CH718413B1 - Lead-free brass watch component and its manufacturing process. - Google Patents

Abstract

The invention relates to a method of manufacturing a watch component (1) made of CuZn42 brass with a hardness of between 120 and 190 HV2, said method comprising the following steps: – Provision of a semi-finished part having been placed shaped by deformation, said semi-finished part having a hardness of between 130 and 220 HV2 and being made of a CuZn42 brass material, – Thermal relaxation treatment of said semi-finished part at a temperature of between 170 and 230°C with a maintaining time at said 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 of said semi-finished part to produce the watch component ( 1). The invention also relates to the watch component made from CuZn42 brass.

Description

Technical field of the invention

[0001] The invention relates to a watch component made from lead-free brass, more specifically from the CuZn42 alloy, having a Pb content by weight ≤ 0.2%, and its manufacturing process.

Technology background

[0002] In the watchmaking field, many components are made from traditional brass containing lead such as the CuZn38Pb2 alloy. This element, the content of which in the brass is 2 to 3%, allows better machinability. However, lead presents some toxicity, even at low concentrations. The elimination of lead in materials is therefore becoming a necessity today.

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

[0004] Indeed, the material in the semi-finished state after a shaping step by deformation (rolling, extrusion, etc.) presents internal constraints which affect the dimensioning of the part during its machining. It is known to carry out a relaxation income before the machining step so as to relax these internal stresses and therefore to avoid unwanted deformations during machining. To date, the stress relief temperature ranges are optimized for Pb brasses with typically a tempering temperature between 250°C and 300°C. Heat treatment in this temperature range allows stresses to be relaxed while maintaining a similar hardness after tempering the material. It turns out that these parameters are not suitable for Pb-free brass, with too significant a drop in hardness being observed at these temperature ranges.

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

Summary of the invention

[0006] The invention aims to overcome the aforementioned drawbacks by proposing a new process for manufacturing a watch component made from lead-free brass with an internal stress relaxation step optimized for the CuZn42 alloy. In addition to its absence of lead, this alloy has the following advantages. It has a higher zinc content with the corollary a higher β phase rate, typically 30%, which improves machinability. Then, the CuZn42 alloy has a higher work hardening potential than leaded brass, which allows it to achieve a hardness greater than 200HV during the shaping stage by deformation. These advantages make it a good candidate to replace leaded brass in watch components.

[0007] According to the invention, the manufacturing process, and in particular the stress-relieving tempering step, has been optimized to reduce the loss of hardness after tempering to a difference less than or equal to 30 HV2, or even 20 HV2, or even at 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 is variable depending on the work hardening rate, a greater or lesser loss of hardness after tempering is authorized.

[0008] More precisely, the invention relates to the process of manufacturing a CuZn42 brass watch component having a hardness of between 120 and 190 HV2, said process comprising the following steps: – Provision of a semi-finished part finished having been shaped by deformation, said semi-finished part being made of a CuZn42 brass material and having a hardness of 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, – Thermal relaxation treatment of said semi-finished part at a temperature of between 170 and 230°C with a maintenance time at said 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 of said semi-finished part to produce the watch component.

[0009] The invention also relates to the watch component resulting from the manufacturing process. It has the characteristic of having a hardness of between 120 and 190 HV2, preferably between 150 and 190 HV2, more preferably between 170 and 190 HV2, even more preferably between 180 and 190 HV2 and of being relaxed. Watch components, in particular those of the movement, made from this relaxed alloy are characterized by minimal deformation, typically a few tenths of microns maximum, after machining by material subtraction. This condition ensures flatness and movement between the different mechanical levels of the movement. Likewise, the deviation in position of the characteristic machining (bores, recesses, etc.) of each assembly level is minimal, which ensures the adjustment of the components mechanically connecting the levels together and, in particular , to guarantee the co-axiality of the axes which are retained by the bridges.

[0010] To characterize this state of relaxation of the material on the final product, a methodology has been developed to differentiate between a watch component having been subjected to the optimized relaxation temper according to the invention and a watch component which has not been relaxed. with the process according to the invention. It consists of measuring the dynamic shear modulus M100 on the final product and measuring it again after a heat treatment at 200°C for 1 hour, the delta M100 (ΔM100) before and after heat treatment being a measure of the state of relaxation of stresses within the material. A small variation in the dynamic shear modulus indicates that the heat treatment no longer significantly affects the mechanisms at play during stress relaxation. Typically, a delta M100 of less than 0.4 GPa ensures that the watch component placed on the market has indeed been subjected to stress relief according to the process of the invention.

Brief description of the figures

Other characteristics and advantages of the present invention will appear in the following description of preferred embodiments, presented by way of non-limiting example with reference to the appended drawings. Figure 1 represents a watch component according to the invention made from CuZn42 brass. Figures 2A and 2B comparatively represent the evolution of the hardness as a function of the tempering temperature for respectively a brass with Pb CuZn38Pb2 and the brass without Pb CuZn42 used in the context of the invention. Figure 3 shows the evolution of the shear modulus at 100°C M100 as a function of the holding time at 180°C (T1) and at 200°C (T2) for CuZn42 with a hardness in the work-hardened state of 175 HV2. Figure 4 shows the evolution of the shear modulus at 100°C M100 as a function of the holding time at 180°C for CuZn42 brasses having different hardnesses in the work-hardened state as well as a result at 220°C for 1 hour for a CuZn42 brass having a hardness in the work-hardened state of 210 HV2. Figure 5 shows the geometry of the strain gauge used to determine the relaxation state of CuZn42 brass. The A-A axis is parallel to the rolling direction.

Detailed description of the invention

The present invention relates to the process for manufacturing a watch component made from Pb-free brass and more specifically from the CuZn42 alloy. The CuZn42 alloy according to the ASTM C28500 standard has the following composition by weight: Cu between 57 and 59% (limits inclusive), Pb ≤ 0.2%, Sn ≤ 0.3%, Fe ≤ 0.3%, Ni ≤ 0.2%, Al ≤ 0.05 %, other elements ≤ 0.2%, Zn balances at 100%. It is specified here that adaptations in terms of composition, and in particular for the elements Sn, Fe, Ni and In, are possible and deviate very significantly from the ASTM C28500 standard. For example, the weight contents of Fe, Sn, Ni and In could rise to 0.5, 0.5, 0.5 and 0.3% respectively. Such adaptations are considered to cover the CuZn42 alloy.

[0013] The manufacturing process according to the invention is suitable for all watch components and in particular movement components. However, it is more specifically suitable for components with significant precision requirements in terms of dimensions such as the plate, the 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 a thin wall for a large external diameter with typically an external diameter/wall thickness ratio of 45, the production of thin walls without residual deformation being particularly critical during machining . More generally, the external diameter/thickness ratio of the wall is between 20 and 70.

[0014] According to the invention, the CuZn42 brass watch component has an HV2 hardness of between 120 and 190, preferably between 150 and 190, more preferably between 170 and 190, even more preferably between 180 and 190, the Vickers hardness being measured for example on a Shimadzu HMV-G20 semi-automatic machine with a load of 2kg. The detection of the size of the imprints is done manually with the aforementioned average values determined on the basis of at least 3 measurements. The manufacturing process is therefore optimized to obtain this target hardness in the final product while relaxing the stresses during stress-relieving to avoid unwanted deformations during machining.

[0015] The method of manufacturing the watch component according to the invention thus comprises at least the following steps: – Provision of a semi-finished part having been shaped by deformation by rolling, extrusion, etc.; in other words, provision of a semi-finished part in the work-hardened state. This semi-finished part has a hardness of 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. At equivalent chemical composition, the hardness of the semi-finished part can be modulated as a function of the work hardening rate and therefore the rate of deformation applied during shaping, – Heat treatment of said semi-finished part, also called tempering expansion, in a temperature range of between 170°C and 230°C (limits included), preferably between 180°C and 220°C, with a maintenance 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.

[0016] The semi-finished part made available is typically a rolled strip or an extruded bar. It may already have been cut, possibly made to thickness, after shaping by deformation, for example in the form of trays or washers and possibly pre-machined for example by trimming. Alternatively, the process may include an additional step of cutting and optionally of thicknessing and pre-machining before the heat reduction treatment. This cutting step is carried out on the work-hardened material, i.e. before the relaxation income, so as to have a hard material, which facilitates this cutting.

[0017] After the stress relief, the semi-finished part can be machined to obtain the final shape of the watch component without residual deformation. Machining is carried out by milling, drilling and/or tapping or any other machining operation by removing chips. Machining may be followed by a finishing treatment, such as polishing and/or engraving for decoration.

[0018] According to the invention, the stress relief is carried out in a temperature range between 170°C and 230°C. Typically, tempering is carried out in a temperature range between 175°C and 195°C for a time between 1 hour and 4 hours. The purpose of the stress relief is to relax the internal stresses without significantly affecting the hardness. More precisely, the physical mechanisms at play during the relaxation tempering have as their main function the local reorganization of the defects generated during shaping. The provision of thermal energy during tempering mainly allows the activation of the diffusion of defects which, thanks to their mobility, can be annihilated or reconfigured in such a way as to minimize the local energy. Defects on the atomic scale are mainly linear defects in grains (dislocations), vacancies, interstitials, substitutionals or other point defects. In order to maintain the hardness level, it is necessary to avoid, during relaxation, activating a large-scale structural modification such as recrystallization, which profoundly modifies the metallurgical state of the material (grain size, ratio and composition). phase chemistry). According to the invention, the loss of hardness between before and after the stress relief is less than or equal to 30 HV2, preferably less than or equal to 20 HV2, more preferably less than or equal to 10 HV2. The authorized hardness delta is determined on the basis of the target hardness on the final product and the initial hardness modulated according to the composition of the alloy and the rate of deformation applied during shaping. 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 authorized to reach the hardness target around 180 HV2. As the hardness drop increases 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, the thermal relaxation treatment can be carried out at a temperature of between 175° and 195°C for a time of between 30 minutes and 5 hours, preferably between 1 and 4 hours. Advantageously, when the semi-finished part has a hardness of between 180 and 220 HV2, the thermal relaxation treatment can be carried out at a temperature of between 195°C and 220°C for a time of between 30 minutes and 5 hours, preferably between 1 and 4 hours.

[0019] Numerous tests have been carried out to determine the optimum range of temperatures and times to achieve relaxation without significantly softening the material. As illustrated in Figures 2A and 2B, brass with Pb (CuZn38Pb2 with HV2 in the work-hardened state of 169) conventionally used in the watchmaking field and brass without Pb (CuZn42 with HV2 in the work-hardened state of 163) used in the watchmaking field. framework of the present invention have very different behaviors during 30-minute tempering carried out in the same temperature range. Unlike the hardening behaviors observed on leaded brass for tempering temperatures below 250°C, the hardness of CuZn42 brass continuously decreases with tempering temperature. More precisely, we observe the appearance of successive levels, between 180°C and 210°C, then between 220°C and 240°C. According to these observations, the choice of a tempering temperature greater than or equal to 250°C, as recommended for leaded brass, causes 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.

[0020] To evaluate the state of relaxation of the material for these temperature ranges, measurements were carried out by mechanical spectroscopy. Mechanical spectroscopy is a physical analysis method in which a torsion pendulum, which incorporates the test piece made with the material to be analyzed, is subjected to forced oscillations in a vacuum chamber whose temperature is controlled. For a given excitation, the device measures, as a function of temperature, the amplitude and phase of deformation of the specimen during heating/cooling cycles. The amplitude and phase shift of the deformation with the forced excitation are linked to the viscoelastic properties of the material, i.e. to the way in which the internal defects are reorganized to accommodate the variation in 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 state of relaxation 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 ., vol. 2, p. 9247, 1990). This indicator makes it possible to follow the kinetics of the evolution of the relaxation as a function of the temperature and the duration of the tempering. The tests were carried out according to one of the following two protocols which give similar results: 1) simple temperature scanning: the pendulum is heated at 5°C/min to the set temperature, maintained for the duration chosen for tempered at this temperature, then cooled at a rate of 2°C/min to 100°C. The values of M are recorded throughout the scanning, up to the temperature of 100°C where the value of M100 is recorded. The value of this last temperature is chosen arbitrarily as “almost ambient”. The duration of income maintenance varies from 30 minutes to 8 hours. 2) multiple temperature sweep: rapid heating ramp of 5°C/min to the initial set temperature, maintenance or very slow heating (0.3°C/min) for 30 minutes, followed by cooling by 2° C/min up to 100°C, heating at 5°C/min to a second set temperature, usually 10°C or 20°C higher than the initial value, cooling, measurement of M100, etc. The cooling/heating steps are repeated until the chosen upper set temperature value is reached. The value of the shear modulus is measured at 100°C, a temperature arbitrarily chosen as “almost ambient” and is indicated below M100.

[0021] This involves maximizing the difference ΔM100 between the initial state before tempering and that after tempering to optimize the relaxation of stresses within the material. The evolution of the dynamic shear modulus M100 as a function of the tempering duration is studied for CuZn42 having a hardness after shaping of 175 HV2. The behavior at 200°C (T2) and at 180°C (T1) is illustrated in Figure 3. After 30 minutes of holding at 180°C and 200°C, we already observe a significant variation in the shear modulus M100with a ΔM100 greater than 1 GPa. The maximum value of M100 is reached after holding for more than 180 minutes at 180°C while an equivalent value of M100 is obtained after only 30 minutes at 200°C. The gain recorded on the value of M100 becomes negligible beyond 180 minutes. The maximum ΔM100 is 1.2 GPa at 180°C and 1.5 GPa at 200°C, therefore with more effective expansion with increasing temperature. Regarding hardness, after 180 minutes at 180°C, it is 170 HV2, or only a loss of 5 HV2. By increasing the tempering time to 5 hours at 180°C, no additional drop in hardness is observed. After 30 minutes at 200°C, it is 166 HV2, or only a loss of 9 HV2. After 180 minutes at 200°C, it is 164 HV2, or only a loss of 11 HV2. These tests show that an increase in temperature makes it possible to maximize ΔM100 with a slightly more marked reduction in hardness. Tests were also carried out on a CuZn42 brass having an initial hardness of 200 HV2. After relaxing at 180°C for 180 minutes, the reduction in hardness is limited to 13 HV2.

[0022] In Figure 4, the dynamics of the increase in M100 during tempering at 180°C as well as at 220°C was followed for CuZn42 brasses having initial hardnesses between 162 HV2 and 210 HV2. The main increase in M100 occurs during the first hour of relaxation. At 180°C, it is relatively similar for all shades. The dynamics of the expansion at 220°C of the hardest grade (HV2=210) confirms that the expansion temperature is the determining factor for maximizing M100. The relaxation treatment of 180°C/3h makes it possible to achieve a similar state of relaxation for all the grades of CuZn42 brass studied. Depending on the admissible loss of hardness, depending on the desired final hardness, relaxing at 220°C for 1 hour makes it possible to obtain a substantial additional gain in the value obtained for M100.

[0023] To qualify the state of relaxation of a material, an alternative to maximizing ΔM100 is the minimization of the deformation of a gauge specifically designed to represent the watchmaking machining of bridges or any other watchmaking component machined in a semi-finished part. -finished in laminated strip or bar form. The strain gauge has a geometry chosen so as to deform, preferably by buckling, when it is detached from the die in which it is machined. Its preferably circular geometry is characterized in that the thickness/diameter ratio is greater than 10, preferably greater than 100 and that it is easily detachable from the matrix in which it is machined. The design of the strain gauge is based on the principle of buckling which means that when the residual tensions in the membrane constituting its bottom are greater than a critical value, the gauge will deform by buckling during its detachment and reach a form of equilibrium characteristic of the state of residual stresses present in the material constituting the membrane of the gauge. In order to guarantee good relaxation of the brass, it is a question of minimizing the buckling of the gauge when it is detached. As an example, the measurements were carried out with a gauge whose geometry is shown in Figure 5. The gauge is made up of a low cylinder with an internal diameter of 32 mm having a very thin bottom of 0.3 mm (thickness ratio /diameter equal to approximately 100) in which six recesses of diameter 4 mm and depth 0.15 mm are machined. The gauge is machined from a tray extracted by stamping or milling from the rolled strip with a thickness of one to a few millimeters. Regardless of the initial thickness of the strip, the bottom thickness is set at 0.3 mm. After machining the cylinder and the recesses, the gauge is then partially cut out to remain held by three fasteners to the tray, so as to be easily detachable in a later step. The thin bottom is designed to deform significantly in the presence of residual stresses. It can be partially deformed during trimming, the maximum deformation being expressed when detaching the gauge. The approach applied in this study consists of qualifying the relaxation of the material by quantitatively measuring the deformations of the gauge during detachment. These are deduced from the values of two indicators, measured by qualifying the topography of the bottom of the part a first time after machining of the part (gauge attached to the tray) and a second time after detachment by rupture of the three fasteners ( detached gauge). The maximum deformation, i.e. the relative flatness observed on the bottom is an indicator of the relaxation of the material. Measurements are made by optical microscopy, a dedicated installation for measuring devices to ensure precise and repeatable positioning of the gauge, whether attached or detached. It will be noted that another indicator could be the maximum relative displacement observed on the centers of the hollows between the “attached” state and the “detached” state. This is why the gauge has recesses. It would also be possible to produce a gauge without these recesses and to use the maximum deformation as the only indicator.

The flatness is evaluated from the optical measurement of the distribution of the heights of the bottom of the gauge carried out by confocal microscopy in white light (FRT Microprof instrument with dedicated installation ensuring the reproducibility of the positioning of the gauge). The z height value is measured in steps of 0.2 mm in x and y. The topography of the internal surface of the bottom is established by overcoming the effects of residual roughness by averaging the z value calculated over a surface of 1 mm<2> (average over approximately 25 points). The possible error in overall inclination of the gauge in the installation is reduced by subtracting the average plane of the part. We thus obtain the distribution of the values of the residuals zlau mean plane. Flatness P is defined as the distance separating two parallel planes containing the entire surface, quantified by the value zmax-zmin. The relative deformation of the gauge is evaluated between the “attached” state and the “detached” state, by point-by-point subtraction of the two topographies za(x;y) and zd(x;y). The maximum deformation (relative flatness) is obtained by taking the maximum value of the height difference, i.e. max|zd-za|.

The measurements were carried out on a CuZn42 brass having a hardness in the work-hardened state of 173 HV2. In the work-hardened state, the maximum deformation is 7.1 µm. After relaxing at 180°C for 3 hours, the maximum deformation drops to 2.2 µm. On a CuZn42 brass having a hardness in the work-hardened state of 210 HV2, subjected to a stress-relieving treatment at 220°C for 1 hour, the maximum deformation is 2.2 µm. For another test carried out on a CuZn42 grade with a hardness in the work-hardened state of 200 HV2 and relaxed at 180°C for 3 hours, the maximum deformation is 2.7 µm while 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 state of relaxation of the material.

The present invention also relates to the watch component made from this alloy and obtained following the process described above. As mentioned above, this component is characterized by the choice of the CuZn42 brass material, by its hardness with values between 120 and 190 HV2, preferably between 150 and 190 HV2, more preferably between 170 and 190 HV2, even more preferably between 180 and 190 HV2. It is also characterized by its relaxed state as opposed to the hardened state after its shaping by deformation. To characterize this state on 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. Then, 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 in the dynamic shear modulus ΔM100 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 the relaxed state, and has therefore been manufactured with the process according to the invention, if the ΔM100 is less than 0.4 GPa, or even 0.2 GPa, which corresponds to the variations of the M100 in the zone „ plateau“ in Figures 3 and 4 after the sudden increase in M100 during the first hour.

[0027] Less preferably, a means of differentiating a relaxed watch component according to the manufacturing process of the invention and a non-relaxed watch component may also consist of measuring the maximum deformation as described previously on a sample machined in the component. watchmaker, with a value which must be less than or equal to the threshold value determined, for the chosen geometry, on reference samples machined in relaxed material. The specimen is designed to buckle when released after machining.

Claims (11)

1. Process for manufacturing a watch component (1) in CuZn42 brass with a hardness of between 120 and 190 HV2, said process 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 of 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, – Thermal relaxation treatment of said semi-finished part at a temperature of between 170 and 230°C with a maintenance time at said temperature of between 20 minutes and 10 hours, preferably between 30 minutes and 5 hours, more preferably between 1 hour and 4 o'clock, – Machining and finishing of said semi-finished part to produce the watch component (1). 2. Manufacturing process according to the preceding claim, characterized 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. Manufacturing process according to the preceding claim, characterized 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. Manufacturing method according to one of the preceding claims, characterized in that, when the CuZn42 brass material of the semi-finished part has a hardness greater than or equal to 130 HV2 and less than 180 HV2, the thermal relaxation treatment is 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. 5. Manufacturing method according to one of claims 1 and 2, characterized in that, when the CuZn42 brass material of the semi-finished part has a hardness of between 180 and 220 HV2, the thermal relaxation treatment is carried out at a temperature of between 195°C and 220°C for a time of between 30 minutes and 5 hours, preferably between 1 and 4 hours. 6. Manufacturing method according to one of the preceding claims, characterized in that it comprises a cutting step between the provision step and the heat treatment step. 7. Manufacturing method according to the preceding claim, characterized in that it comprises a pre-machining step after the cutting step and before the heat treatment step. 8. Watch component (1) made from a CuZn42 brass material with the manufacturing process according to one of the preceding claims, the material of said watch component (1) having a hardness of between 120 and 190 HV2 and being in the state relaxed, the state of relaxation of the material being determined on the basis of 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 for 1 hour at a temperature of 200°C with a heating rate up to 200°C of 5°C/min and a cooling rate after maintaining 1 hour of 2°C/min and the dynamic shear modulus M100measured on a sample taken on said watch component (1) without undergoing subsequent heat treatment, the ΔM100 being less than 0.4 GPa when the material of the watch component (1) is in the relaxed state. 9. Watch component (1) according to the preceding claim, characterized in that it has a hardness of between 150 and 190 HV2, preferably between 170 and 190 HV2, more preferably between 180 and 190 HV2. 10. Watch component (1) according to claim 8 or 9, characterized in that it is a watch component (1) of a movement. 11. Watch component (1) according to one of claims 8 to 10, characterized in that it is a plate, a bridge, a blank, a barrel, the drum of a barrel or the lid of a barrel.