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

Abstract

The invention relates to a method for producing a part made of a nickel-based alloy with a Y / Y' microstructure in which at least one hot-forging step is performed, which method is characterised in that the temperature at which the part is heated in the forging step is maintained within a temperature range lower than the abnormal grain growth temperature range of the alloy, the hot-forging temperature being maintained at a temperature lower than the temperature of the part, the hot-forging temperature being such that the difference compared with the temperature at which the part is heated is less than 250°C and preferably less than 150°C.

Description

[0001] METHOD FOR MANUFACTURING A NICKEL-BASED ALLOY PART OF THE y / y' TYPE WITH HOT FORGING TOOLS

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to the field of manufacturing y / y' alloy parts with hot forging tools.

[0004] It finds advantageous application in the aeronautics field, particularly for the manufacture of turboshaft engine parts, such as high-pressure or low-pressure turbine discs, or even high-pressure compressor discs.

[0005] STATE OF THE ART

[0006] The new nickel-based alloys with a y / y' microstructure (such as AD730® from Aubert & Duval or Rene65 chosen by Safran Aircraft Engines for some of its engines) are traditionally used in aeronautics for parts subjected to extreme stresses in service.

[0007] Such alloys are, for example, chosen by turboshaft manufacturers as components of high-pressure turbine discs or low-pressure turbine discs, or for high-pressure compressor discs on the latest generations of aircraft engines.

[0008] More generally, they are now considered for any turboshaft engine part for which we wish to increase the operating temperature and resistance to mechanical stress at these temperatures.

[0009] The forging process for these parts is a sequence of hot forming steps (slug crushing, rough forging, finishing forging, etc.) and heat treatments. Hot forming is generally carried out on hydraulic presses with conventional tools heated up to 650°C / 680°C.

[0010] Due to their high content of the hardening phase y', these alloys have a very narrow forgeability temperature range. During press treatments, the parts are heated to temperatures between 1040° G and 1070°C, with a skin temperature for the part above 800 ° C throughout the forging process.

[0011] Two major types of problems must be mastered when manufacturing parts with these alloys.

[0012] During forging operations, cooling during transfer between the heating furnace and the press or during contact with colder tools during forging, leads to the appearance of surface cracks which must be eliminated after forging by finishing operations.

[0013] Furthermore, these alloys are sensitive to the phenomenon of grain bursting (abnormal grain growth). Under very specific forging conditions, this phenomenon appears and results in, locally, a very significant coarsening of the grain. This phenomenon - which must be absolutely avoided - is a cause of rejection of the part because the mechanical properties, particularly fatigue resistance, of the part in these areas are prohibitive with regard to the required specifications.

[0014] Various studies have been carried out on these subjects. Addressing these issues generally leads to very restrictive forging conditions.

[0015] Typically, this can lead to imposing minimal deformations throughout the part during forging operations.

[0016] Also, the proposed solutions generally require a greater material implementation weight, on the one hand to anticipate the loss of material during finishing operations which aim to eliminate forging cracks and on the other hand, due to the addition of material in certain areas, to be able to respect the minimum deformation criterion in order to avoid the phenomenon of grain bursting.

[0017] One consequence is an additional machining operation before the heat treatment operation. Since the forged blanks are more massive, there is a risk that the heat treatment will not generate the required mechanical properties. Indeed, on these y / y' alloys, the static mechanical properties are highly dependent on the cooling rate during heat treatment. An increase in mass causes a decrease in this rate and therefore in the mechanical properties.

[0018] The elimination of cracks on raw forged parts, either by finishing or by machining before heat treatment, must be accompanied by specific checks to ensure their total elimination. Indeed, the presence of residual surface cracks before heat treatment can lead to their propagation in the part during hardening. These additional checks generate additional costs.

[0019] STATEMENT OF THE INVENTION

[0020] An aim of the invention is to propose a technique for manufacturing y / y' alloy parts with hot press tooling which makes it possible to resolve the problems of grain bursting and cracks, without presenting the complexity and weight disadvantages of the solutions proposed to date.

[0021] In particular, one aim of the invention is to propose a press forging technique which makes it possible to reduce the quantity of material and to optimize the weight of the part, while making it possible to obtain parts with very few cracks, free from grain bursting zones.

[0022] The present invention proposes to carry out forgings with a new design of forging range at a lower temperature compared to current ranges.

[0023] It was in fact found by the inventors that it was possible to eliminate the phenomenon of grain bursting on this type of alloy by carrying out forging at a lower temperature. This reduction in temperature makes it possible to move beyond the bursting range and therefore to no longer risk damaging the microstructure of the part during forging.

[0024] To this end, according to one aspect, the invention proposes a method for manufacturing a nickel-based alloy part with a y / y' microstructure in which at least one forging step is carried out using hot forging tools, characterized in that the heating temperature of the part is maintained in a temperature range below the grain bursting temperature range of the alloy, the hot tool being maintained at a temperature below the temperature of the part, the difference between this temperature and the heating temperature of the part being less than 325°C, preferably less than 250°C and more preferably less than 150°C.

[0025] By grain bursting temperature of the alloy, we mean here and throughout this text, the temperature below which a small deformation in a conventional forging speed range does not generate abnormal grain growth, i.e. a burst grain size at least twice the nominal grain size. In this respect, we can usefully refer to the thesis of Marie Agathe Charpagne:

[0026] “Microstructural Evolutions During Forging of the Rene65 Alloy” - PSL Research University - Mines Paris Tech - https: / / pastel, archives-ouvertes.fr / tel-01764932

[0027] A snapshot of shattered grains in a fine-grained matrix is ​​shown in Figure 1. This snapshot is from the thesis mentioned above (p.151). The shattered grains correspond to the white areas in the center.

[0028] Thus, forging is carried out with parts at low temperature, so as not to enter the area of ​​grain bursting which degrades the microstructure.

[0029] This change in heating temperature is also accompanied by a change in forging tool temperatures, the hot tool temperature (higher) allowing, by reducing thermal losses during tool / part contact, to keep the part within its forgeability range and not generate cracks.

[0030] The alloy can be Udimet720™.

[0031] In preferred embodiments, the alloy is of the Rene65 or AD730® type.

[0032] At least one roughing or finishing forging step is carried out at a heating temperature of the part equal to the solvus temperature y' of the alloy minus 80°C (+ / - 10°C) or lower, in particular 80°C or lower, the tooling temperature being higher than 700°C, preferably 750°C and lower than 900°C, or even 850°C. In a preferred embodiment, the difference with the heating temperature of the part is then lower than 150°C.

[0033] The heating temperature can advantageously be between 1000°C and 1025°C.

[0034] For example, the heating temperature of the part is 1025°C or lower (in the case where the alloy is Rene65 or AD730® in particular, whose y' solvus temperatures are respectively 1105°C and 1110°C, the y' solvus temperature of Udimet720™ being 1155°C).

[0035] The invention further relates to an aircraft turbine engine part, manufactured using a manufacturing method as proposed, in particular a high pressure turbine disk part, low pressure turbine disk, or high pressure compressor disk.

[0036] It also relates to an aircraft turbine engine comprising such a part.

[0037] DESCRIPTION OF FIGURES

[0038] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which:

[0039] - figure 1 is a photograph of burst grains;

[0040] - figure 2a illustrates a turbine disc produced according to a manufacturing method in accordance with the state of the art;

[0041] - figure 2b illustrates a turbine disc produced according to a manufacturing method in accordance with the invention;

[0042] - Figure 3 schematically illustrates an example of a turbojet structure.

[0043] DETAILED DESCRIPTION OF THE INVENTION

[0044] Nickel-based superalloys with y-y' microstructure The alloy used to manufacture the part is a nickel-based superalloy with y-y' microstructure.

[0045] Nickel-based superalloys are typically composed of a y-Ni face-centered cubic austenitic y phase (or matrix), possibly containing a-substitution solid solution additives (Co, Cr, W, Mo, Re), and a y'-Ni^X type y phase (or precipitates), with X = Àl, Ti or Ta. The y' phase has an ordered L12 structure, derived from the face-centered cubic structure, consistent with the matrix, i.e. having an atomic mesh very close to it.

[0046] Due to its ordered nature, the y' phase has the remarkable property of having a mechanical resistance which increases with temperature up to approximately 800°C. The very strong coherence between the y and y' phases gives nickel-based superalloys very high mechanical resistance when hot, which itself depends on the y / y' ratio and the size of the hardening precipitates.

[0047] The chosen superalloy may be mainly composed of nickel and preferably have a mass fraction of chromium, cobalt, aluminum, titanium, molybdenum, and in particular preferably between 15 and 17% in chromium, between 8 and 15.5% in cobalt, between 1.5 and 4% in aluminum, between 3 and 5.2% in titanium, between 2 and 4% in molybdenum, between 2 and 4.2% of Tungsten.

[0048] The superalloy may also include carbon, zirconium, iron, etc.

[0049] Typically, for example, the manufacturing alloy may be ÀD730®, Rene65.

[0050] An example of mass composition is as follows (ÀD730®):

[0051] • Cr: 15% to 17%,

[0052] • Co: 8% to 10%,

[0053] • Mo: 2.5% to 3.5%,

[0054] • W: 2.3% to 3.3%,

[0055] • Nb: 0.8% to 1.4%,

[0056] • Ti: 3.2% to 3.8%,

[0057] • Al: 2% to 2.6%, • B: 0.005% to 0.025%,

[0058] • Zr: 0.01% to 0.05%,

[0059] • Fe: 3% to 5%

[0060] • C: 0.005% to 0.02%,

[0061] • Mn < 0.5%,

[0062] Another example of mass composition is still (Rene65)

[0063] • Cr: 15.5% to 16.5%,

[0064] • Co: 12.5% ​​to 13.5%,

[0065] • Àl: 1.95% to 2.3%,

[0066] • Ti: 3.55% to 3.9%,

[0067] • Mo: 3.8% to 4.2%,

[0068] • W: 3.8% to 4.2%,

[0069] • Nb: 0.6% to 0.8%,

[0070] • B: 0.012% to 0.02%,

[0071] • Zr: 0.03% to 0.06%,

[0072] • C: 0.005% to 0.011%

[0073] • Mn < 0.1%,

[0074] • Fe < 1.2%

[0075] • Ta: traces (1000ppm max).

[0076] Other compositions are of course possible. The alloy can, for example, also be Udimet720™, which has the following composition:

[0077] UDIMET 720 Hot forging tools

[0078] Different tools can be provided depending on the operations envisaged: crushing of the billet, roughing of the blank, finishing of the blank, etc.

[0079] Typically, the tooling is mounted on a press with press speeds between 0.5 and 20mm / s and pressures between 2000 and 60000 T.

[0080] A possible press is, for example, a hot die type forging press of the type described in patent application FR2880827.

[0081] A hot heating system maintains the temperature of the tool so that its contact surface with the part is permanently above 750°C. Several systems can be provided for this purpose: heating by heating rods immersed in the tool, induction heating via a peripheral heating system, heating by peripheral electrical resistances.

[0082] Examples of forging

[0083] The y' solvus temperatures are as follows: Rene65, or Udimet720™

[0084] • Udimet720™: 1155°C

[0085] • ÀD730®: 1110°C

[0086] • Rene65: 1105° C

[0087] In the case of alloys of the Rene65 and ÀD730® type, in particular (but also in the case of Udimet720 TM), forgings can take place under the following conditions:

[0088] Rough and finishing forgings:

[0089] • Room heating temperature: between 1000°C and 1040°C

[0090] • Tool temperature: between 750°C and 900°C

[0091] • Maintaining tools at temperature under the press

[0092] Preferably, the heating temperature of the part is more particularly between 1000°C and 1025°C. Preferably, the tooling temperature is more particularly between 800°C and 900°C.

[0093] Alternatively, the tooling temperature is more particularly between 750°C and 850°C

[0094] Other upstream forgings can be carried out under different conditions:

[0095] • Heating temperature: between 1040°C and 1060°C

[0096] • Forging tool temperature: between 400°C and 650°C In the case of rolled blanks, this rolling operation is carried out in the conventional manner, the finishing forging stages are then carried out under the conditions indicated above.

[0097] The manufacturing process is used, for example, for the manufacture of an aircraft turbine engine part, in particular a high-pressure turbine or low-pressure turbine part, or even a high-pressure compressor part.

[0098] Different tests were carried out to produce different types of parts.

[0099] Example 1

[0100] In particular, a test campaign was carried out for the production of crowns by circular rough rolling, then low deformation forging at a temperature between 1000°C and 1025°C with a Rene65 type alloy.

[0101] The crowns obtained do not have any broken grains.

[0102] As illustrated in Figures 2a and 2b, significant differences in crack formation were observed depending on the tooling temperature at the contact surface with the part (heated flat pile tooling).

[0103] For a tooling temperature of 650°C (Figure 2a), deep cracks were observed (up to 1.5 mm) over a large part of the circumference. For a tooling temperature of 750°C or higher (typically 850°C and higher), the crown did not show any cracks (Figure 2b).

[0104] Example 2

[0105] Tests were also conducted on reduced-scale slugs heated to between 1000°C and 1025°C and forged in two low-deformation operations, with hot tools at contact surface temperatures maintained between 800°C and 900°C.

[0106] It was found that the pawns did not have any split grains and also did not have any cracks.

[0107] Turbojet

[0108] The double-flow turbojet 1 of figure 3 extends along an axis À-À and comprises a flow vein of a primary flow or primary vein 2 comprising, from upstream to downstream in the direction of circulation of the gas flow within the turbomachine, 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.

[0109] The discs of the low pressure compressor 3 are for example made of titanium alloy, while all or part of the discs of the high pressure and low pressure turbines and the discs of the last stages of the high pressure compressor can be produced using a manufacturing process of the type described above.

Claims

CLAIMS A method for manufacturing a part made of a nickel-based alloy with a y / y' microstructure, in which at least one forging step is carried out under hot forging tooling, characterized in that the heating temperature of the part during the forging step is maintained in a temperature range below the grain bursting temperature range of the alloy, the tooling temperature being maintained at a temperature lower than the temperature of the part, said tooling temperature being such that the difference with the heating temperature of the part is less than 325°C. A method according to claim 1, characterized in that the tooling temperature is maintained at a temperature whose difference with the heating temperature of the part is less than 150°C. A method according to claim 1 or 2, characterized in that the alloy is of the Rene65, AD730® or Udimet720™ type.A process according to claim 3, characterized in that at least one roughing or finishing forging step is carried out at a workpiece heating temperature equal to or lower than the solvus temperature y' of the alloy less 80°C (+ / - 10°C), the tooling temperature being greater than 700°C (+ / - 10°C) and less than 900°C (+ / - 10°C). A process according to claim 4, characterized in that the workpiece heating temperature is 1025°C (+ / - 10°C) or lower.

6. Method according to claim 5, characterized in that the heating temperature of the part is 1000°C (+ / - 10°C) or higher.

7. Method according to claim A, characterized in that the temperature of the tooling is greater than 800° C.

8. Method according to claim 7, characterized in that the tooling temperature is 850°C or higher.

9. Aircraft turboshaft engine component, in particular high-pressure turbine disc, low-pressure turbine disc, or high-pressure compressor disc, characterized in that it is manufactured by implementing a manufacturing process according to any one of claims 1 to 5.

10. Aircraft turboshaft engine, characterized in that it comprises a part according to claim 9.

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