Lead-free, free-cutting beryllium copper alloy

Abstract

Provided is a lead-free free-cutting beryllium copper alloy having excellent machinability. This lead-free free-cutting beryllium copper alloy comprises 1.80-2.10 wt% of Be, 0.10-3.00 wt% of Si, 0.20-0.40 wt% of Co, 0-0.10 wt% of Fe, and 0-0.10 wt% of Ni, with the remainder being Cu and unavoidable impurities. The lead-free free-cutting beryllium copper alloy comprises Co-Be-Si intermetallic compound particles containing a Si-rich phase which is a κ phase rich in Si, a parent phase which is an α phase, Co, Be, Si, and optionally Fe and / or Ni.

Description

[Technical Field]

[0001] The present invention relates to a lead-free, free-cutting beryllium copper alloy. [Background technology]

[0002] Beryllium copper alloys have traditionally been widely used in electronic components such as connectors due to their high strength and high electrical conductivity. As an example of a beryllium copper alloy, Patent Document 1 (JP 50-139017 A) discloses a quaternary copper alloy for spring materials that contains 0.5-1.5% Be, 0.2-3.0% Sn, 0.5-2.0% Si, and the balance being Cu and unavoidable impurities.

[0003] Among beryllium copper alloys, the free-cutting beryllium copper alloy (UNS number: C17300) is generally known as an alloy with excellent machinability. This alloy has improved machinability by incorporating approximately 0.2 to 0.6 weight percent lead (Pb) into beryllium copper. For example, Patent Document 2 (JP 54-30369 B) discloses a free-cutting beryllium copper alloy containing 0.5 to 4 weight percent Be, 0.01 to 3 weight percent of one of Pb, Te, and Bi, 0.01 to 5 weight percent of a rare earth element, and 0.1 to 5 weight percent Al or Si.

[0004] In addition to beryllium copper alloys, free-cutting brasses using brass materials have also been developed. For example, Patent Document 3 (JP 2000-119775 A) discloses a lead-free free-cutting copper alloy characterized by an alloy composition containing 69 to 79 weight percent Cu and 2.0 to 4.0 weight percent Si, with the balance being Zn. Also, Patent Document 4 (JP 2021-42459 A) discloses a free-cutting copper alloy containing 58.5 to 63.5 mass percent Cu, more than 0.4 to 1.0 mass percent Si, 0.003 to 0.25 mass percent Pb, and 0.005 to 0.19 mass percent P, with the balance being Zn and unavoidable impurities. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 50-139017 [Patent Document 2] Special Publication No. 54-30369 [Patent Document 3] Japanese Patent Application Laid-Open No. 2000-119775 [Patent Document 4] Patent Publication No. 2021-42459 Summary of the Invention

[0006] As described above, lead-containing copper alloys such as those disclosed in Patent Document 2 have excellent machinability, and therefore have been used as components of various products. However, because lead is a toxic substance that adversely affects the human body and the environment, their applications have tended to be significantly restricted in recent years. For these reasons, lead-free free-cutting brass materials have been developed, such as those disclosed in Patent Documents 3 and 4. On the other hand, there are no practical lead-free free-cutting beryllium copper alloys, and therefore the development of lead-free free-cutting beryllium copper alloys is eagerly awaited.

[0007] The present inventors have now discovered that a lead-free beryllium copper alloy with excellent machinability can be provided by adding 0.10 to 3.00 weight percent Si to a beryllium copper alloy containing 1.80 to 2.10 weight percent Be to form a predetermined microstructure.

[0008] SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a lead-free, free-cutting beryllium copper alloy having excellent machinability.

[0009] According to the present invention, the following aspects are provided. [Aspect 1] Be: 1.80~2.10% by weight, Si: 0.10~3.00% by weight, Co: 0.20 to 0.40% by weight, Fe: 0 to 0.10% by weight, Ni: 0 to 0.10% by weight, and the balance Cu and unavoidable impurities A lead-free free-cutting beryllium copper alloy consisting of, wherein the beryllium copper alloy has a matrix phase which is an α phase, a Si-rich phase which is a κ phase rich in Si, Co-Be-Si intermetallic compound particles containing Co, Be, Si, and optionally Fe and / or Ni A lead-free free-cutting beryllium copper alloy having. [Aspect 2] The lead-free free-cutting beryllium copper alloy according to Aspect 1, wherein the Co-Be-Si intermetallic compound particles have a hardness of 1.0 to 12.0 GPa measured by a nanoindentation test conforming to ISO 14577. [Aspect 3] In the cross-section of the lead-free free-cutting beryllium copper alloy, per unit area of 1 mm , , , The number of the Co-Be-Si intermetallic compound particles present in the area per hit is 320 or less, the lead-free free-cutting beryllium copper alloy according to Aspect 1 or 2. [Aspect 4] When observing the cross-section of the lead-free free-cutting beryllium copper alloy, the cross-sectional area per one of the Co-Be-Si intermetallic compound particles is 0.3 to 70 μm 2 The lead-free free-cutting beryllium copper alloy according to any one of Aspects 1 to 3. [Aspect 5]<​​​​In a phase map of a 75 μm × 75 μm field obtained by analyzing a cross section of the lead-free, free-cutting beryllium copper alloy using electron backscatter diffraction (EBSD), the area S of the FCC region identified as a face-centered cubic (FCC) lattice is FCC and the area S of the BCC domain identified as a body-centered cubic (BCC) lattice. BCC The area of ​​the BCC region S relative to the total area of BCC The ratio of , i.e., 100 × S BCC / (S FCC +S BCC 6. The lead-free, free-cutting beryllium copper alloy according to any one of Aspects 1 to 5, wherein ) is 5% or more. [Brief explanation of the drawings]

[0010] [Figure 1] 1 shows cross-sectional SEM images and SEM-EDX results obtained for the copper alloy samples of Examples 4, 6 and 7. [Figure 2A] 1 shows cross-sectional SEM images at various magnifications obtained for a copper alloy sample (Si: 1.09 wt%) of Example 6. [Figure 2B] 2B shows an EPMA mapping image of Example 6 measured in the area corresponding to the SEM image at the bottom right of FIG. 2A. [Figure 3A] 1 shows cross-sectional SEM images at various magnifications obtained for the copper alloy sample (Si: 2.98 wt %) of Example 7. [Figure 3B] 3B shows an EPMA mapping image of Example 7 measured in the area corresponding to the SEM image at the bottom right of FIG. 3A. [Figure 3C] 3B shows an EPMA mapping image of Example 7 measured in the area corresponding to the SEM image at the bottom right of FIG. 3A. [Figure 4A] 1 shows cross-sectional STEM images at various magnifications obtained for the copper alloy sample (Si: 1.09 wt %) of Example 6. [Figure 4B] 4B shows a STEM-EELS mapping image of Example 6 measured in a region corresponding to the STEM image on the far right of FIG. 4A. [Figure 5A]1 shows a CCD image measured for the copper alloy sample (Si: 0.29 wt %) of Example 4 and the hardness distribution measured for the rectangular area marked thereon. [Figure 5B] 1 shows a histogram of the distribution of hardness of intermetallic compound particles measured for the copper alloy sample (Si: 0.29 wt %) of Example 4. [Figure 6] 1 shows a cross-sectional SEM image of the copper alloy sample (Si: 2.98 wt %) of Example 7. [Figure 7] FIG. 2 is a schematic diagram showing a cutting method for a copper alloy sample in machinability evaluation 1 of the examples. [Figure 8A] 1 shows SEM images of cross sections of cutting chips from copper alloy samples in Examples 2 to 4. [Figure 8B] 1 shows SEM images of cross sections of cutting chips from copper alloy samples in Examples 5 to 7. [Figure 9] FIG. 1 is a schematic diagram showing the distance h1 between recesses in the unevenness of the cross section of the cutting chip and the maximum height h2 of the protrusions in machinability evaluation 1 of the example. [Figure 10] FIG. 2 is a schematic diagram showing a cutting method for a copper alloy sample in machinability evaluation 2 of the example. [Figure 11] Table 2 shows cross-sectional SEM images of the copper alloy samples of Examples 1 and 5 to 7 and EBSD phase maps of the corresponding regions, together with the area ratio of the BCC region and the cutting resistance (thrust force). DETAILED DESCRIPTION OF THE INVENTION

[0011] Lead-free, free-cutting beryllium copper alloy Lead-free, free-machining beryllium according to the present invention copper alloy The beryllium alloy contains 1.80 to 2.10 weight percent Be, 0.10 to 3.00 weight percent Si, 0.20 to 0.40 weight percent Co, 0 to 0.10 weight percent Fe, 0 to 0.10 weight percent Ni, and the balance being Cu and unavoidable impurities. copper alloydoes not contain lead (Pb). This copper alloy has an α-phase matrix, a Si-rich phase which is a κ-phase rich in Si, and Co-Be-Si intermetallic compound particles. The Co-Be-Si intermetallic compound particles contain Co, Be, Si, and optionally Fe and / or Ni. In this way, by adding 0.10 to 3.00 wt% of Si to a beryllium copper alloy containing 1.80 to 2.10 wt% of Be to form a predetermined microstructure, a lead-free beryllium copper alloy with excellent machinability can be provided.

[0012] As mentioned above, lead-containing copper alloys, including free-cutting beryllium copper alloys, have excellent machinability and have been used as components of various products. However, because lead is a toxic substance that adversely affects the human body and the environment, their applications have tended to be significantly restricted in recent years. Furthermore, the lack of practical lead-free free-cutting beryllium copper alloys presents a problem. The lead-free free-cutting beryllium copper alloy of the present invention conveniently solves this problem. Specifically, by incorporating Si into the beryllium copper alloy, the cutting resistance of the beryllium copper alloy is reduced. Furthermore, since Si-containing beryllium copper alloys easily shear the chips generated during cutting, the chips are less likely to become chip-shaped and wrap around the tool. Thus, the beryllium copper alloy of the present invention can be said to exhibit excellent machinability not only in terms of reduced cutting resistance but also in terms of improved chip shape. The term "lead-free" in the context of lead-free free-cutting beryllium copper alloys refers to the fact that the lead content of the copper alloy is below the detection limit when subjected to elemental analysis.

[0013] The mechanism by which the inclusion of Si (particularly the presence of the Si-rich phase and Co-Be-Si intermetallic compound particles) improves machinability is unclear, but it is thought that the Si-rich phase and Co-Be-Si intermetallic compound particles containing Si act as stress concentrations for shear fracture, making it easier for cutting chips to break apart.

[0014] Be provides the copper alloy with excellent basic properties (strength, workability, fatigue properties, heat resistance, corrosion resistance, etc.) required for a beryllium copper alloy. The Be content in the copper alloy of the present invention is 1.80 to 2.10 wt %, and preferably 1.80 to 2.00 wt %. A Be content within this range can effectively achieve the basic properties described above, while avoiding a decrease in electrical conductivity due to an excessive amount of Be.

[0015] Si forms a Si-rich phase and Co-Be-Si intermetallic compound particles, thereby providing excellent machinability to the beryllium copper alloy. The Si content in the copper alloy of the present invention is 0.10 to 3.00 wt%, preferably 0.30 to 2.50 wt%, more preferably 0.45 to 2.50 wt%, even more preferably 0.50 to 2.20 wt%, and particularly preferably 0.80 to 2.00 wt%, for example, 1.00 to 2.00 wt%. A Si content within the above range effectively improves machinability and avoids the reduction in productivity in actual operation due to excessive Si (the occurrence of cracks during forging). In particular, when the Si content is 0.45 wt% or more, the Si-rich phase significantly increases, and shearing of the Si-rich phase during cutting becomes significant, thereby achieving further improvement in machinability. From this viewpoint, the Si content in the copper alloy is preferably 0.45 to 3.00% by weight, more preferably 0.50 to 3.00% by weight, and particularly preferably 1.00 to 3.00% by weight, for example, 2.00 to 3.00% by weight.

[0016] Co forms Co-Be-Si intermetallic compound particles, thereby providing excellent machinability to the beryllium copper alloy. The Co content in the copper alloy of the present invention is 0.20 to 0.40 wt%, preferably 0.20 to 0.35 wt%, more preferably 0.22 to 0.30 wt%, and particularly preferably 0.22 to 0.28 wt%. A Co content within the above range can effectively refine the crystal grains and improve the properties of the copper alloy, while also avoiding a decrease in productivity in actual operation due to an excessive amount of Co.

[0017] Fe and Ni are optional elements that are also considered as impurities in the copper alloy of the present invention, and since a high content of these elements leads to a decrease in mechanical properties, it is desirable that the Fe and Ni contents be as low as possible. From this perspective, the Fe and Ni contents in the copper alloy of the present invention are each 0 to 0.10 wt %, preferably 0 to 0.005 wt %.

[0018] As described above, the copper alloy of the present invention has a microstructure including a matrix, a Si-rich phase, and Co-Be-Si intermetallic compound particles. Typically, the Si-rich phase is present in the matrix, and the Co-Be-Si intermetallic compound particles are present at the interface between the Si-rich phase and the matrix.

[0019] The parent phase is the α phase, which contributes to the excellent basic performance of beryllium copper alloys (strength, workability, fatigue properties, heat resistance, corrosion resistance, etc.).

[0020] The Si-rich phase is a κ-phase rich in Si, which contributes to improved machinability. In particular, the inclusion of Si in the matrix improves shear strength and facilitates fragmentation of cutting chips. The term "Si-rich" means that a higher concentration of Si is detected in elemental analysis than in the matrix (α-phase). Therefore, it does not necessarily mean that a higher concentration of Si is detected than in the Co-Be-Si intermetallic compound particles.

[0021] Typically, the parent phase has a face-centered cubic (FCC) crystal structure, while the Si-rich phase has a body-centered cubic (BCC) crystal structure. The BCC structure is less susceptible to deformation and has a higher shear strength than the FCC structure. For this reason, the Si-rich phase with a BCC structure can also contribute to improving machinability. From this perspective, in a phase map with a field of view of 75 μm × 75 μm obtained by analyzing the cross section of a beryllium copper alloy using electron backscatter diffraction (EBSD), the area S of the FCC region identified as a face-centered cubic (FCC) lattice is FCC and the area S of the BCC domain identified as a body-centered cubic (BCC) lattice. BCC The area of ​​the BCC region S relative to the total area of BCC The ratio of (i.e., 100 × S BCC / (S FCC +S BCC )) is preferably 5% or more, more preferably 5 to 40%, even more preferably 10 to 30%, particularly preferably 15 to 30%, and most preferably 15 to 25%. By increasing the proportion of the BCC structure in this way, cutting resistance (particularly thrust force) can be reduced, resulting in further improvement of machinability. EBSD measurement can be performed according to the procedures and conditions described in the Examples below.

[0022] The Co-Be-Si intermetallic compound particles also contribute to improved machinability. The Co-Be-Si intermetallic compound particles contain Co, Be, Si, and optionally Fe and / or Ni. That is, the Co-Be-Si intermetallic compound particles contain Co, Be, and Si as essential elements, and these essential elements are dominant. As mentioned above, Fe and Ni are optional elements or trace elements that can be considered impurities, and therefore are not positioned as dominant elements in the Co-Be-Si intermetallic compound particles.

[0023] The Co-Be-Si intermetallic compound particles preferably have a hardness of 1.0 to 12.0 GPa, more preferably 1.5 to 7.5 GPa, and even more preferably 2.0 to 6.0 GPa, as measured by a nanoindentation test in accordance with ISO 14577. A hardness within this range effectively achieves machinability. In a nanoindentation test, the hardness of a microscopic region is measured at multiple measurement points, resulting in a wide hardness distribution. Therefore, it is not necessary for 100% of the measurement points on the Co-Be-Si intermetallic compound particles to fall within the above range; it is sufficient for the majority of the measurement points (e.g., 90% or more) to fall within the above range. Therefore, it is acceptable for the measured hardness distribution to include a small number (e.g., less than 10%) of hardnesses below 1.0 GPa or above 12.0 GPa.

[0024] The number of Co-Be-Si intermetallic compound particles is not particularly limited as long as it is within a range that can improve machinability without impairing the above-mentioned basic performance of the beryllium copper alloy.2 The number of Co-Be-Si intermetallic compound particles present in the hit area is preferably 320 or less, more preferably 50 to 300, and even more preferably 80 to 200.

[0025] The shape of the Co-Be-Si intermetallic compound particles is not limited to spherical, and may be plate-shaped, rod-shaped, needle-shaped, or other irregular shapes, and is not particularly limited. Therefore, it is preferable to specify the size of the Co-Be-Si intermetallic compound particles by cross-sectional area rather than by diameter. For example, the cross-sectional area per particle of the Co-Be-Si intermetallic compound particles in the cross-section of the beryllium copper alloy is 0.3 to 70 μm 2 is preferable, more preferably 1.0 to 65 μm 2 and even more preferably 5.0 to 60 μm 2 is.

[0026] As described above, the copper alloy of the present invention is excellent in machinability. When observing the cross-section along the longitudinal direction of the cutting chips generated by cutting the copper alloy, it is preferable that the cross-section of the cutting chips has a shear shape that brings about zigzag irregularities. In this case, as shown in FIG. 8, when the average value of the intervals between the concave portions in the zigzag irregularities is h1 and the average value of the heights of the convex portions in the irregularities is h2, it is preferable to satisfy the relational expression of 1.10 < h2 / h1 < 6.60, more preferably 2.0 < h2 / h1 < 6.6, and even more preferably 2.5 < h2 / h1 < 6.6. When the cutting chips generated when cutting the copper alloy have the above-described shear shape, the cutting chips are easy to shear and thus become chip-shaped, and it is difficult for them to wrap around the tool. It can be said that such a copper alloy is excellent in machinability. On the other hand, when the cutting chips have a flow shape (smooth irregular shape) rather than a shear shape, the cutting chips are likely to be continuous and are likely to wrap around the tool, resulting in a decrease in productivity.

[0027] Manufacturing method The method for producing the lead-free, free-cutting beryllium copper alloy of the present invention is not particularly limited, but it can be preferably produced by sequentially carrying out the following steps: (a) melting and casting of raw materials that result in the aforementioned composition, (b) homogenization heat treatment, (c) hot working, (d) cold working, (e) solution heat treatment, and (f) aging treatment. The preferred embodiments of the copper alloy have been described above, so further description will be omitted here.

[0028] (a) Melting and Casting First, one or more raw materials whose compositions have been adjusted to yield the above-described composition (i.e., a composition consisting of 1.80-2.10 wt% Be, 0.10-3.00 wt% Si, 0.20-0.40 wt% Co, 0-0.10 wt% Fe, 0-0.10 wt% Ni, and the balance being Cu and unavoidable impurities) are melted to obtain a molten copper alloy. When a specific element is added, a single element or a master alloy may be added to the raw materials. Alternatively, raw materials containing these additional elements may be melted together with the copper raw material. Then, the molten copper alloy whose composition has been adjusted to yield the above-described composition is poured into a mold to produce an ingot. Note that, when considering mass production, it is preferable to use a continuous casting method. In this manner, an ingot (e.g., a cylindrical ingot or billet) can be obtained.

[0029] (b) Homogenization heat treatment The resulting ingot is subjected to homogenization heat treatment. That is, the ingot is homogenized by heating. In the homogenization heat treatment, the ingot is preferably heated to a temperature within a range of 500 to 900°C, and the holding time within this temperature range is preferably 1 to 24 hours.

[0030] (c) Hot working The ingot that has been subjected to the homogenization heat treatment is then hot worked to produce a hot-worked material of a predetermined diameter. Prior to the hot working, annealing may be performed, if necessary, to soften the material and improve its workability. The annealing conditions are not particularly limited, but the heating temperature is preferably in the range of 500 to 900°C, and the holding time at this temperature range is preferably 0.2 to 6 hours.

[0031] (d) Cold working The resulting hot-worked material is cold-worked to a predetermined diameter. The cold-working ratio is preferably 0.5 to 95%. Prior to cold working, annealing may be performed, if necessary, to soften the material and improve workability. The annealing conditions are not particularly limited, but the heating temperature is preferably within the range of 500 to 900°C, and the holding time at this temperature range is preferably 0.2 to 6 hours.

[0032] (e) Solution heat treatment The resulting cold-worked material is subjected to solution heat treatment to uniformly dissolve the elements in the material, thereby producing a solution-treated material. The solution temperature in the solution heat treatment is preferably in the range of 600 to 900°C, and the holding time within this temperature range is preferably 0.2 to 3 hours.

[0033] (f) Ageing The resulting solution-treated material is subjected to aging treatment to obtain the beryllium copper alloy of the present invention. The aging temperature in the aging treatment is preferably in the range of 200 to 500°C, and the holding time at this temperature range is preferably 0.2 to 3 hours. Prior to the aging treatment, the solution-treated material may be subjected to cold working and oxide film removal, if necessary. The cold working conditions are not particularly limited, but a working ratio of 0.5 to 95% is preferred.

[0034] By undergoing the above steps (a) to (f), a lead-free beryllium copper alloy having excellent machinability can be preferably produced. [Example]

[0035] The present invention is further illustrated by the following examples.

[0036] Examples 1-7 Beryllium copper alloys were prepared and evaluated according to the following procedure.

[0037] (1) Melting and Casting First, a copper alloy raw material that provides the composition shown in Table 1 was prepared. This copper alloy raw material was melted, and the molten metal was poured into a mold to produce a cylindrical ingot (billet).

[0038] (2) Homogenization heat treatment The obtained ingot was subjected to homogenization heat treatment by holding it at 800 °C for 4 hours.

[0039] (3) Hot working After annealing the ingot subjected to homogenization heat treatment at 800 °C for 1 hour, hot working was performed to obtain a cylindrical hot-worked material with a diameter of 1.8 cm.

[0040] (4) Cold working The hot-worked material was annealed at 800 °C for 1 hour before processing, and then cold working was performed at a processing rate of 40% to obtain a cylindrical cold-worked material with a diameter of 1.4 cm.

[0041] (5) Solution heat treatment The obtained cold-worked material was subjected to solution heat treatment at 800 °C for 1 hour to obtain a solution-treated material.

[0042] (6) Aging treatment Cold working was performed on the solution-treated material at a processing rate of 38%. The thus obtained solution-treated material was subjected to aging treatment at 320 °C for 2 hours to obtain a cylindrical beryllium copper alloy sample with a diameter of 1.1 cm and a length of 100 cm.

[0043] (7) Evaluation The following evaluation was performed on the obtained beryllium copper alloy sample (hereinafter referred to as the copper alloy sample).

[0044] <SEM-EDX and EPMA> A cross section of the copper alloy sample was cut out and processed into a thin piece using a focused ion beam (FIB). The obtained cross section was observed using a scanning electron microscope (SEM), and elemental analysis of the cross section was performed using an energy dispersive X-ray analyzer (EDX, product name: JXA-8530FPlus, manufactured by JEOL Ltd.) attached to the SEM at an accelerating voltage of 15 kV. Elemental analysis of the same cross section was also performed using an electron probe microanalyzer (EPMA, product name: JXA-8530FPlus, manufactured by JEOL Ltd.) at an accelerating voltage of 15 kV.

[0045] As a result, it was confirmed that the beryllium copper alloys of Examples 3 to 7 had a matrix, a Si-rich phase containing Si at a higher concentration than the matrix, and Co-Be-Si intermetallic compound particles containing Co, Be, Si, Fe, and Ni. It was also confirmed that the Co-Be-Si intermetallic compound particles contained Si at an even higher concentration than the Si-rich phase. Figure 1 shows SEM images and SEM-EDX results at each measurement point for the samples of Examples 4, 6, and 7.

[0046] Figure 2A shows cross-sectional SEM images of the copper alloy sample (Si: 1.09 wt%) of Example 6 at various magnifications. In Figure 2A, the three SEM images on the left are secondary electron images, clearly showing the fine structure of the sample surface, while the three SEM images on the right are backscattered electron composition images (COMPO images), showing contrast dependent on atomic number. All six SEM images were obtained by observing the same surface of the sample. Figure 2B shows an EPMA mapping image of Example 6 measured in the area corresponding to the SEM image in the lower right of Figure 2A.

[0047] Similarly, Figure 3A shows cross-sectional SEM images at various magnifications obtained for the copper alloy sample (Si: 2.98 wt%) of Example 7. In Figure 3A, the three SEM images on the left are secondary electron images that clearly show the fine structure of the sample surface, while the three SEM images on the right are backscattered electron composition images (COMPO images) that show contrast depending on the atomic number. All six SEM images were obtained by observing the same surface of the sample. Figures 3B and 3C show EPMA mapping images of Example 7 measured in the area corresponding to the SEM image in the lower right of Figure 3A.

[0048] <stem-eels> Cross sections of copper alloy samples were cut and processed into thin pieces using a focused ion beam (FIB). The cross sections were observed using a spherical aberration-corrected scanning transmission electron microscope (STEM, product name: HD-2700, Hitachi High-Technologies Corporation) at an accelerating voltage of 200 kV. Elemental analysis of the interface between the matrix and intermetallic compound particles was also performed using an electron energy loss spectrometer (EELS, product name: Enfinium, Gatan) / energy dispersive X-ray analyzer (EDX, product name: XMAXN 100TLE, Oxford University Press) attached to the STEM at a voltage of 200 kV. The results showed that the intermetallic compound particles in the beryllium copper alloys of Examples 3 to 7 were dominated by Co, Be, and Si, with only trace amounts of Ni and Fe. This confirmed the presence of Co-Be-Si intermetallic compound particles. Furthermore, although the matrix mainly contained Be and Cu, Cu was found to be predominant. Furthermore, the presence of the α phase in the matrix and the κ phase in the Si-rich phase was confirmed. Figure 4A shows cross-sectional STEM images at various magnifications obtained for the copper alloy sample of Example 6 (Si: 1.09 wt%), while Figure 4B shows a STEM-EELS mapping image of Example 6 measured in the region corresponding to the STEM image on the far right of Figure 4A.

[0049] <Hardness of intermetallic compound particles> The hardness (GPa) of each microscopic region of the Co-Be-Si intermetallic compound particles in the cross section of the beryllium copper alloy was measured by nanoindentation testing. This test was performed in accordance with ISO 14577 using a nanoindenter (product name: iMicro type nanoindenter, manufactured by KLA Corporation) under the following measurement conditions: maximum load: 0.25 mN, measurement area: 60 μm (X axis) × 60 μm (Y axis), number of measurement points: 60 points (X axis) × 60 points (Y axis), and sample Poisson's ratio: 0.3. The hardness distribution of the Co-Be-Si intermetallic compound particles measured in this manner was plotted as a histogram. As a result, as shown in Table 1, it was confirmed that the Co-Be-Si intermetallic compound particles in samples 4, 6, and 7 had hardnesses of 1.0 to 12.0 GPa. FIG. 5A shows a CCD image measured for the copper alloy sample (Si: 0.29 wt %) of Example 4 and the hardness distribution measured for the rectangular area marked thereon, while FIG. 5B shows a histogram of the hardness distribution thus obtained.

[0050] <Number of intermetallic compound particles> The cross section of the copper alloy sample was observed by SEM at 500x magnification, revealing a 2 A cross-sectional SEM image was obtained in a field of view of 1 mm. The number of Co-Be-Si intermetallic compound particles in this field of view was counted, and the count was divided into 1 mm2 units. 2 In this way, the number of particles per unit area of ​​1 mm2 in the cross section of the beryllium copper alloy was calculated. 2 The number of Co-Be-Si intermetallic compound particles present in the area per unit area was determined. The results are shown in Table 1. Figure 6 shows a cross-sectional SEM image (field area: 48118.52 μm) of the copper alloy sample (Si: 2.98 wt%) of Example 7. 2 ) in Fig. 6. In Fig. 6, the black dots represent Co-Be-Si intermetallic compound particles, and there were 15 of these dots. 2 It was found that the number of Co-Be-Si intermetallic compound particles present in the area per unit area was 311.

[0051] <Area of ​​intermetallic compound particles> The cross section of the copper alloy sample was observed with a SEM at 1000 to 2500 times magnification to determine the area (μm) of each Co-Be-Si intermetallic compound particle contained in the beryllium copper alloy. 2 The results are shown in Table 1.

[0052] <Cutting performance evaluation 1 (h2 / h1 and chip shape)> A copper alloy sample was used as the workpiece, and the chips generated when this workpiece was cut with a tool (bite) were evaluated. Specifically, as shown in Figure 7, workpiece 2 was run in a straight line, and the upper surface of the workpiece was cut with tool 4 (similar to planing). The cutting conditions were a cutting speed of 150 m / min, a cutting depth of 0.10 mm from the copper alloy surface, a cutting width of 2 mm, and a rake angle of 5°. The cross-sections of the chips of the copper alloy sample were observed with an SEM at 200x magnification to confirm their cross-sectional shapes. The results are shown in Table 1. Figures 8A and 8B show SEM images of the cross-sections of the chips observed in Examples 2 to 7. Here, it is desirable for the cross-section of the chips to have a sheared shape that results in zigzag irregularities. This is because when the chips generated when cutting copper alloys have a sheared shape, they are easily sheared, forming chips and less likely to wrap around the tool. On the other hand, if the chips are not sheared but rather flow-shaped (with a gentle unevenness), they tend to connect and wrap around the tool, resulting in reduced productivity. Next, as shown in Figure 9, the distance between the recesses in the unevenness of the obtained chips was measured to calculate the average value h1, while the height of the protrusions in the unevenness was measured to calculate the average value h2. Figures 8A and 8B also retain the auxiliary lines added by hand for calculating the distance. The obtained average value h2 was divided by the average value h1 to determine the ratio h2 / h1 (degree of unevenness). The results are shown in Table 1. For Examples 1 and 5 to 7, the thrust force, one of the components of cutting resistance, was measured during the cutting process as an indicator of the cutting resistance of the workpiece using a three-component force dynamometer (Type 9601A32, manufactured by KISTLER). The values ​​shown in Table 2 (see Figure 11) were obtained.

[0053] <Cutting performance evaluation 2 (cutting resistance)> A copper alloy sample was used as the workpiece, and the cutting resistance (N) was evaluated when this workpiece was cut with a tool (bite). Specifically, as shown in Figure 10, workpiece 2 was lowered while rotating in the following test environment, and workpiece 2 was cut in a spiral shape with tool 4 under the following cutting conditions. At this time, the cutting resistance of the workpiece was measured using a multi-component dynamometer (9129AA, manufactured by KISTLER). The results are shown in Table 1.

[0054] (Test environment) Machine used: NV5000α 1B / 40 (manufactured by DGM Mori Seiki Co., Ltd.) Holder 1: BBT40-HMC25S-75 (manufactured by Daishowa Seiki Co., Ltd.) Holder 2: ST14-MEGA6S-160 (manufactured by Daishowa Seiki Co., Ltd.) Tool: MVLNR2525M-16 (Kyocera Corporation) Lubricant: Yusikelon FGE234 (Yushiro Chemical Industry Co., Ltd., concentration 5-10%) (Cutting conditions) Cutting speed: 40m / min Feed rate per revolution: 0.01 mm / rev Depth of cut for copper alloy: 0.25 mm (2 passes)

[0055] [Table 1]

[0056] As shown in Table 1, the inclusion of Si in the beryllium copper alloy resulted in improved machinability, including reduced cutting resistance, improved chip shape, reduced surface roughness of the workpiece, and improved tool life. In other words, the lower the cutting resistance, the better the machinability. By incorporating Si into the beryllium copper alloy, the cutting resistance was reduced compared to beryllium copper alloys that did not contain Si, and the alloy exhibited machinability equivalent to that of beryllium copper alloys containing Pb. It is also believed that the reduced cutting resistance can improve tool life. Furthermore, by incorporating Si into the beryllium copper alloy, the cross-section of the chips became sheared with a zigzag irregularity, resulting in a more desirable chip shape, compared to beryllium copper alloys that did not contain Si.

[0057] <EBSDによるB C Measurement of area ratio of C region> The copper alloy samples obtained in Examples 1 and 5 to 7 were cut out and subjected to Ar ion milling to obtain measurement cross sections. The area ratio of the BCC phase by EBSD was measured using a scanning electron microscope (FE-SEM, JEOL Ltd., JSM-7800F) and an OIM crystal orientation analyzer (TSL Solutions, OIM Data Collection / OIM). The EBSD measurements were performed under the conditions of an accelerating voltage of 15 kV and a step size of 0.2 μm.

[0058] As a result, the SEM images shown in Figure 11 and the EBSD phase maps of the corresponding regions were obtained. That is, Figure 11 shows the EBSD phase maps obtained for the regions within the frames shown in each SEM image. In the EBSD phase map, FCC regions identified as face-centered cubic lattice (FCC) and BCC regions identified as body-centered cubic lattice (BCC) (hereinafter referred to as BCC regions) are displayed in different colors. In the obtained EBSD phase map, the area S of the FCC regions is FCC and the area S of the BCC region BCC The area of ​​the BCC region S relative to the total area of BCC The ratio of (i.e., 100 × S BCC / (S FCC +S BCC ) was calculated, the values ​​shown in Table 2 (see FIG. 11) were obtained. Table 2 (see FIG. 11) also shows the values ​​of cutting resistance (thrust force). The results shown in Table 2 (see FIG. 11) show that the area ratio of the BCC phase (i.e., Si-rich phase) increases with increasing Si addition, and that the cutting resistance (especially the thrust force) decreases with increasing BCC phase area ratio (i.e., machinability improves).

Claims

1. Be: 1.80 to 2.10% by weight, Si: 0.10 to 3.00% by weight, Co: 0.20 to 0.40% by weight, Fe: 0 to 0.10% by weight, Ni: 0 to 0.10 wt %; and The balance is Cu and unavoidable impurities A lead-free, free-cutting beryllium copper alloy, comprising: A parent phase that is an α phase, a Si-rich phase, which is a κ phase rich in Si; Co—Be—Si intermetallic compound particles containing Co, Be, Si, and optionally Fe and / or Ni; A lead-free, free-cutting beryllium copper alloy having the following properties.

2. A lead-free, free-cutting beryllium copper alloy as described in claim 1, wherein in a histogram of the hardness distribution of Co-Be-Si intermetallic compound particles obtained by measuring a cross section of the lead-free, free-cutting beryllium copper alloy using a nanoindentation test in accordance with ISO 14577, 90% or more of all Co-Be-Si intermetallic compound particles have a hardness of 1.0 to 12.0 GPa.

3. The unit area of ​​the cross section of the lead-free, free-cutting beryllium copper alloy is 1 mm ２ 3. The lead-free, free-cutting beryllium copper alloy according to claim 1, wherein the number of Co-Be-Si intermetallic compound particles present in the contact region is 320 or less.

4. When a cross section of the lead-free, free-cutting beryllium copper alloy is observed, the cross-sectional area of ​​each of the Co—Be—Si intermetallic compound particles is 0.3 to 70 μm ２ 3. The lead-free, free-cutting beryllium copper alloy according to claim 1 or 2, wherein

5. When a cross section along the longitudinal direction of cutting chips generated by cutting the lead-free free-cutting beryllium copper alloy is observed, the cross section of the cutting chips has a shear shape that causes zigzag irregularities, and the average value of the distance between concave portions in the zigzag irregularities is h １ The average height of the convex portions of the unevenness is h ２ When this is the case, 1.10<h ２ / h １ 3. The lead-free, free-cutting beryllium copper alloy according to claim 1, wherein the alloy satisfies the relationship:

6. In a phase map of a 75 μm×75 μm field of view obtained by analyzing a cross section of the lead-free, free-cutting beryllium copper alloy by electron backscatter diffraction (EBSD), the area S of an FCC region identified as a face-centered cubic (FCC) lattice is ＦＣＣ and the area S of the BCC domain identified as a body-centered cubic (BCC) lattice. ＢＣＣ The area of ​​the BCC region S relative to the total area of ＢＣＣ The ratio of 100 × S ＢＣＣ / (S ＦＣＣ +S ＢＣＣ 3. The lead-free, free-cutting beryllium copper alloy according to claim 1, wherein ZnO is 5% or more.

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