A medium temperature microstructurally stable ferritic heat-resistant alloy material for nuclear fuel cladding and a method for manufacturing the same

Abstract

This invention discloses a medium-temperature stable ferritic heat-resistant alloy material for nuclear fuel cladding. Its composition is as follows (by mass percentage): C ≤ 0.02%, Cr: 9.8–11.8%, Al: 5.0–6.0%, Mo: 1.5–2.5%, Pr: 0.02–0.2%, Re: 0.5–5.0%, with the remainder being iron and unavoidable impurities. After batching and vacuum induction melting, the material is cast into ingots. These ingots are then subjected to a series of processes including hot forging at 1200℃–1250℃, hot rolling or hot extrusion at 1050℃–1180℃, warm rolling at 300℃–500℃, and recrystallization annealing at 950℃–1050℃, ultimately yielding medium-temperature stable ferritic heat-resistant alloy tubing or plates for nuclear fuel cladding. This invention effectively suppresses the 475℃ brittleness problem of ferritic heat-resistant alloys and improves the alloy's mechanical properties, high-temperature resistance, and hot working properties.

Description

Technical Field

[0001] This invention relates to a material for nuclear fuel cladding, specifically a medium-temperature stable ferritic heat-resistant alloy material for nuclear fuel cladding, which is applied to core components of nuclear reactors. Background Technology

[0002] Nuclear energy is widely used in the nuclear power field due to its advantages such as high efficiency, environmental friendliness, safety, and economy. Developing nuclear power can effectively solve energy problems and is an inevitable trend in national economic development. The nuclear reactor is a crucial component of a nuclear power plant, maintaining the self-controlled chain reaction. As a core component of the nuclear reactor, the performance of the nuclear fuel cladding material directly affects the stable operation of the reactor.

[0003] Zirconium alloys are currently commonly used as cladding materials for nuclear fuel. FeCrAl heat-resistant alloys, due to their excellent resistance to high-temperature oxidation, radiation swelling, and high-temperature mechanical properties, are considered ideal cladding materials for accident-tolerant fuel (ATF). The normal operating temperature of a nuclear reaction is 300–500℃; however, when FeCrAl heat-resistant alloys are used at these temperatures, they are prone to the separation of Fe-rich α-phase and Cr-rich α′-phase, causing hardening and embrittlement of the material, severely affecting the alloy's mechanical properties. This situation is particularly pronounced at 475℃, known as the mid-temperature "475℃ brittleness" problem.

[0004] Furthermore, existing FeCrAl heat-resistant alloys for nuclear fuel cladding suffer from problems such as coarse grains, uneven wall thickness, lack of an optimal manufacturing process, and insufficient research on weldability, and therefore cannot completely replace zirconium alloys. Thus, solving the "475℃ brittleness" problem at medium temperatures, refining the grain size, improving hot workability, and enhancing mechanical properties are the key technical challenges that need to be addressed in developing FeCrAl heat-resistant alloys for nuclear fuel cladding. Summary of the Invention

[0005] To address the problems existing in current materials and technologies, this invention aims to overcome their shortcomings and provide a medium-temperature stable ferritic heat-resistant alloy material for nuclear fuel cladding, along with its preparation method. The medium-temperature stable ferritic alloy of this invention possesses advantages such as high-temperature oxidation resistance, excellent strength and plasticity, fine grain size, and good processability. After continuous processing including hot forging, hot rolling or extrusion, warm rolling, and recrystallization annealing, the alloy material exhibits a grain size no larger than 30 μm, a room temperature yield strength of 400–600 MPa, a room temperature tensile strength of 500–700 MPa, and a total elongation after fracture of 25–40%. This invention incorporates a certain amount of rhenium into ferritic stainless steel, effectively suppressing the medium-temperature "475℃ brittleness" problem, refining the grain size, improving the alloy's strength and plasticity, high-temperature oxidation resistance, and hot working properties. This provides important reference for the development of novel FeCrAl heat-resistant alloys for nuclear fuel cladding.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following inventive concept:

[0007] Rhenium (Re) possesses advantages such as high melting point, chemical stability, high-temperature corrosion resistance, excellent creep resistance, good plasticity, and mechanical properties, and is currently widely used in nuclear energy, aerospace, space stations, and reactors. Adding an appropriate amount of rhenium to FeCrAl alloys can significantly improve the alloy's high-temperature oxidation resistance, mechanical properties, and processing performance. Furthermore, according to the Re-Fe phase diagram, when the Re content is less than 70%, it dissolves in the body-centered cubic structure of the FeCrAl alloy matrix, increasing the alloy's strength. Rhenium, with its close-packed hexagonal structure and large atomic radius, causes severe lattice distortion, hindering the diffusion of alloying elements and thus suppressing high-temperature grain growth and the formation of brittleness at 475℃ in the intermediate temperature range. Therefore, adding rhenium to FeCrAl alloys can also effectively improve the alloy's strength and microstructure. This invention, through extensive experimental research, has found that FeCrAl heat-resistant alloys with stable microstructures at intermediate temperatures can operate for extended periods under nuclear reactor operating conditions, ensuring the stable operation of nuclear reactors.

[0008] Based on the above inventive concept, the present invention adopts the following technical solution:

[0009] A medium-temperature stable ferritic heat-resistant alloy material for nuclear fuel cladding, the composition of which is as follows by mass percentage: C≤0.02%, Cr: 9.8~11.8%, Al: 5.0~6.0%, Mo: 1.5~2.5%, Pr: 0.02~0.2%, Re: 0.5~5.0%, with the remainder being iron and unavoidable impurities.

[0010] The addition of an appropriate amount of rare earth praseodymium (Pr) to the alloy of this invention can prevent segregation of the alloy structure, refine the grains, reduce impurities, improve the alloy structure, and also play a certain role in solid solution strengthening, thereby improving the alloy performance.

[0011] As a further preferred technical solution of the present invention, the main components of the medium-temperature stable FeCrAl alloy material for nuclear fuel cladding of the present invention are composed of the following mass percentages: C≤0.01%, Cr: 10.5~11.5%, Al: 5.0~5.5%, Mo: 1.8~2.2%, Pr: 0.05~0.1%, Re: 0.5~2.5%, and the remaining components are iron and unavoidable impurities.

[0012] As a second further preferred technical solution of the present invention, the main components of the medium-temperature stable FeCrAl alloy material for nuclear fuel cladding of the present invention are composed of the following mass percentages: C≤0.008%, Cr: 10.5~11.0%, Al: 5.0~5.4%, Mo: 1.8~2.1%, Pr: 0.06~0.1%, Re: 0.5~2.0%, and the remaining components are iron and unavoidable impurities.

[0013] As a third further preferred technical solution of the present invention, the main components of the medium-temperature stable FeCrAl alloy material for nuclear fuel cladding of the present invention are composed of the following mass percentages: C≤0.005%, Cr: 10.5~10.8%, Al: 5.1~5.3%, Mo: 1.8~2.0%, Pr: 0.07~0.1%, Re: 0.8~2.0%, and the remaining components are iron and unavoidable impurities.

[0014] As a fourth further preferred technical solution of the present invention, the main components of the medium-temperature stable FeCrAl alloy material for nuclear fuel cladding of the present invention are composed of the following mass percentages: C≤0.002%, Cr: 10.5~10.7%, Al: 5.1~5.2%, Mo: 1.9~2.0%, Pr: 0.08~0.1%, Re: 1.0~1.5%, and the remaining components are iron and unavoidable impurities.

[0015] As a preferred technical solution of the present invention, the ferritic heat-resistant alloy material with medium-temperature stable structure for nuclear fuel cladding is characterized in that its room temperature tensile strength is not less than 500 MPa, its room temperature yield strength is not less than 400 MPa, and its total elongation after fracture is not less than 20%.

[0016] As a further preferred technical solution of the present invention, the ferritic heat-resistant alloy material for nuclear fuel cladding with medium-temperature stable structure of the present invention is characterized in that its room temperature tensile strength is 500-700 MPa, its room temperature yield strength is 400-600 MPa, and its total elongation after fracture is 25-40%.

[0017] As a preferred technical solution of the present invention, the grain size of the medium-temperature stable ferritic heat-resistant alloy material for nuclear fuel cladding is not greater than 30 μm.

[0018] A method for preparing a medium-temperature stable ferritic heat-resistant alloy material for nuclear fuel cladding according to the present invention includes the following steps:

[0019] a. Alloy smelting:

[0020] The process employs vacuum induction melting. During raw material preparation, the raw materials are proportioned as follows by mass percentage: C ≤ 0.02%, Cr: 9.8–11.8%, Al: 5.0–6.0%, Mo: 1.5–2.5%, Pr: 0.02–0.2%, Re: 0.5–5.0%, with the remainder being iron and unavoidable impurities. All the weighed raw materials are then subjected to vacuum induction melting to obtain the alloy melt.

[0021] b. Alloy solidification:

[0022] The alloy melt prepared in step a is cast into shape; the alloy ingot obtained by casting is subjected to hot forging at 1200℃-1250℃, hot rolling or hot extrusion at 1050℃-1180℃, warm rolling at 300℃-500℃ and recrystallization annealing at 950℃-1050℃ in sequence to finally obtain ferritic heat-resistant alloy pipes or plates with medium temperature structure stability for nuclear fuel cladding.

[0023] As a further preferred technical solution of the present invention, in step a, the main components of the raw materials are composed of the following mass percentages: C≤0.01%, Cr: 10.5~11.5%, Al: 5.0~5.5%, Mo: 1.8~2.2%, Pr: 0.05~0.1%, Re: 0.5~2.5%, and the remaining components are iron and unavoidable impurities.

[0024] As a second further preferred technical solution of the present invention, in step a, the main components of the raw materials are composed of the following mass percentages: C≤0.008%, Cr: 10.5~11.0%, Al: 5.0~5.4%, Mo: 1.8~2.1%, Pr: 0.06~0.1%, Re: 0.5~2.0%, and the remaining components are iron and unavoidable impurities.

[0025] As a third further preferred technical solution of the present invention, in step a, the main components of the raw materials are composed of the following mass percentages: C≤0.005%, Cr: 10.5~10.8%, Al: 5.1~5.3%, Mo: 1.8~2.0%, Pr: 0.07~0.1%, Re: 0.8~2.0%, and the remaining components are iron and unavoidable impurities.

[0026] As a fourth further preferred technical solution of the present invention, in step a, the main components of the raw materials are composed of the following mass percentages: C≤0.002%, Cr: 10.5~10.7%, Al: 5.1~5.2%, Mo: 1.9~2.0%, Pr: 0.08~0.1%, Re: 1.0~1.5%, and the remaining components are iron and unavoidable impurities.

[0027] As a preferred technical solution of the present invention, in step a, a vacuum induction melting process is adopted, in which all the raw materials weighed after batching are placed into a vacuum induction heating furnace and a vacuum of 5×10⁻⁶ is drawn. -4 Below Pa, high-purity argon gas is introduced as a protective gas; then the temperature is raised to not less than 1600℃ at a heating rate of not less than 200℃ / min, and held for at least 2min to obtain the alloy melt.

[0028] As a preferred technical solution of the present invention, in step b, when hot rolling or hot extrusion is performed, the rolling or extrusion is repeated at least 3 times, and the amount of reduction deformation in each rolling or extrusion does not exceed 50%.

[0029] As a preferred technical solution of the present invention, in step b, during warm rolling, multiple passes and small reduction deformation are adopted; the warm rolling is repeated at least 3 times, and the reduction deformation in each pass does not exceed 30%.

[0030] The FeCrAl heat-resistant alloy for nuclear fuel cladding of this invention exhibits excellent comprehensive mechanical properties, high-temperature oxidation resistance, processing and forming performance, and structural stability. After process optimization, the alloy material of this invention has a room temperature tensile strength of not less than 500 MPa, a room temperature yield strength of not less than 400 MPa, and a total elongation after fracture of not less than 20%. In particular, the addition of a certain amount of rhenium to the FeCrAl alloy effectively suppresses or even eliminates the 475℃ brittleness problem of ferritic stainless steel, refines the alloy grains, and improves the alloy's mechanical properties, high-temperature oxidation resistance, and processing performance, making it a promising alternative to zirconium alloys as an accident-tolerant material. The preferred amount of rhenium is 0.5% to 5.0%. When the amount of Re is less than 0.5%, the room temperature yield strength is less than 400 MPa, the room temperature tensile strength is less than 500 MPa, the elongation after fracture is less than 25%, and the grain size is greater than 40 μm. When the Re content is higher than 5.0%, the material strength decreases. Furthermore, when the amount of Re is 0.5% to 1.0%, the grains are finer. When the amount of Re reaches 1.0%, the room temperature yield strength of the alloy is greater than 450 MPa, the tensile strength is greater than 610 MPa, the elongation after fracture is not less than 25%, and the generation of Cr-rich brittle phase at medium temperature of 475℃ is suppressed.

[0031] The FeCrAl alloy material with stable microstructure at medium temperature exhibits superior mechanical properties and high-temperature oxidation resistance compared to zirconium alloys. It can be used as a core component of nuclear reactors—nuclear fuel cladding tubes—and is also an ideal candidate material for nuclear fuel cladding to replace zirconium alloys in the future.

[0032] Compared with the prior art, the present invention has the following obvious and prominent substantive features and significant advantages:

[0033] 1. Compared with traditional zirconium alloy materials, the tin-containing heat-resistant ferritic stainless steel alloy material for nuclear energy of the present invention has excellent comprehensive mechanical properties, good structural stability, and easy processing and forming characteristics;

[0034] 2. The tin-containing heat-resistant ferritic stainless steel alloy material for nuclear fuel cladding of this invention, after being processed by hot forging, hot rolling or hot extrusion, annealing, warm rolling and recrystallization annealing, has a grain size of approximately 30 μm, a room temperature yield strength of 400-600 MPa, a room temperature tensile strength of 500-700 MPa, and a total elongation after fracture of 25-40%. It effectively suppresses the brittleness of FeCrAl alloy at 475℃ in the middle temperature, refines the grain, and improves the strength, high-temperature oxidation resistance, and processing performance of the alloy. It is also an ideal candidate material for nuclear fuel cladding to replace zirconium alloy in the future. Attached Figure Description

[0035] Figure 1 Metallographic images of the annealed state of Embodiment 1 and the comparative example without Re of the present invention. Detailed implementation method:

[0036] The above solution will be further described below with reference to specific embodiments. The preferred embodiments of the present invention are described in detail below:

[0037] Example 1:

[0038] In this embodiment, a method for preparing a medium-temperature structurally stable FeCrAl alloy material for nuclear fuel cladding includes the following steps:

[0039] a. The vacuum induction arc melting process is adopted. When preparing raw materials, the main raw material components are prepared according to the composition table in Table 1:

[0040] Table 1. Composition (wt.%)

[0041]

[0042] Place all the weighed raw materials after batching into a vacuum induction heating furnace, and evacuate the furnace to a vacuum level of 5×10⁻⁶. -4 Below Pa, high-purity argon gas is introduced as a protective gas; then the temperature is raised to 1630℃ at a heating rate of 200℃ / min and held for 2min to obtain the alloy melt.

[0043] b. Cast the alloy melt prepared in step a into shape; subject the cast alloy ingot to hot forging at 1200-1250℃, hot rolling at 1050-1180℃, warm rolling at 300-500℃ and recrystallization annealing at 950-1050℃ in sequence to finally obtain ferritic heat-resistant alloy pipes or plates with medium-temperature structure stability for nuclear fuel cladding.

[0044] In step b, when hot rolling or hot extrusion is performed, the rolling or extrusion is repeated at least 3 times, and the reduction deformation in each rolling or extrusion does not exceed 50%; when warm rolling is performed, multiple passes and small reduction deformation are used; the warm rolling is repeated at least 3 times, and the reduction deformation in each pass does not exceed 30%.

[0045] Experimental tests showed that the medium-temperature stable FeCrAl alloy prepared in this embodiment has a room temperature yield strength greater than 400 MPa, a room temperature tensile strength greater than 500 MPa, a fracture elongation greater than 25%, and a grain size less than 40 μm. The medium-temperature stable FeCrAl alloy prepared in this embodiment exhibits superior mechanical properties and high-temperature oxidation resistance compared to zirconium alloys. It can be used as a core component of nuclear reactors—nuclear fuel cladding tubes—and is also an ideal candidate material for future replacement of zirconium alloys for nuclear fuel cladding. The method in this embodiment suppresses high-temperature grain growth and the occurrence of brittleness at 475℃ in the medium temperature range. The addition of rhenium to the FeCrAl alloy also effectively improves the alloy's strength and microstructure.

[0046] Example 2:

[0047] In this embodiment, a method for preparing a medium-temperature structurally stable FeCrAl alloy material for nuclear fuel cladding includes the following steps:

[0048] a. The vacuum induction arc melting process is adopted. When preparing raw materials, the main raw material components are prepared according to the composition table in Table 2:

[0049] Table 2 Composition Table (wt.%)

[0050]

[0051] Place all the weighed raw materials after batching into a vacuum induction heating furnace, and evacuate the furnace to a vacuum level of 5×10⁻⁶. -4 Below Pa, high-purity argon gas is introduced as a protective gas; then the temperature is raised to 1650℃ at a heating rate of 200℃ / min and held for 2min to obtain the alloy melt.

[0052] b. This step is the same as in Example 1.

[0053] Experimental tests showed that the medium-temperature stable FeCrAl alloy prepared in this embodiment has a room temperature yield strength greater than 440 MPa, a room temperature tensile strength greater than 530 MPa, a fracture elongation greater than 30%, and a grain size of 38 μm. The medium-temperature stable FeCrAl alloy prepared in this embodiment exhibits superior mechanical properties and high-temperature oxidation resistance compared to zirconium alloys. It can be used as a core component of nuclear reactors—nuclear fuel cladding tubes—and is also an ideal candidate material for future replacement of zirconium alloys for nuclear fuel cladding. The method in this embodiment suppresses high-temperature grain growth and the occurrence of brittleness at 475℃ in the medium temperature range. The addition of rhenium to the FeCrAl alloy also effectively improves the alloy's strength and microstructure.

[0054] Example 3:

[0055] In this embodiment, a method for preparing a medium-temperature structurally stable FeCrAl alloy material for nuclear fuel cladding includes the following steps:

[0056] a. The vacuum induction arc melting process is adopted. When preparing raw materials, the main raw material components are prepared according to the composition table in Table 3:

[0057] Table 3. Composition Table (wt.%)

[0058]

[0059] Place all the weighed raw materials after batching into a vacuum induction heating furnace, and evacuate the furnace to a vacuum level of 5×10⁻⁶. -4Below Pa, high-purity argon gas is introduced as a protective gas; then the temperature is raised to 1680℃ at a heating rate of 200℃ / min and held for 2min to obtain the alloy melt.

[0060] b. This step is the same as in Example 1.

[0061] Experimental tests showed that the medium-temperature stable FeCrAl alloy prepared in this embodiment has a room temperature yield strength greater than 480 MPa, a room temperature tensile strength greater than 570 MPa, a fracture elongation greater than 30%, and a grain size of 35 μm. The medium-temperature stable FeCrAl alloy prepared in this embodiment exhibits superior mechanical properties and high-temperature oxidation resistance compared to zirconium alloys. It can be used as a core component of nuclear reactors—nuclear fuel cladding tubes—and is also an ideal candidate material for future replacement of zirconium alloys for nuclear fuel cladding. The method in this embodiment suppresses high-temperature grain growth and the occurrence of brittleness at 475℃ in the intermediate temperature range. The addition of rhenium to the FeCrAl alloy also effectively improves the alloy's strength and microstructure.

[0062] Example 4:

[0063] In this embodiment, a method for preparing a medium-temperature structurally stable FeCrAl alloy material for nuclear fuel cladding includes the following steps:

[0064] a. The vacuum induction arc melting process is adopted. When preparing raw materials, the main raw material components are prepared according to the composition table in Table 4:

[0065] Table 4. Composition Table (wt.%)

[0066]

[0067] Place all the weighed raw materials after batching into a vacuum induction heating furnace, and evacuate the furnace to a vacuum level of 5×10⁻⁶. -4 Below Pa, high-purity argon gas is introduced as a protective gas; then the temperature is raised to 1680℃ at a heating rate of 200℃ / min and held for 2min to obtain the alloy melt.

[0068] b. This step is the same as in Example 1.

[0069] Experimental tests showed that the medium-temperature stable FeCrAl alloy prepared in this embodiment has a room temperature yield strength greater than 560 MPa, a room temperature tensile strength greater than 630 MPa, a fracture elongation greater than 35%, and a grain size of 28 μm. The medium-temperature stable FeCrAl alloy prepared in this embodiment exhibits superior mechanical properties and high-temperature oxidation resistance compared to zirconium alloys. It can be used as a core component of nuclear reactors—nuclear fuel cladding tubes—and is also an ideal candidate material for future replacement of zirconium alloys for nuclear fuel cladding. The method in this embodiment suppresses high-temperature grain growth and the occurrence of brittleness at 475℃ in the intermediate temperature range. The addition of rhenium to the FeCrAl alloy also effectively improves the alloy's strength and microstructure.

[0070] Example 5:

[0071] In this embodiment, a method for preparing a medium-temperature structurally stable FeCrAl alloy material for nuclear fuel cladding includes the following steps:

[0072] a. The vacuum induction arc melting process is adopted. When preparing raw materials, the main raw material components are prepared according to the composition table in Table 5:

[0073] Table 5. Composition Table (wt.%)

[0074]

[0075] Place all the weighed raw materials after batching into a vacuum induction heating furnace, and evacuate the furnace to a vacuum level of 5×10⁻⁶. -4 Below Pa, high-purity argon gas is introduced as a protective gas; then the temperature is raised to 1650℃ at a heating rate of 200℃ / min and held for 2min to obtain the alloy melt.

[0076] b. This step is the same as in Example 1.

[0077] Experimental tests showed that the medium-temperature stable FeCrAl alloy prepared in this embodiment has a room temperature yield strength greater than 470 MPa, a room temperature tensile strength greater than 560 MPa, a fracture elongation greater than 30%, and a grain size of 25 μm. The medium-temperature stable FeCrAl alloy prepared in this example exhibits superior mechanical properties and high-temperature oxidation resistance compared to zirconium alloys. It can be used as a core component of nuclear reactors—nuclear fuel cladding tubes—and is also an ideal candidate material for future replacement of zirconium alloys in nuclear fuel cladding.

[0078] Example 6:

[0079] In this embodiment, a method for preparing a medium-temperature structurally stable FeCrAl alloy material for nuclear fuel cladding includes the following steps:

[0080] a. The vacuum induction arc melting process is adopted. When preparing raw materials, the main raw material components are prepared according to the composition table in Table 6:

[0081] Table 6. Composition Table (wt.%)

[0082]

[0083] Place all the weighed raw materials after batching into a vacuum induction heating furnace, and evacuate the furnace to a vacuum level of 5×10⁻⁶. -4 Below Pa, high-purity argon gas is introduced as a protective gas; then the temperature is raised to 1680℃ at a heating rate of 200℃ / min and held for 2min to obtain the alloy melt.

[0084] b. This step is the same as in Example 1.

[0085] Experimental tests showed that the medium-temperature stable FeCrAl alloy prepared in this embodiment has a room temperature yield strength greater than 520 MPa, a room temperature tensile strength greater than 610 MPa, a fracture elongation greater than 25%, and a grain size of 22 μm. The medium-temperature stable FeCrAl alloy prepared in this embodiment exhibits superior mechanical properties and high-temperature oxidation resistance compared to zirconium alloys. It can be used as a core component of nuclear reactors—nuclear fuel cladding tubes—and is also an ideal candidate material for future replacement of zirconium alloys for nuclear fuel cladding. The method in this embodiment suppresses high-temperature grain growth and the occurrence of brittleness at 475℃ in the intermediate temperature range. The addition of rhenium to the FeCrAl alloy also effectively improves the alloy's strength and microstructure.

[0086] Example 7:

[0087] In this embodiment, a method for preparing a medium-temperature structurally stable FeCrAl alloy material for nuclear fuel cladding includes the following steps:

[0088] a. The vacuum induction arc melting process is adopted. When preparing raw materials, the main raw material components are prepared according to the composition table in Table 7:

[0089] Table 7. Composition Table (wt.%)

[0090]

[0091] Place all the weighed raw materials after batching into a vacuum induction heating furnace, and evacuate the furnace to a vacuum level of 5×10⁻⁶. -4 Below Pa, high-purity argon gas is introduced as a protective gas; then the temperature is raised to 1670℃ at a heating rate of 200℃ / min and held for 2min to obtain the alloy melt.

[0092] b. Cast the alloy melt prepared in step a into shape; subject the cast alloy ingot to processes such as hot forging at 1200℃-1250℃, hot rolling at 1050℃-1180℃, warm rolling at 300℃-500℃, and recrystallization annealing at 950℃-1050℃ in sequence to finally obtain ferritic heat-resistant alloy pipes or plates with medium-temperature structure stability for nuclear fuel cladding.

[0093] Experimental tests showed that the medium-temperature stable FeCrAl alloy prepared in this embodiment has a room temperature yield strength greater than 500 MPa, a room temperature tensile strength greater than 600 MPa, a fracture elongation greater than 30%, and a grain size less than 25 μm. The medium-temperature stable FeCrAl alloy prepared in this embodiment exhibits superior mechanical properties and high-temperature oxidation resistance compared to zirconium alloys. It can be used as a core component of nuclear reactors—nuclear fuel cladding tubes—and is also an ideal candidate material for future replacement of zirconium alloys for nuclear fuel cladding. The method in this embodiment suppresses high-temperature grain growth and the occurrence of brittleness at 475℃ in the medium temperature range. The addition of rhenium to the FeCrAl alloy also effectively improves the alloy's strength and microstructure.

[0094] Example 8:

[0095] In this embodiment, a method for preparing a medium-temperature structurally stable FeCrAl alloy material for nuclear fuel cladding includes the following steps:

[0096] a. The vacuum induction arc melting process is adopted. When preparing raw materials, the main raw material components are prepared according to the composition table in Table 8:

[0097] Table 8. Composition Table (wt.%)

[0098]

[0099] Place all the weighed raw materials after batching into a vacuum induction heating furnace, and evacuate the furnace to a vacuum level of 5×10⁻⁶. -4 Below Pa, high-purity argon gas is introduced as a protective gas; then the temperature is raised to 1680℃ at a heating rate of 200℃ / min and held for 2min to obtain the alloy melt.

[0100] b. Cast the alloy melt prepared in step a into shape; subject the cast alloy ingot to processes such as hot forging at 1200℃-1250℃, hot rolling at 1050℃-1180℃, warm rolling at 300℃-500℃, and recrystallization annealing at 950℃-1050℃ in sequence to finally obtain ferritic heat-resistant alloy pipes or plates with medium-temperature structure stability for nuclear fuel cladding.

[0101] Experimental tests showed that the medium-temperature stable FeCrAl alloy prepared in this embodiment has a room temperature yield strength greater than 560 MPa, a room temperature tensile strength greater than 630 MPa, a fracture elongation greater than 35%, and a grain size less than 25 μm. The medium-temperature stable FeCrAl alloy prepared in this embodiment exhibits superior mechanical properties and high-temperature oxidation resistance compared to zirconium alloys. It can be used as a core component of nuclear reactors—nuclear fuel cladding tubes—and is also an ideal candidate material for future replacement of zirconium alloys for nuclear fuel cladding. The method in this embodiment suppresses high-temperature grain growth and the occurrence of brittleness at 475℃ in the intermediate temperature range. The addition of rhenium to the FeCrAl alloy also effectively improves the alloy's strength and microstructure.

[0102] The medium-temperature stable ferritic heat-resistant alloy materials for nuclear fuel cladding described in Examples 1 to 8 above have the following composition by mass percentage: C ≤ 0.02%, Cr: 9.8–11.8%, Al: 5.0–6.0%, Mo: 1.5–2.5%, Pr: 0.02–0.2%, Re: 0.5–5.0%, with the remainder being iron and unavoidable impurities. The grain size of the medium-temperature stable ferritic heat-resistant alloy materials for nuclear fuel cladding described in the above embodiments of the present invention is no greater than 22–40 μm. After batching and vacuum induction melting, the above embodiments of the present invention are cast and formed, and then subjected to continuous processes such as hot forging, hot rolling or extrusion, warm rolling, and recrystallization annealing to finally obtain the medium-temperature stable ferritic heat-resistant alloy material for nuclear fuel cladding. The present invention effectively solves the problem of brittleness of ferritic heat-resistant alloys at 475℃ in the medium temperature range, improves the mechanical properties, high-temperature resistance, and hot working properties of the alloy, refines the grains, and improves the alloy microstructure. Through extensive experimental research, this invention has discovered that FeCrAl heat-resistant alloy materials with stable microstructure at medium temperatures can serve for extended periods under nuclear reactor operating conditions, ensuring the stable operation of nuclear reactors.

[0103] The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments. Various changes can be made according to the purpose of the invention. Any changes, modifications, substitutions, combinations or simplifications made based on the spirit and principle of the technical solution of the present invention shall be equivalent substitutions. As long as they meet the purpose of the invention and do not deviate from the technical principle and inventive concept of the medium-temperature stable ferritic heat-resistant alloy material for nuclear fuel cladding, they shall fall within the protection scope of the present invention.

Claims

1. A medium temperature, microstructurally stable, ferritic heat resistant alloy material for nuclear fuel cladding, characterized by: Its composition is as follows by mass percentage: C≤0.02%, Cr:9.8~11.8%, Al:5.0~6.0%, Mo:1.5~2.5%, Pr:0.02~0.2%, Re:0.5~5.0%, with the remainder being iron and unavoidable impurities.

2. The medium temperature, microstructurally stable ferritic heat resistant alloy material for nuclear fuel cladding according to claim 1, characterized in that, Its composition is as follows by mass percentage: C≤0.01%, Cr: 9.8~11.8%, Al: 5.0~5.3%, Mo: 1.8~2.0%, Pr: 0.02~0.2%, Re: 0.5~5.0%, with the remainder being iron and unavoidable impurities.

3. The medium temperature, microstructurally stable ferritic heat resistant alloy material for nuclear fuel cladding of claim 1, wherein, Its room temperature tensile strength is not less than 500 MPa, its room temperature yield strength is not less than 400 MPa, and its total elongation after fracture is not less than 20%.

4. The medium temperature, microstructurally stable ferritic heat resistant alloy material for nuclear fuel cladding according to claim 3, characterized in that, Its room temperature tensile strength is 500-700 MPa, its room temperature yield strength is 400-600 MPa, and its total elongation after fracture is 25-40%.

5. The medium temperature, microstructurally stable, ferritic heat resistant alloy material for nuclear fuel cladding of claim 1, wherein Its grain size is no greater than 30μm.

6. A method of producing the medium temperature, microstructurally stable ferritic heat resistant alloy material for nuclear fuel cladding as claimed in claim 1, characterized by: Includes the following steps: a. Alloy smelting: The process employs vacuum induction melting. During raw material preparation, the raw materials are proportioned as follows by mass percentage: C ≤ 0.02%, Cr: 9.8–11.8%, Al: 5.0–6.0%, Mo: 1.5–2.5%, Pr: 0.02–0.2%, Re: 0.5–5.0%, with the remainder being iron and unavoidable impurities. All the weighed raw materials are then subjected to vacuum induction melting to obtain the alloy melt. b. Alloy solidification: The alloy melt prepared in step a is cast into shape; the alloy ingot obtained by casting is subjected to hot forging at 1200-1250℃, hot rolling or hot extrusion at 1050-1180℃, warm rolling at 300-500℃ and recrystallization annealing at 950℃-1050℃ in sequence to finally obtain ferritic heat-resistant alloy pipes or plates with medium temperature structure stability for nuclear fuel cladding.

7. The method for preparing the medium-temperature microstructure stable ferritic heat-resistant alloy material for nuclear fuel cladding according to claim 6, characterized in that, In step a, the raw material components are prepared according to the following mass percentages: C ≤ 0.01%, Cr: 9.8-11.8%, Al: 5.0-5.3%, Mo: 1.8-2.0%, Pr: 0.02-0.2%, Re: 0.5-5.0%, and the remainder is iron and unavoidable impurities.

8. The method of producing a medium temperature, microstructurally stable ferritic heat resistant alloy material for nuclear fuel cladding according to claim 6, characterized by, In step a), a vacuum induction melting process is used. All the raw materials weighed after batching are placed into a vacuum induction heating furnace, and a vacuum of 5×10⁻⁶ is drawn. -4 Below Pa, high-purity argon gas is introduced as a protective gas; then the temperature is raised to not less than 1600℃ at a heating rate of not less than 200℃ / min, and held for at least 2min to obtain the alloy melt.

9. The method of producing a medium temperature, microstructurally stable ferritic heat resistant alloy material for nuclear fuel cladding according to claim 6, characterized by, In step b, when hot rolling or hot extrusion is performed, the rolling or extrusion is repeated at least 3 times, and the amount of reduction deformation in each rolling or extrusion does not exceed 50%.

10. The method of producing a medium temperature, microstructurally stable ferritic heat resistant alloy material for nuclear fuel cladding according to claim 6, characterized by, In step b, during warm rolling, multiple passes with small reductions are used for deformation; the warm rolling is repeated at least 3 times, and the reduction deformation in each pass does not exceed 30%.

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