Method for producing a fecral alloy tube blank based on vacuum centrifugal casting

Abstract

The application discloses a FeCrAl alloy pipe blank preparation method based on vacuum centrifugal casting and belongs to the technical field of metal centrifugal casting. The problems of coarse and uneven original as-cast structure of the FeCrAl alloy and premature failure of subsequent piercing are solved. The nuclear fuel cladding tube FeCrAl alloy prepared by the vacuum centrifugal casting technology has fine, uniform and dense structure, the subsequent punching is omitted, and the premature brittle fracture of the alloy material is avoided, so that the failure is avoided. In addition, the production process flow of the application is short, the cost is low, and the engineering application is easy to promote.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of cladding tube material for nuclear power plants, and particularly relates to a FeCrAl alloy tube blank preparation method based on vacuum centrifugal casting. BACKGROUND

[0002] Nuclear fuel cladding material is the first barrier for nuclear safety protection. FeCrAl alloy, as a kind of accident-tolerant fuel cladding material with great application potential, has achieved rapid research and development progress and has become one of the main development directions. FeCrAl alloy has excellent oxidation resistance in high-temperature environments, far exceeding that of zirconium alloy. In addition, it also has excellent mechanical properties, high-temperature corrosion resistance and considerable neutron irradiation resistance. These characteristics make FeCrAl alloy an ideal candidate material for accident-tolerant fuel cladding applications in nuclear power plants.

[0003] Under complex service conditions, the existing FeCrAl alloy cannot fully meet the various challenges faced by the nuclear fuel cladding system. The length of the single tube required for nuclear fuel cladding is at least 3-4 m, so a large-size alloy ingot is needed as the raw material for the preparation of the cladding tube. However, the solidification structure of the large-size ingot has serious dendritic and composition segregation problems, which seriously affect the subsequent processing deformation performance, making it difficult for traditional processes to prepare seamless FeCrAl thin-walled tubes. The reasons are as follows: first, FeCrAl does not undergo phase transformation during solidification, and always maintains single-phase ferrite, resulting in coarse original grain structure; second, FeCrAl alloy is brittle and has a narrow processing window, making it difficult to achieve effective processing deformation.

[0004] In addition, the traditional seamless FeCrAl cladding tube preparation process needs to go through vacuum melting and ingot making, forging, quenching, hot extrusion tube blank preparation and multi-pass rolling and annealing, etc. to obtain the finished cladding tube. These complex preparation processes are prone to cause cracking of FeCrAl alloy and decrease in yield strength due to excessive strain. At the same time, the complex preparation process requires additional equipment, increasing the preparation cost. Therefore, it is urgent to develop a new low-cost short-process FeCrAl tube blank preparation process.

[0005] FeCrAl alloy prepared by arc melting and vacuum induction melting has coarse and developed dendritic grain structure, which is difficult to achieve precise structure control. In addition, powder metallurgy preparation of FeCrAl alloy also cannot meet the full-size requirement under service conditions. Due to the special chemical composition of FeCrAl alloy and the application requirements under high-temperature environments, higher requirements are put forward for the preparation process. SUMMARY

[0006] Centrifugal casting is an effective casting technology, which can effectively purify the alloy melt, convert the developed dendritic grains into equiaxed grains, and realize the homogenization of the structure. In addition, the FeCrAl pipe blank prepared by centrifugal casting is easy to be cold-rolled to prepare a thin-walled pipe, which avoids the large deformation required by the traditional process, thereby reducing the cracking tendency. Centrifugal casting includes vertical centrifugal casting and horizontal centrifugal casting. The horizontal centrifugal casting is suitable for producing larger and more complex parts, because its horizontal layout can provide larger casting space and more flexibility, but in the horizontal centrifugal casting process, the metal liquid is easy to produce specific gravity segregation under the action of centrifugal force.

[0007] The vertical centrifugal casting is suitable for small and medium-sized pipe blanks, and compared with the horizontal centrifugal casting, the device structure is simple, the operation and maintenance are convenient, and the equipment investment and operation and maintenance costs are lower. The cooling speed of the vertical centrifugal casting is relatively fast and the cooling efficiency is higher, which helps to reduce shrinkage holes and grain refinement, and effectively shortens the production cycle, thereby improving the production efficiency and easily realizing large-scale automatic production. Although the grain size of the FeCrAl pipe blank prepared by the vertical centrifugal casting is more refined than that prepared by the horizontal centrifugal casting, it is still difficult to meet the use requirements of the nuclear fuel cladding system application scenario.

[0008] Therefore, the application discloses a FeCrAl alloy pipe blank preparation method based on vacuum centrifugal casting for further refining the grain size of the FeCrAl alloy pipe blank, and specific schemes are as follows:

[0009] The FeCrAl alloy pipe blank preparation method based on vacuum centrifugal casting comprises the following steps:

[0010] S1. Under the vacuum condition, argon is introduced into a vacuum melting centrifugal casting furnace to melt FeCrAl alloy raw materials, so as to obtain FeCrAl alloy metal liquid;

[0011] S2. After the FeCrAl alloy metal liquid is cooled to a pouring temperature, the vertical centrifugal casting machine is started to rotate the centrifugal casting mold under the vacuum environment, the rotating speed is 150-1000 r / min, the FeCrAl alloy metal liquid is poured into the centrifugal casting mold, after pouring is completed, the centrifugal casting mold is kept rotating until the FeCrAl alloy metal liquid is completely solidified, the vertical centrifugal casting machine is stopped to stop the rotation of the centrifugal casting mold, the FeCrAl alloy pipe blank is obtained, then the FeCrAl alloy pipe blank is cooled to room temperature in the centrifugal casting mold, and finally the FeCrAl alloy pipe blank is taken out from the centrifugal casting mold.

[0012] As a supplement to the technical scheme of the present application, the composition and mass percentage of the FeCrAl alloy are as follows: Cr: 12-18%, Al: 3-6%, Mo: 0.5-2%, Si: 0.5-2%, C≤0.05%, Mn≤0.02%, P≤0.05%, S≤0.008%, N≤0.0005%, and the remaining components are Fe and impurities meeting the industrial standards.

[0013] As a supplement to the technical scheme of the present application, the rotating speed of the centrifugal casting mold is 150-300 r / min.

[0014] As a supplement to the technical scheme of the present application, in step S1, the melting temperature of the FeCrAl alloy is 1751-1950°C, and in step S2, the pouring temperature of the FeCrAl alloy is 1550-1750°C.

[0015] As a supplement to the technical scheme of the present application, in step S2, the centrifugal casting mold is kept rotating for 10-30 min after pouring is completed.

[0016] As a supplement to the technical scheme of the present application, the centrifugal casting mold comprises a base plate, a cylinder, a runner groove, and a core;

[0017] The base plate is arranged on the main shaft of a vertical centrifugal casting machine.

[0018] The cylinder is a hollow cylindrical structure with one open end and one closed end, which is arranged horizontally on the base plate; the core is arranged in the cylinder, and one end of the core is connected to the bottom of the closed end of the cylinder; the axis of the core and the line of the cylinder are on the same straight line.

[0019] The runner groove is a groove structure with an open upper end, and one end of the runner groove is connected to the sidewall at the position of the open end of the cylinder, so that the groove body of the runner groove is in communication with the internal space of the cylinder.

[0020] As a supplement to the technical scheme of the present application, the base plate is a disc-shaped structure, the line connecting the center of the open end of the cylinder and the center of the closed end does not pass through the axis of the base plate, and the extension line of the line connecting the center of the open end of the cylinder and the center of the closed end intersects the axis of the base plate.

[0021] As a supplement to the technical scheme of the present application, when the core is of a single material, the melting point of the core is higher than 2000°C.

[0022] As a supplement to the technical scheme of the present application, when the core is of a composite material, the core comprises an inner core and an outer core; the inner core is a cylindrical structure, and the outer core is wrapped outside the inner core; the melting points of the outer core and the inner core are both higher than 2000°C; and the radius of the inner core accounts for 50-90% of the overall radius of the core.

[0023] Beneficial effects: The centrifugal casting mold disclosed by the application can effectively optimize the cooling efficiency, can reduce the temperature of the melt, thereby shortening the solidification time of the casting and improving the production efficiency. Avoid the quality problems such as deformation and cracks of the casting due to uneven cooling. The melt starts to solidify to form a solid shell at the position close to the bottom of the mold, thereby reducing the influence of gravity on the alloy flow and solidification, which can effectively avoid the quality problems such as internal defects and surface cracks of the casting. Increase the size of the casting pipe blank. The centrifugal casting mold disclosed by the application can realize the preparation of FeCrAl alloy pipe blank, can realize the phase change of FeCrAl alloy during the solidification process, realize the efficient and accurate pipe blank preparation, and can realize the improvement of the performance of FeCrAl alloy and the regulation and control of the fine and uniform organization grain without adding a refining agent. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 It is a centrifugal casting mold structure schematic diagram of the application.

[0025] Figure 2 It is a centrifugal casting mold structure schematic diagram of the application.

[0026] Figure 3 (a) is the macrostructure diagram of the FeCrAl alloy pipe blank prepared in example 1 of the application.

[0027] Figure 3 (b) is the macrostructure diagram of the FeCrAl alloy pipe blank prepared in example 1 of the application.

[0028] Figure 4 (a) is the microstructure diagram of the FeCrAl alloy pipe blank prepared in example 1 of the application.

[0029] Figure 4 (b) is the grain size statistical diagram of the FeCrAl alloy pipe blank prepared in example 1 of the application.

[0030] Figure 5 (a) is the macrostructure diagram of the FeCrAl alloy pipe blank prepared in example 3 of the application.

[0031] Figure 5 (b) is the macrostructure diagram of the FeCrAl alloy pipe blank prepared in example 3 of the application.

[0032] Figure 6 (a) is the microstructure diagram of the FeCrAl alloy pipe blank prepared in example 3 of the application.

[0033] Figure 6 (b) is the grain size statistical diagram of the FeCrAl alloy pipe blank prepared in example 3 of the application.

[0034] Figure 7(a) Macrostructure of FeCrAl alloy pipe blank prepared for Invention Comparative Example 1.

[0035] Figure 7 (b) Macrostructure of FeCrAl alloy pipe blank prepared for Invention Comparative Example 1.

[0036] Figure 7 (c) Macrostructure of FeCrAl alloy pipe blank prepared for Invention Comparative Example 1.

[0037] Figure 8 (a) Microstructure of FeCrAl alloy pipe blank prepared for Invention Comparative Example 1.

[0038] Figure 8 (b) Grain size statistics of FeCrAl alloy pipe blank prepared for Invention Comparative Example 1.

[0039] Figure 9 (a) Macrostructure of FeCrAl alloy pipe blank prepared for Invention Comparative Example 2.

[0040] Figure 9 (b) Macrostructure of FeCrAl alloy pipe blank prepared for Invention Comparative Example 2.

[0041] Figure 9 (c) Macrostructure of FeCrAl alloy pipe blank prepared for Invention Comparative Example 2.

[0042] In the figure: 1. base, 2. cylinder, 3. runner groove, 4. core. DETAILED DESCRIPTION

[0043] In the description of the application, it is to be understood that the terms "first", "second", "third" and the like, are used merely as a label to distinguish between different features, and do not imply or suggest a relative importance of the indicated technical features or a number of the indicated technical features. Thus, a feature defined with "first", "second", "third" can explicitly or implicitly include at least one of the feature. In the description of the application, the meaning of "a plurality of" is at least two, for example, two, three, etc., unless otherwise explicitly and specifically limited.

[0044] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting", "fixing" and the like should be understood in a broad sense, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanically connected, or it can be electrically connected or in communication with each other; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the internal communication of two elements or the interaction relationship between two elements, unless otherwise explicitly limited. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0045] The application discloses a preparation method for producing FeCrAl alloy pipe blanks by a centrifugal casting mold, and comprises the following steps:

[0046] S1. Low-vacuum pre-extraction is performed on a vacuum melting centrifugal casting furnace, and the furnace is washed with argon gas for 1-3 times. After the furnace washing is completed, argon gas is continuously supplied into the furnace to ensure an inert atmosphere in the furnace body, and the vacuum degree in the furnace body is 1-103 Pa. Alloy raw materials are configured according to the composition of the target FeCrAl alloy, and are melted in the vacuum melting centrifugal casting furnace. The melting temperature is 1751-1950 DEG C. After the metals such as iron, chromium and molybdenum in the crucible are completely melted, the temperature is kept for 0-1 h to ensure the uniformity of the composition, and the FeCrAl alloy liquid is obtained.

[0047] The composition and mass percentage of the target FeCrAl alloy are as follows: Cr: 12-18%, Al: 3-6%, Mo: 0.5-2%, Si: 0.5-2%, C≤0.05%, Mn≤0.02%, P≤0.05%, S≤0.008%, N≤0.0005%, and the remaining components are Fe and impurities meeting the industrial standards.

[0048] S2. The FeCrAl alloy liquid is cooled to 1550-1750 DEG C, and then the molten FeCrAl alloy liquid is smoothly poured into a rotating centrifugal casting mold through a pouring channel 3 of the centrifugal casting mold for pouring. The pouring speed is controlled during the pouring process, the centrifugal rotation speed is 150-1000 r / min, and after the alloy liquid in the crucible is completely poured, the mold is kept rotating normally until the alloy is completely solidified to obtain the FeCrAl alloy pipe blank, and the rotation of the centrifugal casting mold is stopped. Preferably, after the pouring is completed, the mold should be kept rotating normally for 10-30 min, so that the FeCrAl alloy pipe blank is cooled with the furnace in the centrifugal casting mold. After cooling, the FeCrAl alloy pipe blank is taken out from the centrifugal casting mold.

[0049] The application improves the mold on the basis of a vertical centrifugal casting equipment, and prepares high-quality FeCrAl alloy pipe blanks. Figures 1 to 2 As shown in the above centrifugal casting mold, the mold is used for being installed in a vertical vacuum centrifugal casting machine, and comprises a base plate 1, a pouring channel 3, a core, and a cylinder 2.

[0050] The base plate 1 is arranged on a main shaft of the vertical centrifugal casting machine, and rotates together with the main shaft under the driving of the main shaft. Specifically, the upper end of the main shaft is provided with a base, and the base plate 1 is arranged on the base of the main shaft.

[0051] The cylinder 2 is a hollow cylindrical structure with one open end and one closed end, which is used as a mold body. The open end of the cylinder 2 is used for alloy solution to enter, which is transversely arranged on the base plate 1. The core 4 is arranged in the cylinder 2, one end of the core 4 is connected with the bottom of the closed end of the cylinder 2, and the axis is in the same straight line with the axis of the cylinder 2. Since the mold is used for preparing pipe blank, the setting of the core makes the metal solution form a hollow tubular structure after solidification.

[0052] The pouring channel 3 is a groove structure with an open upper end. One end of the pouring channel 3 is connected with the sidewall of the open end of the cylinder 2, so that the groove body of the pouring channel 3 is connected with the internal space of the cylinder 2, and the metal solution poured into the pouring channel 3 can smoothly flow from the open end of the source cylinder 2 into the internal space of the cylinder 2.

[0053] The size of the open upper end of the pouring channel 3 directly affects the pouring speed, and the pouring speed affects the cooling time of the whole solution. In addition, the size of the open upper end of the pouring channel 3 also affects the cooling rate of the metal solution. The size of the open upper end of the pouring channel 3 can be adjusted according to actual selection.

[0054] The base plate 1 is a disc structure, and the axis of the base plate 1 is collinear with the axis of the vertical centrifugal casting machine.

[0055] As a preferred technical solution of the present application, the line connecting the center of the open end of the cylinder 2 with the center of the closed end does not pass through the straight line where the axis of the base plate 1 is located, so that the cylinder 2 is eccentrically arranged. After the metal solution is poured into the pouring channel 3, it can smoothly flow to the direction of the cylinder 2 under the action of centrifugal force and enter the cylinder 2. The pouring channel 3 should also be eccentrically arranged.

[0056] In order to make the flowing direction of the metal solution poured into the internal space of the cylinder 2 be able to move along the axial direction of the cylinder 2, and facilitate the forming of the pipe blank, the axis of the cylinder 2 should be parallel to the radial direction of the base plate 1, and the extension line of the line connecting the center of the open end of the cylinder 2 with the center of the closed end intersects with the axis of the base plate 1, so that the axis of the cylinder 2 is in the same vertical plane with the axis of the base plate 1, and the two lines are perpendicular to each other. Through the above arrangement, the metal solution can enter the cylinder 2 along the axial direction of the cylinder 2.

[0057] The center of the open end of the above-mentioned cylinder 2 specifically refers to the intersection of the axis of the cylinder 2 with the open end surface, and the center of the closed end specifically refers to the intersection of the axis with the closed end surface.

[0058] As a supplement to the above technical solution, the cross section of one end of the pouring channel 3 connected with the open end of the cylinder 2 can be a U-shaped structure, or can be designed as an O-shaped structure, or can be designed as other structures, which should ensure that the connection between the pouring channel 3 and the cylinder 2 does not have the technical problem of liquid leakage during pouring or rotation of the vertical centrifugal casting machine.

[0059] As a preferred technical solution of the present application, the core 4 is a cylindrical structure.

[0060] As a preferred technical solution of the present application, the core 4 material should have good heat resistance and thermal stability, can withstand the thermal shock of high-temperature metal liquid, and maintain its physical and chemical properties stability in high-temperature environment. At the same time, the core 4 should have good shape stability and easy removal, can keep its shape unchanged during pouring process, and is easy to remove, facilitating the post-processing of the cast pipe blank. The core 4 material is not limited to graphite, metal materials with a melting point higher than FeCrAl alloy, or a core 4 made of composite materials.

[0061] When the core 4 is selected as a single material, the material melting point should be greater than 2000℃, which is suitable for high-temperature alloy casting, such as silicon carbide, graphite, and other refractory metals.

[0062] When the core 4 is selected as a composite structure, the core includes an inner core and an outer core, the outer core is wrapped outside the inner core, the inner core is in a cylindrical structure, the inner core and the outer core are made of different materials, the outer core and the outer core should be made of materials with a melting point greater than 2000℃, the inner and outer cores can be made of different materials according to functional requirements, the inner core can be made of high-temperature resistant and low-thermal expansion materials to reduce deformation, and the outer core can be made of materials with higher strength or lower cost to meet the structural support requirements. The material of the inner core needs high melting point and corrosion resistance, with a melting point greater than 2000℃.

[0063] Preferably, the radius of the inner core accounts for 50-90% of the entire core radius, and the corresponding thickness ratio of the inner and outer cores ranges from 1:1 to 9:1.

[0064] The design of inner and outer cores with different thicknesses helps to control the heat conduction and cooling rate, thereby improving the solidification process of the casting. Larger inner core thickness (such as ratio 9:1) can delay heat conduction and reduce the generation of thermal stress and cracks, because when the inner core is thicker, it can play a role in thermal insulation, and the heat conduction speed is slower, which helps to control the temperature gradient and reduce cracks caused by excessive thermal stress. Smaller inner core thickness (such as ratio 1:1) helps to improve cooling efficiency and prevent defects caused by rapid solidification, because heat can be transferred from the inside of the casting to the outside more quickly, thereby accelerating the cooling process. This helps to prevent defects such as pores and shrinkage holes caused by rapid cooling, because rapid cooling can cause uneven metal flow, thereby affecting the quality of the casting. By reasonably configuring the thickness of the inner and outer cores, the process requirements can be met, the material use can be optimized, the production cost can be reduced, and the quality and consistency of the casting can be ensured.

[0065] The centrifugal casting mold disclosed in the present application has the following advantages when applied to a vertical vacuum centrifugal casting machine:

[0066] 1. The cooling efficiency is effectively optimized, the temperature of the melt is reduced, the solidification time of the casting is shortened, and the production efficiency is improved. After the metal liquid enters the cavity, it moves along the thin wall of the metal mold under the action of centrifugal force. When the metal liquid reaches the end of the cavity, it fills the gate in the reverse direction, while the metal liquid continuously fills the gate in the forward direction. Therefore, due to the forward filling and reverse filling of the metal liquid, the uniformity of the metal liquid flow is promoted, the mixing and convection of the metal liquid inside are enhanced, the heat transfer speed is accelerated, and the cooling speed and efficiency are significantly improved.

[0067] 2. The generation of pores and inclusions is effectively reduced. Since the centrifugal force is proportional to the centrifugal radius, during the filling process, the centrifugal force experienced by the metal liquid increases with the distance from the rotating shaft. The variable acceleration continuously fills the cavity, which can effectively reduce the dead angle and stagnant area, and reduce the generation of shrinkage holes and inclusions.

[0068] 3. The refinement of the as-cast structure is realized, and the generation of columnar crystals is significantly reduced. The mixing and convection of the metal liquid enhance the fragmentation process of the dendrites, and the broken dendrite fragments continuously migrate during the flow of the liquid metal. When these fragments reach the dendrite front, they promote the nucleation process as heterogeneous nucleation sources, thereby leading to grain refinement. A part of the broken dendrite fragments remelt when entering the high temperature zone, and the other part gathers at the columnar crystal front, inhibiting the further growth of the columnar crystals. Therefore, a continuous columnar to equiaxed transition (CET) process is formed. As the metal liquid flows to the end of the cavity and contacts the mold, rapid cooling produces a large degree of supercooling, which promotes the occurrence of a large number of heterogeneous nucleation, thereby forming a small equiaxed crystal zone.

[0069] 4. The quality problems such as deformation and cracks of the casting due to uneven cooling and stress concentration are avoided. The use of the centrifugal casting mold disclosed in the present application makes the casting in a horizontal state after pouring. This is beneficial to realize a more uniform cooling process, avoids the occurrence of uneven shrinkage due to too large local temperature difference of the casting, thereby reducing the occurrence of deformation and cracks. In addition, the way of supporting the casting by the centrifugal casting mold disclosed in the present application makes the stress received by the casting more uniform, and it is not easy to produce a concentrated stress point. This helps to reduce the deformation and cracks caused by excessive internal stress.

[0070] 5. Shape stability. The use of the centrifugal casting mold disclosed in the present application can better fix the shape of the casting, reduce the volume shrinkage of the casting during the cooling process, can effectively avoid the phenomenon that the pipe blank with a height greater than the diameter prepared by vertical pouring appears thin at the top and thick at the bottom, and ensures the dimensional accuracy and shape stability of the casting.

[0071] 6. Increase the size of the size. Due to the combined action of centrifugal force and gravity, the inner surface of the vertical centrifugal casting presents a shape of a rotating parabola, which makes the distribution of the casting uneven during the cooling process, easily causing the pipe blank to be thin on the top and thick on the bottom, affecting the quality and dimensional accuracy of the pipe blank, so it is suitable for producing pipe blanks with a height less than the diameter. The centrifugal casting mold disclosed in the present application can effectively adjust the wall thickness distribution of the inner surface of the casting, avoiding the wall thickness difference caused by uneven centrifugal force in the traditional vertical mold, thereby making the wall thickness more uniform, significantly improving the dimensional accuracy and quality of the pipe blank. This horizontal layout not only improves the uniformity of the wall thickness, but also expands the size range of the pipe blank that can be produced, especially for producing larger size pipe blanks with more uniform wall thickness. The present application can be used to prepare pipe blanks with a length of 80cm to 900cm.

[0072] By using the centrifugal casting mold of the present application in combination with the centrifugal casting process, compared with the prior art, efficient and accurate pipe blank preparation can be achieved without adding refiner, which can improve the performance of FeCrAl alloy and control the grain size.

[0073] Since the metal liquid is poured from the gate slot position, it is close to the near-end of the centrifugal radius at this time, and the melt is not subjected to relative movement under the action of centrifugal force. Under the action of centrifugal force, the metal liquid starts to accelerate towards the far-end of the centrifugal radius, and when the pressure obtained by the inner wall of the mold is greater than the centrifugal force, the melt starts to decelerate until the far-end of the centrifugal radius. The grains in the melt in contact with the inner wall of the mold first nucleate and begin to grow. During the solidification process of the centrifugal casting metal melt, the shear torque acting on the root of the dendrite arm in the melt is the largest. When the shear torque acting on the root of the dendrite arm is greater than the strength of the dendrite arm, the dendrites between the dendrites begin to break, and the broken dendrites enter the melt to become new nucleation points, increasing the number of nucleation in the melt, thereby refining the structure.

[0074] In the present application, the centrifugal speed is selected to be 150-1000 rpm, the main purpose is to further realize the effect of refining the grain, and increasing the speed will increase the turbulence degree of the metal liquid, forming a self-stirring convection impact effect, the flow rate and filling pressure of the metal liquid increase, the temperature gradient increases during the solidification process, and the solidification speed of the casting is accelerated, which is helpful for grain refinement, but too high centrifugal speed will cause excessive centrifugal force, resulting in cracks in the casting, and even metal liquid turbulence or spatter, increasing the wear and maintenance cost of the centrifugal machine equipment.

[0075] The present application changes the filling characteristics of the metal liquid by using a vertical vacuum centrifugal casting machine combined with a horizontally arranged mold, the metal liquid in the mold cavity continuously impacts and convects, the cooling efficiency of the metal liquid is improved, and the pouring process parameters are optimized, on this basis, the microstructure is significantly refined, and the proportion of columnar crystals is effectively reduced.

[0076] Example 1: In this example, a vertical vacuum centrifugal casting machine is used in combination with the centrifugal casting mold disclosed in the present application to prepare a FeCrAl alloy pipe blank, and the specific steps are as follows:

[0077] S1. Under vacuum conditions, argon is introduced into the vacuum melting centrifugal casting furnace, and the pre-configured FeCrAl alloy raw materials are melted to obtain a FeCrAl alloy liquid metal, and the melting temperature is 1900°C.

[0078] S2. Reduce the power of the vacuum melting centrifugal casting furnace to cool the metal liquid to 1700°C, and pour the molten metal liquid into the centrifugal casting mold for pouring, and continuously rotate at a centrifugal speed of 200 r / min. After the metal liquid is completely poured, the mold is rotated for 30 minutes and then stopped, and in this process, the metal liquid completely solidifies to form a FeCrAl alloy pipe blank, so that the FeCrAl alloy pipe blank cools in the centrifugal casting mold, and after cooling, the FeCrAl alloy casting is taken out from the centrifugal casting mold;

[0079] As shown in Figure 3 , Figure 4 , they are the macrostructure and microstructure diagrams of the FeCrAl alloy pipe blank prepared in this example. The mold is placed horizontally, which changes the filling characteristics of the metal liquid, the metal liquid in the mold cavity continuously impacts convection, the metal liquid cools quickly, the structure is effectively refined, and the proportion of columnar crystals is significantly reduced, but the uniformity of the structure still has some differences.

[0080] Example 2: In this example, a vertical vacuum centrifugal casting machine is used in combination with the centrifugal casting mold disclosed in the present application to prepare a FeCrAl alloy pipe blank, and the specific steps are as follows:

[0081] S1. Under vacuum conditions, argon is introduced into the vacuum melting centrifugal casting furnace, and the pre-configured FeCrAl alloy raw materials are melted to obtain a FeCrAl alloy liquid metal, and the melting temperature is 1900°C.

[0082] S2. Reduce the power of the vacuum melting centrifugal casting furnace to cool the metal liquid to 1700°C, and pour the molten metal liquid into the centrifugal casting mold for pouring, and continuously rotate at a centrifugal speed of 200 r / min. After the metal liquid is completely poured, the mold is rotated for 30 minutes and then stopped, and in this process, the metal liquid completely solidifies to form a FeCrAl alloy pipe blank, so that the FeCrAl alloy pipe blank cools in the centrifugal casting mold, and after cooling, the FeCrAl alloy casting is taken out from the centrifugal casting mold;

[0083] On the basis of embodiment 1, in order to further refine the grain, the rotating speed is selected to be increased. The increase of the rotating speed increases the turbulence degree of the metal liquid, forms the self-stirring convection impact effect, and increases the flow rate and filling pressure of the metal liquid. In the solidification process, the temperature gradient is increased, and the solidification speed of the casting is accelerated, which is helpful for the grain refinement. In this process, the mixing and convection of the metal liquid promote the fragmentation of the dendrites, the fragments migrate and act as heterogeneous nucleation points at the dendrite front, further accelerating the grain refinement. At the same time, part of the broken dendrite fragments partially remelt and partially gather at the dendrite front to inhibit the growth. As shown in FIGS. Figure 5 、 Figure 6 It can be seen that the grain size and uniformity of the FeCrAl alloy pipe blank prepared in this embodiment are obviously improved.

[0084] Embodiment 3: In this embodiment, a vertical vacuum centrifugal casting machine is used in combination with the centrifugal casting mold disclosed in the present application to prepare a FeCrAl alloy pipe blank, which comprises the following steps:

[0085] S1. Under vacuum conditions, argon is introduced into the vacuum melting centrifugal casting furnace, and the pre-configured FeCrAl alloy raw material is melted at a temperature of 1900°C to obtain FeCrAl alloy metal liquid.

[0086] S2. The power of the vacuum melting centrifugal casting furnace is reduced to cool the metal liquid to 1600°C, and the molten metal liquid is smoothly poured into the centrifugal casting mold for casting. The mold is continuously and smoothly rotated at a centrifugal rotating speed of 250 r / min. After the metal liquid is completely cast, the mold is rotated for 30 min and then stopped. In this process, the metal liquid is completely solidified to form a FeCrAl alloy pipe blank, so that the FeCrAl alloy pipe blank is cooled with the furnace in the centrifugal casting mold. After cooling, the FeCrAl alloy casting is taken out of the centrifugal casting mold;

[0087] On the basis of embodiment 2, the process parameters are optimized in this embodiment, and the pouring temperature is adjusted to 1600°C. Reducing the pouring temperature helps to increase the cooling rate of the metal, and the increase of the cooling rate will inhibit the growth of the grain. Because the grain growth time is shortened in a shorter time, the FeCrAl alloy is more rapidly converted from a liquid state to a solid state, which is conducive to the formation of crystal nucleus and promotes the control of the metal crystallization process. Therefore, the grain is significantly refined, the proportion of equiaxed grains is increased, and the uniformity of the structure is improved.

[0088] Embodiment 4: In this embodiment, a vertical vacuum centrifugal casting machine is used in combination with the centrifugal casting mold disclosed in the present application to prepare a FeCrAl alloy pipe blank, and the specific steps are as follows:

[0089] S1. Under vacuum conditions, argon is introduced into the vacuum melting centrifugal casting furnace, and the pre-configured FeCrAl alloy raw material is melted, with a melting temperature of 1900℃, to obtain FeCrAl alloy liquid metal;

[0090] S2. Reduce the power of the vacuum melting centrifugal casting furnace to cool the metal liquid to 1550℃, and pour the molten metal liquid into the centrifugal casting mold for casting, with a centrifugal rotation speed of 150r / min for continuous and smooth rotation. After the metal liquid is completely cast, the mold is rotated for 15 minutes and then stopped. In this process, the metal liquid completely solidifies to form a FeCrAl alloy pipe blank, allowing the FeCrAl alloy pipe blank to cool in the centrifugal casting mold. After cooling, the FeCrAl alloy casting is removed from the centrifugal casting mold;

[0091] Under such process conditions, the pouring temperature and centrifugal rotation speed are both low, and the centrifugal force is weak during pouring. The temperature of the molten metal liquid is also low, which can cause poor flowability of the metal liquid, more pores and inclusions, and uneven solidification, increasing the risk of crack formation.

[0092] Example 5: In this example, a vertical vacuum centrifugal casting machine is used to prepare a FeCrAl alloy pipe blank in combination with the centrifugal casting mold disclosed in this application. The specific steps are as follows:

[0093] S1. Under vacuum conditions, argon is introduced into the vacuum melting centrifugal casting furnace, and the pre-configured FeCrAl alloy raw material is melted, with a melting temperature of 1900℃, to obtain FeCrAl alloy liquid metal.

[0094] S2. Reduce the power of the vacuum melting centrifugal casting furnace to cool the metal liquid to 1550℃, and pour the molten metal liquid into the centrifugal casting mold for casting, with a centrifugal rotation speed of 150r / min for continuous and smooth rotation. After the metal liquid is completely cast, the mold is rotated for 15 minutes and then stopped. In this process, the metal liquid completely solidifies to form a FeCrAl alloy pipe blank, allowing the FeCrAl alloy pipe blank to cool in the centrifugal casting mold. After cooling, the FeCrAl alloy casting is removed from the centrifugal casting mold;

[0095] Under such process conditions, the viscosity of the metal liquid is high, and the flowability is reduced. At this time, the centrifugal rotation speed is high, which can cause the metal liquid to rapidly fill the mold. However, the low temperature and high centrifugal force can cause the flow speed of the metal liquid in the mold to be uneven, resulting in uneven distribution of the structure of the casting, thereby increasing the internal stress.

[0096] Comparative Example 1: In this example, a traditional vertical vacuum centrifugal casting machine is used to prepare a FeCrAl alloy pipe blank in combination with a vertical casting mold. The specific process steps are as follows:

[0097] S1. Under vacuum condition, and argon gas is introduced. The pre-configured FeCrAl alloy raw material is smelted to make it melt into FeCrAl alloy liquid metal, and the smelting temperature is 1900°C.

[0098] S2. The liquid metal is cooled to 1650°C by reducing the power, and the molten metal liquid is smoothly poured into a rotating vertical casting mold for pouring. The mold is continuously and smoothly rotated at a centrifugal speed of 600 r / min. After the metal liquid is completely poured, the mold is rotated for 30 min and then stopped. In this process, the metal liquid is completely solidified to form a FeCrAl alloy pipe blank, so that the FeCrAl alloy pipe blank is cooled with the furnace in the centrifugal casting mold. After cooling, the FeCrAl alloy casting is taken out of the centrifugal casting mold.

[0099] As shown in Figure 7 , Figure 8 , the as-cast structure of the FeCrAl alloy is coarse and has poor uniformity. The microstructure is finer and more uniform than that of the as-cast structure prepared by vacuum induction smelting. Although the as-cast structure is refined to a certain extent, a large number of columnar crystals are still formed along the cooling direction, which is not conducive to subsequent processing and forming.

[0100] Comparative Example 2: In this comparative example, a FeCrAl ingot is prepared by vacuum induction smelting. An industrial pure metal is used as the raw material to prepare a 25 kg FeCrAl ingot, including the following steps:

[0101] S1. Under vacuum condition, and argon gas is introduced. The pre-configured FeCrAl alloy raw material is smelted to make it melt into FeCrAl alloy liquid metal, and the smelting temperature is 1700°C.

[0102] S2. The alloy melt is poured into a graphite crucible prepared in advance in the vacuum induction furnace. The flow rate of the FeCrAl alloy liquid metal into the cavity follows the principle of slow- medium fast-slow. After pouring, it is naturally cooled to room temperature to obtain a FeCrAl alloy ingot.

[0103] The microstructure thereof is shown in Figure 9 , which has poor uniformity and large grain size.

[0104] The average equiaxed grain size and average columnar grain size of Examples 1 to 5, Comparative Example 1 and Comparative Example 2 are detected, and the results are as follows.

[0105] Table 1. Grain size detection of each example

[0106]

[0107] From the above table, it can be clearly seen that the average equiaxed grain size and the average columnar grain width of the FeCrAl alloy pipe blank prepared in Examples 1-5 are significantly higher than those of Comparative Example 1 and Comparative Example 2.

[0108] By the centrifugal casting mold + vertical centrifugal casting machine of the present application, compared with the traditional process, the FeCrAl alloy pipe blank preparation method disclosed in the present application can realize that the FeCrAl alloy does not undergo phase transition during the solidification process, realizes efficient and accurate pipe blank preparation, and does not need to add a refining agent, so as to realize the improvement of the performance of the FeCrAl alloy and the regulation and control of the fine and uniform microstructure grain.

[0109] It should be noted that the centrifugal casting mold and the centrifugal casting method disclosed in the present application are not limited to the preparation of the FeCrAl alloy pipe blank, but can also be applied to other alloy materials. By using the method proposed in the present application, an alloy pipe material with the characteristics of increased size, uniform and fine and dense equiaxed grain structure, etc. can be obtained.

[0110] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can make equivalent replacements or changes to the technical scheme and the inventive concept of the present application within the technical range disclosed in the present application, which should be covered within the protection scope of the present application.

Claims

1. Process for the production of a FeCrAl alloy pipe blank based on vacuum centrifugal casting, characterized in that, The method comprises the following steps: S1. Under vacuum conditions, argon is introduced into a vacuum melting centrifugal casting furnace to melt FeCrAl alloy raw materials, and FeCrAl alloy liquid metal is obtained; S2. After the FeCrAl alloy liquid metal is cooled to a pouring temperature, a vertical centrifugal casting machine is started to rotate a centrifugal casting mold at a speed of 150-1000 r / min, the FeCrAl alloy liquid metal is poured into the centrifugal casting mold, the centrifugal casting mold is kept rotating until the FeCrAl alloy liquid metal is completely solidified after pouring is completed, the vertical centrifugal casting machine is turned off to stop the rotation of the centrifugal casting mold, and a FeCrAl alloy pipe blank is obtained, the FeCrAl alloy pipe blank is cooled to room temperature in the centrifugal casting mold, and finally the FeCrAl alloy pipe blank is taken out from the centrifugal casting mold; The centrifugal casting mold comprises a base plate (1), a cylinder (2), a runner groove (3), and a core (4); The base plate (1) is arranged on a main shaft of the vertical centrifugal casting machine; The cylinder (2) is a hollow cylindrical structure with one open end and one closed end, and is arranged horizontally on the base plate (1); the core (4) is arranged in the cylinder (2), and one end of the core (4) is connected to the bottom of the closed end of the cylinder (2), and the axis of the core (4) is on the same straight line as the line direction of the cylinder (2); The runner groove (3) is a groove structure with an open upper end, and one end of the runner groove (3) is connected to the sidewall at the position of the open end of the cylinder (2), so that the groove body of the runner groove (3) is connected to the internal space of the cylinder (2); The base plate (1) is a disc-shaped structure, the line connecting the center of the open end of the cylinder (2) and the center of the closed end does not pass through the axis of the base plate (1), and the extension line of the line connecting the center of the open end of the cylinder (2) and the center of the closed end intersects the axis of the base plate (1).

2. The method according to claim 1, characterized in that, The composition and mass percentage of the FeCrAl alloy are as follows: Cr: 12-18%, Al: 3-6%, Mo: 0.5-2%, Si: 0.5-2%, C≤0.05%, Mn≤0.02%, P≤0.05%, S≤0.008%, N≤0.0005%, and the remaining components are Fe and impurities meeting the industrial standards.

3. The method according to claim 1, wherein the vacuum centrifugal casting-based FeCrAl alloy pipe blank production method is characterized by, The rotation speed of the centrifugal casting mold is 150-300 r / min.

4. The FeCrAl alloy tube blank production method according to claim 1, characterized by In step S1, the melting temperature of the FeCrAl alloy is 1751-1950°C, and in step S2, the pouring temperature of the FeCrAl alloy is 1550-1750°C.

5. The FeCrAl alloy tube blank production method according to claim 1, characterized by In step S2, the centrifugal casting mold is kept rotating for 10-30 min after pouring is completed.

6. The FeCrAl alloy tube blank production method according to claim 1, characterized by The core (4) is made of a single material, and the melting point of the core (4) is higher than 2000°C.

7. The FeCrAl alloy tube blank production method according to claim 1, characterized by The core (4) comprises an inner core and an outer core, the inner core is a cylindrical structure, the outer core is wrapped outside the inner core, the melting points of the outer core and the inner core are both higher than 2000°C, and the radius of the inner core accounts for 50%-90% of the overall radius of the core (4).

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