Method for manufacturing nuclear reactor component and nuclear reactor component obtained

Abstract

The manufacturing method comprises obtaining a nickel-based alloy strip having the following composition in percentage by weight: trace < = C < = 0.08%; trace < = Mn < = 0.35%; trace < = Si < = 0.35%; trace amount < = P < = 0.015%; trace < = S < = 0.015%; 17.0% < = Cr < = 21.0%; trace < = Co < = 1.0%; 2.80% < = Mo < = 3.30%; 4.75% < = Nb + Ta < = 5.50%; 0.65% < = Ti < = 1.15%; 0.20% < = Al < = 0.80%; trace < = Cu < = 0.30%; 50.0% < = Ni < = 55.0%; trace < = B < = 0.006%; the remainder being Fe and impurities resulting from processing, and desensitizing annealing in a static furnace at an annealing temperature equal to or higher than 900 DEG C and / or equal to or lower than 1050 DEG C for an annealing time equal to or greater than 1 minute and / or equal to or less than 180 minutes.

Description

Technical Field

[0001] This invention relates to the field of nickel superalloys, and more specifically, to nickel-based alloys corresponding to the UNS N07718 standard, known as INCONEL. ® 718 (or NC19F eNb), which is used, for example, to manufacture components of light water nuclear reactors (or LWRs, “Light Water Reactors”), such as structural components or components of nuclear fuel assemblies, intended for insertion, for example, into these light water nuclear reactors. Background Technology

[0002] INCONEL ® The classic chemical composition of Alloy 718 (hereinafter referred to as "Alloy 718") is as follows:

[0003] - Trace levels ≤ C ≤ 0.08%;

[0004] - Trace amounts ≤ Mn ≤ 0.35%;

[0005] - Trace amounts ≤ Si ≤ 0.35%;

[0006] - Trace levels ≤ P ≤ 0.015%;

[0007] - Trace amount ≤ S ≤ 0.015%;

[0008] - 17.0%≤Cr≤21.0%;

[0009] - Trace levels ≤ Co ≤ 1.0%;

[0010] - 2.80≤Mo≤3.30%;

[0011] - 4.75%≤Nb+Ta≤5.50%;

[0012] - 0.65%≤Ti≤1.15%;

[0013] - 0.20%≤Al≤0.80%;

[0014] - Trace amounts ≤ Cu ≤ 0.30%;

[0015] - 50.0%≤Ni≤55.0%;

[0016] - Trace levels ≤ B ≤ 0.006%;

[0017] The balance consists of Fe and impurities generated during processing.

[0018] Nuclear reactor components, especially those for nuclear fuel assemblies, are typically limited in size and thickness. Many of these components are manufactured by forming one or more metal plates.

[0019] These types of components require exceptionally high dimensional accuracy.

[0020] In addition, the environment of light water nuclear reactors is very special and will exert very special stress on alloy 718, especially related to radioactivity.

[0021] Light water nuclear reactor components are particularly exposed to the risk of environmentally induced cracking, and especially to the risk of stress corrosion cracking.

[0022] US5244515 and US5047093 propose a high-temperature heat treatment or "annealing" to slow the propagation of stress corrosion cracks in Alloy 718 used in nuclear applications, thereby reducing the presence of the δ phase in the microstructure of Alloy 718.

[0023] US8470106 discloses an annealing process for desensitizing environmentally induced cracking, wherein the desensitizing annealing is performed in a hydrogen atmosphere and is designed to eliminate interstitial elements in alloy 718 as much as possible. Summary of the Invention

[0024] One of the objectives of this invention is to obtain an alloy that improves its resistance to environmentally induced cracking, particularly under conditions that may cause stress corrosion, while maintaining its mechanical properties, especially in the aged state.

[0025] Therefore, the present invention provides a method for manufacturing nuclear reactor components, particularly light water nuclear reactor components, the manufacturing method comprising the following steps:

[0026] - Obtain a strip made of a nickel-based alloy having the following chemical composition by weight percentage: trace ≤C≤0.08%; trace ≤Mn≤0.35%; trace ≤Si≤0.35%; trace ≤P≤0.015%; trace ≤S≤0.015%; 17.0%≤Cr≤21.0%; trace ≤Co≤1.0%; 2.80%≤Mo≤3.30%; 4.75%≤Nb+Ta≤5.50%; 0.65%≤Ti≤1.15%; 0.20%≤Al≤0.80%; trace ≤Cu≤0.30%; 50.0%≤Ni≤55.0%; trace ≤B≤0.006%; balance Fe and impurities generated during processing;

[0027] - Desensitizing annealing of the strip in a static furnace to obtain annealed strip, comprising holding the strip at an annealing temperature equal to or greater than 900°C, particularly equal to or greater than 920°C, preferably equal to or greater than 940°C, and / or equal to or less than 1050°C, particularly equal to or less than 1000°C, preferably equal to or less than 980°C, for an annealing duration equal to or greater than 1 minute, particularly equal to or greater than 15 minutes, preferably equal to or greater than 30 minutes, and / or equal to or less than 180 minutes; and

[0028] - The annealed strip is shaped to obtain the component.

[0029] Annealing Alloy 718 in strip form before strip forming at a limited temperature and for an appropriate duration can increase the content of the δ phase in the microstructure of Alloy 718.

[0030] Studies have found that such increases in δ-phase content reduce sensitivity to environmentally assisted cracking.

[0031] The increase in δ phase content does not significantly reduce the ambient temperature ductility of the resulting alloy 718, which is easy to form and has a high elongation at break value, which can be as high as 40% or higher.

[0032] This allows for the maintenance of low stress on both hot and cold forming tools, and / or the benefit of better dimensional accuracy in the strip. This good dimensional accuracy is important, especially for nuclear fuel assembly components.

[0033] Performing the final annealing step of the solution in a static furnace and on a metal strip (preferably coil) enables the controlled emergence of the δ phase to be promoted in an economical manner.

[0034] The strip is treated as a whole before it is shaped to form parts (preferably multiple parts).

[0035] An annealing step is performed on the strip, i.e., after obtaining the strip through the required transformation (e.g., hot forging, hot rolling, and / or cold rolling), so that the obtaining of the strip is separated from the annealing.

[0036] The strip is manufactured at a first manufacturing location and preferably coiled, for example, and then transported by road, rail, sea and / or air to a second manufacturing location far from the first manufacturing location, where it is heat-treated and formed, for example, to obtain one, preferably multiple, components from the strip.

[0037] Annealing the metal strip before forming it into a component can produce a specific microstructure that is neither fully recrystallized nor restored and contains a non-negligible δ-phase component.

[0038] However, it is able to maintain the mechanical properties of the final product, which are comparable to those of conventionally treated Alloy 718 used in the nuclear industry, and Alloy 718 was previously thought to contain no δ phase at all, as described in the paper “Thermomechanical treatment and the role of δ phase in stress corrosion cracking of Alloy 718 in native water” by M. Wang et al. (CorrosionScience 160 (2019) 108168).

[0039] In a specific instance, the manufacturing method includes one or more of the following optional features, which can be used individually or in any technically feasible combination:

[0040] - During the desensitization annealing step, the strip is heated from an initial temperature, such as ambient temperature, to the annealing temperature, and then maintained at the annealing temperature for the duration of the annealing;

[0041] - During the desensitization annealing step, the heating rate of the strip is less than 100°C / min, preferably less than 50°C / min, and particularly less than 20°C / min, and / or the heating rate of the strip is greater than 0.5°C / min, preferably greater than 2°C / min, and particularly greater than 4°C / min;

[0042] - The manufacturing method includes performing an active cooling step on the annealed strip after the desensitizing annealing step and before the forming step, preferably, at least when the temperature of the strip is equal to or greater than the cooling temperature, such as 600°C.

[0043] - The desensitization annealing step is carried out under vacuum or in a protective atmosphere, such as a non-oxidizing atmosphere, especially a non-oxidizing atmosphere formed by argon and / or hydrogen;

[0044] - The desensitization annealing step is performed on the strip that has been adjusted into a coil form;

[0045] - The strip has a thickness equal to or less than 0.70 mm, particularly equal to or less than 0.60 mm, and preferably equal to or less than 0.30 mm;

[0046] - At the end of the desensitization annealing step, the δ phase content of the nickel-based alloy microstructure is equal to or greater than 0.1%, particularly equal to or greater than 1%, preferably equal to or greater than 3%, and / or equal to or less than 17%, particularly equal to or less than 12%, preferably equal to or less than 8%;

[0047] - The forming step includes one or more sub-steps such as leveling, cutting, stamping, bending and / or machining;

[0048] - The step of obtaining the strip includes one or more of the following steps: obtaining an ingot made of a nickel-based alloy; homogenizing the ingot with annealing; thermally converting the ingot to obtain a thermally converted product; and cold converting the thermally converted product to obtain the strip, wherein the cold conversion is carried out in a cold conversion step or a series of cold conversion sub-steps, and an intermediate annealing sub-step is provided between each cold conversion sub-step and the next cold conversion sub-step; and / or an intermediate annealing step is provided between the thermal conversion step and the cold conversion step;

[0049] - The manufacturing method does not perform annealing between the cold transformation step and the desensitizing annealing step.

[0050] - The manufacturing method includes an aging annealing step performed after the desensitizing annealing step, preferably at a temperature equal to or greater than 500°C and / or equal to or less than 800°C, and / or for a duration equal to or greater than 1 hour and / or equal to or less than 100 hours.

[0051] - The aging annealing step is performed after the forming step and / or during the forming step;

[0052] - The manufacturing method does not anneal the nickel-based alloy between the desensitization annealing step and the aging annealing step;

[0053] - The manufacturing method does not anneal the nickel-based alloy after the desensitization annealing step;

[0054] - The component is a nuclear fuel assembly element, particularly an element of the positioning grid of a nuclear fuel assembly, an element of the mixing grid of a nuclear fuel assembly, or a spring of a nuclear fuel assembly.

[0055] The present invention also relates to nickel-based alloy components for nuclear reactors, particularly light water reactors, manufactured according to the manufacturing method described above.

[0056] In an exemplary embodiment, at the end of the desensitization annealing step, the δ phase content of the nickel-based alloy microstructure is equal to or greater than 0.1%, particularly equal to or greater than 1%, preferably equal to or greater than 3%, and / or less than 17%, particularly equal to or less than 12%, preferably equal to or less than 8%. Attached Figure Description

[0057] The invention and its advantages will become apparent from the following description, which is given by way of non-limiting example only and with reference to the accompanying drawings, wherein a single Figure 1 The steps of a method for manufacturing nuclear reactor components are shown. Detailed Implementation

[0058] like Figure 1 As shown, the manufacturing method aims to obtain component C of a nuclear reactor, particularly a light water nuclear reactor, which is made of alloy 718 and has a specific microstructure.

[0059] The manufacturing method includes:

[0060] - Step E1: Obtain strip B made of alloy 718 with the following chemical composition in weight percentages: trace ≤ C ≤ 0.08%; trace ≤ Mn ≤ 0.35%; trace ≤ Si ≤ 0.35%; trace ≤ P ≤ 0.015%; trace ≤ S ≤ 0.015%; 17.0% ≤ Cr ≤ 21.0%; trace ≤ Co ≤ 1.0%; 2.80% ≤ Mo ≤ 3.30%; 4.75% ≤ Nb + Ta ≤ 5.50%; 0.65% ≤ Ti ≤ 1.15%; 0.20% ≤ Al ≤ 0.80%; trace ≤ Cu ≤ 0.30%; 50.0% ≤ Ni ≤ 55.0%; trace ≤ B ≤ 0.006%; balance Fe and impurities from processing;

[0061] - Step E2: Anneal strip B in a static furnace FS to obtain heat-treated strip B, and

[0062] - Step E3: Shape the annealed strip B to obtain part C.

[0063] Step E1 for obtaining strip B includes one or more of the following steps, for example:

[0064] - Step E11: Obtain the ingot L of alloy 718;

[0065] - Step E12: Homogenize the ingot L;

[0066] - Step E13: Thermal conversion of ingot L to obtain thermal conversion product P;

[0067] - Step E14: After thermal conversion, the thermal conversion product P is annealed;

[0068] - Step E15: Cold conversion of the thermally converted product P, which may be followed by annealing to obtain strip B. This cold conversion step is performed as a single cold conversion sub-step E151 or a series of cold conversion sub-steps E151, with an intermediate annealing sub-step E152 between each cold conversion sub-step E151 and the next; and / or

[0069] - Step E16: Wind strip B into a roll.

[0070] Preferably, step E1 of obtaining strip B includes: step E11 of obtaining ingot, step E12 of homogenizing annealing of ingot L, step E13 of thermal conversion of ingot L to obtain thermal conversion product P, step E14 of annealing after thermal conversion, and step E15 of cold conversion of thermal conversion product P.

[0071] In possible variations, the homogenization annealing step E12, the thermal conversion step E13, the annealing step E14 after thermal conversion, and / or the cold conversion step E15 are omitted.

[0072] Step E11, which obtains ingot L, typically includes, for example, producing and casting alloy 718 having the composition described above in a liquid state, in the form of ingot L.

[0073] Typically, this production is carried out through one or a series of processes that impart good purity to Alloy 718 in terms of chemical composition and inclusion cleanliness.

[0074] Producing liquid alloy 718 in a vacuum induction furnace (VIM), then casting it into ingots, and then remelting it under conductive slag to improve its purity and inclusion cleanliness is a non-limiting example of such a series of processes.

[0075] If applicable, the homogenization annealing step E12 of the ingot L (which is optional) is carried out, for example, at a homogenization temperature between 1,000°C and 1,400°C and / or for a homogenization duration between 30 minutes and 24 hours.

[0076] The homogenization annealing step E12 of ingot L is carried out in a static furnace.

[0077] If applicable, the thermal conversion step E13 is carried out, for example by hot rolling and / or hot forging, in a temperature range between 750°C and 1,200°C.

[0078] Preferably, the heat conversion step E13 is carried out with a forging rate of at least 0.5 (the ratio between the section after heat conversion and the section before heat conversion).

[0079] Preferably, step E13 of thermal conversion is carried out to obtain thermal conversion product P in the form of strip or sheet.

[0080] For example, when step 14, which involves annealing after thermal conversion, is performed, the annealing temperature after thermal conversion is between 750°C and 1,200°C, and / or the annealing duration after thermal conversion is between 1 minute and 5 hours.

[0081] The annealing step E14 following this type of thermal conversion, performed after the thermal conversion step, ensures a uniform and reproducible microstructure, regardless of the precise implementation conditions of the thermal conversion step E13.

[0082] For example, the annealing step E14 after thermal conversion is carried out in a continuous furnace or a static furnace.

[0083] During the thermal conversion step E13, the thermal conversion product P is subjected to a cold conversion step E15, and can be annealed during the annealing step E14 after the thermal conversion to obtain strip B.

[0084] The cold conversion step E15 is carried out by any type of cold conversion. For example, the cold conversion step E15 includes at least one sub-step E151 of cold rolling.

[0085] The cold conversion step E15 may include, for example, a single cold rolling step E151, or a series of cold rolling steps E151, with an intermediate annealing sub-step E152 between each cold rolling step E151 and the next cold rolling step.

[0086] Each cold rolling sub-step E151 is performed in one or more rolling passes. Each rolling pass corresponds to the product passing between two rolls of the mill, and the thickness of the product P decreases between rolling passes.

[0087] For example, each rolling pass has a reduction rate of at least 10%. This reduction rate is the difference between the area of ​​the cross-section before rolling and the area of ​​the cross-section after rolling, expressed as a percentage.

[0088] If applicable, each intermediate annealing sub-step 152 includes heating the product P to a temperature equal to or greater than 940°C for a duration equal to or greater than 10 seconds.

[0089] Each intermediate annealing sub-step 152 restores the ductility of alloy 718 before the next cold conversion sub-step E151.

[0090] For example, each intermediate annealing sub-step E152 is carried out in a continuous furnace.

[0091] The cold conversion step E15 may be carried out, for example, by a single cold rolling in the cold rolling sub-step E151, or by alternating a series of cold rolling sub-steps E151 with intermediate annealing sub-steps E152.

[0092] If applicable, the winding step E16 is carried out in a winding device placed downstream of the mill used during the cold conversion step E15, for example, to recover the strip B at the exit of the mill and roll it into a coil.

[0093] The thickness of the strip B obtained at the end of step E1 is preferably equal to or less than 0.70 mm, particularly equal to or less than 0.60 mm, and preferably equal to or less than 0.30 mm.

[0094] The desensitizing annealing step E2 involves processing strip B (preferably adjusted to coil) in a static furnace FS to obtain annealed strip B.

[0095] During step E2 of the desensitizing annealing, strip B is heated to an annealing temperature of 900°C or greater, particularly 920°C or greater, preferably 940°C or greater, and / or 1050°C or less, particularly 1000°C or less, preferably 980°C or less, and maintained at the annealing temperature for an annealing duration of 1 minute or greater, particularly 15 minutes or greater, preferably 30 minutes or greater, and / or 180 minutes or less.

[0096] During the desensitization annealing step E2, the strip B is heated from an initial temperature, such as ambient temperature, to the annealing temperature, and then maintained at the annealing temperature for the duration of annealing.

[0097] During the desensitization annealing step E2, the heating rate of strip B is less than 100°C / min, preferably less than 50°C / min, and especially less than 20°C / min, and / or the heating rate of strip is greater than 0.5°C / min, preferably greater than 2°C / min, and especially greater than 4°C / min.

[0098] The desensitizing annealing step E2 is preferably carried out in a static furnace FS under a controlled atmosphere or vacuum.

[0099] Preferably, the controlled atmosphere is a non-oxidizing atmosphere formed by, for example, a neutral gas or a mixture of neutral gases (e.g., argon (Ar), nitrogen (N2) and mixtures thereof) or a reducing atmosphere (e.g., hydrogen (H2) or an Ar / H2 mixture).

[0100] For example, desensitizing annealing is performed under vacuum, at temperatures less than 10... -2 The test was conducted under a pressure of mbar.

[0101] In the variant, the desensitizing annealing step E2 is carried out in an oxidizing atmosphere, provided that pickling and / or descaling operations are performed after the desensitizing annealing, with the aim of removing the oxide layer formed on the strip surface during the desensitizing annealing.

[0102] At the end of step E2 of the desensitization annealing, the δ phase content of the microstructure of alloy 718 is equal to or greater than 0.1%, particularly equal to or greater than 1%, preferably equal to or greater than 3%, and / or equal to or less than 17%, particularly equal to or less than 12%, preferably equal to or less than 8%.

[0103] Optionally, the manufacturing method includes an active cooling step E21 performed at the end of the desensitizing annealing step E2.

[0104] Active cooling is understood as, for example, by forcing a heat exchanger to cool the annealed strip B faster than simply placing it in open air. For instance, active cooling of strip B can be achieved by injecting cold, neutral gas into the furnace cavity.

[0105] The active cooling step E21 can prevent the precipitation of hardened phases in the microstructure of alloy 718.

[0106] Active cooling step E21 is performed, for example, between the desensitizing annealing temperature and a cooling temperature strictly below the desensitizing annealing temperature, such as 600°C.

[0107] Below the cooling temperature, cooling can be slower. For example, it can occur in ambient air.

[0108] Preferably, the active cooling step E21 is carried out in a non-oxidizing protective atmosphere, which is, for example, composed of Ar, H2 or an Ar / H2 mixture with a dew point of -51°C or lower.

[0109] Once the strip reaches the temperature required to be exposed to open air (e.g., approximately 150°C), remove the non-oxidizing protective atmosphere.

[0110] The active cooling step E21 is preferably performed on the strip B that has been adjusted into a coil.

[0111] After the desensitizing annealing step E2, which may be followed by the active cooling step E21, the alloy 718 of strip B is about to be formed, especially cold-formed.

[0112] The desensitizing annealing step E2 is preferably the final annealing that alloy 718 undergoes during the manufacturing of the part.

[0113] For example, the forming step E3 includes cutting strip B, stamping strip B, bending strip B, and / or machining strip B to form part C. A leveling step of strip B may be performed before the forming step E3.

[0114] Component C is, for example, a spring R of a lattice of a nuclear fuel assembly, or a plate of a lattice of a nuclear fuel assembly formed by multiple staggered plates that define multiple units, for example, each unit is designed to accommodate nuclear fuel rods, each plate including a (rigid) recess D and a (elastic) spring R formed in and / or added to the plate to laterally support the nuclear fuel rods and / or fins A, disposed on the upper and / or lower edges of the plate, for example, to force the cooling fluid passing through the nuclear fuel assembly to mix during operation of the nuclear reactor.

[0115] Component C is obtained by: leveling the strip B initially wound into a coil to obtain a flat strip B, for example, then shaping the strip B by cutting the strip B, and shaping the strip B by cutting, stamping and / or machining, for example, to form one or more springs R and / or a plate including recesses D and / or springs R and / or fins A in the plate.

[0116] The manufacturing method may optionally include an aging annealing step E4 performed after the desensitizing annealing step E2.

[0117] For example, the aging annealing step E4 is performed before, after, and / or during the forming step E3, or between sub-steps of the forming step E3.

[0118] The aging annealing step E4 is carried out in one or more steps, during which the 718 base alloy is maintained at an aging temperature of 500°C to 800°C and / or an aging duration of 1 hour to 100 hours.

[0119] The implementation of the aging annealing step E4 can increase hardness without changing the δ phase content obtained after the desensitization treatment.

[0120] Metal strips manufactured in Alloy 718 were tested, with the composition expressed as a percentage by weight: Cr = 19.0%; Mo = 3.0%; Nb + Ta = 5.15%; Ti = 0.90%; Al = 0.50%; Ni = 52%, with the balance being Fe and impurities from processing.

[0121] Each strip is obtained by performing the following steps: step E11 to obtain an ingot L of alloy 718, step E12 to homogenize and anneal the ingot L, step E13 to thermally convert the ingot L to obtain a thermally converted product P, step E14 to anneal the thermally converted product P after thermal conversion, and step E15 to cold convert the thermally converted product P and anneal it after thermal conversion to obtain strip B. The cold conversion step is performed as a single cold conversion sub-step E151, or as a series of cold conversion sub-steps E151, with an intermediate annealing sub-step E152 between each cold conversion sub-step E151.

[0122] Then, the strip undergoes different desensitization annealing (desensitization step E2), forming step E3 to form the spring R of the nuclear fuel assembly frame, and aging annealing (aging step E4).

[0123] Measurements were taken before and after aging annealing to determine the Vickers hardness (Hv) of alloy 718 in spring R and the volume fraction of the δ phase.

[0124] In Comparative Example A (not based on the present invention), the strip was annealed at a high temperature of 1060°C, which is above the solid solution line of the δ phase. Furthermore, the heating rate of the strip during the desensitization step E2 was greater than 100°C / min.

[0125] In Examples 1 to 3 (according to the invention), the strip was subjected to desensitization annealing at temperatures of 920°C, 940°C, and 970°C, respectively, below the solid solution line of the δ phase. Furthermore, during the desensitization step E2, the heating rate of the strip was from 7°C / min to 13°C / min.

[0126] In Embodiment 4 (according to the invention), strip B is annealed at a temperature of 970°C below the solid solution line of the δ phase. Furthermore, during the desensitization step E2, the heating rate of the strip is greater than 100°C / min.

[0127] The results are presented in the table below.

[0128] [Table 1]

[0129]

[0130] The results show that when the strip is subjected to a desensitization annealing step at a temperature between 920°C and 970°C, its hardness is greater while maintaining a significant δ phase portion, which is 6% to 8% in Examples 1 to 3 of this paper; while as shown in Comparative Example A, without the recommended desensitization treatment, the δ phase content is very low, practically almost zero.

[0131] In Example 4, strip B was subjected to a desensitizing annealing step at a heating rate greater than 100°C / min, and its hardness and δ phase content were higher than those of Comparative Example A, but lower than those of Examples 1 to 3. In this example, strip B was subjected to a desensitizing annealing step at a heating rate of 7°C / min to 13°C / min.

[0132] Stress corrosion testing was performed on specimens taken from the strips obtained according to Comparative Examples and Examples 1 to 4. According to ASTM E21 (Standard Test Method for High Temperature Tensile Testing of Metallic Materials), the specimens were subjected to strain rates less than or equal to 10⁻⁶ in a thermally conditioned air environment at 650°C. -3 s -1 These tests are conducted until fracture. After the specimen fractures, the ISCC stress corrosion index (in percentage) is determined by measuring the proportion of the total perimeter occupied by the intergranular fracture surface.

[0133] The stress corrosion test results of different embodiments (comparative examples and examples 1 to 3) are shown in Table 2 below.

[0134] [Table 2]

[0135]

[0136] The tests conducted showed that the strips of Examples 1 to 3, which underwent a desensitization step and had a reduced heating rate, were less susceptible to stress corrosion than those obtained according to Comparative Example A and Example 4, in which strip B underwent a desensitization step but the heating rate was greater than 100°C / min.

[0137] The aging step can achieve hardness without changing the δ phase content obtained after desensitization treatment.

[0138] Therefore, the desensitizing annealing step, especially when combined with the aging annealing step, can yield a product that provides a sufficient δ phase while exhibiting enough hardness to fulfill its function.

[0139] Desensitization annealing is performed at a relatively low desensitization annealing temperature and duration, which allows a portion of the δ phase to be retained in alloy 718 and enables it to undergo partial work hardening during shaping after desensitization annealing, surprisingly effectively improving its resistance to crack initiation.

[0140] Limiting the heating rate during the desensitization step allows recrystallization to be restricted. Higher heating rates result in faster recrystallization. In Comparative Example A, complete recrystallization occurred.

[0141] The proposed manufacturing method can maintain mechanical properties similar to those obtained by high-temperature annealing at temperatures above 1050°C (i.e. above the δ-phase solidus) under aging conditions.

[0142] Needless to say, in addition to the operations described, in order to obtain the properties and characteristics of Alloy 718, especially to improve its resistance to crack initiation and propagation, some conventional additional operations may be performed, such as removing unsatisfactory portions of the initial ingot, pickling, straightening of semi-finished or final products, etc.

[0143] Importantly, these operations do not alter the microstructure of Alloy 718, thereby affecting the final product's attainment of the properties desired by this invention.

Claims

1. A method for manufacturing nuclear reactor components, particularly light water nuclear reactor components, the manufacturing method comprising the following steps: - Obtain a strip made of a nickel-based alloy, the nickel-based alloy being composed of the following components in weight percentages: trace ≤C≤0.08%; trace ≤Mn≤0.35%; trace ≤Si≤0.35%; trace ≤P≤0.015%; trace ≤S≤0.015%; 17.0%≤Cr≤21.0%; trace ≤Co≤1.0%; 2.80%≤Mo≤3.30%; 4.75%≤Nb+Ta≤5.50%; 0.65%≤Ti≤1.15%; 0.20%≤Al≤0.80%; trace ≤Cu≤0.30%; 50.0%≤Ni≤55.0%; trace ≤B≤0.006%; the balance being Fe and impurities generated during processing; - Desensitizing annealing of the strip in a static furnace to obtain annealed strip, comprising holding the strip at an annealing temperature equal to or greater than 900°C, particularly equal to or greater than 920°C, preferably equal to or greater than 940°C, and / or equal to or less than 1050°C, particularly equal to or less than 1000°C, preferably equal to or less than 980°C, for an annealing duration equal to or greater than 1 minute, particularly equal to or greater than 15 minutes, preferably equal to or greater than 30 minutes, and / or equal to or less than 180 minutes; and - The annealed strip is shaped to obtain the component.

2. The method according to claim 1, wherein, During the desensitization annealing step, the strip is heated from an initial temperature, such as ambient temperature, to the annealing temperature, and then maintained at the annealing temperature for the duration of the annealing.

3. The method according to claim 1 or 2, wherein, During the desensitization annealing step, the strip is heated to the annealing temperature at a heating rate of less than 100°C / min, preferably less than 50°C / min, particularly less than 20°C / min and / or greater than 0.5°C / min, preferably greater than 2°C / min, particularly greater than 4°C / min.

4. The method according to any one of the preceding claims, comprising performing an active cooling step on the annealed strip after the desensitizing annealing step and before the forming step, preferably performing the step at least when the temperature of the strip is equal to or greater than the cooling temperature, such as 600°C.

5. The method according to any one of the preceding claims, wherein, The desensitization annealing step is carried out under vacuum or in a protective atmosphere, such as a non-oxidizing atmosphere, particularly a non-oxidizing atmosphere formed by argon and / or hydrogen.

6. The method according to any one of the preceding claims, wherein, The desensitization annealing step is performed on the strip material that has been adjusted into a roll form.

7. The method according to any one of the preceding claims, wherein, The strip has a thickness of 0.70 mm or less, particularly 0.60 mm or less, and preferably 0.30 mm or less.

8. The method according to any one of the preceding claims, wherein, At the end of the desensitization annealing step, the δ phase content of the nickel-based alloy microstructure is equal to or greater than 0.1%, particularly equal to or greater than 1%, preferably equal to or greater than 3%, and / or equal to or less than 17%, particularly equal to or less than 12%, preferably equal to or less than 8%.

9. The method according to any one of the preceding claims, wherein, The forming step includes one or more sub-steps such as leveling, cutting, stamping, bending and / or machining.

10. The method according to any one of the preceding claims, wherein, The steps for obtaining the strip include one or more of the following steps: - Obtain ingots made of nickel-based alloys; - The ingot is subjected to homogenization annealing; - The ingot is subjected to thermal conversion to obtain thermal conversion products; - The thermal conversion product is subjected to cold conversion to obtain the strip, wherein the cold conversion is carried out in a cold conversion step or a series of cold conversion sub-steps, and an intermediate annealing sub-step is provided between each cold conversion sub-step and the next; and / or - An intermediate annealing step is provided between the thermal conversion step and the cold conversion step.

11. The method of claim 10, wherein no annealing is performed between the cold conversion step and the desensitizing annealing step.

12. The method according to any one of the preceding claims, comprising an aging annealing step performed after the desensitization annealing step, preferably performed at a temperature equal to or greater than 500°C and / or equal to or less than 800°C, and / or for a duration equal to or greater than 1 hour and / or equal to or less than 100 hours.

13. The method according to claim 12, wherein, The aging annealing step is performed after the forming step and / or during the forming step.

14. The method according to claim 12 or claim 13, wherein the nickel-based alloy is not annealed between the desensitization annealing step and the aging annealing step.

15. The method according to any one of the preceding claims, wherein the nickel-based alloy is not annealed after the desensitization annealing step.

16. The method according to any one of the preceding claims, wherein, The component is a nuclear fuel assembly element, particularly an element of the positioning grid of a nuclear fuel assembly, an element of the mixing grid of a nuclear fuel assembly, or a spring of a nuclear fuel assembly.

17. A nickel-based alloy component of a nuclear reactor, particularly a light water reactor, manufactured by the manufacturing method according to any one of the preceding claims.

18. The component according to claim 17, wherein, At the end of the desensitization annealing step, the δ phase content of the nickel-based alloy microstructure is equal to or greater than 0.1%, particularly equal to or greater than 1%, preferably equal to or greater than 3%, and / or equal to or less than 17%, particularly equal to or less than 12%, preferably equal to or less than 8%.

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