Steel component for aircraft and method for manufacturing same

Abstract

A method for manufacturing a steel component (10) for an aircraft, comprising welding together at least two steel elements (12, 14) to form the component (10); subjecting the component (10) to a resistance treatment comprising austenitizing (30) followed by quenching (32) and at least one tempering (34); and subjecting the weld (16) between the at least two elements (12, 14) to a local softening treatment, said softening treatment comprising heating the weld (16) to a softening temperature below the starting temperature Ac1 at which the steel transitions from ferrite to austenite.

Description

Technical Field

[0001] The present disclosure relates to the field of metallurgy, and more specifically to a method for manufacturing a steel component for an aircraft. The present disclosure also relates to a steel component obtained by the method. Such a component can be used in a variety of applications, for example, in any type of aircraft, such as airplanes, helicopters, drones, etc., and in particular in landing gear. Background Art

[0002] For example, structural components of aircraft landing gear may be manufactured from forged steel parts that are first stamped to obtain the overall shape (or preform) and then machined. Afterwards, the entire component is subjected to one or more heat treatments to achieve the desired mechanical properties.

[0003] In order to reduce manufacturing costs, it is envisaged that such components are no longer manufactured from a single blank, but rather by assembling multiple elements. However, the certification of the components thus obtained is problematic, since the assembly areas constitute weak points and it is not known how to properly treat them.

[0004] Therefore, a new method for manufacturing steel components is needed. Summary of the invention

[0005] To this end, the present disclosure relates to a method for manufacturing a steel component for an aircraft, the method comprising welding at least two steel elements together to form the component; subjecting the component to a resistance treatment, the resistance treatment comprising austenitizing, quenching and at least one tempering; and then subjecting the weld between the at least two elements to a local softening treatment, the softening treatment comprising heating the weld to a softening temperature that is lower than the starting temperature Ac1 at which the steel transforms from ferrite to austenite.

[0006] The method is particularly suitable for low alloy steel components having a mechanical tensile strength Rm greater than or equal to 1800 MPa. It is also of particular interest for forged steel components. A forged steel component is a steel component in which at least one element has been subjected to at least one forging step.

[0007] Each steel element is welded together with at least one other steel element, so that these steel elements together constitute a steel component. Hereinafter, for the sake of brevity, elements and components refer to steel elements and steel components, respectively. In addition, unless otherwise specified, "one" or "the" element or other expressions hereafter refers to "at least one" or "at least one of the" or even "each" element or others. Conversely, general expressions of the plural number may include the singular number.

[0008] At least one of the elements may optionally be machined before the resist treatment: this facilitates machining, since the resist treatment makes the element more difficult to machine. Furthermore, machining may be performed before welding, since it is easier to process a single element than the entire part. In both cases, this is called pre-machining.

[0009] Welding two components together forms a weld at their interface.

[0010] The resistance treatment, so named because it imparts a high degree of mechanical resistance to the component, is a heat treatment consisting of austenitizing, followed by quenching and then at least one tempering. The resistance treatment is applied to the component, that is to say at least to the elements that are welded together. The resistance treatment can be applied to the entire component.

[0011] Austenitization involves heating the component to a temperature above Ac1, the start temperature at which the steel transforms from ferrite to austenite, and even above Ac3, the end temperature at which the steel transforms from ferrite to austenite.

[0012] Quenching, for example in air, water, oil or a polymer bath, allows the steel to be cooled rapidly, for example to a temperature substantially equal to room temperature, or more typically to below 100° C. Quenching can increase the resistance of the steel.

[0013] Tempering may include heating the component to a temperature below temperature Ac1. Tempering may adjust the balance between resistance and ductility of the component.

[0014] The resistance treatment may also include a cryogenic treatment, for example after quenching and / or before tempering. Such a treatment consists in keeping the part at a temperature less than or equal to 0°C.

[0015] The softening treatment, so named because it increases toughness and resistance to crack growth, consists of heating the weld to a softening temperature. A softening temperature below temperature Ac1 prevents the weld from austenitizing, which would otherwise counteract the effect of the resistance treatment. Unlike the resistance treatment, which is a treatment of the entire component, the softening treatment is a local treatment that targets mainly (if not only) the weld and the areas affected by the welding heat.

[0016] Welding, resistance treatment and softening treatment are carried out in this order so that the resistance treatment can also act on the weld, and the softening treatment further improves the properties of the weld. In other words, the resistance treatment normalizes the microstructure of the weld before softening so that the weld can obtain the best mechanical properties after softening.

[0017] Since the component is subjected to a hardening treatment and then the weld is locally softened, the non-welded part retains the good mechanical properties associated with the hardening treatment and can be certified using the same certification method as before. In addition, the softening treatment ensures that the weld has good crack propagation resistance, which allows the component part containing the weld to be certified by methods that take into account criteria such as crack propagation. Therefore, the proposed manufacturing method can reduce the manufacturing cost of steel components while ensuring their good mechanical properties and certifiability.

[0018] In some embodiments, during the softening treatment, the region of the component containing the weld is heated more than the regions away from the weld. Thus, the softening treatment is truly local so as not to reduce the mechanical strength or yield strength of the regions away that do not require softening. The regions away may not be heated at all or at most their temperature may increase due to heat conduction from the region containing the weld. Optionally, a heat insulation or even a cooling system can be provided to limit the temperature increase in the regions away.

[0019] In some embodiments, at least one element has a locally thicker part in the region containing the weld. This can provide a margin to ensure that even after the softening treatment, the maximum stress reached in this region does not exceed the strength level of this region. In any case, the softening treatment is local and avoids affecting the entire element.

[0020] In some embodiments, the softening temperature is at most 150 °C lower than the temperature Ac1. In other words, the softening temperature is greater than or equal to Ac1 - 150 °C and lower than Ac1. In this temperature range, the crack propagation resistance can be significantly improved.

[0021] In some embodiments, the hardening treatment includes a second tempering after the first tempering. The initial tempering can also be referred to as the first tempering. The second tempering can be the same as or different from the first tempering.

[0022] In some embodiments, the manufacturing method includes a finishing operation after the hardening treatment. The finishing operation can bring the component to its final shape with high precision. Since the component has high hardness, the finishing operation is more difficult to perform and may remove less material from the component compared to the pre-processing before welding.

[0023] In some embodiments, the heating of the weld is performed by conduction or induction. Conduction can be achieved by means of a heating resistor or a heating pad. The heating resistor or heating pad can be placed on the weld and can be limited to the area to be heated, excluding other areas of the component (the boundary condition for other areas can be room temperature). Induction can be achieved by using one or more coils at a certain distance from the component, through which an alternating current is passed, generating a magnetic field, thereby locally heating the component. While conduction heating is easy to implement, induction heating can be easily adapted to complex component geometries. Different heating methods, such as the two described above, can also be used in combination, for example to improve temperature uniformity.

[0024] In some embodiments, welding includes at least one of electron beam welding, laser welding, and friction welding.

[0025] In some embodiments, at least two elements are welded without the use of filler metal. Thus, the elements are joined end to end, without the need for adding material, and the welding is achieved by heating their common interface. This allows good continuity in both the chemical composition and the mechanical properties obtained at the end of the resistance treatment.

[0026] In some embodiments, the steel has a mass composition of 0.38-0.45% carbon, 0.60-0.90% manganese, 1.45-1.80% silicon, 1.65-2.00% nickel, 0.70-0.95% chromium, 0.35-0.50% molybdenum, 0.05-0.10% vanadium, 0.35% or less copper, 0.01% or less phosphorus, 0.0010% or less sulfur, 0.0080% or less titanium, 0.0050% or less niobium, and the remainder iron and unavoidable impurities. This steel, designated 40NiSiCrMo7 according to European standards, is called "300M" in the American Iron and Steel Institute (AISI) standard, or "6417-6419" in AMS. This steel may also have a composition defined by reference standard "AMS 6257". It has high mechanical properties, good impact resistance and fatigue resistance, and is suitable for aircraft components, especially landing gear components.

[0027] Unavoidable impurities are elements that are not intentionally added to the composition but are brought in with other elements. Although the above composition gives maximum contents for some impurities (such as copper, phosphorus or sulfur), other impurities may also be present, such as antimony, which has a maximum mass content of 0.01%.

[0028] In some embodiments, the manufacturing method further comprises certifying the components by a first method and certifying the welds between the components by a second, different method. The welds between the components may refer to the welds and optionally the directly adjacent areas. For example, the first method aims to verify whether the dimension design of the component is able to withstand a given load and achieve a given fatigue life: for example, the dimension design of the component is, among other things, able to withstand the limiting load conditions that may occur during the life cycle of the component (under which the component shall not undergo plastic deformation), the ultimate load conditions (which produce a greater deviation than the limiting load conditions and the component shall not break) and / or a fatigue life cycle with a predetermined life. For example, the second method aims to verify whether the dimension design of the weld is able to tolerate damage: for example, the dimension design of the weld is, among other things, able to resist crack propagation for a long time to allow crack detection and maintenance; provide multiple force transmission paths to ensure redundancy of force transmission; and / or have a shape that can limit crack propagation. Certification, in particular the first method and / or the second method, may include physical tests performed on the steel component. These physical tests include, for example, fatigue crack propagation resistance tests. In some embodiments, these physical tests are performed in accordance with standard ASTM E647, such as ASTM E647-23a.

[0029] Hybrid certification of steel components through two methods applied in different areas allows for better compliance with certification standards: this hybrid or combined certification approach adapts to the development of components by using the second method for welds between elements, while relying on the experience gained from the first method to manufacture steel elements, as the manufacturing methods of steel elements are well understood.

[0030] The present disclosure also relates to a steel component for aircraft, in particular for aircraft landing gear, which is made by the above manufacturing method. The component may have the characteristics produced by all or part of the features of the above method.

[0031] In some embodiments, the toughness of the region containing the weld in the component is greater than or equal to 80 MPa√m, preferably 90 MPa√m, more preferably 100 MPa√m. Therefore, the crack growth resistance of this region is very good. Toughness can be measured in a manner known to those skilled in the art, for example, according to standard ASTM E399-22. Brief introduction of the attached figure

[0032] Other characteristics and advantages of the present disclosure will emerge from the following description of embodiments given as non-limiting examples, with reference to the accompanying drawings.

[0033] Figure 1 The steps of a manufacturing method according to one embodiment are schematically represented.

[0034] Figure 2is a time-temperature graph illustrating an example of a resistance treatment. DETAILED DESCRIPTION

[0035] refer to Figure 1 and Figure 2 A method of manufacturing a steel component 10 for an aircraft according to one embodiment is described. Figure 1 Schematically represented are two steel elements, for example forged steel elements, namely a first element 12 and a second element 14 (collectively referred to as elements 12, 14), which are intended to be assembled with each other to form the component 10. However, more elements may also be provided.

[0036] Here, the components 12, 14 have the same composition. Alternatively, components with different compositions can also be provided, as long as their compositional differences are compatible with the welding assembly described later.

[0037] More specifically, the components 12, 14 are made of 300M steel, the composition of which is given above. The starting temperature Ac1 of this steel for transformation from ferrite to austenite is 725°C, and the end temperature Ac3 of the transformation is 870°C.

[0038] The elements 12, 14 may be in a normalized and tempered state. Normalizing consists, for example, in austenitizing the steel and then cooling it in air to recrystallize the grains produced by the thermomechanical transformation and to redissolve the cementite, thereby controlling its distribution. Tempering consists, for example, in heating the steel to a temperature generally between 650°C and 720°C, in any case below the temperature Ac1, to improve its machinability. In the normalized and tempered state, the tensile strength Rm of the element is about 1100 MPa.

[0039] At least one of the components 12, 14 may be pre-machined, for example if the component is initially provided in blank form. Figure 1 The stick-like shapes shown in FIG. 5 are merely schematic.

[0040] As described above, the manufacturing method includes welding the elements 12, 14 together to form the component 10. The welding operation creates a weld 16 at the weld interface of the first element 12 and the second element 14.

[0041] For example, welding can be performed by electron beam, laser and / or friction, in particular by inertial rotation friction. These welding methods are known per se and will not be described further here. More generally, welding can be performed without the use of filler metal, which ensures good control of the composition of the weld 16.

[0042] After welding, the component 10 is subjected to a resistance treatment. Figure 1As shown, the resist treatment may be applied to the entire component 10, such as by placing the entire component 10 into a suitable heat treatment apparatus 20. At a minimum, the resist treatment is applied to at least the first element 12, the second element 14, and the weld 16, preferably simultaneously.

[0043] Figure 2 Illustrating the resistance treatment in more detail, the graph shows the temperature to which the component 10 is subjected over time. Figure 2 The temperature and duration shown are schematic, so they may not be proportional and may not be consistent between different heat treatments. The origin of the ordinate is room temperature, usually between 20°C and 25°C.

[0044] The resistance treatment comprises austenitization 30: the part 10 is kept at a temperature above the temperature Ac1, for example above 800°C for 300M steel, for a period ranging from 25 minutes to 9 hours, in order to transform the ferrite in the elements 12, 14 and in the weld 16 into austenite. In the present disclosure, the temperatures given refer to the temperature in the closed space in which the part to be treated is placed.

[0045] After austenitization, the component 10 is quenched 32 by cooling it by immersion in a medium (air, water, oil, polymer, etc.) at a much lower temperature, typically in a temperature interval of 800° C. to 100° C., with an average cooling rate greater than or equal to 0.8° C. / s. According to a particular embodiment, during the quenching process, the component can be cooled rapidly, for example with an average cooling rate greater than or equal to 0.8° C. / s, to a temperature between 150° C. and 300° C., and then kept at this temperature for at least 10 minutes. After quenching, the temperature of the component 10 is increased again in order to subject the component 10 to a first tempering 34. The temperature of the component 10 is kept below the temperature Ac1 during the tempering 34. For example, during the first tempering 34, the component 10 can be kept at a temperature between 290° C. and 310° C. for 2 hours to 12 hours. The first tempering 34 can be followed by a second tempering 36, which can be the same or different from the first tempering 34. Between the first tempering 34 and the second tempering 36, the temperature of the component 10 can be reduced substantially to room temperature.

[0046] At the end of the resistance treatment, the entire component 10, including the elements 12, 14 and the weld 16, is in a homogeneous state, with very high mechanical properties of static and fatigue strength. However, the resistance to crack growth may be relatively low. While this is not a problem for the elements 12, 14, since a lot of experience has been accumulated, it may be a problem for the certification of the weld 16.

[0047] To this end, the manufacturing method includes locally softening the weld 16, that is, heating the weld 16 to a softening temperature lower than the temperature Ac1. However, in order to fully improve the crack propagation resistance, the softening temperature can be relatively close to the temperature Ac1, for example, greater than or equal to Ac1-150°C (for example, greater than or equal to 600°C). Preferably, the softening temperature can be between Ac1-125°C and Ac1-25°C. The control of the softening temperature can refer to previous tests on components equipped with temperature sensors (such as thermocouples and / or pyrometers). The weld 16 can be kept at the softening temperature for 5 minutes to 15 hours, depending on the expected softening duration: the higher the temperature, the faster the softening rate.

[0048] like Figure 1 As shown, the local device 22 can be arranged so that the area of ​​the component 10 containing the weld 16 is heated more than the area away from the weld 16. The local device 22 can include a heater of the type of a heating resistor or a heating pad, which is placed on the area containing the weld 16 so as to heat the component 10 by conduction. Alternatively, the local device 22 can also include a conductive coil, for example, coaxially placed around the component 10 and aligned with the weld 16; an alternating current is passed through the coil to generate a local magnetic field, induce a current in the component 10, and thus heat the component 10 by induction.

[0049] Although Figure 1 The local device 22 is shown as being placed around the component 10, but the local device 22 can also be placed inside the component 10 as needed, for example, when the component 10 is hollow. In addition, as an alternative to the local device 22, the softening treatment can be performed locally by placing the component 10 in a furnace, where at least one area does not contain a weld, while ensuring that the at least one area of ​​the component 10 is locally cooled.

[0050] If necessary, the manufacturing method may include further machining steps after the softening treatment. Such finishing generally involves operations that would not be possible due to the required precision if they were performed before the resistance treatment and / or softening treatment.

[0051] The component 10 thus obtained can be used in an aircraft, for example, in a landing gear. Due to the addition of the softening treatment on top of the other treatments, the toughness of the region of the component 10 containing the weld 16 is increased, which helps to reduce the crack propagation in the weld 16. For example, the toughness of the region of the component containing the weld 16 can be greater than or equal to 80 MPa.√m, preferably 90 MPa.√m, and more preferably 100 MPa.√m.

[0052] The manufacturing method may also include certifying the component 10. The elements 12, 14 may be certified using a first certification method 24, while the weld 16 may be certified using a second certification method 26 different from the first method 24.

[0053] For example, the first method 24 may include verifying that the dimensions of the elements 12, 14 are capable of withstanding limiting load conditions, extreme load conditions, and / or a specific fatigue life cycle, as described above. Under limiting load conditions, the elements 12, 14 must not undergo plastic deformation that could impede safe operation. The forces on which the extreme load conditions are based do not occur during normal operation and are greater than the forces used to design the limiting load conditions, for example 50% greater. Finally, the fatigue life cycle may be predetermined, for example defined by the aircraft manufacturer. Typically, landing gear components must be able to withstand 60,000 landings or takeoffs. Therefore, the first method 24 may include physical testing.

[0054] In practice, the first method 24 can be verified by comparison with experience gained on similar components 12 , 14 , which helps accumulate experience and speeds up the certification process.

[0055] For example, the second method 26 may include verifying that the dimensions of the weld 16 are designed to tolerate damage. Due to the softening process, the weld 16 not only limits the propagation of cracks therein (under equal forces, the length of crack propagation is shorter), but also helps to prevent the propagation of cracks that may be initiated in one of the elements 12, 14. Therefore, the second method 26 may include physical testing.

[0056] A specific implementation example of the manufacturing method is described in detail below.

[0057] In a first example, the two elements 12, 14 are hollow cylinders of revolution forged from 300M steel, with a mass composition of 0.415% carbon, 0.79% manganese, 1.68% silicon, 1.76% nickel, 0.81% chromium, 0.39% molybdenum, 0.068% vanadium, 0.07% copper, 0.005% phosphorus, 0.0006% sulfur. The two elements 12, 14 are welded by electron beam. The austenitizing process is to keep the part 10 in a furnace at 870°C for 45 minutes. The part 10 is quenched in oil to 30°C and then tempered twice at 300°C, each time for 2 hours.

[0058] The weld 16 is then maintained at 635°C for 1 hour using a heating resistor across the weld 16, preferably after the parts have returned to room temperature.

[0059] In the tests, toughness values ​​between 90 MPa√m and 130 MPa√m were measured, depending on the size of the component and the actual softening temperature.

[0060] In a second example, the same method can be implemented according to the same parameters using 35NCD16 alloy (AFNOR standard), which has a mass composition range of: carbon 0.32%-0.39%, manganese 0.30%-0.60%, silicon 0.10%-0.40%, nickel 3.60%-4.10%, chromium 1.60%-2.00%, molybdenum 0.25%-0.40%, phosphorus 0.035% or less, and sulfur 0.0035% or less.

[0061] Although this description relates to specific exemplary embodiments, these examples may be modified without departing from the overall scope of the invention as defined by the claims. In addition, the various features of the different embodiments shown or described may be combined in other embodiments. Therefore, the description and drawings should be regarded as illustrative rather than restrictive.

Claims

1. A method for manufacturing a steel component (10) for an aircraft, include: At least two steel elements (12, 14) are welded together to form the component (10); the component (10) is subjected to a resistance treatment, the resistance treatment comprising austenitizing (30), followed by quenching (32) and at least one tempering (34); then, the weld (16) between the at least two elements (12, 14) is subjected to a local softening treatment, the softening treatment comprising heating the weld (16) to a softening temperature below the starting temperature Ac1 of the steel transformation from ferrite to austenite.

2. The manufacturing method according to claim 1, wherein during the softening process, the area of ​​the component (10) containing the weld (16) is heated more than the area of ​​the component (10) remote from the weld (16).

3. The production method according to claim 1 or 2, wherein the softening temperature is at most 150°C lower than the temperature Ac1.

4. The manufacturing method according to any one of claims 1 to 3, wherein the resistance treatment comprises a second tempering (36) after the tempering (34).

5. The production method according to any one of claims 1 to 4, wherein the heating of the weld seam (16) is performed by conduction, in particular by means of a heating resistor or a heating mat, or by induction. 6 . The manufacturing method according to claim 1 , wherein the welding comprises at least one of electron beam welding, laser welding and friction welding.

7. A method of manufacturing according to any one of claims 1 to 6, wherein the welding of at least two elements is performed without the use of filler metal.

8. The manufacturing method according to any one of claims 1 to 7, wherein the mass composition of the steel is as follows: carbon content 0.38-0.45%, manganese content 0.60-0.90%, silicon content 1.45-1.80%, nickel content 1.65-2.00%, chromium content 0.70-0.95%, molybdenum content 0.35-0.50%, vanadium content 0.05-0.10%, copper content 0.35% or less, phosphorus content 0.01% or less, sulfur content 0.0010% or less, titanium content 0.0080% or less, niobium content 0.0050% or less, and the remainder is iron and unavoidable impurities.

9. The manufacturing method according to any one of claims 1 to 8, further comprising certifying the components (12, 14) by a first method (24) and certifying the weld between the components (12, 14) by a second, different method (26).

10. A steel component (10) for aircraft, in particular for aircraft landing gear, produced by the production method according to any one of claims 1 to 9.

11. The steel component (10) according to claim 1, wherein the toughness of the region of the component containing the weld (16) is greater than or equal to 80 MPa√m, preferably 90 MPa√m, more preferably 100 MPa√m.

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