Method for manufacturing a nuclear reactor component and resulting nuclear reactor component

Abstract

The manufacturing method comprises obtaining a strip of nickel-based alloy having a composition, in percentages by weight: trace amounts ≤ C ≤ 0.08%; trace amounts ≤ Mn ≤ 0.35%; trace amounts ≤ Si ≤ 0.35%; trace amounts ≤ P ≤ 0.015%; trace amounts ≤ S ≤ 0.015%; 17.0% ≤ Cr ≤ 21.0%; trace amounts ≤ 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 amounts ≤ Cu ≤ 0.30%; 50.0% ≤ Ni ≤ 55.0%; trace amounts ≤ B ≤ 0.006%; the balance being Fe and impurities resulting from the production, and performing desensitization annealing in a static furnace at an annealing temperature equal to or higher than 900°C and / or equal to or lower than 1050°C for an annealing time equal to or greater than 1 min and / or equal to or less than 180 min.

Description

[0001] Method for manufacturing a nuclear reactor component and nuclear reactor component thus obtained

[0002] The present invention relates to the field of nickel superalloys, and more precisely the nickel-based alloy known as INCONEL® 718 (or NC19FeNb) corresponding to the UNS N07718 standard, which is used, for example, to manufacture components of light water nuclear reactors (or LWR), for example structural components or components of nuclear fuel assemblies intended to be inserted into these light water nuclear reactors.

[0003] The typical chemical composition of the INCONEL®718 alloy (a name which will subsequently be abbreviated to “alloy 718”) is as follows: traces < C < 0.08%; traces < Mn < 0.35%; traces < Si < 0.35%; traces < P < 0.015%; traces < S < 0.015%;

[0004] - 17.0% < Cr < 21.0%; traces < Co < 1.0%;

[0005] - 2.80 < Mo < 3.30%;

[0006] - 4.75% < Nb + Ta < 5.50%;

[0007] - 0.65% < Ti < 1.15%;

[0008] - 0.20% < Al < 0.80%; traces < Cu < 0.30%;

[0009] - 50.0% < Ni < 55.0%; traces < B < 0.006%; the remainder being Fe and impurities resulting from the production.

[0010] Nuclear reactor components, particularly those in nuclear fuel assemblies, are often of limited size and thickness. Many of these components are manufactured by forming one or more metal sheets.

[0011] Such components require particularly high dimensional accuracy.

[0012] Furthermore, the environment of a light water nuclear reactor is very specific and imposes very specific stresses on alloy 718, linked in particular to radioactivity. Light water nuclear reactor components are particularly exposed to the risk of environmentally assisted cracking, and in particular to the risk of stress corrosion cracking.

[0013] US5244515 and US5047093 propose a high temperature heat treatment or "annealing" to slow the propagation of stress corrosion cracks in a 718 alloy used in a nuclear application, to reduce the occurrence of phase 5 in the microstructure in the 718 alloy.

[0014] US8470106 discloses an environmentally assisted crack desensitization anneal, wherein the desensitization anneal is performed under a hydrogen atmosphere and is intended to eliminate as much interstitial elements in the 718 alloy as possible.

[0015] One of the aims of the invention is to make it possible to obtain an alloy whose resistance to environmentally assisted cracking, particularly under conditions likely to lead to stress corrosion, is improved, while preserving the mechanical properties, particularly in the aged state.

[0016] For this purpose, the invention provides a method for manufacturing a component of a nuclear reactor, in particular a light water nuclear reactor, the manufacturing method comprising the steps of: obtaining a strip made of nickel-based alloy of chemical composition, expressed in weight percentages: traces < C < 0.08%; traces < Mn < 0.35%; traces < Si < 0.35%; traces < P < 0.015%; traces < S < 0.015%; 17.0% < Cr < 21.0%; traces < Co < 1.0%; 2.80 < Mo < 3.30%; 4.75% < Nb + Ta < 5.50%; 0.65% < Ti < 1.15%; 0.20% < Al < 0.80%; traces < Cu < 0.30%; 50.0% < Ni < 55.0%; traces < B < 0.006%; the remainder being Fe and impurities resulting from the production;carrying out a desensitization annealing of the strip in a static furnace to obtain an annealed strip, comprising maintaining the strip at an annealing temperature equal to or greater than 900°C, in particular equal to or greater than 920°C, preferably equal to or greater than 940°C and / or equal to or less than 1050°C, in particular equal to or less than 1000°C, preferably equal to or less than 980°C, for an annealing time equal to or greater than 1 min, in particular equal to or greater than 15 min, preferably equal to or greater than 30 min and / or equal to or less than 180 min; and shaping the annealed strip to obtain the component.;

[0017] Annealing alloy 718 in the form of a metal strip and before shaping the strip, at a limited temperature and with an appropriate duration, makes it possible to increase the phase 5 content of the microstructure of alloy 718. It has been found that such an increase in the phase 5 content makes it possible to reduce the sensitivity to environmentally assisted cracking.

[0018] The increase in the phase 5 content does not significantly degrade the ductility at room temperature of the 718 alloy obtained for easy forming, with a high value, up to 40% or more, for the elongation at break.

[0019] This has the advantage of maintaining low stress on the hot and cold processing tools and / or thus allowing better dimensional accuracy of the strip. This good dimensional accuracy is important to achieve, particularly on nuclear fuel assembly components.

[0020] Carrying out the final solution annealing step in a static furnace and on the metal strip, preferably packaged in a coil, makes it possible to promote the appearance of phase 5 in a controlled manner, with economical implementation.

[0021] The strip is processed as a whole before the strip is formed into a component, and preferably multiple components.

[0022] Carrying out the annealing step on the strip, i.e. after the transformation steps necessary to obtain the strip, such as hot forging, hot rolling and / or cold rolling, makes it possible to decouple the production of the strip and the annealing.

[0023] The strip is for example manufactured and preferably wound at a first manufacturing location, then transported to a second manufacturing location distant from the first manufacturing location, for example by road transport, rail transport, sea transport and / or air transport, then heat treated and shaped at the second manufacturing location to obtain one and preferably several components from the strip.

[0024] The annealing carried out on the metal strip before shaping it to obtain the component makes it possible to obtain a particular microstructure which is neither totally recrystallized nor restored, and which includes a significant fraction of phase 5.

[0025] However, it allows the final product to retain mechanical properties comparable to those of conventionally treated 718 alloys used by the nuclear industry, which were previously thought not to contain any 5 phase at all, as indicated for example in the article “The Roles of Thermal Mechanical Treatment and 5 Phase in the Stress Corrosion Cracking of Alloy 718 in Primary Water” by M. Wang et al., Corrosion Science 160 (2019) 108168. In particular examples, the manufacturing process comprises one or more of the following optional features, taken individually or in all technically possible combinations:

[0026] - during the desensitization annealing step, the strip is heated from an initial temperature, for example room temperature, to the annealing temperature and then maintained at the annealing temperature for the annealing time;

[0027] - during the desensitization annealing step, the heating rate of the strip is less than 100°C / min, preferably less than 50°C / min, in particular 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, in particular greater than 4°C / min

[0028] - the manufacturing method comprises, after the desensitization annealing step, a step of active cooling of the annealed strip implemented before the shaping step, preferably at least as long as the temperature of the strip is equal to or greater than a cooling temperature, for example equal to 600°C;

[0029] - the desensitization annealing step is carried out under vacuum or under a protective atmosphere, for example a non-oxidizing atmosphere, in particular a non-oxidizing atmosphere formed of argon and / or hydrogen;

[0030] - the desensitization annealing step is carried out on the strip packaged in the form of a coil;

[0031] - the strip has a thickness equal to or less than 0.70 mm, in particular a thickness equal to or less than 0.60 mm, preferably a thickness equal to or less than 0.30 mm;

[0032] - at the end of the desensitization annealing step, the phase 5 content of the microstructure of the nickel-based alloy is equal to or greater than 0.1%, in particular equal to or greater than 1%, preferably equal to or greater than 3% and / or equal to or less than 17%, in particular equal to or less than 12%, preferably equal to or less than 8%;

[0033] - the shaping step comprises one or more sub-steps of planing, cutting, stamping, bending and / or machining

[0034] - the step of obtaining the strip comprises one or more of the following steps: obtaining an ingot made from the nickel-based alloy; carrying out a homogenization annealing of the ingot; hot transformation of the ingot to obtain a hot transformed product; cold transformation of the hot transformed product to obtain the strip, the cold transformation being carried out in a cold transformation step or a series of cold transformation sub-steps with an intermediate annealing sub-step between each cold transformation sub-step and the next; and / or an intermediate annealing step between the hot transformation step and the cold transformation step;

[0035] - the manufacturing process is carried out without annealing between the cold transformation step and the desensitization annealing step.

[0036] - the manufacturing method comprises an aging annealing step carried out after the desensitization annealing step, preferably carried out 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 h and / or equal to or less than 100 h;

[0037] - the aging annealing step is carried out after the shaping step and / or during the shaping step;

[0038] - the manufacturing process is carried out without annealing the nickel-based alloy between the desensitization annealing step and the aging annealing step;

[0039] - the manufacturing process is carried out without annealing without annealing of the nickel-based alloy after the desensitization annealing step;

[0040] - the component is a nuclear fuel assembly element, in particular an element of a spacer grid of a nuclear fuel assembly, an element of a mixing grid of a nuclear fuel assembly or a spring of a nuclear fuel assembly.

[0041] The invention also relates to a nickel-based alloy component of a nuclear reactor, in particular a light water reactor, produced according to a manufacturing method as defined above.

[0042] In exemplary embodiments, at the end of the desensitization annealing step, the phase 5 content of the microstructure of the nickel-based alloy is equal to or greater than 0.1%, in particular equal to or greater than 1%, preferably equal to or greater than 3% and / or equal to or less than 17%, in particular equal to or less than 12%, preferably equal to or less than 8%.

[0043] The invention and its advantages will become apparent upon reading the following description, given solely as a non-limiting example, and made with reference to the appended drawing, in which the single Figure 1 illustrates steps in a method of manufacturing a nuclear reactor component.

[0044] As illustrated in Figure 1, the manufacturing process aims to obtain a component C of a nuclear reactor, in particular a light water nuclear reactor, the component being made of alloy 718 and having a particular microstructure. The manufacturing process comprises:

[0045] - a step E1 of obtaining a strip B made of alloy 718 with the following chemical composition, expressed in weight percentages: traces < C < 0.08%; traces < Mn < 0.35%; traces < Si < 0.35%; traces < P < 0.015%; traces < S < 0.015%; 17.0% < Cr

[0046] <21.0%; traces < Co < 1.0%; 2.80 < MB < 3.30%; 4.75% < Nb + Ta < 5.50%; 0.65% < Ti

[0047] < 1.15%; 0.20% < Al < 0.80%; traces < Cu < 0.30%; 50.0% < Ni < 55.0%; traces < B < 0.006%; the remainder being Fe and impurities resulting from the elaboration;

[0048] - a step E2 of carrying out an annealing of the strip B in a static furnace FS to obtain a heat-treated strip B, and

[0049] - a step E3 of shaping the annealed strip B to obtain component C.

[0050] Step E1 of obtaining the strip B comprises for example one or more of the following steps: a step E11 of obtaining an ingot L of alloy 718; a step E12 of carrying out a homogenization annealing of the ingot L; a step E13 of hot transformation of the ingot L to obtain a hot-transformed product P; a step E14 of annealing after hot transformation applied to the hot-transformed product P; a step E15 of cold transformation of the hot-transformed product P and optionally annealed after hot transformation to obtain the strip B, the cold transformation step being carried out in a single cold transformation sub-step E151 or a series of cold transformation sub-steps E151, with an intermediate annealing sub-step E152 between each cold transformation sub-step E151 and the next; and / or a winding step E16 to package the strip B in the form of a coil.

[0051] Preferably, step E1 of obtaining band B comprises step E11 of obtaining an ingot, step E12 of carrying out a homogenization annealing of the ingot L, step E13 of hot transformation of the ingot L to obtain a hot transformed product P, step E14 of annealing after hot transformation and step E15 of cold transformation of the hot transformed product P.

[0052] In possible variants, the homogenization annealing step E12 is omitted, the hot transformation step E13 is omitted, the annealing step E14 after hot transformation and / or the cold transformation step E15 is omitted. The step E11 of obtaining an ingot L comprises, for example, in a conventional manner, the production in the liquid state and the casting, in the form of an ingot L, of an alloy 718 of composition as mentioned above.

[0053] Typically, this elaboration is carried out by a process or a series of processes which give the alloy 718 a good purity in terms of chemical composition and inclusion cleanliness.

[0054] The production of alloy 718 in the liquid state in a vacuum induction furnace (VIM), followed by the casting of an ingot which then undergoes remelting under electroconductive slag to improve its purity and inclusion cleanliness, is a non-limiting example of such a sequence of processes.

[0055] Where appropriate, step E12 of homogenization annealing of the ingot L, which is optional, is carried out for example at a homogenization temperature of between 1,000°C and 1,400°C and / or for a homogenization time of between 30 min and 24 h.

[0056] Step E12 of homogenization annealing of ingot L is carried out in a static furnace.

[0057] Where appropriate, the hot transformation step E13 is carried out in a temperature range between 750°C and 1,200°C, for example by hot rolling and / or hot forging.

[0058] Preferably, the hot transformation step E13 is carried out with a working ratio (the ratio between the section after hot transformation and the section before hot transformation) of at least 0.5.

[0059] The hot transformation step E13 is preferably carried out so as to obtain a hot transformed product P having the shape of a strip or a plate.

[0060] When a post-hot transformation annealing step 14 is implemented, this is for example carried out at a post-hot transformation annealing temperature of between 750°C and 1,200°C and / or for a post-hot transformation annealing time of between 1 min and 5 h.

[0061] Such an E14 annealing step after hot transformation, carried out after a hot transformation step, makes it possible to ensure that a homogeneous and reproducible microstructure is obtained regardless of the precise conditions of implementation of the E13 hot transformation step.

[0062] The annealing step E14 after hot transformation is carried out for example in a flow furnace or a static furnace. The cold transformation step E15 is carried out on the product P hot transformed during the hot transformation step E13 and possibly annealed during the annealing step E14 after hot transformation, to obtain the strip B.

[0063] Cold processing step E15 is carried out by any type of cold processing. Cold processing step E15 comprises, for example, at least one cold rolling sub-step E151.

[0064] The cold transformation step E15 comprises, for example, a single cold rolling sub-step E151 or a series of cold rolling sub-steps E151 with an intermediate annealing sub-step E152 between each cold rolling step E151 and the next.

[0065] Each cold rolling sub-step E151 is carried out in one or more rolling passes. Each rolling pass corresponds to the passage of the product between two rollers of a rolling mill between which the thickness of the product P is reduced.

[0066] For example, each rolling pass has a reduction rate of at least 10%. The reduction rate is the difference between the area of ​​the section before rolling and the area of ​​the section after rolling, expressed as a percentage.

[0067] Where appropriate, each intermediate annealing sub-step 152 comprises heating the product P to a temperature equal to or greater than 940°C for a duration equal to or greater than 10 seconds.

[0068] Each intermediate annealing sub-step 152 makes it possible to restore ductility to the alloy 718 before the following cold transformation sub-step E151.

[0069] Each intermediate annealing sub-step E152 is carried out, for example, in a continuous furnace.

[0070] The cold transformation step E15 is for example carried out solely by cold rolling in a cold rolling sub-step E151 or a series of cold rolling sub-steps E151 alternating with intermediate annealing sub-steps E152.

[0071] Where appropriate, the winding step E16 is carried out in a winding device, for example arranged downstream of a rolling mill used during the cold transformation step E15, to recover the strip B at the outlet of this rolling mill and wind it into a coil.

[0072] The strip B obtained at the end of the obtaining step E1 preferably has a thickness equal to or less than 0.70 mm, in particular a thickness equal to or less than 0.60 mm, preferably a thickness equal to or less than 0.30 mm. The desensitization annealing step E2 is carried out on the strip B, preferably packaged in a coil, in a static furnace FS, to obtain an annealed strip B.

[0073] During the desensitization annealing step E2, the strip B is heated to an annealing temperature equal to or greater than 900°C, in particular equal to or greater than 920°C, preferably equal to or greater than 940°C and / or equal to or less than 1050°C, in particular equal to or less than 1000°C, preferably equal to or less than 980°C, and maintained at the annealing temperature for an annealing time equal to or greater than 1 min, in particular equal to or greater than 15 min, preferably equal to or greater than 30 min and / or equal to or less than 180 min.

[0074] In the desensitization annealing step E2, the strip B is heated from an initial temperature, for example room temperature, to the annealing temperature and then maintained at the annealing temperature for the annealing time.

[0075] In the desensitization annealing step E2, the heating rate of the strip B is less than 100°C / min, preferably less than 50°C / min, in particular 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, in particular greater than 4°C / min.

[0076] The desensitization annealing step E2 is preferably carried out in the static furnace FS under controlled atmosphere or vacuum.

[0077] The controlled atmosphere is preferably a non-oxidizing atmosphere, formed for example by a neutral gas or a mixture of neutral gases such as argon (Ar), nitrogen (N2) and their mixtures, or a reducing atmosphere such as hydrogen (H2) or an Ar / H2 mixture.

[0078] Vacuum desensitization annealing is for example carried out at a pressure below 10 -2 mbar.

[0079] In a variant, the desensitization annealing step E2 is carried out under an oxidizing atmosphere, provided that the desensitization annealing is followed by a pickling and / or peeling operation aimed at removing an oxidized layer which has formed on the surface of the strip during the desensitization annealing.

[0080] At the end of the desensitization annealing step E2, the phase 5 content of the microstructure of the alloy 718 is equal to or greater than 0.1%, in particular equal to or greater than 1%, preferably equal to or greater than 3% and / or equal to or less than 17%, in particular equal to or less than 12%, preferably equal to or less than 8%.

[0081] Optionally, the manufacturing method includes an active cooling step E21 implemented after the desensitization annealing step E2. Active cooling means that the annealed strip B is cooled more quickly than if it were simply left in the open air, for example by forcing a heat exchanger. Active cooling of the strip B is, for example, implemented by injecting cold neutral gas into the furnace enclosure.

[0082] Active cooling step E21 prevents the hardening phases from precipitating into the microstructure of alloy 718.

[0083] The active cooling step E21 is for example implemented between the desensitization annealing temperature and a cooling temperature strictly lower than the desensitization annealing temperature, and for example equal to 600°C.

[0084] Below the cooling temperature, cooling may be slower. For example, it can be carried out in ambient air.

[0085] Preferably, the active cooling step E21 is carried out under a non-oxidizing protective atmosphere, for example consisting of Ar, H2 with a dew point of -51°C or lower, or an Ar / H2 mixture.

[0086] The non-oxidizing protective atmosphere is, for example, removed as soon as the strip temperature reaches a venting temperature, for example approximately 150°C.

[0087] Active cooling step E21 is preferably carried out on the tape B packaged in a reel.

[0088] After the desensitization annealing step E2, possibly followed by the active cooling step E21, the alloy 718 of band B is capable of undergoing shaping, in particular cold shaping.

[0089] Desensitization annealing step E2 is preferably the last annealing undergone by the 718 alloy during the manufacture of the component.

[0090] The shaping step E3 comprises, for example, cutting the strip B, stamping the strip B, bending the strip B and / or machining the strip B to form the component C. The shaping step E3 is optionally preceded by a step of planishing the strip B.

[0091] The component C is for example a spring R of a grid of a nuclear fuel assembly, or for example a plate of a grid of a nuclear fuel assembly formed of a plurality of intersecting plates delimiting cells, each cell being intended to receive a nuclear fuel rod, each plate comprising dimples D (rigid), springs R (elastic) formed in the plate and / or attached to the plate to transversely support the nuclear fuel rods and / or fins A, arranged for example on an upper edge and / or a lower edge of the plate to force a mixture of a coolant passing through the nuclear fuel assembly during operation of the nuclear reactor.

[0092] Component C is for example obtained by planing the strip B initially wound into a coil to obtain a flat strip B, then shaping the strip B, for example by cutting into the strip B and shaping by cutting, stamping and / or machining to form one or more springs R and / or plates comprising dimples D and / or springs R and / or fins A formed in the plate.

[0093] The manufacturing process optionally includes an aging annealing step E4 implemented after the desensitization annealing step E2.

[0094] The aging annealing step E4 is implemented before the shaping step E3, after the shaping step E3 and / or during the shaping step E3, for example between sub-steps of the shaping step E3.

[0095] 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 between 500°C and 800°C and / or for an aging time of between 1 h and 100 h.

[0096] The implementation of an E4 aging annealing step makes it possible to increase the hardness without modifying the quantity of phase 5 obtained after the desensitization treatment.

[0097] Tests were carried out on metal strips made from alloy 718 with the following composition, expressed in weight percentages: Cr = 19.0%; Mo = 3.0%; Nb + Ta = 5.15%, Ti = 0.90%; Al = 0.50%; Ni = 52%; the remainder being Fe and impurities resulting from the production.

[0098] Each strip was obtained by implementing a step E11 of obtaining an ingot L of alloy 718, a step E12 of carrying out a homogenization annealing of the ingot L, a step E13 of hot transformation of the ingot L to obtain a hot transformed product P, a step E14 of annealing after hot transformation applied to the hot transformed product P, a step E15 of cold transformation of the hot transformed product P and annealing after hot transformation to obtain the strip B, the cold transformation step being carried out in a single cold transformation sub-step E151 or a series of cold transformation sub-steps E151, with an intermediate annealing sub-step E152 between each cold transformation sub-step E151.The strips then underwent different desensitization anneals (desensitization step E2), a shaping step E3 to form nuclear fuel assembly grid R springs and an aging anneal (aging step E4).

[0099] Measurements were performed before and after age annealing to determine the Vickers hardness (Hv) of alloy 718 in R springs, as well as the phase 5 volume fraction.

[0100] In Comparative Example A (not in accordance with the invention), the strip was annealed at a high temperature of 1060°C, which is higher than the solvus of phase 5. Furthermore, the heating rate of the strip during the desensitization step E2 was higher than 100°C / min.

[0101] In Examples 1 to 3 (in accordance with the invention), the strips underwent desensitization annealing at temperatures of 920°C, 940°C and 970°C respectively, which are lower than the solvus of phase 5. Furthermore, the heating rate of the strips during the desensitization step E2 was between 7°C / min and 13°C / min.

[0102] In Example 4 (according to the invention), strip B was annealed at a temperature of 970°C, which is lower than the solvus of phase 5. Furthermore, the heating rate of the strip during the desensitization step E2 was higher than 100°C / min.

[0103] The results are presented in the table below.

[0104] [Table 1]

[0105] The results show a greater hardness when the strip has undergone a desensitization annealing step at a temperature between 920°C and 970°C, while retaining a significant fraction of phase 5, here between 6 and 8% in examples 1 to 3, whereas the phase 5 content is very low, and in particular practically zero, in the absence of desensitization as recommended, as illustrated by comparative example A.

[0106] In Example 4 in which strip B underwent a desensitization annealing step with a heating rate greater than 100°C / min, the hardness and phase 5 content are higher than in Comparative Example A, but lower than in Examples 1 to 3 in which strip B underwent a desensitization annealing step with a heating rate between 7°C / min and 13°C / min.

[0107] Stress corrosion tests were carried out using specimens taken from strips obtained according to the comparative examples and examples 1 to 4. These tests were carried out on the specimens at a strain rate less than or equal to 10 -3 s -1 according to ASTM E21 (Standard Test Methods for Elevated Temperature Tension Tests of Metallic Materials) in a thermally regulated air environment at 650°C until rupture. Following rupture of the specimen, a stress corrosion index ISCC (in %) is determined by measuring the proportion of the total perimeter affected by intergranular fracture surfaces.

[0108] The results of the stress corrosion tests are presented in Table 2 below for the different examples (comparative example and examples 1 to 3).

[0109] [Table 2]

[0110] The tests carried out show that the strips of examples 1 to 3 having undergone the desensitization step with a reduced heating rate of strip B are much less sensitive to stress corrosion than those obtained according to comparative example A and example 4 in which strip B has undergone a desensitization step but with a heating rate greater than 100°C / min. The aging step makes it possible to gain in hardness without modifying the quantity of phase 5 obtained after the desensitization treatment.

[0111] Thus, the desensitization annealing step, particularly in combination with the aging annealing step, makes it possible to obtain a product sufficiently provided in phase 5, while presenting sufficient hardness to fulfill its functions.

[0112] Carrying out a desensitization annealing at a relatively low desensitization annealing temperature and a desensitization annealing duration allowing a fraction of phase 5 to remain in the 718 alloy, possibly subject to partial work hardening due to the shaping carried out after the desensitization annealing, is, surprisingly, effective in improving protection against crack initiation.

[0113] Limiting the heating rate during the desensitization step helps limit recrystallization. The higher the heating rate, the faster the recrystallization. In Comparative Example A, recrystallization was complete.

[0114] The proposed manufacturing process allows to maintain a level of mechanical properties in the aged state similar to that obtained with high temperature annealing, carried out at a temperature above 1050°C, i.e. above the solvus of phase 5.

[0115] It goes without saying that in addition to the operations described which aim to obtain the characteristics and properties of alloy 718, particularly aimed at improving its resistance to the initiation and propagation of cracks, additional operations which are usual can be carried out, such as dropping parts of the initial ingot whose properties would not be satisfactory in any case, pickling, straightening of semi-finished products or of the final product, etc.

[0116] The main thing is that these operations do not lead to modifications of the microstructure of the 718 alloy which would go against obtaining the properties targeted by the invention on the final products.

Claims

CLAIMS 1. A method of manufacturing a component of a nuclear reactor, in particular a light water nuclear reactor, the manufacturing method comprising the steps of: obtaining a strip made of nickel-based alloy of chemical composition, expressed in weight percentages: traces < C < 0.08%; traces < Mn < 0.35%; traces < Si < 0.35%; traces < P < 0.015%; traces < S < 0.015%; 17.0% < Cr < 21.0%; traces < Co < 1.0%; 2.80 < Mo < 3.30%; 4.75% < Nb + Ta < 5.50%; 0.65% < Ti < 1.15%; 0.20% < Al < 0.80%; traces < Cu < 0.30%; 50.0% < Ni < 55.0%; traces < B < 0.006%; the remainder being Fe and impurities resulting from the production;carrying out a desensitization annealing of the strip in a static furnace to obtain an annealed strip, comprising maintaining the strip at an annealing temperature equal to or greater than 900°C, in particular equal to or greater than 920°C, preferably equal to or greater than 940°C and / or equal to or less than 1050°C, in particular equal to or less than 1000°C, preferably equal to or less than 980°C, for an annealing time equal to or greater than 1 min, in particular equal to or greater than 15 min, preferably equal to or greater than 30 min and / or equal to or less than 180 min; and shaping the annealed strip to obtain the component.; 2. The method of claim 1, wherein, during the desensitization annealing step, the strip is heated from an initial temperature, for example room temperature, to the annealing temperature and then maintained at the annealing temperature for the annealing time.

3. Method according to claim 1 or 2, wherein, in the desensitization annealing step, the strip is heated to the annealing temperature with a heating rate of less than 100°C / min, preferably less than 50°C / min, in particular 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, in particular greater than 4°C / min.

4. Method according to any one of the preceding claims, comprising, after the desensitization annealing step, a step of active cooling of the annealed strip carried out before the shaping step, preferably at least as long as the temperature of the strip is equal to or greater than a cooling temperature, for example equal to 600°C.

5. A method according to any one of the preceding claims, wherein the desensitization annealing step is carried out under vacuum or under a protective atmosphere, for example a non-oxidizing atmosphere, in particular a non-oxidizing atmosphere formed of argon and / or hydrogen.

6. A method according to any preceding claim, wherein the desensitization annealing step is performed on the strip packaged in the form of a coil.

7. Method according to any one of the preceding claims, wherein the strip has a thickness equal to or less than 0.70 mm, in particular a thickness equal to or less than 0.60 mm, preferably a thickness equal to or less than 0.30 mm.

8. Method according to any one of the preceding claims, in which, at the end of the desensitization annealing step, the phase 5 content of the microstructure of the nickel-based alloy is equal to or greater than 0.1%, in particular equal to or greater than 1%, preferably equal to or greater than 3% and / or equal to or less than 17%, in particular equal to or less than 12%, preferably equal to or less than 8%.

9. A method according to any preceding claim, wherein the shaping step comprises one or more sub-steps of planing, cutting, stamping, bending and / or machining.

10. A method according to any one of the preceding claims, wherein the step of obtaining the strip comprises one or more of the following steps: obtaining an ingot made from the nickel-based alloy; carrying out a homogenization annealing of the ingot; hot processing of the ingot to obtain a hot processed product; cold processing of the hot processed product to obtain the strip, the cold processing being carried out in one cold processing step or a series of cold processing sub-steps with an intermediate annealing sub-step between each cold processing sub-step and the next; and / or an intermediate annealing step between the hot processing step and the cold processing step.

11. Method according to claim 10, carried out without annealing between the cold transformation step and the desensitization annealing step.

12. Method according to any one of the preceding claims, comprising an aging annealing step carried out after the desensitization annealing step, preferably carried out 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 h and / or equal to or less than 100 h.

13. The method of claim 12, wherein the aging annealing step is performed after the shaping step and / or during the shaping step.

14. Method according to claim 12 or claim 13, without annealing of the nickel-based alloy between the desensitization annealing step and the aging annealing step.

15. Method according to any one of the preceding claims, without annealing of the nickel-based alloy after the desensitization annealing step.

16. A method according to any one of the preceding claims, wherein the component is a nuclear fuel assembly element, in particular an element of a spacer grid of a nuclear fuel assembly, an element of a mixing grid of a nuclear fuel assembly or a spring of a nuclear fuel assembly.

17. Nickel-based alloy component of a nuclear reactor, in particular a light water reactor, produced according to a manufacturing method according to any one of the preceding claims.

18. Component according to claim 17, wherein, at the end of the desensitization annealing step, the phase 5 content of the microstructure of the nickel-based alloy is equal to or greater than 0.1%, in particular equal to or greater than 1%, preferably equal to or greater than 3% and / or equal to or less than 17%, in particular equal to or less than 12%, preferably equal to or less than 8%.

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