Method for producing part made of gamma / gamma'nickel-based alloy by hot forging

Abstract

The invention relates to a method for producing a part made of a nickel-based alloy having a gamma / gamma'microstructure, in which at least one hot forging step is carried out, characterized in that the temperature at which the part is heated during the hot forging step is maintained within a temperature range lower than the temperature range of abnormal grain growth of the alloy, the hot forging temperature is maintained at a temperature lower than the temperature of the component and such that the difference between the hot forging temperature and the temperature at which the component is heated is less than 250 DEG C, and preferably less than 150 DEG C.

Description

Technical Field

[0001] The invention relates to the field of producing components made of gamma / gamma' alloys by hot forging tools.

[0002] It finds advantageous use in the aviation sector, in particular in the production of turboshaft engine components, such as high-pressure turbine disks or low-pressure turbine disks, or also high-pressure compressor disks. Background Art

[0003] New nickel-based alloys with a γ / γ' microstructure, such as those from Aubert & Duval, are commonly used in aerospace engineering. or Rene 65, chosen by Safran Aircraft Engines for some of its engines) for components subject to extreme stresses.

[0004] This alloy is chosen by turbine shaft manufacturers, for example, as a component of high-pressure or low-pressure turbine disks or for high-pressure compressor disks on the latest generation aircraft engines.

[0005] More generally, they are now being considered for use in any turboshaft engine component where elevated operating temperatures are desired and resistance to mechanical stresses at these temperatures is desired.

[0006] The forging process for these components is a series of hot deformation steps (breaking billet, blank stamping, finish stamping, etc.) and heat treatment. Hot deformation is usually carried out on a hydraulic press, using conventional hot forging tools heated to 650°C / 680°C.

[0007] Due to the high content of the hardening phase γ', these alloys have a very narrow temperature forgeability range. During the pressure treatment, the component is heated to a temperature between 1040°C and 1070°C, with the surface temperature of the component being maintained above 800°C throughout the forging process.

[0008] There are two main types of issues that must be addressed when producing components from these alloys.

[0009] During the forging operation, cooling during transfer between the heating furnace and the press or during contact with the cooler hot forging tools during forging can lead to the appearance of surface cracks which must be eliminated by a finalization operation after forging.

[0010] Furthermore, these alloys are sensitive to the phenomenon of abnormal grain growth. Under very specific forging conditions, this phenomenon can occur and lead to significant local grain coarsening. This phenomenon must be absolutely avoided, as it would lead to the rejection of the component, since the mechanical properties of the component in these areas, in particular the fatigue resistance, would not be permissible relative to the required specifications.

[0011] Various studies have been carried out on these subjects. The treatment of these problems usually leads to very severe forging conditions.

[0012] Typically, this may result in minimal deformation being imparted across the component during the forging operation.

[0013] Furthermore, the proposed solutions generally require a greater material implementation weight, on the one hand to compensate for the material lost during the shaping operations aimed at eliminating forging cracks, and on the other hand to be able to comply with minimum deformation criteria due to the increase of material in certain areas in order to avoid abnormal grain growth phenomena.

[0014] The result is that an additional mechanical treatment operation is performed before the heat treatment operation. Since the original forged part is larger, there is a risk that the heat treatment will not produce the required mechanical properties. In fact, for these γ / γ' alloys, the static mechanical properties are strongly dependent on the cooling rate during the heat treatment. An increase in mass causes a decrease in this rate, resulting in a decrease in the mechanical properties.

[0015] Elimination of cracks on raw forged parts by finishing or by mechanical treatment before heat treatment must be accompanied by specific checks to ensure complete elimination of the cracks. In fact, the presence of residual surface cracks before heat treatment can cause them to propagate in the part during quenching. These additional checks generate additional costs. Summary of the invention

[0016] The aim of the present invention is to propose a technique for producing gamma / gamma' alloy components by hot pressing tools, which is able to overcome the problems of abnormal grain growth and cracks, without the complexity and weight drawbacks of the solutions proposed so far.

[0017] In particular, one object of the invention is to propose a press forging technique that makes it possible to reduce the amount of material and optimize the weight of the component while making it possible to obtain a component with few cracks and without areas of abnormal grain growth.

[0018] The present invention proposes forging with a new design which is performed within a forging range at a lower temperature than the existing range.

[0019] The inventors have indeed discovered that the phenomena of abnormal grain growth of this type of alloy can be eliminated by forging at a lower temperature. This temperature reduction allows leaving the abnormal growth range and therefore no longer risks deteriorating the microstructure of the part during forging.

[0020] To this end, according to one aspect, the invention proposes a method for producing a component made of a nickel-based alloy with a γ / γ' microstructure, wherein at least one hot forging step is carried out, the method being characterized in that the temperature to which the component is heated is maintained in a temperature range below the temperature range of abnormal grain growth of the alloy, the hot forging tool is maintained at a temperature lower than the temperature of the component, and the difference between this temperature and the temperature to which the component is heated is less than 325°C, preferably less than 250°C, more preferably less than 150°C.

[0021] Here and throughout the text, the abnormal grain growth temperature of the alloy is the temperature below which a small deformation within the conventional forging speed range does not produce abnormal grain growth, that is to say a burst grain size at least 2 times larger than the nominal grain size. In this regard, reference may be made to the paper by Marie Agathe Charpagne:

[0022] "Evolutions of microstructures and processes of forgeage Rene65"-PSL Research University-Mines Paris Tech- https: / / pastel.archives- ouvertes.fr / tel-01764932

[0023] Figure 1 A snapshot of a cracked grain in a fine-grained matrix is ​​shown. This snapshot is from the above mentioned paper (page 151). The cracked grain corresponds to the white area in the middle.

[0024] Therefore, the component is forged at a low temperature so as not to enter the abnormal grain growth region that degrades the microstructure.

[0025] This change in heating temperature is also accompanied by a change in forging tool temperature, with the hot tool temperature (higher) enabling the part to remain in its forgeability range and not crack by reducing heat losses during tool / part contact.

[0026] The alloy can be Udimet720 TM .

[0027] In a preferred embodiment, the alloy is Rene 65 or type.

[0028] At least one semi-finishing forging or finishing step is carried out after the part has been heated to a temperature equal to the solvus temperature γ' of the alloy minus 80°C (+ / -10°C) or lower, in particular 80°C or lower; the hot forging temperature is higher than 700°C, preferably 750°C and lower than 900°C, or even 850°C.

[0029] In a preferred embodiment, the temperature difference is less than 150°C compared to the temperature to which the component is heated.

[0030] The heating temperature may advantageously be between 1000°C and 1025°C.

[0031] For example, the component is heated and the temperature is 1025°C or lower (especially in the case of alloys such as Rene 65 or In the case of the above alloys, the solvus temperatures γ' are 1105℃ and 1110℃ respectively, while Udimet720 TM The solvus temperature γ' is 1155℃).

[0032] The invention also relates to an aviation turbine engine component, in particular a high-pressure turbine disk component, a low-pressure turbine disk or a high-pressure compressor disk, produced using the proposed production method.

[0033] The invention also relates to an aviation turbine engine comprising such a component. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Other features, objects and advantages of the present invention will appear from the following description, which is purely illustrative and not restrictive and must be read in conjunction with the accompanying drawings, in which:

[0035] Figure 1 It’s a snapshot of bursting particles;

[0036] Figure 2a A turbine disk produced using a production method according to the prior art is shown;

[0037] Figure 2b shows a turbine disk produced according to the production method of the present invention;

[0038] Figure 3 An example of a turbojet engine structure is schematically shown. DETAILED DESCRIPTION

[0039] Nickel-based superalloys with γ / γ' microstructure

[0040] The alloy used to produce this component is a nickel-based superalloy with a gamma / gamma' microstructure.

[0041] Nickel-based superalloys are usually composed of: a γ phase (or matrix) of the γ-Ni face-centered cubic austenite type, which may contain substitutional additives (Co, Cr, W, Mo, Re) in solid solution; and a γ' phase (or precipitate) of the γ'-Ni3X type, where X = Al, Ti or Ta. The γ' phase has an ordered L12 structure, derived from the face-centered cubic structure, consistent with the matrix, that is, with an atomic grid very close to it.

[0042] Due to its ordered nature, the γ' phase has remarkable properties, with its mechanical strength increasing with temperature up to about 800° C. The very strong coherence between the γ and γ' phases gives the nickel-base superalloys very high mechanical strength when hot, which itself depends on the γ / γ' ratio and the size of the hardening precipitates.

[0043] The selected superalloy can be composed mainly of nickel and preferably has certain mass fractions of chromium, cobalt, aluminum, titanium, molybdenum, and particularly preferably between 15% and 17% chromium, between 8% and 15.5% cobalt, between 1.5% and 4% aluminum, between 3% and 5.2% titanium, between 2% and 4% molybdenum, and between 2% and 4.2% tungsten.

[0044] Superalloys may also contain carbon, zirconium, iron, ...

[0045] Typically, for example, the alloy can be produced Rene65.

[0046] Examples of mass composition are as follows

[0047] Cr: 15% to 17%,

[0048] Co: 8% to 10%,

[0049] ·Mo: 2.5% to 3.5%,

[0050] W: 2.3% to 3.3%,

[0051] Nb: 0.8% to 1.4%

[0052] Ti: 3.2% to 3.8%

[0053] Al: 2% to 2.6%

[0054] B: 0.005% to 0.025%,

[0055] Zr: 0.01% to 0.05%,

[0056] ·Fe: 3% to 5%,

[0057] C: 0.005% to 0.02%,

[0058] Mn<0.5%

[0059] An example of mass composition is as follows (Rene65)

[0060] Cr: 15.5% to 16.5%,

[0061] Co: 12.5% ​​to 13.5%,

[0062] Al: 1.95% to 2.3%,

[0063] Ti: 3.55% to 3.9%,

[0064] ·Mo: 3.8% to 4.2%,

[0065] W: 3.8% to 4.2%,

[0066] Nb: 0.6% to 0.8%,

[0067] ●B: 0.012% to 0.02%,

[0068] Zr: 0.03% to 0.06%,

[0069] C: 0.005% to 0.011%

[0070] ●Mn<0.1%,

[0071] Fe < 1.2%

[0072] ●Ta: trace amount (up to 1000ppm).

[0073] Other compositions are of course possible. The alloy may also be Udimet 720, for example. TM , which is composed as follows:

[0074] UDIMET 720

[0075]

[0076] Hot forging tools

[0077] Depending on the operation considered, different hot forging tools may be provided: crushing of blanks, stamping of semi-finished products, finish stamping, etc.

[0078] Typically, the hot forging tool is mounted on a press with a press speed between 0.5 mm / s and 20 mm / s and a pressure between 2000 T and 60000 T.

[0079] One possible press is a hot forging press of the type described, for example, in patent application FR2880827.

[0080] The hot heating system maintains the temperature of the hot forging tool so that its contact surface with the component is permanently above 750° C. Several systems are available for this purpose: heating by heating rods immersed in the hot forging tool, inductive heating via a peripheral heating system, heating by peripheral resistance.

[0081] Example of forging

[0082] Melting temperature γ' is as follows: Rene65 or Udimet720 TM

[0083] Udimet720 TM :1155℃

[0084] · 1110℃

[0085] Rene65: 1105℃

[0086] Especially in Rene65 and In the case of type alloys (but also in Udimet720 TM In the case of ), forging can be carried out under the following conditions:

[0087] Semi-finished forging and finishing:

[0088] Heating temperature of components: between 1000℃ and 1040℃

[0089] ●Hot forging temperature: between 750℃ and 900℃

[0090] ●Keep the tool at temperature under the press

[0091] Preferably, the temperature at which the component is heated is more particularly between 1000°C and 1025°C.

[0092] Preferably, the hot forging temperature is more particularly between 800°C and 900°C.

[0093] Alternatively, the hot forging temperature is more specifically between 750°C and 850°C.

[0094] Other upstream forging can be performed under different conditions:

[0095] ●Heating temperature: between 1040℃ and 1060℃

[0096] Temperature of the punching tool: between 400° C. and 650° C. In the case of rolled semi-finished products, the rolling operation is carried out in a conventional manner, followed by a finish forging step under the conditions described above.

[0097] Embodiment of the component

[0098] The production method is used, for example, for producing aircraft turbine engine components, in particular high-pressure turbine components or low-pressure turbine components, or high-pressure compressor components.

[0099] Different tests may be performed for the production of different types of components.

[0100] Example 1

[0101] In particular, a test campaign was carried out to produce crowns by rolling of round semi-finished products followed by low deformation stamping of a Rene 65 type alloy at temperatures between 1000°C and 1025°C.

[0102] The crown obtained was free of any bursting particles.

[0103] like Figure 2a and Figure 2b As shown, significant differences in crack formation are observed depending on the hot forging temperature at the contact surface with the component (heated flat-stack hot forging tool).

[0104] For hot forging temperature of 650℃ ( Figure 2a ), deep cracks (up to 1.5 mm deep) can be observed over most of the circumference.

[0105] For hot forging temperatures of 750°C or higher (usually 850°C or higher), there are no cracks in the crown ( Figure 2b ).

[0106] Example 2

[0107] Tests were also conducted on reduced scale slugs heated to between 1000°C and 1025°C and forged between two low deformation operations, wherein the contact surface temperature of the hot tool was maintained between 800°C and 900°C.

[0108] It was found that these blanks had no burst particles and no cracks.

[0109] Turbojet engine

[0110] Figure 3The twin-flow turbojet engine 1 extends along an axis AA and comprises a flow path or main flow path 2 for the main airflow, which comprises, from upstream to downstream in the direction of airflow circulation in the turbine, a low-pressure compressor 3, a high-pressure compressor 4, a combustion chamber 5, a high-pressure turbine 6 and a low-pressure turbine 7.

[0111] The disks of the low-pressure compressor 3 are made of titanium alloy, for example, while all or part of the disks of the high-pressure turbine and the low-pressure turbine and the disks of the high-pressure compressor final stage can be produced according to the above-mentioned type of production method.

Claims

1. A method for producing a component made of a nickel-based alloy with a γ / γ' microstructure, wherein at least one hot forging step is carried out, the method being characterized in that the temperature at which the component is heated during the hot forging step is kept within a temperature range below the temperature range of abnormal grain growth of the alloy, the hot forging temperature is kept below the temperature of the component, and the difference between the hot forging temperature and the temperature at which the component is heated is made less than 325°C.

2. The method according to claim 1, characterized in that The hot forging temperature is maintained less than 150°C different from the temperature at which the part is heated.

3. The method according to claim 1 or 2, characterized in that: The alloy is Rene65, or Udimet720 TM type.

4. The method according to claim 3, characterized in that At least one semi-finishing forging or finishing step is performed while the part is heated to a temperature equal to the solvus temperature γ' of the alloy minus 80°C (+ / -10°C) or lower; the hot forging temperature is higher than 700°C (+ / -10°C) and lower than 900°C (+ / -10°C).

5. The method according to claim 4, characterized in that The temperature at which the component is heated is 1025°C (+ / - 10°C) or less.

6. The method according to claim 5, characterized in that The temperature at which the component is heated is 1000°C (+ / - 10°C) or higher.

7. The method according to claim 4, characterized in that The hot forging temperature is higher than 800°C.

8. The method according to claim 7, characterized in that The hot forging temperature is 850° C. or higher.

9. An aviation turbine engine component, in particular a high-pressure turbine disk, a low-pressure turbine disk or a high-pressure compressor disk, characterized in that: The aviation turbine engine component is produced using the production method according to any one of claims 1 to 5 .

10. An aviation turbine engine, characterized in that: The aircraft turbine engine comprises a component according to claim 9.

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