Nuclear high-temperature-resistant radiation-resistant ODS ferrite alloy and preparation method of tubular product thereof

Abstract

The invention relates to the technical field of nuclear energy fuel cladding materials, in particular to a nuclear high-temperature-resistant and radiation-resistant ODS ferrite alloy and a preparation method of a pipe of the nuclear high-temperature-resistant and radiation-resistant ODS ferrite alloy. The ODS ferrite alloy comprises the following components in percentage by mass: 11.0 to 15.0 percent of Cr, 1.0 to 3.0 percent of W, 0.1 to 1.0 percent of Mn, 0.0 to 0.6 percent of Ta, 0.2 to 0.6 percent of Ti, 0.15 to 0.5 percent of Y, 0.11 to 0.26 percent of O and Clt, 0.1%, Zirt; %, 0.01%, Allt; the mass ratio of Y to Ti is equal to 0.4-1.0, and the pipe is prepared by adopting the processes of hot forging, low-temperature quick forging and room-temperature rolling. The ODS ferrite alloy and the pipe thereof provided by the invention have a microstructure with fine grains and uniformly distributed nano oxides, the alloy and the pipe have excellent high-temperature mechanical properties, the quality of the inner surface and the outer surface of the pipe is good, and the linear precision is high.

Description

Technical Field

[0001] This invention relates to the field of nuclear fuel cladding materials, specifically to a method for preparing a high-temperature and radiation-resistant ODS ferritic alloy for nuclear use and its tubing, which meets the performance requirements of structural materials in strong neutron and high-temperature nuclear environments. Background Technology

[0002] Advanced nuclear power equipment is essential for building a strong nuclear power nation, and high-temperature and radiation-resistant structural materials are fundamental to ensuring the operation of advanced nuclear energy systems. Currently, based on its mastery of the third-generation hard-core technologies of Hualong One and Guohe One, my country is vigorously deploying fourth-generation nuclear energy equipment such as high-temperature gas-cooled reactors, sodium-cooled fast reactors, and integrated fast reactors. Advanced fourth-generation nuclear energy equipment means higher operating temperatures (>600℃) and stronger neutron radiation (>100dPa). At this point, traditional austenitic stainless steel, ferritic stainless steel, and ferritic / martensitic stainless steel are no longer suitable. Oxide dispersion-strengthened (ODS) ferritic alloys, due to their excellent high-temperature mechanical properties, high-temperature radiation resistance, and high-temperature corrosion resistance, have become the most promising cladding and structural materials for advanced nuclear energy systems.

[0003] The excellent properties of ODS alloys are inseparable from the dispersed distribution of nano-oxides in the matrix: the nano-oxides are uniformly distributed and in sufficiently high quantities, >10 23 m -3 Only by effectively pinning grain boundaries and dislocation movement can the high-temperature resistance of ODS alloys be achieved. The small size of the nano-oxide particles, ≤5nm, is essential to provide sufficient oxide / matrix interfaces to effectively capture irradiated atoms and defects, suppressing irradiation embrittlement, hardening, and swelling, thus ensuring the radiation resistance of ODS alloys. However, during the tube rolling process, mechanisms such as grain boundary dragging and dislocation cutting can cause dissolution-re-precipitation and Ostwald coarsening of nano-oxides, leading to an increase in the size of nano-oxides in the finished ODS tubes, reaching approximately 10nm or even exceeding 100nm. This results in a loss of the high-temperature mechanical properties and high-temperature radiation swelling resistance of the ODS material, reducing the safety and economy of nuclear power system operation.

[0004] Existing ODS steels (such as CN110863152A and CN111057958A) are mostly designed with FeCrAl-based alloys, adding high Al content (3.0-5.5%) to improve high-temperature oxidation resistance, and Zr (0.1-1.0%) to refine grain size. However, Al and Zr easily form large-sized oxides (often 50-100 nm in diameter) such as Y-Al-O, Y-Zr-O, ZrO2, and Al2O3 with Y, which cannot provide a strengthening effect. In existing pipe manufacturing processes, CN116926401A is rolled at 550-650℃ (35-45% deformation per pass). High temperature and large deformation can easily lead to the dissolution of nano-oxides through dislocation cutting mechanisms. The cold rolling deformation of CN114134429A reaches 5-30%, and the intermediate annealing temperature range is wide (700-1200℃), which easily causes Ostwald coarsening of nano-oxides (the size of nano-oxides in the finished product often reaches more than 10nm).

[0005] Therefore, how to manufacture high-temperature and radiation-resistant ODS alloys and their tubing through precise composition design and process innovation, solve the problems of directional generation of nano-oxides in ODS alloys and non-coarsening during deformation, and achieve simultaneous improvement in high-temperature mechanical properties, radiation resistance and forming quality of tubing has become a technical bottleneck that urgently needs to be overcome. Summary of the Invention

[0006] In view of the above background, the present invention aims to provide a method for preparing nuclear high-temperature and radiation-resistant ODS ferritic alloy and its tubing, solving the problems of dissolution, growth, and coarsening of nano-oxides in the deformation process, and achieving simultaneous improvement in the strength, plasticity, toughness and radiation resistance of ODS tubing.

[0007] The technical solution involved in this invention is as follows:

[0008] A nuclear-grade high-temperature and radiation-resistant ODS ferritic alloy, wherein the composition of the ODS ferritic alloy, by mass percentage, includes: Cr 11.0–15.0%, W 1.0–3.0%, Mn 0.1–1.0%, Ta 0.0–0.6%, Ti 0.2–0.6%, Y 0.15–0.5%, O 0.11–0.26%, C < 0.1%, Zr < 0.01%, Al < 0.02%, Fe balance, and the mass ratio of Y to Ti is Y / Ti = 0.4–1.0.

[0009] The aforementioned nuclear-grade high-temperature and radiation-resistant ODS ferritic alloy, by mass percentage, comprises: Cr 11.5–14.0%, W 1.0–2.0%, Mn 0.2–0.6%, Ta 0.1–0.3%, Ti 0.25–0.45%, Y 0.2–0.35%, O 0.12–0.22%, C < 0.07%, Zr < 0.001%, Al < 0.01%, Fe balance, and the mass ratio of Y to Ti is Y / Ti = 0.5–0.8.

[0010] A method for preparing a nuclear-grade high-temperature resistant and radiation-resistant ODS ferritic alloy tubing includes the following steps:

[0011] Step 1: Prepare iron-based powder as a pre-alloyed powder;

[0012] Step 2: After mixing the pre-alloyed powder with the oxide powder, mechanical ball milling is performed to achieve mechanical alloying of the powder;

[0013] Step 3: Use mild steel to make a sleeve, put the ball mill powder obtained in step 2 into the sleeve, degas it under vacuum, and then solidify it by hot isostatic pressing to obtain ODS alloy ingot blank.

[0014] Step four: The ODS alloy ingot with the cladding removed is subjected to high-temperature forging;

[0015] Step 5: The high-temperature forged ODS bar is subjected to low-temperature rapid forging, followed by heat treatment of the ODS bar, and then drilling to produce ODS tube blanks.

[0016] Step 6: The ODS tube blank is processed using a room temperature rolling + vacuum annealing process to obtain the finished ODS tube.

[0017] In the preparation method of the nuclear high-temperature resistant and radiation-resistant ODS ferritic alloy pipe, in step one, the iron-based powder is Fe-Cr-W-Mn-Ta-Ti-Y pre-alloyed powder.

[0018] In the preparation method of the nuclear high-temperature resistant and radiation-resistant ODS ferritic alloy tubing, in step two, the oxide powder used for mixing and ball milling is one or more of iron oxide, chromium oxide and yttrium oxide, the particle diameter of the pre-alloyed powder and oxide powder is less than 150 μm, and the mechanical ball milling is carried out under the protection of high-purity argon gas.

[0019] In the preparation method of the nuclear high-temperature resistant and radiation-resistant ODS ferritic alloy tubing, in step three, the cladding material is Q235 or 304 stainless steel; the vacuum degassing conditions are: based on the powder packaging volume, the system vacuum degree is not less than 10... -3 Under Pa conditions and at temperatures of 200–500℃, vacuum for 3–60 hours.

[0020] In the preparation method of the nuclear high-temperature resistant and radiation-resistant ODS ferritic alloy tubing, in step four, the high-temperature forging temperature is 900-1200℃, and the forging ratio is not less than 5.

[0021] In the preparation method of the nuclear high temperature resistant and radiation resistant ODS ferritic alloy tubing, in step five, the low temperature rapid forging of the bar is a rotary forging process, the rotary forging is carried out at a temperature below 300°C, and the forging ratio is not less than 1.5; the ODS bar is heat-treated before drilling at a temperature of 750-1050°C for a holding time of 40-120 minutes.

[0022] In the preparation method of the nuclear high-temperature resistant and radiation-resistant ODS ferritic alloy tube, in step six, the linear speed of the rolls rolled at room temperature is 10-40 mm / s, the deformation per pass is 10-25%, and the elongation coefficient is not greater than 1.5; the vacuum annealing is an intermediate pass annealing, the temperature is 800-1150℃, and the holding time is 30-120 minutes.

[0023] The design concept of this invention is:

[0024] The superior mechanical properties of the ODS ferritic alloy of this invention originate from the dispersed Y-Ti-O phase nanoparticles in the matrix. Compared to the orthorhombic Y2TiO5 and cubic YTiO3 nano-oxides, the pyrochlore-structured Y2Ti2O7 exhibits superior chemical and structural inertness, which helps the ODS alloy maintain long-term high-temperature strength and high-temperature radiation resistance. Based on traditional nuclear structural materials, this invention makes micro-adjustments to the matrix composition of the ODS alloy, specifically proposing the control of the Y / Ti content to achieve high number-density precipitation of small-sized Y2Ti2O7 nano-oxides in the alloy. Simultaneously, this invention proposes the control of Zr and Al element content to avoid the potential threat to alloy performance from the precipitation of large-sized Y-Zr-O phases, Y-Al-O phases, ZrO2, and Al2O3 oxides.

[0025] The tubes of this invention are manufactured using a hot forging + low-temperature fast forging + room-temperature rolling process. Low-temperature rotary forging + cold rolling is a key step in ensuring the dimensional accuracy and mechanical properties of the ODS tubes. Adding a rotary forging process before tube rolling refines the grains and increases the viscosity of the grain boundaries, reducing the risk of grain boundary cracking due to nano-oxide pinning during subsequent tube rolling, thus promoting defect-free ODS tube fabrication. Simultaneously, the lower rolling rate and smaller per-pass deformation in the tube rolling process reduce or even eliminate the probability of small-sized nano-oxides being cut and dissolved; combined with a lower intermediate annealing temperature, it releases rolling deformation stress and suppresses the potential risks of dissolution-re-precipitation and Ostwald coarsening of nano-oxides, achieving efficient fabrication of ODS tubes with dispersed distribution of small-sized nano-oxides.

[0026] The advantages and beneficial effects of this invention are:

[0027] 1. This invention provides an ODS alloy whose reinforcing phase is mainly Y2Ti2O7 nanoparticles. By strictly controlling the matrix composition of Y, Ti, Zr, Al elements and the Y / Ti ratio, it ensures that structurally stable, small-sized (average diameter ~2.5nm) Y2Ti2O7 nano-oxides precipitate at high density in the alloy matrix, meeting the stringent requirements of ODS ferritic alloys in terms of material microstructure stability, mechanical properties, and radiation swelling resistance under high temperature and strong neutron environments.

[0028] 2. This invention provides a method for preparing pipes without the coarsening of nano-oxides during deformation. Utilizing low-temperature rapid forging and room-temperature rolling processes, by controlling the deformation amount and rate of each pass and the intermediate annealing process (with the intermediate annealing temperature limited to 800–1150℃), rolling stress is effectively released while avoiding Ostwald coarsening of nano-oxides caused by high temperatures. This ensures the small size of nano-oxides in the finished pipe. Room-temperature rolling combined with a small deformation amount (10–25%) and a low rolling speed (10–40 mm / s) minimizes the damage to nano-oxides caused by dislocation cutting, preventing the dissolution of nanoparticles and achieving small size (average diameter ≤ 5 nm) and high number density (number density ≥ 1 × 10⁻⁶). 23 m -3 The Y2Ti2O7 nano-oxide is dispersed in the thin-walled tube, achieving a balance between the strength and toughness of the ODS tube under high temperature and strong radiation service environment. Attached Figure Description

[0029] Figure 1 This is a transmission electron microscope (TEM) image of the distribution of nano-reinforcing phases in the hot isostatically pressed ODS ferrite alloy of Example 1.

[0030] Figure 2 This is a high-resolution TEM (HRTEM) image of nano-oxides in the hot isostatically pressed ODS ferrite alloy of Example 1.

[0031] Figure 3 This is the Fourier transform diffraction pattern of nano-oxides in the hot isostatically pressed ODS ferrite alloy of Example 1.

[0032] Figure 4 This is the tensile curve of the ODS ferritic alloy in Example 2 at 700°C.

[0033] Figure 5 This is the creep curve of the ODS ferritic alloy in Example 2 under a load of 800℃ and 200MPa. The arrow indicates that the creep test is still ongoing and the sample has not broken.

[0034] Figure 6This is a diagram of the ODS ferritic alloy tube blank in Example 3.

[0035] Figure 7 This is a diagram of the finished ODS pipe from Example 3.

[0036] Figure 8 This is a diagram of the finished ODS pipe from Example 4.

[0037] Figure 9 This is a transmission electron microscope (TEM) image of the distribution of nano-oxides in the finished ODS pipe material in Example 4. Detailed Implementation

[0038] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0039] Example 1

[0040] A pre-alloyed powder with the composition (mass percentage, the same below) of Fe-11.5Cr-1.8W-0.4Mn-0.18Ta-0.05C-0.25Ti-0.2Y was prepared. After sieving, 1 kg of pre-alloyed powder with a size less than 150 μm was mixed with 4.0 g of Cr2O3 powder with a size of 100 μm, and ball-milled using a high-energy ball mill under the protection of high-purity argon gas (volume purity of 99.999%) to achieve mechanical alloying of the powder. Then, a package for encapsulating the powder was prepared using Q235 stainless steel. After the ball-milled powder was loaded, it was degassed at room temperature for 4 hours + degassed at 450℃ for 3 hours, and then vacuum-sealed. The encapsulated powder was cured by hot isostatic pressing at high temperature and high pressure to obtain an ODS alloy. The composition of the ODS alloy, by mass percentage, is Fe-11.5Cr-1.8W-0.4Mn-0.18Ta-0.05C-0.25Ti-0.25Y2O3.

[0041] like Figure 1 As shown, after hot isostatic pressing (HIP), nano-oxides are dispersed and precipitated within the ODS alloy. The nano-oxides are small in size, with particle diameters concentrated between 1.5 and 4.0 nm, resulting in an average particle diameter of 2.46 nm. Figures 2-3 As shown, when an arbitrary nano-oxide is selected under the HRTEM field of view, its diffraction spots after Fourier transform prove that the nano-oxide is a Y2Ti2O7 oxide particle.

[0042] Example 2

[0043] According to the alloy composition ratio, a pre-alloyed powder with the composition Fe-13.5Cr-2.0W-0.3Mn-0.08Ta-0.35Ti-0.1Y was prepared. After sieving, 3 kg of pre-alloyed powder with a size less than 100 μm was mixed with 5.8 g of Y2O3 powder with a size of 50–100 nm. The powder was then ball-milled under the protection of high-purity argon gas (volume purity 99.999%) using a high-energy ball mill to achieve mechanical alloying of the powder. A casing for encapsulating the powder was prepared using 304 stainless steel. After the ball-milled powder was loaded, the casing was degassed at room temperature for 6 hours and then at 400℃ for 8 hours. The casing was then welded to achieve a vacuum seal. The ODS ferritic alloy with the composition Fe-13.5Cr-2.0W-0.3Mn-0.08Ta-0.35Ti-0.3Y2O3 was obtained by high-temperature and high-pressure curing using hot isostatic pressing. Afterwards, the cladding is removed, and the alloy is hot-forged at 1050°C. The bar stock has a forging ratio of 6.

[0044] High-temperature instantaneous and long-term mechanical property tests were conducted on the forged bars. For example... Figure 4 As shown, the yield strength at 700℃ is 393±10MPa, the tensile strength is 458±4MPa, and the alloy also exhibits good plasticity with an elongation of 26±3%. Figure 5 As shown, creep performance tests were conducted on the ODS alloy at 800℃ and 200MPa. After 8000h of loading, the sample still did not fracture. The fine and dispersed nano-oxides of the alloy have a strong pinning effect on dislocations and grain boundaries during high-temperature deformation, which significantly enhances the high-temperature mechanical properties of the ferritic alloy.

[0045] Example 3

[0046] The 30mm diameter ODS alloy bar from Example 2 was annealed again at 1000℃ for 1 hour, and then processed using a rotary forging process, i.e., low-temperature rapid forging at room temperature, to form... The billets are approximately [size missing]. After heat treatment at 1000℃ for 1 hour, surface defects are removed by turning, and holes are drilled to obtain [the desired shape / finish]. Figure 6 shown Tube blank.

[0047] The drilled tube blank is cold-rolled using a three-roll mill, with the deformation per pass controlled at approximately 15%. The intermediate annealing process is vacuum, 980℃, and 1 hour. After multiple rolling passes, the desired result is obtained as shown below. Figure 7 The dimensions shown are ODS pipes.

[0048] Example 4

[0049] According to the alloy composition ratio, a pre-alloyed powder with the composition Fe-12.5Cr-2.0W-0.5Mn-0.15Ta-0.03C-0.45Ti-0.35Y was prepared. After sieving, 5 kg of pre-alloyed powder with a size less than 150 μm was mixed with 5.0 g of Fe2O3 powder with a size less than 150 μm, and the powder was ball-milled using a high-energy ball mill under the protection of high-purity argon gas (volume purity of 99.999%). A casing for encapsulating the powder was prepared using Q235 stainless steel. After the ball-milled powder was loaded, the mixture was degassed at room temperature for 8 hours + at 480℃ for 15 hours, and then the casing was welded to complete the vacuum encapsulation of the powder. ODS ferritic alloy with the composition Fe-12.5Cr-2.0W-0.5Mn-0.15Ta-0.03C-0.45Ti-0.45Y2O3 was obtained by high-temperature and high-pressure curing using hot isostatic pressing. Then, the cladding is removed, and the alloy is hot-forged at 1150°C. The forging ratio of the bar stock is controlled at 9. After annealing the ODS alloy bars at 1000℃ for 1 hour, the bars are then machined using a rotary forging process, i.e., low-temperature rapid forging at 200℃. Then, heat-treated at 1000°C. After 1 hour of bar milling, surface defects on the heat-treated bar mill are removed by auxiliary turning process, followed by drilling to obtain the desired product. Tube blank.

[0050] The drilled tube blank is cold-rolled using a three-roll mill, with each pass deforming no more than 20%. The intermediate annealing process is vacuum, 1040℃, 1 hour. After multiple rolling passes, the tube blank is obtained as shown in the figure. Figure 8 The dimensions shown are ODS pipes. For example... Figure 9 As shown, transmission electron microscopy (TEM) observation of the ODS tube revealed that the nano-oxide particles within the tube were small in size and diffusely distributed, with no coarsened oxide particles at the grain boundaries. The average oxide particle size was 3.4 nm, and the volume number density was (7.5–8.6) × 10⁻⁶. 23 m -3 The abundance of nano-oxides provides a large number of oxide / matrix interfaces, which can provide sufficient absorption sites for irradiation-induced defects and ex-situ atoms, giving ODS tubing a good advantage in radiation resistance.

[0051] The results show that the ODS ferritic alloy and its tubing provided by this invention have a microstructure with fine grains and uniform distribution of nano-oxides; the alloy and tubing have excellent high-temperature mechanical properties, with a creep life of >13000h at 650℃ and 300MPa and a creep life of >8000h at 800℃ and 200MPa; the tubing has good internal and external surface quality and high straightness accuracy; the average particle size of the nano-oxides inside the tubing is ≤5nm, providing sufficient absorption sites for irradiation-induced defects and ex-situ atoms, resulting in strong irradiation resistance.

[0052] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable researchers skilled in this art to understand the content of the present invention and implement it accordingly. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A high temperature and radiation resistant ODS ferritic alloy for nuclear applications, characterized in that, The ODS ferrite alloy comprises, by mass percent: Cr 11.0-15.0%, W 1.0-3.0%, Mn 0.1-1.0%, Ta 0.0-0.6%, Ti 0.2-0.6%, Y 0.15-0.5%, O 0.11-0.26%, C <0.1%, Zr <0.01%, Al <0.02%, Fe balance, and the mass ratio of Y to Ti Y / Ti = 0.4-1.

0.

2. The high temperature radiation resistant ODS ferritic alloy for nuclear applications of claim 1, wherein, The ODS ferrite alloy comprises, by mass percent: Cr 11.5-14.0%, W 1.0-2.0%, Mn 0.2-0.6%, Ta 0.1-0.3%, Ti 0.25-0.45%, Y 0.2-0.35%, O 0.12-0.22%, C <0.07%, Zr <0.001%, Al <0.01%, Fe balance, and the mass ratio of Y to Ti Y / Ti = 0.5-0.

8.

3. A method of producing the nuclear high-temperature and radiation resistant ODS ferritic alloy pipe material according to claim 1 or 2, characterized by, The method comprises the following steps: Step one, preparing an iron-based powder as a pre-alloyed powder; Step two, mixing the pre-alloyed powder with an oxide powder and then performing mechanical ball milling to realize mechanical alloying of the powder; Step three, using soft steel to make a package, loading the ball-milled powder obtained in step two into the package, performing vacuum degassing, and then performing hot isostatic pressing to obtain an ODS alloy ingot; Step four, high-temperature forging the ODS alloy ingot after removing the package; Step five, low-temperature fast forging the ODS rod after high-temperature forging, then performing heat treatment on the ODS rod, and then drilling the ODS rod to obtain an ODS tube blank; Step six, processing the ODS tube blank using a room-temperature rolling + vacuum annealing process to obtain an ODS finished tube.

4. The method of producing a high-temperature and radiation resistant ODS ferritic alloy pipe for nuclear use according to claim 3, characterized by, In step one, the iron-based powder is a Fe-Cr-W-Mn-Ta-Ti-Y pre-alloyed powder.

5. The method of making a nuclear grade high temperature and radiation resistant ODS ferritic alloy tubing of claim 3, wherein, In step two, the oxide powder used for mixing and ball milling is one or more than two of iron oxide, chromium oxide and yttrium oxide, the particle diameter of the pre-alloyed powder and the oxide powder is less than 150 μm, and the mechanical ball milling is performed under high-purity argon protection.

6. The method of making a nuclear grade high temperature radiation resistant ODS ferritic alloy tubing of claim 3, wherein, In step three, the sheath material is Q235 or 304 stainless steel; the vacuum degassing conditions are: according to the powder packaging volume, the system vacuum degree is not less than 10 -3 Pa, and the temperature is 200-500℃, and the degassing time is 3-60h.

7. The method of making a nuclear grade high temperature and radiation resistant ODS ferritic alloy tubing of claim 3, wherein, In step four, the high-temperature forging temperature is 900-1200 °C, and the forging ratio is not less than 5.

8. The method of making a nuclear grade high temperature and radiation resistant ODS ferritic alloy tubing of claim 3, wherein, In step five, the low-temperature fast forging of the rod is a rotary forging process, the rotary forging is performed at a temperature lower than 300 °C, the forging ratio is not less than 1.5, the ODS rod is heat treated before drilling, the temperature is 750-1050 °C, and the holding time is 40-120 minutes.

9. The method of making a nuclear grade high temperature and radiation resistant ODS ferritic alloy tubing of claim 3, wherein, In step six, the roller linear speed of the room-temperature rolling is 10-40 mm / s, the deformation per pass is 10-25%, and the elongation coefficient is not greater than 1.5; the vacuum annealing is intermediate pass annealing, the temperature is 800-1150 °C, and the holding time is 30-120 minutes.

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