Method for eliminating helium bubble defect in nuclear power steel and product
The pulsed current treatment method eliminates helium bubble defects in nuclear power steel, solves the problem of material thermal aging caused by high-temperature annealing, and achieves low-cost and rapid dynamic self-healing effect.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- UNIV OF SCI & TECH BEIJING
- Filing Date
- 2026-01-14
- Publication Date
- 2026-04-21
AI Technical Summary
Existing technologies are insufficient to effectively eliminate helium bubble defects in nuclear power steel, and high-temperature annealing leads to thermal aging of the material, resulting in high costs and difficulty in in-situ repair.
By employing a pulsed current processing method, and controlling the current density, frequency, pulse width, and temperature, the helium bubble is eliminated through the current bypass effect, thereby achieving dynamic self-repair.
It can rapidly eliminate helium bubbles at low temperatures, avoid thermal aging of materials, restore material hardness, and is suitable for in-situ repair of large nuclear power components.
Smart Images
Figure CN121896437A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of nuclear material damage repair technology, specifically relating to a method and product for eliminating helium bubble defects in nuclear power steel. Background Technology
[0002] In the operational environments of nuclear fusion reactors and advanced fission reactors, nuclear structural materials (such as 316 series austenitic stainless steel and Z3CN20.09M cast duplex stainless steel) are subjected to prolonged and intense irradiation by high-energy neutrons and ions. During neutron irradiation, (n, a) nuclear transmutation reactions occur within the material, producing a large number of helium (He) atoms. Due to the extremely low solubility of helium in the metallic matrix, these helium atoms tend to trap vacancies, rapidly agglomerating into stable helium-vacancy clusters, and further evolving into high-density nanoscale helium bubbles. These helium bubbles exert a strong pinning effect within the material, hindering dislocation movement and leading to significant radiation hardening and high-temperature helium embrittlement. For austenitic-ferritic duplex stainless steel, helium bubbles are also prone to segregation at phase boundaries, inducing intergranular fracture and seriously threatening the safe operation of critical nuclear power plant components (such as main pipelines and reactor internals) throughout their entire service life.
[0003] Currently, the repair of irradiation damage mainly relies on traditional thermal annealing techniques. However, this method has significant limitations in eliminating helium bubbles. Helium bubbles exhibit extremely high thermal stability, typically requiring materials to be heated to above 800°C and held at that temperature for an extended period to induce their dissociation or migration. However, for duplex stainless steel commonly used in nuclear power plants, prolonged exposure to the 700°C to 850°C temperature range induces severe thermal aging effects, leading to the precipitation of brittle phases such as sigma, chi, or Cr-rich phases, which degrades material properties and impairs corrosion resistance. Furthermore, traditional high-temperature annealing is insufficient for in-situ repair of large, already installed components, necessitating reactor shutdown and dismantling, resulting in extremely high engineering costs and time consumption. Therefore, developing a rapid, low-heat-budget, and efficient helium bubble elimination technology is a critical challenge for the industry. Summary of the Invention
[0004] To address the existing problems, this invention provides a method and product for eliminating helium bubble defects in nuclear power steel. This addresses the issues in the prior art where helium bubbles are difficult to eliminate through traditional low-temperature annealing, while high-temperature annealing easily induces thermal aging and embrittlement in duplex stainless steel.
[0005] A method for eliminating helium bubble defects in nuclear power steel, the method comprising treating the nuclear power steel, which has been damaged by helium ion irradiation resulting in helium bubble aggregation and surface hardening, with pulsed current treatment to eliminate helium bubble defects and restore its surface hardness, and to achieve dynamic self-repair of the irradiation-damaged structure of the nuclear power steel.
[0006] In addition to the aspects and any possible implementations described above, a further implementation is provided, wherein the method includes the following steps: S1. Conduct a distribution assessment of nuclear power steel samples damaged by helium ion irradiation and set the working parameters of the pulse current and the corresponding energizing time based on the assessment results; S2. Connect the nuclear power steel sample to be repaired to a pulse power supply, apply a pulse current with set working parameters under the set conditions until the predetermined power-on processing time is reached, and obtain the repaired nuclear power steel sample. S3. The repaired nuclear power steel samples were subjected to hardness testing and transmission electron microscopy observation, and compared with the original nuclear power steel samples before repair to evaluate the helium bubble elimination effect and the degree of material hardness recovery.
[0007] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the nuclear power steel includes austenitic stainless steel, austenitic-ferritic duplex stainless steel, ferritic or martensitic stainless steel, nickel-based alloys or molybdenum-rhenium alloys.
[0008] In addition to the aspects described above and any possible implementations, an implementation is further provided in which the operating parameters include processing temperature, current density, pulse frequency, and pulse width.
[0009] In addition to the aspects described above and any possible implementations, a further implementation is provided in which the processing temperature is 100–650°C and the current density is 1.0 × 10⁻⁶. 3 ~2.0×10 4 A / mm 2 The pulse frequency is 50–1000 Hz, the pulse width is 50–500 μs, and the processing time is 10 s–30 min.
[0010] In addition to the aspects and any possible implementations described above, a further implementation is provided, wherein the evaluation results include mild damage and severe damage, wherein mild damage is defined as a surface hardening rate of less than 50% for nuclear power steel samples, or an average helium bubble diameter of less than 2 nm, and the operating parameters used include: processing temperature [100, 300] °C, current density [1.0 × 10⁻⁶]. 3 1.0×10 4 A / mm 2 The pulse frequency is [50, 200] Hz, the pulse width is [200, 500] μs, and the processing time is [15, 30] min.
[0011] Severe damage is defined as a surface hardening rate of ≥50% for nuclear power steel samples, or the presence of significant helium bubble aggregation or a helium bubble size ≥2 nm. The operating parameters used include: processing temperature (300-650℃), current density (1.0×10⁻⁶ / ℃).4 2.0×10 4 A / mm 2 , pulse frequency (200, 1000) Hz, pulse width [50~200) μs, processing time [10s, 15min).
[0012] In addition to the aspects described above and any possible implementations, a further implementation is provided in which the processing temperature is 200°C and the current density is 8.0 × 10⁻⁶. 3 A / mm 2 The pulse frequency was 100Hz, the pulse width was 300μs, and the processing time was 20min.
[0013] In addition to the aspects described above and any possible implementations, a further implementation is provided in which the processing temperature is 350°C and the current density is increased to 1.2 × 10⁻⁶. 4 A / mm 2 The pulse frequency was 600 Hz, the pulse width was 100 μs, and the processing time was 5 min.
[0014] In addition to the aspects described above and any possible implementations, a further implementation is provided in which the processing temperature is 550°C and the current density is 1.0 × 10⁻⁶. 4 A / mm 2 The pulse frequency was 1000Hz, the pulse width was 50μs, and the processing time was 1min.
[0015] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the austenitic stainless steel is 316L austenitic stainless steel and the austenitic-ferritic duplex stainless steel is Z3CN20.09M duplex stainless steel.
[0016] The present invention also provides a nuclear power steel, which is obtained by the method described above.
[0017] Beneficial effects of the present invention The present invention discloses a method for eliminating helium bubble defects in nuclear power steel. The method includes treating the nuclear power steel, which has suffered helium bubble aggregation and surface hardening due to helium ion irradiation damage, with pulsed current to eliminate the helium bubble defects, restore its surface hardness, and achieve dynamic self-repair of the irradiation-damaged structure of the nuclear power steel. Compared with the prior art, the present invention has the following advantages: (1) Significant defect repair capability: This invention utilizes the coupling of the non-thermal effect and thermal effect of pulsed current to efficiently eliminate nanoscale helium bubbles that are difficult to remove with traditional heat treatment. Experiments have shown that after treatment by this method, the nano-indentation hardness of the material surface is significantly reduced, basically returning to the original level before irradiation, effectively eliminating radiation hardening.
[0018] (2) Avoiding thermal aging damage to materials: Compared with traditional annealing which requires temperatures above 800℃, the present invention can complete the repair in a short time at a lower temperature (e.g., 100 to 650℃). For austenitic-ferritic duplex stainless steel, this method effectively avoids the precipitation of brittle phases such as sigma phase, chi phase, or Cr-rich phase caused by prolonged exposure to the sensitive temperature range of 700℃-850℃, thereby eliminating helium bubbles while preserving the material's excellent toughness and corrosion resistance.
[0019] (3) High efficiency and in-situ repair potential: This method has a short processing time, low energy consumption, and does not require damage to the overall structure of the casting or complex disassembly. It relies on the dynamic self-repair mechanism achieved by the difference in electrical conductivity, and is particularly suitable for the life extension maintenance of large key components such as main pipelines and pressure vessels in nuclear power plants. Attached Figure Description
[0020] Figure 1 This is a schematic diagram of the pulse processing device of the present invention; Figure 2 This is a bar chart comparing the hardness of different nuclear power steels before and after pulsed current treatment according to the present invention. Figure 3 This is a schematic diagram of the method flow of the present invention. Detailed Implementation
[0021] To better understand the technical solution of this invention, the content of this invention includes, but is not limited to, the specific embodiments described below. Similar technologies and methods should be considered within the scope of protection of this invention. To make the technical problems to be solved, the technical solutions, and advantages of this invention clearer, a detailed description will be provided below in conjunction with the accompanying drawings and specific embodiments.
[0022] It should be understood that the embodiments described in this invention are merely some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.
[0023] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.
[0024] This invention provides a method for eliminating helium bubble defects in nuclear power steel, including treating nuclear power steel that has suffered helium bubble accumulation and surface hardening due to helium ion irradiation damage with pulsed current to eliminate helium bubble defects and restore its surface hardness, and to achieve dynamic self-repair of the irradiation-damaged structure of nuclear power steel.
[0025] This method targets nuclear power steel damaged by helium ion irradiation. Its mechanism lies in the fact that helium bubble defects primarily originate from the combination of helium atoms generated by nuclear transmutation and vacancies, forming nanoscale cavities or bubbles within the metal lattice (such as an austenite or ferrite matrix). Since helium and the vacuum region are insulating media with near-zero conductivity, while the metal matrix (including lattices composed of iron, chromium, nickel, etc.) possesses good electrical conductivity (with a conductivity of 10⁻⁶). 6 (On the order of S / m). Therefore, the irradiated damage region exhibits a non-uniform electrical structure of "insulating helium bubble-conductive matrix" at the microscopic level. When a high-energy pulse current with specific parameters is applied, the current cannot pass through the insulating helium bubble, resulting in a current-around-the-bubble effect. This effect causes the current lines to be highly concentrated near the equatorial plane of the helium bubble, making the instantaneous current density in this region much higher than the macroscopic average. The concentration of current density causes a sharp increase in instantaneous temperature around the helium bubble, forming an extremely high temperature gradient centered on the helium bubble. This provides thermal activation energy for the dissociation of helium atoms. At this point, the stable helium-vacancy complex becomes unstable, and the trapped helium atoms gain enough energy to escape the vacancy binding. After solvent extraction, helium atoms and damaged vacancies, driven by both electron wind and temperature gradient, converge and escape towards the material surface or grain boundaries via rapid diffusion channels such as grain boundaries, phase boundaries, or dislocation lines. Meanwhile, lattice positions previously occupied by helium bubbles are filled by excited interstitial atoms in the matrix or healed through the migration of vacancies to grain boundary absorption traps, thus achieving the physical elimination of helium bubbles and the restoration of lattice integrity. This invention is applicable to the pulsed current elimination of helium bubble defects in nuclear power steels such as austenitic stainless steel and austenitic-ferritic duplex stainless steel. Since the physical property of helium bubbles causing conductivity differences in the metal matrix is universal, this method is also applicable to the elimination of helium bubble defects inside other metallic materials (such as ferritic or martensitic steels, nickel-based alloys, etc.). Experiments have shown that irradiation-induced helium bubbles lead to severe surface hardening. After eliminating helium bubbles through pulsed current treatment, nanoindentation tests show a significant decrease in material hardness, essentially returning to the original pre-irradiation level.
[0026] Specifically, the process of this invention is as follows: like Figure 3 As shown, this method includes the following steps: S1. Nanoindentation tests or transmission electron microscopy sampling were performed on nuclear power steel samples damaged by helium ion irradiation to assess the degree of radiation hardening and helium bubble density. Based on the assessment results, the damage degree was classified into mild and severe damage, and pulsed current operating parameters were set for each: The current density, frequency, pulse width, and processing time of the pulsed current were precisely controlled according to the irradiation dose and helium bubble aggregation degree of the nuclear power steel. Utilizing the current's flow-around effect at the helium bubble interface, the helium bubble-matrix interface was destabilized and helium atoms dissociated, driving helium atoms and vacancy clusters to migrate rapidly towards the grain boundary or surface to achieve annihilation. The processing temperature was 100–650℃, and the current density was 1.0 × 10⁻⁶. 3 ~2.0×10 4 A / mm 2 The pulse frequency is 50–1000 Hz, the pulse width is 50–500 μs, and the processing time is 10 s–30 min.
[0027] For samples with mild damage, i.e., the surface hardening rate of the nuclear power steel sample is less than 50%, or the average diameter of the helium bubbles is less than 2 nm: a low energy density, long pulse width processing strategy is adopted to avoid overheating damage. The processing temperature is set at [100, 300] °C, and the current density is [1.0 × 10⁻⁶]. 3 1.0×10 4 A / mm 2 The pulse frequency is [50, 200] Hz, the pulse width is [200, 500] μs, and the processing time is [15, 30] min.
[0028] Severe damage state, i.e., surface hardening rate greater than or equal to 50%, or obvious helium bubble aggregation, or helium bubble size greater than or equal to 2 nm: a high energy density, high frequency, short time processing strategy is adopted to enhance dissociation kinetics, with the processing temperature set at (300, 650] °C and the current density at (1.0 × 10⁻⁶) °C. 4 2.0×10 4 A / mm 2 The pulse frequency is (200, 1000) Hz, the pulse width is [50~200) μs, and the processing time is [10s, 15min].
[0029] S2. Connect the nuclear power steel sample to be repaired to the pulse power supply using a fixture, such as... Figure 1 As shown, the fixture includes a positive electrode, a negative electrode, and an insulating pad. The sample is placed between the positive and negative electrodes, and an insulating pad is used to isolate the sample from the negative electrode at one end and from the positive electrode at the other end. The sample is connected to a thermocouple, and a pulse current is applied through the thermocouple under set conditions until the predetermined processing time is reached. S3. Perform nanoindentation hardness testing and transmission electron microscopy on the repaired sample, and compare it with the sample before repair to evaluate the helium bubble elimination effect and the degree of material hardness recovery.
[0030] Furthermore, the nuclear power steel includes, but is not limited to, austenitic stainless steel, austenitic-ferritic duplex stainless steel, ferritic or martensitic stainless steel, nickel-based alloys or molybdenum-rhenium alloys, etc.
[0031] Therefore, the method of the present invention has the advantages of short processing time, low energy consumption, and can effectively extend the service life of key components such as nuclear-grade main pipelines.
[0032] As an embodiment of the present invention, the present invention also provides a nuclear power steel, which is obtained by the method described in the present invention. Its surface nano-indentation hardness is restored to the level of the original state before irradiation, and the irradiation hardening layer is eliminated.
[0033] The following specific examples will be used for illustration.
[0034] Example 1 This embodiment selects 316L austenitic stainless steel, commonly used in nuclear power plant reactor internals, as the experimental object. First, a 316L stainless steel sample, mechanically polished to a mirror finish, was placed in an ion implanter and irradiated with helium ions at 400 keV at room temperature, with a cumulative irradiation dose of 0.5 dpa. After irradiation, the sample's microstructure and mechanical properties were evaluated (step S1). Transmission electron microscopy (TEM) revealed numerous tiny helium bubbles with a diameter less than 2 nm within the austenitic grains. Nanoindentation testing showed that the average surface hardness increased from the original 2.35 GPa to 3.20 GPa, an increase of approximately 36%, indicating slight damage. Subsequently, the irradiated sample was clamped between the electrodes of a pulsed current processing device, and parameters were set according to the "slight damage" strategy (step S2): the processing temperature was controlled at 200℃ (far below the material's recrystallization temperature), and the applied current density was 8.0 × 10⁻⁶. 3 A / mm 2 The pulse frequency was 100 Hz, the pulse width was 300 μs, and the processing time was 20 minutes. After processing, the sample was air-cooled to room temperature with the furnace. TEM characterization and nanoindentation testing were performed again (step S3), and the results showed that the originally tiny helium bubbles within the crystals had completely disappeared; Figure 2 As shown, the average surface hardness of the sample decreased to 2.40 GPa.
[0035] Example 2 This embodiment selects Z3CN20.09M cast duplex stainless steel, a key material for the main pipeline of a nuclear power plant. First, the sample was subjected to high-dose helium ion irradiation to simulate severe damage in the later stages of service. Evaluation showed (step S1): helium bubbles showed significant aggregation and growth at the phase boundaries, with an average size exceeding 5 nm; the nanoindentation hardness surged from the original 3.10 GPa to 5.95 GPa (a hardening increase of 92%, judged as severe damage). This embodiment employs a "medium-temperature, high-frequency, high-current" enhanced repair strategy (step S2). The treatment temperature was set at 350℃, and the current density was increased to 1.2 × 10⁻⁶. 4 A / mm 2 The pulse frequency was increased to 600 Hz, and the pulse width was shortened to 100 μs (utilizing the high-frequency skin effect to enhance the dissociation of large helium bubbles), with a processing time of 5 minutes. Microscopic analysis after processing (step S3) showed that no Sigma phase precipitation was found within the ferrite phase, and the aggregated helium bubble clusters were effectively dispersed and eliminated. Figure 2 As shown, the sample's nanoindentation hardness recovered to 3.25 GPa, successfully achieving synergistic repair of tissue and properties under severe damage.
[0036] Example 3 This embodiment selects low-activation ferritic / martensitic steel as a candidate material for the first wall of a fusion reactor. After high-dose helium ion irradiation, the surface hardness of this material increased from 2.80 GPa to 5.50 GPa (a 96% increase in hardening, indicating severe damage). Taking advantage of the material's good heat resistance, this embodiment employs a "high-temperature, ultra-high-frequency, and extremely short-time" impact repair process (step S2). The processing temperature is set at 550℃, and the current density is further increased to 1.5 × 10⁻⁶. 4 A / mm 2 The pulse frequency was set to 1000Hz (reaching the device's high-frequency limit), the pulse width to 50μs, and the processing time to only 60 seconds. Despite the extremely short duration, the ultra-high-frequency pulsed current induced intense non-thermal effects and electron wind impacts at the helium bubble interface. The final test results (step S3) show that... Figure 2 As shown, the nanoindentation hardness of the treated material rapidly decreased to 2.90 GPa. This example verifies that for severe damage, efficient repair within seconds can be achieved by increasing the frequency and current density. For details, see Table 1, which compares the hardness values of different nuclear power steels before and after pulsed current treatment.
[0037] Table 1 Comparison of hardness values of different nuclear power steels before and after pulsed current treatment. The data in Table 1 are the average values of multiple nanoindentation tests, with an error range within ±0.15 GPa.
[0038] The foregoing description illustrates and describes several preferred embodiments of the present invention. However, as previously stated, it should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the inventive concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.
Claims
1. A method for eliminating helium bubble defects in nuclear power steel, characterized in that, The method involves treating nuclear power steel that has suffered helium bubble accumulation and surface hardening due to helium ion irradiation damage with pulsed current to eliminate helium bubble defects and restore its surface hardness, thereby achieving dynamic self-repair of the irradiation-damaged structure of the nuclear power steel.
2. The method according to claim 1, characterized in that, The method includes the following steps: S1. Evaluate the nuclear power steel sample to be repaired that has been damaged by helium ion irradiation, and set the pulse current operating parameters and corresponding energizing time based on the evaluation results: S2. Connect the nuclear power steel sample to be repaired to a pulse power supply, apply a pulse current with set working parameters under the set conditions until the predetermined power-on processing time is reached, and obtain the repaired nuclear power steel sample. S3. The repaired nuclear power steel samples were subjected to hardness testing and transmission electron microscopy observation, and compared with the original nuclear power steel samples before repair to evaluate the helium bubble elimination effect and the degree of material hardness recovery.
3. The method according to claim 1, characterized in that, The steel used in nuclear power includes austenitic stainless steel, austenitic-ferritic duplex stainless steel, ferritic or martensitic stainless steel, nickel-based alloys or molybdenum-rhenium alloys.
4. The method according to claim 2, characterized in that, The operating parameters include: processing temperature 100–650℃, current density 1.0 × 10⁻⁶. 3 ~2.0×10 4 A / mm 2 The pulse frequency is 50–1000 Hz, the pulse width is 50–500 μs, and the processing time is 10 s–30 min.
5. The method according to claim 4, characterized in that, The evaluation results included mild and severe damage. Mild damage was defined as a surface hardening rate of less than 50% for nuclear power steel samples, or an average helium bubble diameter of less than 2 nm. The operating parameters used included: processing temperature [100, 300] °C, current density [1.0 × 10⁻⁶]. 3 1.0×10 4 A / mm 2 Pulse frequency [50, 200] Hz, pulse width [200, 500] μs, processing time [15, 30] min; Severe damage is defined as a surface hardening rate of ≥50% for nuclear power steel samples, or the presence of significant helium bubble aggregation or a helium bubble size ≥2 nm. The operating parameters used include: processing temperature (300-650℃), current density (1.0×10⁻⁶ / ℃). 4 2.0×10 4 A / mm 2 , pulse frequency (200, 1000) Hz, pulse width [50~200) μs, processing time [10s, 15min).
6. The method according to claim 5, characterized in that, The processing temperature is 200℃, and the current density is 8.0×10⁻⁶. 3 A / mm 2 The pulse frequency was 100Hz, the pulse width was 300μs, and the processing time was 20min.
7. The method according to claim 5, characterized in that, The processing temperature is 350℃, and the current density is 1.2×10⁻⁶. 4 A / mm 2 The pulse frequency was 600 Hz, the pulse width was 100 μs, and the processing time was 5 min.
8. The method according to claim 5, characterized in that, The processing temperature is 550℃, and the current density is 1.0×10⁻⁶. 4 A / mm 2 The pulse frequency was 1000 Hz, the pulse width was 50 μs, and the processing time was 1 min.
9. The method according to claim 3, characterized in that, The austenitic stainless steel is 316L austenitic stainless steel, and the austenitic-ferritic duplex stainless steel is Z3CN20.09M duplex stainless steel.
10. A type of steel for nuclear power plants, characterized in that, The nuclear power steel is obtained by processing according to any one of claims 1-9.