Nickel-based alloy
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- HITACHI GE NUCLEAR ENERGY LTD
- Filing Date
- 2022-07-07
- Publication Date
- 2026-08-05
Smart Images
Figure 0007900961000004 
Figure 0007900961000005 
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Abstract
Description
[Technical Field]
[0001] This invention relates to a nickel-based alloy with excellent resistance to thermal aging. [Background technology]
[0002] Nickel-based alloys are materials with excellent mechanical properties and corrosion resistance, and are widely used as structural materials in applications ranging from general industrial use to nuclear equipment. For in-core structures and equipment in nuclear power plants, corrosion-resistant stainless steel and Ni-Cr nickel-based alloys are used.
[0003] In boiling water reactors (BWRs), stress corrosion cracking (SCC) is known to occur in materials at points where they come into contact with high-temperature, high-pressure reactor water. Chromium contained in the material reacts with carbon in a high-temperature, high-pressure environment to form chromium carbides. It is known that when a chromium-deficient layer is formed by the formation of chromium carbides, SCC is more likely to occur when stress is applied.
[0004] Patent Document 1 describes a nickel-based alloy welding material that has good resistance to SCC and excellent weldability. This material contains, by mass%, Cr: more than 30.0% and 36.0% or less, C: 0.050% or less, Fe: 1.00% to 3.00%, Si: 0.50% or less, Nb+Ta: 3.00% or less, Ti: 0.70% or less, Mn: 0.10% to 3.50%, and Cu: 0.5% or less, with the remainder being Ni and unavoidable impurities.
[0005] Patent Document 2 describes a method for manufacturing a high-Cr, high-Ni alloy tube that exhibits good toughness and does not experience a decrease in the Charpy impact value at 20°C during manufacturing. This material contains, by mass%, one or two of the following: C: 0.05~0.09%, Si: 0.05~0.4%, Mn: 0.05~1.3%, P: 0.015% or less, S: 0.005% or less, Ni: 44~52%, Cr: 22~32%, Ti: 0.05~1.0%, sol.Al: 0.005~0.2%, B: 0.001~0.008%, and W: 4~10%, as well as Nb: 0.005~0.25%, and Zr: 0.001~0.05%, with the remainder being Fe and impurities.
[0006] Patent Document 3 describes a Ni-based alloy material that can ensure corrosion resistance in harsh environments where erosion and hydrochloric acid or sulfuric acid corrosion occur at temperatures of 100 to 500°C, and which also prevents erosion due to its high surface hardness. This material contains, by mass%, C: 0.03% or less, Si: 0.01 to 0.5%, Mn: 0.01 to 1.0%, P: 0.03% or less, S: 0.01% or less, Cr: 20% or more and less than 30%, Ni: more than 40% and 50% or less, Cu: more than 2.0% and 5.0% or less, Mo: 4.0 to 10%, Al: 0.005 to 0.5%, W: 0.1 to 10%, and N: more than 0.10% and 0.35% or less, and satisfies the formula 0.5Cu + Mo ≥ 6.5···(1), with the remainder being Fe and impurities. [Prior art documents] [Patent Documents]
[0007] [Patent Document 1] Japanese Patent Publication No. 2020-196043 [Patent Document 2] Japanese Patent Publication No. 2011-214141 [Patent Document 3] Japanese Patent Publication No. 2011-063863 [Overview of the project] [Problems that the invention aims to solve]
[0008] As nickel-based alloys, high-Cr materials with increased Cr content have also been developed to improve corrosion resistance and SCC resistance. However, it is known that nickel-based alloys, when the atomic concentration ratio of Ni to Cr is close to 2, form an ordered phase Ni2Cr due to intermetallic compounds when exposed to high-temperature environments for extended periods.
[0009] When a nickel-based alloy is subjected to external loads or internal residual stresses, uniform dislocations typically occur in the matrix phase of the nickel-based alloy. However, if a ordered phase (Ni2Cr) is present, when such a single dislocation propagates to the grain boundary with the ordered Ni2Cr, the slip is hindered, causing it to pile up at the grain boundary. As a result, slip occurs on a new surface, resulting in a so-called non-uniform (discontinuous) dislocation morphology.
[0010] Therefore, when an ordered Ni2Cr phase is formed in nickel-based alloys, macroscopically, hardening and embrittlement reduce fracture toughness, raising concerns about increased susceptibility to SCC (Steel Chloride Crushing). When exposed to high-temperature environments of 250-350°C for several decades, such as in the reactor environment of a nuclear power plant, thermal aging embrittlement due to the formation of the ordered Ni2Cr phase becomes a problem.
[0011] Patent documents 1 to 3 have examined the SCC resistance, toughness, and corrosion resistance of nickel-based alloys. However, no specific measures have been taken to address hardening and embrittlement due to thermal aging, which become problematic when exposed to high-temperature environments for extended periods.
[0012] Therefore, the present invention aims to provide a nickel-based alloy that is less susceptible to hardening and embrittlement due to thermal aging in high-temperature environments and exhibits excellent aging resistance. [Means for solving the problem]
[0013] To solve the aforementioned problems, the nickel-based alloy according to the present invention has Cr as an essential component. :23 mass% or more and 28 mass% or less It contains one or more of the following as optional components: Fe, Nb, Mn, and Mo. , Fe: 8% by mass or more, Nb: 1% by mass or more and 9% by mass or less, Mn: 0.01% by mass or more and 5% by mass or less, Mo: 0.01% by mass or more and 3% by mass or lessA nickel-based alloy that contains arbitrarily and the balance consists of Ni and inevitable impurities, when [%Ni], [%Cr], [%Fe], [%Nb], [%Mn] and [%Mo] are the atomic concentrations of each element, the atomic concentration ratio [%Ni] / [%Cr] of Ni and Cr is 1.8 or more and 2.2 or less, and [%Fe] + 0.49[%Nb] + 0.63[%Mn] + 0.05[%Mo] ≥ 14 is satisfied and used in high-temperature environments between 250°C and 350°C. . [Effect of the Invention]
[0014] According to the present invention, it is possible to provide a nickel-based alloy that is difficult to cause hardening and embrittlement due to thermal aging in a high-temperature environment and has excellent aging resistance. [Brief Description of the Drawings]
[0015] [Figure 1] It is a bubble diagram showing the relationship between the atomic concentration ratio r of Ni and Cr of a nickel-based alloy and the equivalent iron equivalent EqFe. [Figure 2] It is a perspective view showing the internal structure of the pressure vessel of a boiling water reactor (BWR). [Mode for Carrying Out the Invention]
[0016] [[ID=I27]] Hereinafter, a nickel-based alloy (Ni-based alloy) according to an embodiment of the present invention and an in-vessel structure of a nuclear reactor in which the nickel-based alloy is used will be described with reference to the drawings.
[0017] The nickel-based alloy (Ni-based alloy) according to this embodiment is an alloy mainly composed of Ni, contains Cr as an essential additive component, arbitrarily contains one or more of Fe, Nb, Mn and Mo as optional additive components, and the balance consists of Ni and inevitable impurities. In order to suppress hardening and embrittlement due to thermal aging in a high-temperature environment, the ranges of the contents of the essential additive components and the optional additive components are adjusted.
[0018] Ni-based alloys with added Cr may form an ordered phase Ni2Cr due to intermetallic compounds when exposed to high-temperature environments for extended periods, especially when the atomic concentration ratio of Ni to Cr is close to 2. When the ordered phase Ni2Cr is formed, dislocations pile up at grain boundaries, resulting in a non-uniform (discontinuous) morphology. As a result, unintended age hardening due to thermal aging occurs, and thermal embrittlement progresses.
[0019] In contrast, by appropriately limiting the range of content of essential and optional additives, hardening and embrittlement due to thermal aging can be suppressed. Even when the atomic concentration ratio of Ni to Cr is close to 2, it becomes possible to provide a Ni-based alloy that is less susceptible to hardening and embrittlement due to thermal aging and has excellent aging resistance.
[0020] Generally, the ordered phase of a substitutional solid solution is formed by the regular arrangement of solute atoms within the arrangement of solvent atoms. The phase transformation from the matrix to the ordered phase occurs through the diffusion of solute atoms to minimize the Gibbs free energy. Therefore, the enthalpy of formation of the ordered phase differs depending on the type of solvent atoms that were present in the crystal structure before substitution by the diffusion of solute atoms.
[0021] Non-patent document 1 (George A. Young, et al., Physical Metallurgy, Weldability, and In-Service Performance of Nickel-Chromium Filler Metals Used in Nuclear Power Systems, Proceedings of the 15th International Conference on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors (2011), The Minerals, Metals, and Materials Society, pp.2431-2441) describes the formation enthalpy of Ni-Cr alloys.
[0022] According to Non-Patent Document 1, the absolute values of the formation enthalpy of Ni-based alloys are higher than those of Ni-Cr by +3 kJ / mol for Ni-Cr-Mo, +29 kJ / mol for Ni-Cr-Nb, +37 kJ / mol for Ni-Cr-Mn, and +59 kJ / mol for Ni-Cr-Fe.
[0023] However, actual materials contain various solute atoms. The ease with which ordered Ni2Cr is formed when the type and amount of solute atoms differ remains unclear. Ordered Ni2Cr is less likely to form as the absolute value of the enthalpy of formation increases. Therefore, in Ni-based alloys, it is considered effective to adjust the amount of solute atoms that increase the absolute value of the enthalpy of formation to an appropriate range in order to suppress the formation of ordered Ni2Cr.
[0024] Therefore, in the Ni-based alloy according to this embodiment, the equivalent iron equivalent Eq is used to limit the range of content of the added components, with Fe being the reference value for which the absolute value of the formation enthalpy of the ordered phase Ni2Cr is maximum. Fe Set the equivalent iron equivalent (Eq). Fe This is defined as the ratio of the increase in the enthalpy of formation of the ordered phase Ni2Cr due to each added component to the increase in the enthalpy of formation of the ordered phase Ni2Cr due to Fe.
[0025] <Equivalent iron equivalent Eq Fe > In this embodiment, the Ni-based alloy has an equivalent iron equivalent Eq when [%Fe], [%Nb], [%Mn], and [%Mo] are defined as atomic concentrations (at%) of each element. Fe [at%] is defined as having a chemical composition that satisfies the following equation (1). Eq Fe [at%] =[%Fe]+0.49[%Nb]+0.63[%Mn]+0.05[%Mo]≧14 ...(1)
[0026] When Equation (1) is satisfied, even when the atomic concentration ratio of Ni and Cr is close to the stoichiometric ratio of Ni2Cr, when the Ni-based alloy is exposed to a high-temperature environment for a long time, it becomes difficult to form the regular phase Ni2Cr. In a high-temperature environment, hardening and embrittlement due to thermal aging are suppressed.
[0027] <The atomic concentration ratio r of Ni and Cr> For the Ni-based alloy according to the present embodiment, when [%Ni] and [%Cr] are the atomic concentrations (at%) of each element, the atomic concentration ratio r = [%Ni] / [%Cr] of Ni and Cr is 1.8 or more and 2.2 or less.
[0028] When the atomic concentration ratio r of Ni and Cr is around 2, since it is close to the stoichiometric ratio of Ni2Cr, when the Ni-based alloy is exposed to a high-temperature environment for a long time, it becomes easy to form the regular phase Ni2Cr. However, when the content range of the additive components is limited using the equivalent iron equivalent Eq Fe as an index, the formation of the regular phase Ni2Cr can be suppressed. Therefore, when the atomic concentration ratio r is such, the effect by the setting of the equivalent iron equivalent Eq Fe can be effectively obtained.
[0029] The atomic concentration ratio r of Ni and Cr is preferably 1.85 or more, more preferably 1.9 or more, and still more preferably 1.95 or more. Also, the atomic concentration ratio r of Ni and Cr is preferably 2.15 or less, more preferably 2.1 or less, and still more preferably 2.05 or less. When the atomic concentration ratio r is such, since it becomes easier to form the regular phase Ni2Cr, the effect by the setting of the equivalent iron equivalent Eq Fe can be obtained more effectively.
[0030] <Thermal aging test · Evaluation of aging resistance> Here, the results of performing a thermal aging test on the Ni-based alloy and evaluating the aging resistance to thermal aging are shown.
[0031] As the Ni-based alloys, specimens No. 1 to 7 having the chemical compositions shown in Table 1 were used. After fabricating each of the specimens No. 1 to 7 and subjecting them to a thermal aging test, the presence or absence of aging resistance to thermal aging was evaluated based on the Vickers hardness. The thermal aging test was conducted at a test temperature of 380°C and a test time of 8264 h.
[0032] As the Vickers hardness, for each of the specimens No. 1 to 7, the Vickers hardness H0 before thermal aging and the Vickers hardness H after thermal aging were measured. Then, the difference ΔH = H - H0 and the standard deviation σ of H0 were determined. The Vickers hardness was measured with a load of 1 kgf and a holding time of 15 seconds. The number of measurement points was 10 for each specimen, and the average value of the measured values of the Vickers hardness was calculated.
[0033] The aging resistance to thermal aging was simply determined by whether the ratio of the difference ΔH to the standard deviation σ of H0 (ΔH / σ) exceeded 1. When ΔH / σ exceeded 1, it was determined that significant age hardening occurred due to thermal aging. When ΔH / σ was 1 or less, it was determined that significant age hardening did not occur due to thermal aging.
[0034] Table 1 shows the chemical compositions (mass %) of specimens No. 1 to 7. Table 2 shows the chemical compositions (at %), the measurement results of the Vickers hardness, and the evaluation results of the presence or absence of aging resistance to thermal aging for specimens No. 1 to 7.
[0035]
Table 1
[0036]
Table 2
[0037] Figure 1 is a bubble chart showing the relationship between the atomic concentration ratio r of Ni and Cr in the nickel-based alloy and the equivalent iron equivalent Eq Fe In Figure 1, the horizontal axis represents the atomic concentration ratio r of Ni and Cr = [%Ni] / [%Cr], and the vertical axis represents the equivalent iron equivalent Eq Fe[at%] is shown. The bubbles marked with ● represent the results for each test material No. 1 to 7. The area of the bubble marked with ● represents the magnitude of ΔH / σ, and the area of the bubble marked with ○ represents ΔH / σ = 1.
[0038] As shown in Figure 1, when the atomic concentration ratio r is greater than 2.2, ΔH / σ ≤ 1, and it was determined that significant age hardening due to thermal aging did not occur. On the other hand, when the atomic concentration ratio r is 2.2 or less, there are cases where ΔH / σ > 1, and it was determined that age hardening due to thermal aging may occur. In the range where the atomic concentration ratio r is 2.2 or less, the equivalent iron equivalent Eq Fe A smaller value of ΔH / σ was observed to result in a larger ΔH / σ, and a tendency for thermal aging to progress.
[0039] Of the results for each test material No. 1 to 7, those that satisfy ΔH / σ≦1 and have equivalent iron equivalent Eq Fe Using the result with a large value, the equivalent iron equivalent Eq Fe The limit value was determined. Equivalent iron equivalent Eq Fe The limit value was determined by linear approximation in the range 1.8 ≤ R ≤ 3.0. Equivalent iron equivalent Eq Fe The following equation (2) was obtained as an approximation line showing the limit value. Eq Fe = -14R + 45 ... (2)
[0040] According to equation (2), in order to suppress hardening and embrittlement due to thermal aging, the equivalent iron equivalent Eq must be in the range of 1.8 ≤ R ≤ 2.2. Fe It is necessary that the concentration of chromium be 14 at% or higher. If the chemical composition satisfies equation (1), even if the atomic concentration ratio r of Ni to Cr is close to the stoichiometric ratio of Ni2Cr, the ordered phase Ni2Cr is less likely to form, and hardening and embrittlement due to thermal aging are suppressed in high-temperature environments.
[0041] The rate of change in hardness due to thermal aging can be converted between different thermal aging temperature and time conditions using the KJMA (Kolomogorov-Johnson-Mehl-Avrami) equation. The KJMA equation is generally known as an equation that shows the time dependence of the phase transformation completion volume.
[0042] Non-patent document 2 (George A. Young and Daniel R. Eno, Long Range Ordering in Model Ni-Cr-X Alloys, Fontevraud 8 - Contribution of Materials Investigations and Operating Experience to LWRs' Safety, Performance and Reliability, France, Avignon (2014), September 14) describes the following equation (3) based on the KJMA formula.
[0043] f=(H-H0) / (H max -H0)=1-exp(-(kt) n )···(3) [However, in equation (3), f is the rate of change function, H0 is the Vickers hardness before thermal aging, H is the instantaneous Vickers hardness after thermal aging, Hmax is the maximum Vickers hardness after thermal aging, t is the aging time, k is the rate coefficient, and n is the Avrami index.]
[0044] The velocity coefficient k in equation (3) can be assumed to be the Arrhenius equation and can be expressed by the following equation (4). k = k0 × exp(-Q / RT) ... (4) [However, in equation (4), k0 represents the frequency factor, Q represents the activation energy, R represents the gas constant, and T represents the absolute temperature.]
[0045] In the case of a phase transformation that produces the ordered phase Ni2Cr, the avrami index n is n=0.65, and the frequency factor k0 is k0=3.5×10 7 [h -1 The following can be used: The gas constant R is R = 8.314 J / (mol·K). As the activation energy Q, the apparent activation energy of the ordered phase Ni2Cr, Q = 147 kJ / mol, can be used.
[0046] Using equations (3) and (4), as described above, when the test temperature T of the thermal aging test is T=653K (380℃) and the test time t is t=8264h, the rate of change function f is equivalent to that of the case where T=561K (288℃) and t=700800h (80 years). The environment at 288℃ corresponds to a harsh environment such as the area in a BWR where high temperature and pressure reactor water is in contact with the surface.
[0047] Therefore, if equation (1) is satisfied, it can be said that hardening and embrittlement due to thermal aging can be suppressed for long periods of time, such as about 80 years, in harsh environments of high temperature and high pressure. It can also be said that it is possible to provide a Ni-based alloy with excellent thermal aging resistance even when the atomic concentration ratio r of Ni to Cr is close to the stoichiometric ratio of the ordered phase Ni2Cr.
[0048] <Chemical composition> Here, the chemical composition of the Ni-based alloy according to this embodiment will be described in more detail. The Ni-based alloy may contain, as an optional additive, one or more of Fe, Nb, Mn, and Mo, as well as C, Si, W, Co, Ti, Al, Cu, V, B, Zr, etc. In the following description, the non-limiting unit "%" refers to "mass%".
[0049] (Cr: 23-28%) Cr is effective in improving corrosion resistance, SCC resistance, and high-temperature strength. From the viewpoint of improving corrosion resistance, the Cr content should be 16% or more. However, the ordered phase Ni2Cr is generally formed when the Cr content is 23% or more. On the other hand, if the Cr content is too high, toughness, workability, and weldability decrease, and susceptibility to high-temperature cracking increases. Also, the effect of improving corrosion resistance decreases when it exceeds 28%. Therefore, a Cr content of 23% to 28% is preferable. From the viewpoint of improving high-temperature strength, a Cr content of 26% to 28% is more preferable.
[0050] (Fe: 8% or more) Fe is effective in increasing the formation enthalpy of the ordered phase Ni2Cr. Furthermore, Fe contributes to improved mechanical properties and is less expensive than Ni. On the other hand, too much Fe reduces corrosion resistance. Based on formula (1) and the content of other elements, the Fe content is preferably between 8% and 30%.
[0051] (Nb: 1-9%) Nb is effective in increasing the enthalpy of the ordered phase Ni2Cr. Furthermore, Nb preferentially bonds with C and suppresses the precipitation of Cr carbides, thus contributing to improved corrosion resistance and SCC resistance. It also contributes to improved high-temperature strength and toughness. The amount of Nb is at least 1% or more to suppress the formation of Cr carbides. From the viewpoint of improving corrosion resistance and SCC resistance, and in relation to the content of other elements, the amount of Nb is preferably between 1% and 9%. The amount of Nb is preferably 2% or more, and more preferably 3% or more.
[0052] (Mn:5% or less) Mn is effective in increasing the enthalpy of formation of the ordered phase Ni2Cr. Mn is also added as a deoxidizing agent. On the other hand, if the amount of Mn is too high, inclusions are formed, increasing susceptibility to intergranular corrosion. Since Mn has a smaller effect on increasing the enthalpy of formation compared to Fe, it may or may not be added actively. The amount of Mn is preferably 5% or less, more preferably 3% or less, and even more preferably 1% or less, considering its relationship to the content of other elements. When Mn is added actively, it is preferably 0.01% or more, and more preferably 0.1% or more.
[0053] (Mo: 3% or less) Mo is effective in increasing the formation enthalpy of the ordered phase Ni2Cr. Mo also contributes to improved corrosion resistance and high-temperature strength. On the other hand, too much Mo reduces workability and weldability. Because Mo has a smaller effect on increasing formation enthalpy compared to Fe, it may or may not be added. The amount of Mo is preferably 3% or less, more preferably 2% or less, and even more preferably 1% or less, considering its relationship to the content of other elements. When Mo is added actively, it is preferably 0.01% or more, and more preferably 0.1% or more.
[0054] (C: 0.05% or less) Carbon (C) contributes to improving mechanical properties such as high-temperature strength and grain boundary strength. On the other hand, if the amount of C is too high, carbides are formed, reducing corrosion resistance and SCC resistance. C may or may not be added actively. From the viewpoint of ensuring corrosion resistance and SCC resistance, the amount of C is preferably 0.05% or less, more preferably 0.04% or less, and even more preferably 0.03% or less. When C is added actively, the amount of C is preferably 0.01% or more.
[0055] (Si:0.5% or less) Si is added as a deoxidizing agent and contributes to improving oxidation resistance and molten metal flowability. On the other hand, if the amount of Si is too high, ductility and corrosion resistance will decrease. Si may be added actively or not. From the viewpoint of ensuring ductility and corrosion resistance, the amount of Si is preferably 0.5% or less, more preferably 0.4% or less, and even more preferably 0.3% or less. When Si is added actively, the amount is preferably 0.01% or more, and more preferably 0.05% or more.
[0056] (W: 5% or less) W contributes to improving mechanical properties such as high-temperature strength. On the other hand, if the amount of W is too high, machinability and weldability will decrease. W may or may not be added. When W is added actively, the amount is preferably 0.01% or more, and more preferably 0.1% or more. From the viewpoint of machinability and weldability, the amount of W is preferably 5% or less, more preferably 3% or less, and even more preferably 1% or less.
[0057] (Co:3% or less) Co contributes to ensuring mechanical properties such as high-temperature strength and corrosion resistance. On the other hand, if the amount of Co is too high, processability and cost-effectiveness decrease, and radioactive contamination becomes a problem. Co may or may not be added actively. If Co is added actively, the amount is preferably 0.01% or more, and more preferably 0.1% or more. From the viewpoint of processability, cost-effectiveness, and prevention of radioactive contamination, the amount of Co is preferably 3% or less, more preferably 2% or less, and even more preferably 1% or less.
[0058] (Ti: 1% or less) Ti preferentially bonds with C, suppressing the precipitation of Cr carbides, thus contributing to improved corrosion resistance and SCC resistance. It also contributes to improved high-temperature strength and creep strength. Ti may or may not be added. If Ti is added actively, the amount of Ti is preferably 0.01% or more, and more preferably 0.1% or more. From the viewpoint of processability, the amount of Ti is preferably 1% or less, and more preferably 0.5% or less.
[0059] (Al: 0.5% or less) Al is added as a deoxidizing agent and contributes to improving high-temperature strength and creep strength. On the other hand, if the amount of Al is too high, processability and weldability will decrease. Al may be added actively or not. When Al is added actively, the amount of sol.Al is preferably 0.01% or more, and more preferably 0.1% or more. From the viewpoint of processability and weldability, the amount of sol.Al is preferably 0.5% or less, more preferably 0.4% or less, and even more preferably 0.3% or less.
[0060] (Cu:5% or less) Cu contributes to improved corrosion resistance and strength. On the other hand, if the amount of Cu is too high, machinability and weldability will decrease. Cu may or may not be added actively. From the viewpoint of ensuring corrosion resistance and strength, the amount of Cu is preferably 0.01% or more, and more preferably 0.1% or more. From the viewpoint of machinability and weldability, the amount of Cu is preferably 5% or less, more preferably 3% or less, and even more preferably 1% or less.
[0061] (V:1% or less) V contributes to improving mechanical properties such as strength. On the other hand, if the amount of V is too high, machinability decreases. V may be added actively or not actively. From the viewpoint of ensuring strength, the amount of V is preferably 0.01% or more, and more preferably 0.1% or more. From the viewpoint of machinability, the amount of V is preferably 1% or less, more preferably 0.8% or less, and even more preferably 0.6% or less.
[0062] (B: 0.05% or less) B contributes to improving mechanical properties such as grain boundary strength. B may be added actively or not. On the other hand, if the amount of B is too high, the weldability will decrease. From the viewpoint of improving grain boundary strength, the amount of B is preferably 0.001% or more, and more preferably 0.01% or more. From the viewpoint of weldability, the amount of B is preferably 0.05% or less, and more preferably 0.03% or less.
[0063] (Zr:0.1% or less) Zr contributes to improving mechanical properties such as grain boundary strength. Zr may or may not be added. On the other hand, if the amount of Zr is too high, the weldability will decrease. From the viewpoint of improving grain boundary strength, the amount of Zr is preferably 0.01% or more, and more preferably 0.1% or more. From the viewpoint of weldability, the amount of Zr is preferably 0.1% or less, more preferably 0.08% or less, and even more preferably 0.06% or less.
[0064] (Inevitable impurities) Unavoidable impurities include those present in the raw materials and those introduced during the manufacturing process. Examples include P, S, O, Sn, and Pb. P and S reduce corrosion resistance, workability, and weldability. The amount of P is preferably 0.03% or less, more preferably 0.02% or less, and even more preferably 0.01% or less. The amount of S is preferably 0.02% or less, more preferably 0.015% or less, and even more preferably 0.01% or less. Other elements are preferably 0.05% or less, and the total is preferably 0.5% or less.
[0065] <Manufacturing method> The Ni-based alloy according to this embodiment can be manufactured by any appropriate method. For example, raw materials such as ingots or scrap containing Ni, Cr, Fe, etc., are adjusted to an appropriate chemical composition and then melted in an electric furnace or the like to produce molten metal. Then, decarburization is performed using the AOD (Argon Oxygen Decarburization) method or the VOD (Vacuum Oxygen Decarburization) method, followed by deoxidation, reduction, and desulfurization treatments, after which intermediate materials such as slabs, billets, and blooms are cast. The intermediate materials can be subjected to solution treatment and processing treatments.
[0066] Ni-based alloys can be subjected to appropriate hot or cold forging, rolling, and other processes depending on their intended use. Furthermore, billets can be drawn into wire to produce welding materials from Ni-based alloys. These welding materials can be used for various welding methods, including TIG welding, MIG welding, shielded metal arc welding, electron beam welding, and laser welding.
[0067] <Application> The Ni-based alloy according to this embodiment is preferably used in high-temperature environments where it is exposed to high temperatures for extended periods. Applications of the Ni-based alloy include materials for nuclear power plants, thermal power plants, chemical plants, oil and gas extraction plants, gas engines, gas turbines, and the like. It can be used as structural material, for piping and other equipment, and as a material for welded joints in these facilities.
[0068] The Ni-based alloy according to this embodiment is particularly preferably used in high-temperature environments of 250°C to 350°C, and more preferably in environments in contact with high-temperature water at such temperatures. For example, it can be preferably used as a material for in-reactor structures and in-reactor equipment in boiling water reactors (BWRs) and pressurized water reactors (PWRs). Even in such harsh environments, hardening and embrittlement due to thermal aging over several decades can be suppressed, thus preventing deterioration and damage over time.
[0069] Figure 2 is a perspective view showing the internal structure of a boiling water reactor (BWR) pressure vessel. In Figure 2, a portion of the pressure vessel is cut out to illustrate the internal structure. As shown in Figure 2, the pressure vessel 100 of a boiling water reactor (BWR) is equipped with fuel assemblies 10, control rods 20, a control rod drive system 30, a core shroud 40, a steam-water separator 50, a steam dryer 60, and the like.
[0070] Multiple fuel assemblies 10 are loaded into the core of the pressure vessel 100 in a grid-like arrangement. The core is equipped with removable control rods 20 for controlling the nuclear reaction of the fuel assemblies 10. A control rod drive system 30 is connected to the control rods 20 at the bottom of the pressure vessel 100. The insertion and removal of the control rods 20 are driven by the control rod drive system 30.
[0071] The core of the pressure vessel 100 is surrounded by a cylindrical core shroud 40. Inside the core shroud 40, an upper grid plate is installed to partition the upper end of the core, and a core support plate is installed to partition the lower end of the core. The top of the core shroud 40 is covered by a shroud head.
[0072] The core shroud 40 is supported and fixed on a shroud support. The shroud support is formed by a cylindrical shroud support cylinder that supports the core shroud 40, a plurality of leg-shaped shroud support legs that support the cylinder from below, and an annular shroud support plate that protrudes from the side of the cylinder and is supported from the inner circumferential surface of the pressure vessel 100.
[0073] A steam-liquid separator 50 is installed above the shroud head. A steam dryer 60 is installed above the steam-liquid separator 50. Cooling water flowing into the pressure vessel 100 is supplied to the reactor core loaded with fuel assemblies 10 by a jet pump located at the bottom of the pressure vessel 100. The cooling water is heated by the nuclear reaction of the fuel assemblies 10 and becomes a two-phase gas-liquid flow.
[0074] The steam-liquid separator 50 separates the two-phase gas-liquid flow generated by heating into steam and water. The water descends through the downcomer surrounding the core shroud 40 and becomes cooling water again. Meanwhile, the steam flows into the steam dryer 60 above. The steam dryer 60 removes moisture from the steam. The dehumidified steam is supplied to the turbine and used for power generation. The steam used for power generation is returned to cooling water in the condenser and then supplied back to the pressure vessel 100.
[0075] Structural materials constituting in-core structures such as the core shroud 40, steam-water separator 50, and steam dryer 60, as well as in-core equipment such as feedwater system piping, spargers, and nozzles, and welded joints connecting them, become wetted parts that come into contact with high-temperature water between 250°C and 350°C during reactor operation. Generally, the cladding tubes of the fuel assembly 10, the core shroud 40, the steam-water separator 50, and the steam dryer 60 are made of stainless steel.
[0076] The Ni-based alloy according to this embodiment can be used as a material for in-core structures of nuclear power plants that come into contact with reactor water at temperatures between 250°C and 350°C, as well as for in-core equipment of nuclear power plants. The Ni-based alloy according to this embodiment can be joined to in-core structures made of stainless steel.
[0077] Specific examples of areas to which the Ni-based alloy according to this embodiment is applied include shroud supports, tubular components such as neutron instrumentation detector tubes, control rod guide tubes, and inspection instrument guide tubes, nozzle materials such as nozzles at water supply inlets and recirculation water inlets, and welding materials for welded parts of shrouds. Examples of welded parts include support parts composed of shroud support cylinders, shroud support legs, shroud support plates, etc., and cladding parts of the lower end of pressure vessels.
[0078] According to the Ni-based alloy of this embodiment described above, the equivalent iron equivalent Eq Fe Because the range of additive content is appropriately adjusted under these conditions, even when the atomic concentration ratio of Ni to Cr is close to the stoichiometric ratio of Ni2Cr, ordered phase Ni2Cr is less likely to form when the Ni-based alloy is exposed to a high-temperature environment for a long period of time. Since hardening and embrittlement due to thermal aging are suppressed in high-temperature environments, a Ni-based alloy with excellent resistance to thermal aging can be obtained. For materials used in harsh environments, it is possible to prevent age-related deterioration and damage such as thermal aging embrittlement and SCC while ensuring corrosion resistance, high-temperature strength, creep strength, etc.
[0079] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. For example, the present invention is not necessarily limited to having all the configurations of the embodiments described above. Some configurations of one embodiment may be replaced with other configurations, some configurations of one embodiment may be added to other forms, or some configurations of one embodiment may be omitted. [Examples]
[0080] The present invention will be specifically described below with reference to examples, but the technical scope of the present invention is not limited thereto.
[0081] Equivalent iron equivalent Eq expressed by equation (1) FeNi-based alloys that met the specified conditions were fabricated, and their resistance to thermal aging was evaluated.
[0082] As a Ni-based alloy, an ingot of a quaternary model alloy of Ni-Cr-Fe-Nb was fabricated. Large chunks of each element, with a particle size of approximately 10 mm, were high-frequency induction heated in an alumina crucible under an argon atmosphere at 1 atmosphere. The resulting molten metal was poured into a copper mold to cast a 300 g prismatic ingot.
[0083] The fabricated ingots were subjected to inductively coupled plasma (ICP) emission spectroscopy to analyze the chemical composition of the Ni-based alloy. Furthermore, the fabricated ingots were subjected to thermal aging tests to evaluate the presence or absence of age hardening based on Vickers hardness. The thermal aging tests were conducted at a temperature of 380°C for a test duration of 8264 hours.
[0084] For Vickers hardness, we measured the Vickers hardness H0 before thermal aging and the Vickers hardness H after thermal aging. Then, we calculated the difference between these values, ΔH = H - H0, and the standard deviation σ of H0. Vickers hardness was measured with a load of 1 kgf and a holding time of 15 seconds. Ten measurements were taken for each test material, and the average value of the measured Vickers hardness was calculated.
[0085] Table 3 shows the chemical composition (mass%, at%) of the test material and the evaluation results of whether or not it has resistance to thermal aging.
[0086] [Table 3]
[0087] As shown in Table 3, the atomic concentration ratio r of Ni to Cr was 2.19. Equivalent iron equivalent Eq FeThe value was 14.1 at%. The ratio of the difference ΔH to the standard deviation σ of the Vickers hardness H0 before thermal aging (ΔH / σ) was 60%. It was confirmed that even when Cr was somewhat deficient relative to the stoichiometric ratio of Ni2Cr, significant age hardening due to thermal aging did not occur. [Explanation of symbols]
[0088] 10 Fuel assembly 20 control rods 30 Control rod drive system 40 Core Shroud 50 Steam water separator 60 Steam dryer 100 Pressure Vessels
Claims
1. A nickel-based alloy containing Cr: 23% to 28% by mass as an essential component, and one or more of Fe, Nb, Mn, and Mo as an optional component, in the following amounts: Fe: 8% to 9% by mass, Nb: 1% to 9% by mass, Mn: 0.01% to 5% by mass, Mo: 0.01% to 3% by mass, with the remainder being Ni and unavoidable impurities. When [%Ni], [%Cr], [%Fe], [%Nb], [%Mn], and [%Mo] are the atomic concentrations of each element, The atomic concentration ratio of Ni to Cr [%Ni] / [%Cr] is 1.8 or more and 2.2 or less. A nickel-based alloy that satisfies the condition [%Fe] + 0.49[%Nb] + 0.63[%Mn] + 0.05[%Mo] ≥ 14 and is used in high-temperature environments between 250°C and 350°C.
2. A nickel-based alloy according to claim 1, A nickel-based alloy having C: 0.05% by mass or less, Si: 0.5% by mass or less, P: 0.03% by mass or less, and S: 0.02% by mass or less.
3. A nickel-based alloy according to claim 1 or claim 2, A nickel-based alloy used as a material for in-core structures or in-core equipment in nuclear power plants.