Timepiece component made of lead-free brass and manufacturing method thereof

Abstract

The invention relates to a method for manufacturing a timepiece component (1) made of CuZn42 brass with a hardness of between 120 and 190 HV2, the method comprising the following steps: - providing a semifinished part that has been shaped by deformation, the semifinished part having a hardness of between 130 and 220 HV2 and being made from a CuZn42 brass material, - subjecting the semifinished part to a stress-relieving heat treatment at a temperature of between 170 and 230°C with a holding time at this temperature of between 20 minutes and 10 hours, preferably between 30 minutes and 5 hours, more preferably between 1 hour and 4 hours, - machining and finishing the semifinished part to create the timepiece component (1). The invention also relates to the timepiece component made from a CuZn42 brass.

Description

Technical field of the invention

[0001] The invention relates to a watch component made of lead-free brass and its manufacturing process. Technological background

[0002] In the watchmaking industry, many components are made from traditional brass containing lead, such as the CuZn38Pb2 alloy. This element, present at a concentration of 2 to 3% in brass, allows for improved machinability. However, lead exhibits some toxicity, even at low concentrations. Therefore, eliminating lead from materials has become essential.

[0003] The CuZn42 alloy is a brass with a very low lead content (less than 0.2% by weight) that is nonetheless suitable for machining thanks to its α+β two-phase structure. Its lead-free composition makes it a material of choice for watchmaking applications. However, the current processing of this material for watch components is not yet suitable for achieving the extreme precision in terms of dimensions and flatness required for such a component.

[0004] Indeed, the material in its semi-finished state after a forming step (rolling, extrusion, etc.) exhibits internal stresses that affect the part's dimensions during machining. It is known that stress-relieving tempering before machining can relax these internal stresses and thus prevent unwanted deformations during machining. Currently, stress-relieving tempering temperature ranges are optimized for lead-containing brasses, typically between 250°C and 300°C. Heat treatment within this temperature range allows for stress relaxation while maintaining a similar hardness after tempering. However, these parameters are not suitable for lead-free brasses, as a significant decrease in hardness is observed at these temperature ranges.

[0005] It is therefore necessary to develop a manufacturing process for Pb-free brass adapted to the requirements of watch components.

[0006] From the prior art, we know of document CN 112 251 628, which discloses a lead-free brass in which lead is replaced by silicon with a weight content between 0.5 and 1.5%. The manufacturing process, after casting, involves a solution heating step at a temperature of 600°C ± 50°C and an aging heat treatment at a temperature of 230°C ± 20°C. The addition of silicon allows, after the solution heating and aging heat treatments, the precipitation of silicon-rich intermetallics that act as hard chip breakers. The alloy thus produced exhibits good machinability properties and an increased tensile strength following the aging heat treatment. It is used for valves and fittings to relieve internal stresses.

[0007] Document EP 3 385 795 A1 discloses a lead-free brass hardening treatment. Summary of the invention

[0008] The invention aims to overcome the aforementioned drawbacks by proposing a new manufacturing process for a watch component made from lead-free brass, with an optimized internal stress relaxation step for the CuZn42 alloy, which has been previously formed by deformation. In addition to its lead-free nature, this alloy offers the following advantages. It has a higher zinc content, resulting in a higher β phase percentage, typically 30%, which improves machinability. Furthermore, the CuZn42 alloy has a higher work-hardening potential than leaded brass, allowing a hardness exceeding 200 HV to be achieved during the deformation forming step. These advantages make it a good candidate for replacing leaded brass in watch components.

[0009] According to the invention, the manufacturing process, and in particular the stress-relieving tempering step, has been optimized to reduce the hardness loss after tempering to a difference of less than or equal to 30 HV², or even 20 HV², or even 10 HV². The target hardness after tempering is between 120 and 190 HV², preferably between 150 and 190 HV², more preferably between 170 and 190 HV², and even more preferably between 180 and 190 HV². Depending on the hardness of the material before tempering, which varies according to the work hardening rate, a greater or lesser degree of hardness loss after tempering is permissible.

[0010] More specifically, the invention relates to the method of manufacturing a watch component made of CuZn42 brass having a hardness between 120 and 190 HV2, said method comprising the following steps: Provision of a semi-finished part having been shaped by deformation, said semi-finished part being made of a CuZn42 brass material and having a hardness between 130 and 220 HV2, preferably between 160 and 220 HV2, more preferably between 170 and 220 HV2, and even more preferably between 180 and 220 HV2, Stress-relieving heat treatment of said semi-finished part at a temperature between 170 and 230°C with a holding time at said temperature between 20 minutes and 10 hours, preferably between 30 minutes and 5 hours, more preferably between 1 hour and 4 hours, Machining and finishing of said semi-finished part to produce the watch component.

[0011] The invention also relates to the watch component produced by the manufacturing process, as described in claim 10. It is characterized by having a hardness between 120 and 190 HV2, preferably between 150 and 190 HV2, more preferably between 170 and 190 HV2, and even more preferably between 180 and 190 HV2, and by being stress-relieved. Watch components, particularly those of the movement, made from this stress-relieved alloy are characterized by minimal deformation, typically a few tenths of a micron maximum, after machining by material removal. This condition ensures flatness and clearance between the different mechanical levels of the movement. Similarly, the positional deviation of the characteristic machining operations (bores, recesses, etc.) is also minimized.) of each assembly level is minimal, which ensures the adjustment of the components mechanically linking the levels together and, in particular, guarantees the coaxiality of the axes which are held by the bridges.

[0012] To characterize this stress relaxation state of the material in the final product, a methodology has been developed to differentiate between a watch component that has undergone optimized stress relaxation tempering according to the invention and a watch component that has not been stress relaxed using the process according to the invention. This methodology consists of measuring the dynamic shear modulus M100 on the final product and measuring it again after heat treatment at 200°C for 1 hour. The difference in M100 (ΔM100) before and after heat treatment is a measure of the stress relaxation state within the material. A small change in the dynamic shear modulus indicates that the heat treatment no longer significantly affects the mechanisms involved in stress relaxation. Typically, a difference in M100 below 0.4 GPa ensures that the watch component placed on the market has indeed undergone stress relaxation tempering according to the process of the invention. Brief description of the figures

[0013] Other features and advantages of the present invention will become apparent in the following description of preferred embodiments, presented by way of non-limiting example with reference to the accompanying drawings. There figure 1 represents a watch component according to the invention made of CuZn42 brass. Figures 2A And 2B comparatively represent the evolution of hardness as a function of tempering temperature for, respectively, a lead-containing brass (CuZn38Pb2) and the lead-free brass (CuZn42) used in the context of the invention. figure 3 shows the evolution of the shear modulus at 100°C as a function of the holding time at 180°C (T1) and 200°C (T2) for CuZn42 with a work-hardened hardness of 175 HV2. figure 4This shows the evolution of the shear modulus at 100°C as a function of the holding time at 180°C for CuZn42 brasses with different hardnesses in the work-hardened state, as well as a result at 220°C for 1 hour for a CuZn42 brass with a work-hardened hardness of 210 HV2. figure 5 represents the geometry of the strain gauge used to determine the stress state of CuZn42 brass. The AA axis is parallel to the rolling direction. Detailed description of the invention

[0014] The present invention relates to a method for manufacturing a watch component made of lead-free brass, and more specifically of the CuZn42 alloy. The CuZn42 alloy, according to ASTM C28500, has the following composition by weight: Cu between 57 and 59% (including terminals), Pb ≤ 0.2%, Sn ≤ 0.3%, Fe ≤ 0.3%, Ni ≤ 0.2%, Al ≤ 0.05%, other elements ≤ 0.2%, and Zn at 100%. It thus has a Si content of 0.2% or less. It should be noted that adaptations to the composition, particularly for the elements Sn, Fe, Ni, and In, are possible and deviate significantly from the ASTM C28500 standard. For example, the weight contents of Fe, Sn, Ni and In could reach up to 0.5, 0.5, 0.5 and 0.3% respectively. Such adaptations are considered to cover the CuZn42 alloy.

[0015] The manufacturing process according to the invention is suitable for all watch components and in particular movement components. However, it is more specifically suited for components with high precision requirements in terms of dimensions, such as the mainplate, bridges ( fig.1 ), the blank, the barrel, the barrel cover, the barrel drum, etc. In the case of the barrel, the drum and the cover have thin walls for a large external diameter, typically with an outside diameter / wall thickness ratio of 45. Achieving thin walls without residual deformation is particularly critical during machining. More generally, the outside diameter / wall thickness ratio is between 20 and 70.

[0016] According to the invention, the CuZn42 brass watch component has a Vickers hardness (HV2) between 120 and 190, preferably between 150 and 190, more preferably between 170 and 190, and even more preferably between 180 and 190. The Vickers hardness is measured, for example, on a Shimadzu HMV-G20 semi-automatic machine with a 2 kg load. The size of the indentations is determined manually using the aforementioned average values ​​based on at least three measurements. The manufacturing process is then optimized to achieve this target hardness in the final product while relieving stresses during stress-relieving tempering to prevent unwanted deformations during machining.

[0017] The manufacturing process for the watch component according to the invention thus comprises at least the following steps: Provision of a semi-finished part that has been shaped by deformation through rolling, extrusion, etc.; in other words, provision of a semi-finished part in a work-hardened state. This semi-finished part has a hardness between 130 and 220 HV2, preferably between 160 and 220 HV2, more preferably between 170 and 220 HV2, and even more preferably between 180 and 220 HV2.With equivalent chemical composition, the hardness of the semi-finished part can be modulated according to the rate of work hardening and therefore the rate of deformation applied during shaping. Heat treatment of said semi-finished part, also called stress-relieving tempering, in a temperature range between 170°C and 230°C (inclusive), preferably between 180°C and 220°C, with a holding time in these temperature ranges of between 20 minutes and 10 hours, preferably between 30 minutes and 5 hours and more preferably between 1 hour and 4 hours. Machining and finishing of said product to obtain the watch component.

[0018] The semi-finished part provided is typically a rolled strip or an extruded bar. It may have already been cut, possibly thickened, after forming by deformation, for example into trays or discs, and possibly pre-machined, for example by contouring. Alternatively, the process may include an additional cutting step and optionally thickening and pre-machining before stress-relieving heat treatment. This cutting step is performed on the work-hardened material, i.e., before stress-relieving tempering, so as to have a hard material, which facilitates this cutting.

[0019] After stress-relieving, the semi-finished part can be machined to achieve the final shape of the watch component without residual deformation. Machining is performed by milling, drilling, and / or tapping, or any other machining operation that removes chips. Machining may be followed by a finishing treatment, such as polishing and / or engraving for decoration.

[0020] According to the invention, stress-relieving tempering is carried out within a temperature range of 170°C to 230°C. Typically, tempering is performed within a temperature range of 175°C to 195°C for a time of 1 to 4 hours. The purpose of stress-relieving tempering is to relax internal stresses without significantly affecting hardness. More precisely, the physical mechanisms involved in stress-relieving tempering primarily function to locally reorganize defects generated during shaping. The thermal energy input during tempering mainly activates the diffusion of defects, which, due to their mobility, can annihilate or reconfigure themselves in such a way as to minimize local energy. The atomic-scale defects are primarily linear defects in the grains (dislocations), vacancies, interstitials, substitutionals, or other point defects.To maintain the hardness level, it is necessary to avoid, during stress relieving, activating a large-scale structural modification such as recrystallization, which profoundly alters the metallurgical state of the material (grain size, ratio, and chemical composition of the phases). According to the invention, the hardness loss between before and after stress relieving is less than or equal to 30 HV², preferably less than or equal to 20 HV², and more preferably less than or equal to 10 HV². The permissible hardness delta is determined based on the target hardness of the final product and the initial hardness, adjusted according to the alloy composition and the deformation rate applied during forming. Thus, for a semi-finished part with a higher work hardening rate leading to a hardness of 200 HV², a delta of 20 or 30 HV² is permissible to reach the target hardness of around 180 HV².Since hardness decreases with temperature, a higher tempering temperature may be recommended when the initial hardness is high. Advantageously, when the semi-finished part has a hardness greater than or equal to 130 HV2 and less than 180 HV2, stress-relieving heat treatment may be carried out at a temperature between 175°C and 195°C for a time between 30 minutes and 5 hours, preferably between 1 and 4 hours. Advantageously, when the semi-finished part has a hardness between 180 and 220 HV2, stress-relieving heat treatment may be carried out at a temperature between 195°C and 220°C for a time between 30 minutes and 5 hours, preferably between 1 and 4 hours.

[0021] Numerous tests were conducted to determine the optimum temperature and time range for stress relieving without significantly softening the material. As illustrated in Figures 2A And 2BThe brass with lead (CuZn38Pb2 with HV2 in the work-hardened state of 169), conventionally used in watchmaking, and the lead-free brass (CuZn42 with HV2 in the work-hardened state of 163) used in the context of the present invention exhibit very different behaviors during 30-minute tempering cycles performed within the same temperature range. Unlike the hardening behavior observed in leaded brass at tempering temperatures below 250°C, the hardness of CuZn42 brass decreases continuously with the tempering temperature. More precisely, successive plateaus are observed between 180°C and 210°C, and then between 220°C and 240°C. Based on these observations, choosing a tempering temperature of 250°C or higher, as recommended for leaded brasses, results in a significant loss of hardness. For lead-free brass, the recommended temperature range is between 170°C and 230°C to avoid a drastic drop in hardness.

[0022] To assess the stress state of the material across these temperature ranges, measurements were performed using mechanical spectroscopy. Mechanical spectroscopy is a physical analysis method in which a torsion pendulum, incorporating a specimen made of the material to be analyzed, is subjected to forced oscillations in a temperature-controlled vacuum chamber. For a given excitation, the instrument measures the amplitude and phase of the specimen's deformation as a function of temperature during heating / cooling cycles. The amplitude and phase shift of the deformation with the forced excitation are related to the viscoelastic properties of the material, specifically how internal defects reorganize to accommodate the varying stresses to which the specimen is subjected.The dynamic shear modulus M, a quantity directly linked to the phase shift accessible by mechanical spectroscopy measurement, is an indicator of the relaxation state of the material (W. Benoit, "Dislocation-Lattice interactions", Materials Science Forum, Vols. 366-368, pp. 158-177, 2001. ) ( J. Lauzier, J. Hillaire, G. Gremaud and W. Benoit, “Lubrication agents of dislocation motion at very low temperature in cold worked aluminum,” J. Phys. : Condens. Mater., vol. 2, p. 9247, 1990) .This indicator allows us to monitor the kinetics of the expansion as a function of temperature and tempering time. The tests were carried out according to one of the following two protocols, which give similar results: 1) Single temperature sweep: the pendulum is heated at 5°C / min to the setpoint temperature, held for the chosen tempering time at this temperature, then cooled at a rate of 2°C / min to 100°C. The values ​​of M are recorded throughout the sweep, up to the temperature of 100°C where the value of M 100 is recorded. The value of this last temperature is arbitrarily chosen as "almost ambient". The tempering holding time varies from 30 minutes to 8 hours. 2) Multiple temperature sweep: rapid heating ramp of 5°C / min to the initial setpoint temperature, very slow holding or heating (0.3°C / min) for 30 minutes, followed by cooling at 2°C / min to 100°C, heating at 5°C / min to a second setpoint temperature, typically 10°C or 20°C higher than the initial value, cooling, measurement of M100, etc. The cooling / heating steps are repeated until the higher setpoint temperature is reached. The shear modulus value is measured at 100°C, a temperature arbitrarily chosen as "near room temperature," and is indicated below M100.

[0023] The aim is to maximize the difference ΔM 100 between the initial state before tempering and that after tempering in order to optimize stress relaxation within the material. The evolution of the dynamic shear modulus M 100 as a function of tempering time is studied for CuZn42 with a hardness after forming of 175 HV2. The behavior at 200°C (T2) and 180°C (T1) is illustrated in the figure 3After 30 minutes of holding at 180°C and 200°C, a significant variation in the shear modulus M100 is already observed, with a ΔM100 exceeding 1 GPa. The maximum value of M100 is reached after holding at 180°C for more than 180 minutes, while an equivalent value of M100 is obtained after only 30 minutes at 200°C. The gain in the M100 value becomes negligible beyond 180 minutes. The maximum ΔM100 is 1.2 GPa at 180°C and 1.5 GPa at 200°C, thus indicating more efficient stress relief with increasing temperature. Regarding hardness, after 180 minutes at 180°C, it is 170 HV², representing a loss of only 5 HV². Increasing the tempering time to 5 hours at 180°C did not result in any further decrease in hardness. After 30 minutes at 200°C, the hardness was 166 HV2, representing a loss of only 9 HV2. After 180 minutes at 200°C, it was 164 HV2, representing a loss of only 11 HV2.These tests show that increasing the temperature maximizes ΔM 100 with a slightly more pronounced decrease in hardness. Tests were also carried out on CuZn42 brass with an initial hardness of 200 HV2. After stress-relieving tempering at 180°C for 180 minutes, the decrease in hardness was limited to 13 HV2.

[0024] To the figure 4The dynamics of the increase in M100 during stress relief at 180°C and 220°C were monitored for CuZn42 brasses with initial hardnesses between 162 HV2 and 210 HV2. The main increase in M100 occurs during the first hour of stress relief. At 180°C, it is relatively similar for all grades. The stress relief dynamics at 220°C for the hardest grade (HV2=210) confirm that the stress relief temperature is the determining factor for maximizing M100. The 180°C / 3h stress relief treatment achieves a similar stress-relieving state for all the CuZn42 brass grades studied. Depending on the permissible loss of hardness, according to the desired final hardness, stress relieving at 220°C for 1 hour allows a substantial additional gain to be obtained in the value obtained for M 100.

[0025] To characterize the stress state of a material, an alternative to maximizing ΔM 100 is to minimize the deformation of a gauge specifically designed to represent the watchmaking processes of bridges or any other watch component machined from a semi-finished piece in rolled strip or bar form. The deformation gauge has a geometry chosen so that it deforms, preferably by buckling, when detached from the die in which it is machined. Its preferably circular geometry is characterized by a thickness-to-diameter ratio greater than 10, preferably greater than 100, and by its easy detachment from the die in which it is machined.The design of the strain gauge is based on the principle of buckling, which states that when the residual stresses in the diaphragm forming its base exceed a critical value, the gauge will deform by buckling upon detachment and reach an equilibrium shape characteristic of the residual stress state present in the material constituting the gauge's diaphragm. To ensure proper stress relief of the brass, it is necessary to minimize the gauge's buckling during detachment. As an example, measurements were carried out with a gauge whose geometry is shown in Figure 1. figure 5The gauge consists of a low cylinder with an internal diameter of 32 mm and a very thin bottom of 0.3 mm (thickness-to-diameter ratio of approximately 100) in which six recesses, each 4 mm in diameter and 0.15 mm deep, are machined. The gauge is machined from a tray extracted by stamping or milling from a rolled strip ranging from one to several millimeters thick. Regardless of the initial strip thickness, the bottom thickness is fixed at 0.3 mm. After machining the cylinder and the recesses, the gauge is partially trimmed to remain attached to the tray by three clips, allowing for easy detachment in a subsequent step. The thin bottom is designed to deform significantly under residual stress. It can partially deform during trimming, with maximum deformation occurring when the gauge is detached.The approach used in this study consists of characterizing the material's stress relief by quantitatively measuring the strain gauge's deformations upon detachment. These deformations are deduced from the values ​​of two indicators, measured by characterizing the topography of the part's base: first, after machining (strain gauge attached to the tray), and second, after detachment by breaking the three attachments (strain gauge detached). The maximum deformation, i.e., the relative flatness, observed on the base is an indicator of the material's stress relief. The measurements are performed using optical microscopy, with a dedicated setup for the measuring instruments ensuring precise and repeatable positioning of the strain gauge, whether attached or detached. It should be noted that another indicator could be the maximum relative displacement observed at the centers of the grooves between the "attached" and "detached" states. This is why the strain gauge is equipped with grooves.It would also be possible to create a gauge without these grooves and to use the maximum deformation as the sole indicator.

[0026] Flatness is assessed by optically measuring the height distribution of the gauge base using confocal microscopy in white light (FRT Microprof instrument with a dedicated setup ensuring reproducible gauge positioning). The height value z is measured in 0.2 mm increments in both the x and y axes. The topography of the internal surface of the base is established by eliminating the effects of residual roughness through averaging the calculated z value over a 1 mm² area (average of approximately 25 points). Any overall gauge inclination error in the setup is reduced by subtracting the mean plane of the part. This yields the distribution of residual zi values ​​from the mean plane. Flatness P is defined as the distance between two parallel planes encompassing the entire surface, quantified by the value zmax - zmin.The relative strain of the gauge is evaluated between the "attached" state and the "detached" state, by subtracting point by point the two topographies za (x;y) and zd (x;y). The maximum strain (relative flatness) is obtained by taking the maximum value of the difference in heights, i.e., max|zd - za|.

[0027] The measurements were performed on CuZn42 brass with a work-hardened hardness of 173 HV2. In the work-hardened state, the maximum deformation is 7.1 µm. After stress-relieving tempering at 180°C for 3 hours, the maximum deformation drops to 2.2 µm. On CuZn42 brass with a work-hardened hardness of 210 HV2, subjected to stress-relieving treatment at 220°C for 1 hour, the maximum deformation is 2.2 µm. For another test performed on a CuZn42 grade with a work-hardened hardness of 200 HV2 and stress-relieved at 180°C for 3 hours, the maximum deformation is 2.7 µm, whereas it is 4.7 µm in the work-hardened state. Thus, a maximum deformation less than or equal to 3.5 µm and preferably 3 µm is also an indicator of the relaxation state of the material.

[0028] The present invention also relates to the watch component made from this alloy and obtained by the process described above. As mentioned above, this component is characterized by the choice of CuZn42 brass as the material, and by its hardness, with values ​​ranging from 120 to 190 HV2, preferably from 150 to 190 HV2, more preferably from 170 to 190 HV2, and even more preferably from 180 to 190 HV2. It is also characterized by its relaxed state, as opposed to the work-hardened state after forming. To characterize this state in the final product, the following procedure is used. The dynamic shear modulus M100 is measured on a sample taken from the watch component. The sample can be planar (blade) or cylindrical (wire), the geometry of the sample having no impact on the measured value.Next, the sample taken from this same component is characterized in a mechanical spectroscopy test bench chosen according to the geometry of the sample. The variation of the dynamic shear modulus ΔM 100 between the initial state before tempering and that after tempering is recorded after application of the temperature scanning protocol 1) described previously. The holding time is one hour at a temperature of 200°C. It can be concluded that the component is in a relaxed state, and has therefore been manufactured using the process according to the invention, if the ΔM 100 is less than 0.4 GPa, or even 0.2 GPa, which corresponds to the variations of M 100 in the "plateau" zone of the [unclear]. figures 3 And 4 after the sharp increase in M ​​100 during the first hour.

[0029] Alternatively, and less preferably, a means of differentiating a watch component that has undergone stress reduction according to the manufacturing process of the invention from a watch component that has not. This stress reduction can also be achieved by measuring the maximum deformation, as described above, on a sample machined from the watch component. This measurement must be less than or equal to the threshold value determined, for the chosen geometry, on reference samples machined from stress-relieved material. The test specimen is designed to deform by buckling upon release after machining.

Claims

1. Method for manufacturing a watch component (1) in brass CuZn42 with a hardness between 120 and 190 HV2, said method comprising the following steps: - Provision of a semi-finished piece having been shaped by deformation, said semi-finished piece being realised in brass CuZn42 and having a hardness between 130 and 220 HV2, preferably between 160 and 220 HV2, more preferably between 170 and 220 HV2, and even more preferably between 180 and 220 HV2, - Stress relief heat treatment of said semi-finished piece at a temperature between 170 and 230 °C with a holding time at said temperature between 20 minutes and 10 hours, preferably between 30 minutes and 5 hours, more preferably between 1 hour and 4 hours, - Machining and finishing of said semi-finished piece to produce the watch component (1).

2. Method for manufacturing according to the preceding claim, characterised in that the heat treatment is carried out at a temperature between 175°C and 220°C, preferably between 180°C and 220°C, with a holding time at said temperature between 30 minutes and 5 hours, preferably between 1 hour and 4 hours.

3. Method for manufacturing according to the preceding claim, characterised in that the heat treatment is carried out at a temperature between 175°C and 195°C, preferably between 180°C and 195°C, with a holding time at said temperature between 30 minutes and 5 hours, preferably between 1 hour and 4 hours.

4. Method for manufacturing according to one of the preceding claims, characterised in that, when the brass CuZn42 material of the semi-finished piece has a hardness greater than or equal to 130 HV2 and less than 180 HV2, the stress relief heat treatment is carried out at a temperature between 175°C and 195°C for a duration of between 30 minutes and 5 hours, preferably between 1 and 4 hours.

5. Method for according to one of claims 1 to 2, characterised in that, when the brass CuZn42 material of the semi-finished piece has a hardness between 180 and 220 HV2, the stress relief heat treatment is carried out at a temperature between 195°C and 220°C for a duration of between 30 minutes and 5 hours, preferably between 1 and 4 hours.

6. Method for manufacturing according to one of the preceding claims, characterised in that it includes a cutting step between the provision step and the heat treatment step.

7. Method for manufacturing according to the preceding claim, characterised in that it includes a pre-machining and / or thickness adjustment step after the cutting step and before the heat treatment step.

8. Method for manufacturing according to one of the preceding claims, characterised in that the stress relief heat treatment leads to an increase in the shear modulus M100 of the brass CuZn42 material by a value greater than or equal to 1 GPa.

9. Method for manufacturing according to one of the preceding claims, characterised in that the stress relief heat treatment leads to an increase in the shear modulus M100 of the material by a value greater than or equal to 1.2 GPa.

10. Watch component (1) realised in brass CuZn42 material with, by weight: - 57 ≤ Cu ≤ 59 % , - Pb ≤ 0.2 % , - Sn ≤ 0.5 % , - Fe ≤ 0.5 % , - Ni ≤ 0.5 % , - In ≤ 0.3 % , - Al ≤ 0.05 % , - Any other elements each having a content less than or equal to 0.2%, - Zn: balance to 100%, the material of said watch component (1) having a hardness between 120 and 190 HV2 and being in a relaxed state, the relaxed state of the material being determined based on the difference ΔM100 between the dynamic shear modulus M100 measured on a sample taken from said watch component (1) and then subjected to a heat treatment held for 1 hour at a temperature of 200°C with a heating rate to 200°C of 5°C / min and a cooling rate after the 1-hour hold of 2°C / min and the dynamic shear modulus M100 measured on a sample taken from said watch component (1) without undergoing further heat treatment, the ΔM100 being less than 0.4 GPa when the material of the watch component (1) is in the relaxed state.

11. Watch component (1) according to the preceding claim, characterised in that it has a hardness between 150 and 190 HV2, preferably between 170 and 190 HV2, more preferably between 180 and 190 HV2.

12. Watch component (1) according to claim 10 or 11, characterised in that it is a movement watch component (1).

13. Watch component (1) according to one of claims 10 to 12, characterised in that it is a plate, a bridge, a blank, a barrel, a barrel drum, or a barrel cover.

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