625 nickel-based superalloy melt achieves uniform and rapid solidification, and the Inconel 625 nickel-based superalloy hollow tube blank is obtained by continuous drawing.

[0070] Testing revealed that the inner wall surface roughness Ra of the Inconel 625 nickel-based superalloy hollow tube blank was 2.5 μm. Cross-sectional metallographic analysis showed that the entire wall thickness contained uniform ASTM 7 grade equiaxed crystals. Electron probe microanalysis showed that the macroscopic segregation indices of elements such as Nb and Mo were between 1.02 and 1.04. Ultrasonic testing revealed no internal defects.

[0071] The tube blank produced by the traditional single electromagnetic stirring process has a large paste-like area on the inner wall and a coarse structure.

[0072] Compared with the traditional method, the Inconel 625 nickel-based high-temperature alloy tube blank prepared in this embodiment 1 has significantly improved microstructure uniformity, inner wall quality and composition uniformity.

[0073] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for coreless solidification forming of thick-walled high-temperature alloy hollow tubes, characterized in that: Includes the following steps: Step S1: After melting the high-temperature alloy, pour it into the crystallizer (1); Step S2: The lower part of the crystallizer (1) is heated by medium frequency electromagnetic induction to make the melt in a superheated state to form a high temperature melt zone, and the upper part of the crystallizer (1) is cooled to form a low temperature melt zone. Step S3: After the melt at the outlet of the crystallizer (1) begins to solidify, it begins to be pulled and drawn. The melt in the high-temperature melt zone forms a stable upward vertical directional hot piston flow along the inner wall of the crystallizer (1) and flows to the solidification front of the inner wall of the high-temperature alloy tube blank, replacing the low-temperature melt at that point. Step S4: The low-temperature melt after displacement flows downward back to the high-temperature melt zone, and after being heated, it forms a hot piston flow that flows upward again, forming a circulation flow of high and low temperature melts; Step S5: Apply low-frequency electromagnetic stirring to the melt inside the crystallizer (1) to form a horizontal rotating shear flow, which is superimposed and coupled with the vertical directional hot piston flow to form a composite three-dimensional strong shear flow field; Step S6: The high-temperature alloy melt achieves uniform and rapid solidification under the action of a composite three-dimensional strong shear flow field, and a high-temperature alloy hollow tube blank is obtained by continuous traction drawing.

2. The method for coreless solidification forming of a thick-walled high-temperature alloy hollow tube according to claim 1, characterized in that: In step S1, the high-temperature alloy is an iron-based, nickel-based, cobalt-based, or other high-temperature alloy.

3. The method for coreless solidification forming of a thick-walled high-temperature alloy hollow tube according to claim 1, characterized in that: In step S1, the melting of the high-temperature alloy is carried out under a protective atmosphere or vacuum environment.

4. The method for coreless solidification forming of a thick-walled high-temperature alloy hollow tube according to claim 1, characterized in that: In step S2, the melt temperature in the lower high-temperature melt zone of the crystallizer (1) is 150°C-250°C higher than the liquidus temperature of the high-temperature alloy, and the melt temperature in the upper low-temperature melt zone of the crystallizer (1) forms a radial temperature gradient, with the center temperature higher than the liquidus temperature of the high-temperature alloy and the edge temperature lower than the liquidus temperature of the high-temperature alloy, and the temperature difference is higher than 150°C.

5. The method for coreless solidification forming of a thick-walled high-temperature alloy hollow tube according to claim 1, characterized in that: In step S2, the crystallizer (1) is heated from bottom to top in an area with a height of 1 / 5 to 1 / 3 of the working height of the crystallizer (1) to form a high-temperature melt zone.

6. The method for coreless solidification forming of a thick-walled high-temperature alloy hollow tube according to claim 1, characterized in that: In step S3, the density of the high-temperature melt zone is lower than that of the low-temperature melt zone, and the vertical directional hot piston flow is formed by the combined action of the density difference between the high-temperature melt zone and the low-temperature melt zone and the upward drag force generated by traction.

7. The method for coreless solidification forming of a thick-walled high-temperature alloy hollow tube according to claim 1, characterized in that: In step S4, the cryogenic melt flows downward under the influence of gravity, the hot piston flow, and the entrainment effect of the horizontal rotating shear flow.

8. The method for coreless solidification forming of a thick-walled high-temperature alloy hollow tube according to claim 1, characterized in that: In step S5, the vertically oriented thermal piston flow provides an axial flow core for the horizontal rotating shear flow.

9. The method for coreless solidification forming of a thick-walled high-temperature alloy hollow tube according to claim 1, characterized in that: The wall thickness of the high-temperature alloy hollow tube blank is ≥20mm.

10. A solidification forming apparatus for thick-walled high-temperature alloy hollow tubes, wherein the apparatus is applied to the coreless solidification forming method for thick-walled hollow tubes as described in any one of claims 1-9, characterized in that: include: Crystallizer (1), used to contain high-temperature alloy melt; A medium-frequency electromagnetic induction heating device (2) is installed on the lower outer periphery of the crystallizer (1) to heat the lower region of the crystallizer to form a high-temperature melt zone; A cooling device (3) is provided on the upper outer periphery of the crystallizer (1) to cool the upper region of the crystallizer to form a low-temperature melt zone; A low-frequency electromagnetic stirring device (4) is provided on the outer periphery of the cooling device (3) to apply low-frequency electromagnetic stirring to the melt inside the crystallizer (1) to form a horizontal rotating shear flow. The traction device (5) is located above the crystallizer (1) and is used to continuously draw high-temperature alloy hollow tube blanks.

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