JP6805789B2 - Copper bar - Google Patents

Description

The present invention relates to a copper rod material suitable as a material for an energizing member such as a large terminal or a bus bar.

Conventionally, as a material for large terminals and bus bars through which a large current flows, in order to avoid a temperature rise due to energization heat generation, a copper rod material that is made of pure copper with excellent electrical and thermal conductivity and has a large diameter and a large heat capacity has been used. It is used.
As disclosed in Non-Patent Document 1, for example, the copper rod material described above has an extrusion step of heating a billet to a predetermined temperature and extruding, a cutting step of cutting the extruded material to a predetermined length, and cleaning the surface. It is manufactured by a pickling step and a straightening step of straightening to a predetermined shape.

By the way, in recent years, with the miniaturization of various devices using large terminals and bus bars, miniaturization of large terminals and bus bars used in these electronic devices and electric devices is also required.
In the above-mentioned large terminals and bus bars, since a large current flows, the entire part is subjected to strict plastic working (for example, bending, brimming, etc.) while maintaining the cross-sectional area of the copper bar. We are trying to reduce the volume.
However, as described above, when the copper bar is subjected to stricter plastic working than before, appearance defects such as rough skin and wrinkles may occur on the surface after the processing.

Here, it is known that in copper materials, processability such as bending is improved by making the crystal grain size finer.
For example, Patent Document 1 discloses a technique for precipitating a fine compound, suppressing the growth of crystal grains by the pinning effect of the precipitate, and reducing the crystal grain size.
Further, Patent Documents 2 and 3 propose a technique for refining the crystal grain size of the surface layer by annealing a copper wire that has been cold-drawn under predetermined conditions.

Special Table 2002-518598 Japanese Unexamined Patent Publication No. 2014-222663 Japanese Unexamined Patent Publication No. 2015-162301

Basics and Industrial Technology of Copper and Copper Alloys (1st Edition), p. 157-p. 164

However, as shown in Patent Document 1, when an additive element is added in order to reduce the crystal grain size by the pinning effect of the precipitate, a part of the additive element is solid-solved in the copper matrix and becomes electric. There was a risk that the conductivity and thermal conductivity would decrease. Therefore, it is difficult to apply it to the material of the energizing member through which a large current flows.
Further, as described above, the copper bar is manufactured through an extrusion process, a cutting process, a pickling process, and a straightening process, and plastic working such as cold wire drawing having a high surface reduction rate like a wire rod is performed. Not implemented. Therefore, as in Patent Documents 2 and 3, it is not possible to give sufficient strain to the material by cold working, and it is difficult to miniaturize the crystal grain size by recrystallization.

The present invention has been made against the background of the above circumstances, and an object of the present invention is to provide a copper rod material capable of suppressing the occurrence of poor appearance even when severe plastic working is performed. It is said.

In order to solve this problem, the copper bar material of the present invention is made of pure copper having a purity of 99.90 mass% or more, and in a cross section orthogonal to the extrusion direction, in the outermost layer region up to 200 μm from the outer surface to the center. The average crystal grain size D1 is 60 μm or less, the average crystal grain size D2 in the surface layer region exceeding 200 μm and up to 1000 μm from the outer surface toward the center is 120 μm or less, and the average crystal grain size in the outermost surface layer region. D1 and the average crystal grain size D2 in the surface layer region have a relationship of D2> D1 and are characterized in that the diameter is within the range of 3 mm or more and 50 mm or less .

According to the copper rod having the above-mentioned structure, since it is made of pure copper having a purity of 99.90 mass% or more, it is excellent in electrical conductivity and thermal conductivity.
In the cross section orthogonal to the extrusion direction, the average crystal grain size D1 in the outermost layer region from the outer surface to the center is 60 μm or less, so that the workability is particularly excellent in the outermost layer region. Even when severe plastic working is applied, it is possible to suppress the occurrence of appearance defects such as rough skin and wrinkles.
Further, the average crystal grain size D2 in the surface layer region exceeding 200 μm and up to 1000 μm from the outer surface toward the center is set to 120 μm or less, and further, the average crystal grain size D1 in the outermost layer region and the average crystal grain in the surface layer region. Since the diameter D2 has a relationship of D2> D1, workability is ensured even in the surface layer region, and the occurrence of appearance defects can be suppressed even if particularly intense plastic working is performed. In addition, there is no large difference in crystal grain size between the outermost layer region and the surface layer region, and it is possible to suppress the occurrence of excessive strain at the boundary portion between these regions.

Here, in the copper rod material of the present invention, the diameter is within the range of 3 mm or more and 50 mm or less, and since the diameter of the copper rod material is relatively large, the heat capacity becomes large and a large current is passed. However, it is possible to suppress the temperature rise due to the energization heat generation.

According to the present invention, it is possible to provide a copper rod material capable of suppressing the occurrence of poor appearance even when severe processing is performed.

It is sectional drawing explanatory drawing of the copper bar material which is one Embodiment of this invention. It is a flowchart which shows the manufacturing method of the copper bar material which is one Embodiment of this invention.

The copper rod material according to the embodiment of the present invention will be described below with reference to the attached figure.

The copper bar 10 of the present embodiment is made of pure copper having a purity of 99.90 mass% or more. Specifically, billets such as oxygen-free copper (C1011, C1020), tough pitch copper (C1100), and phosphorus deoxidized copper (C1201, C1220) are used as raw materials.
Further, in the copper bar 10 of the present embodiment, as shown in FIG. 1, the diameter R thereof is within the range of 3 mm or more and 50 mm or less, and the cross-sectional area of the cross section orthogonal to the extrusion direction is 7 mm ^2. It is within the range of 2000 mm ² or less.

Then, in the copper bar 10 of the present embodiment, as shown in FIG. 1, in the cross section orthogonal to the extrusion direction, the average crystal grain size D1 in the outermost layer region 11 from the outer surface to the center is 200 μm. It is said to be 60 μm or less.
Further, the average crystal grain size D2 in the surface layer region 12 exceeding 200 μm and up to 1000 μm from the outer surface toward the center is set to 120 μm or less.
Further, the average crystal grain size D1 in the outermost layer region 11 and the average crystal grain size D2 in the surface layer region 12 have a relationship of D2> D1.
In the present embodiment, the average crystal grain size D3 in the central region 13 on the central side of the surface layer region 12 is larger than the average crystal grain size D2 in the surface layer region 12, and there is a relationship of D3 ≧ D2. doing.

Here, when the average crystal grain size D1 in the outermost layer region 11 is larger than 60 μm, the workability in the outermost surface layer region 11 becomes insufficient, and when severe plastic working is performed, the surface of the copper bar 10 is roughened. There is a risk of appearance defects such as wrinkles and wrinkles.
Therefore, in the present embodiment, the average crystal grain size D1 in the outermost layer region 11 is defined as 60 μm or less. In order to further improve the workability in the outermost layer region 11, the average crystal grain size D1 in the outermost layer region 11 is preferably 50 μm or less, and more preferably 40 μm or less.
The lower limit of the average crystal grain size D1 in the outermost layer region 11 is not particularly limited, but it is industrially difficult to make it less than 5 μm. Therefore, the lower limit of the average crystal grain size D1 in the outermost layer region 11 is substantially 5 μm or more.

Further, when the average crystal grain size D2 in the surface layer region 12 is larger than 120 μm, the workability in the surface layer region 12 becomes insufficient, and particularly severe plastic working is performed so that the surface layer region 12 is formed on the surface of the copper rod material 10. When exposed, there is a risk of appearance defects such as rough skin and wrinkles on the surface.
Therefore, in the present embodiment, the average crystal grain size D2 in the surface layer region 12 is defined as 120 μm or less. In order to further improve the workability in the surface layer region 12, the average crystal grain size D2 in the surface layer region 12 is preferably 110 μm or less, and more preferably 100 μm or less.
Here, since the average crystal grain size D2 in the surface layer region 12 is configured to be larger than the average crystal grain size D1 in the outermost layer region 11 as described above, the lower limit thereof is the outermost layer region 11. Will be defined by the average crystal grain size in.

Next, a method for manufacturing the copper rod 10 according to the present embodiment having such a configuration will be described with reference to the flow chart shown in FIG.

(Hot extrusion step S01)
A billet made of pure copper having a purity of 99.90 mass% or more is prepared, the billet is heated to a predetermined temperature, and hot extrusion is performed. The extrusion temperature is preferably in the range of 600 ° C. or higher and 1000 ° C. or lower. The extrusion ratio is preferably in the range of 23 or more and 6400 or less.

(Cooling step S02)
Next, the rod material obtained in the hot extrusion step S01 described above is spray-cooled, and then the rod material is immersed in a water tank to be cooled.
Here, the lower limit of the cooling rate from the extrusion temperature to the recrystallization start temperature of the bar is set to 100 ° C./sec or more. The above-mentioned recrystallization start temperature was 300 ° C. for oxygen-free copper and tough pitch copper, and 350 ° C. for phosphorylated copper.
In this way, the average crystal grain size D2 of the surface layer region 12 of the copper bar 10 is reduced by setting the lower limit of the cooling rate from the extrusion temperature to the recrystallization start temperature of the bar to 100 ° C./sec or more. Is possible. In order to surely reduce the average crystal grain size D2 of the surface layer region 12 of the copper bar material 10, the lower limit of the cooling rate from the extrusion temperature to the recrystallization start temperature of the bar material is set to 200 ° C./sec or more. The temperature is preferably 300 ° C./sec or higher. Further, the upper limit of the cooling rate from the extrusion temperature to the recrystallization start temperature of the bar is not particularly limited, but the manufacturing cost increases in order to realize the cooling rate exceeding 500 ° C./sec. Therefore, the upper limit of the cooling rate from the extrusion temperature to the recrystallization start temperature of the bar is substantially 500 ° C./sec or less.

(Pickling step S03)
Next, the cooled bar is immersed in a pickling tank to remove the oxide film formed on the surface thereof. Then, it is immersed in a water washing tank and a hot water washing tank to remove the acid solution.

(Surface processing step S04)
Next, surface processing is performed on the bar material. In the surface processing step S04, the processing means is selected so as not to perform plastic working such as cold wire drawing having a high surface reduction rate. For example, it can be selected from peeling, shot blasting, polishing and the like. In the peeling process, surface defects can be removed.

Here, in this surface processing step S04, after processing, it is necessary to process so that the Vickers hardness in the outermost layer region up to 200 μm from the outer surface to the center of the bar increases by 5 Hv or more as compared with that before processing. is there.
By performing surface processing so that the Vickers hardness of the outermost layer region increases by 5 Hv or more, strain that is a driving force for recrystallization is sufficiently accumulated in the outermost layer region in the next recrystallization heat treatment step S05. .. In order to further accumulate strain in the outermost layer region and promote recrystallization, it is preferable that the amount of increase in Vickers hardness in the outermost surface layer region before and after processing is 10 Hv or more. Further, it is very difficult to perform surface processing so that the amount of increase in Vickers hardness in the outermost layer region before and after processing exceeds 15 Hv. Therefore, the upper limit of the amount of increase in Vickers hardness in the outermost layer region before and after processing is substantially 15 Hv or less.

(Recrystallization heat treatment step S05)
The bar material that has undergone surface processing and has accumulated strain in the outermost layer region is subjected to heat treatment to recrystallize the outermost layer region and reduce the crystal grain size thereof. The conditions for the recrystallization heat treatment are preferably such that the heat treatment temperature is in the range of 300 ° C. or higher and 700 ° C. or lower, and the holding time at the heat treatment temperature is in the range of 0.5 hours or more and 24 hours or less.

Here, if the heat treatment temperature is less than 300 ° C., recrystallization may not be sufficiently promoted. On the other hand, if the heat treatment temperature exceeds 700 ° C., crystals may grow and the crystal grain size may become coarse. Therefore, in the present embodiment, the heat treatment temperature is set within the range of 300 ° C. or higher and 700 ° C. or lower. The lower limit of the heat treatment temperature is preferably 350 ° C. or higher, more preferably 400 ° C. or higher. The upper limit of the heat treatment temperature is preferably 650 ° C. or lower, more preferably 600 ° C. or lower.

Further, if the holding time at the heat treatment temperature is less than 0.5 hours, recrystallization may not be sufficiently promoted. On the other hand, if the holding time at the heat treatment temperature exceeds 24 hours, crystals may grow and the crystal grain size may become coarse. Therefore, in the present embodiment, the holding time at the heat treatment temperature is set within the range of 0.5 hours or more and 24 hours or less. The lower limit of the holding time at the heat treatment temperature is preferably 0.75 hours or more, and more preferably 1 hour or more. Further, the upper limit of the holding time at the heat treatment temperature is preferably 18 hours or less, more preferably 12 hours or less.

(Drawing step S06)
Next, the bar material that has undergone the recrystallization heat treatment as described above is cut to a predetermined length and straightened by drawing.

As described above, the copper bar 10 according to the present embodiment in which the crystal grain sizes of the outermost layer region 11 and the surface layer region 12 are controlled is produced.

The copper bar 10 of the present embodiment having the above-described configuration is made of pure copper having a purity of 99.90 mass% or more, and is therefore excellent in electrical conductivity and thermal conductivity. Further, since the diameter R of the copper rod 10 is within the range of 3 mm or more and 50 mm or less, and the cross-sectional area of the cross section orthogonal to the extrusion direction is within the range of 7 mm ² or more and 2000 mm ² or less, sufficient heat capacity is secured. Has been done. Therefore, according to the copper bar 10 of the present embodiment, even when a large current is passed, the temperature rise due to the energization heat generation can be suppressed, and it is particularly suitable for an application in which a large current is passed.

In the copper bar 10 of the present embodiment, the average crystal grain size D1 in the outermost surface region 11 from the outer surface to the center is reduced to 60 μm or less in the cross section orthogonal to the extrusion direction. Therefore, the workability in the outermost surface layer region 11 is particularly excellent, and it is possible to suppress the occurrence of appearance defects such as rough skin and wrinkles even when severe plastic working is performed. Therefore, it is possible to reduce the volume of the energized parts.

Further, in the copper bar 10 of the present embodiment, the average crystal grain size D2 in the surface layer region 12 from the outer surface to the center of more than 200 μm and up to 1000 μm is set to 120 μm or less, and further, in the outermost layer region 11. Since the average crystal grain size D1 and the average crystal grain size D2 in the surface layer region 12 have a relationship of D2> D1, workability is ensured also in the surface layer region 12, and particularly intense plastic working is performed. It is also possible to suppress the occurrence of poor appearance. Further, the crystal grain size does not differ greatly between the outermost layer region 11 and the surface layer region 12, and it is possible to suppress the occurrence of excessive strain at the boundary portion between these regions.

Further, the present embodiment includes a surface processing step S04 for performing surface processing so that the Vickers hardness of the outermost layer region increases by 5 Hv or more before and after the processing, and a recrystallization heat treatment step S05. Sufficient strain can be accumulated in the outermost surface layer region, and the average crystal grain size D1 of the outermost surface layer region 11 of the copper bar 10 can be made finer by the subsequent recrystallization heat treatment. Specifically, the average crystal grain size D1 of the outermost layer region 11 can be set to 60 μm or less.
Further, by the surface processing step S04, it is not necessary to perform processing with a large surface reduction rate, and the diameter R of the copper bar 10 can be secured.

Further, the present embodiment includes a cooling step S02 for cooling the bar obtained by the hot extrusion step S01 at a cooling rate of 100 ° C./sec or more from the extrusion temperature to the recrystallization start temperature of the bar. Therefore, the average crystal grain size D2 of the surface layer region 12 of the copper bar 10 can be made finer. Specifically, the average crystal grain size D2 of the surface layer region 12 can be set to 120 μm or less.

Although the copper rod material according to the embodiment of the present invention has been described above, the present invention is not limited to this, and can be appropriately changed without departing from the technical idea of the present invention.

The results of the confirmation experiment conducted to confirm the effect of the present invention will be described below.
Billets (diameter 240 mm, length 850 mm) made of the materials shown in Table 1 were prepared and hot-extruded at the extrusion temperatures shown in Table 1.
The extruded bar was spray-cooled and then immersed in a water tank. At this time, by changing the spray cooling conditions, the cooling rate from the extrusion temperature to the recrystallization start temperature of the bar was set to the conditions shown in Table 1. The recrystallization start temperature was 300 ° C. for oxygen-free copper and tough pitch copper, and 350 ° C. for phosphorylated copper.

Next, after pickling, the bar material was surface-processed by the method shown in Table 1. Table 1 shows the amount of increase in Vickers hardness in the outermost layer region before and after surface processing of individual pieces. Vickers hardness was measured according to JIS Z 2244.
Next, the recrystallization heat treatment was carried out under the conditions shown in Table 2. As a result, copper rods having the diameters shown in Table 1 were produced.

With respect to the obtained copper bar, in a cross section orthogonal to the extrusion direction, the average crystal grain size D1 in the outermost layer region up to 200 μm from the outer surface toward the center and more than 200 μm from the outer surface toward the center. The average crystal grain size D2 in the surface layer region up to 1000 μm was measured.
The average crystal grain size D1 and the average crystal grain size D2 are located at 0 °, 90 °, 180 °, and 270 ° along the circumferential direction from the axis with respect to an arbitrary axis passing through the center of the cross section orthogonal to the extrusion direction. The four points at each of the four points were measured, and the crystal grain sizes at each of the four points were averaged. The measurement was performed using SEM-EBSD (detector HIKARI, analysis software TSL OIM Data collection 5.31 and OIM Analysis 6.2) between measurement points where the orientation difference between two adjacent crystals is 15 ° or more. The crystal grain boundary was used, and the weighted average value weighted by the area was used as the crystal grain size. The field of view was x = 1000 μm, y = 2000 μm, and the step size was 6 μm. The evaluation results are shown in Table 2.

Further, the obtained copper bar was subjected to a compression test, and then the outer surface roughness of the test piece was measured.
The compression test was carried out at a compression ratio of 60%, with the length of the test piece being the same as the diameter of the copper bar and the compression direction being the extrusion direction.
For the surface roughness of the test piece, a white interferometer manufactured by Hitachi High-Tech Science Co., Ltd. was used, and the outer surface of the test piece after the compression test was cut off: 0.455 μm, evaluation range: extrusion direction 2317.82865 μm × circumference. The measurement was performed under the conditions of direction 1592.2019 μm, correction: fourth-order correction. Then, the arithmetic average roughness Ra in the extrusion direction is "◎", the arithmetic average roughness Ra is 2.0 μm or more and less than 4.0 μm is "○", and the arithmetic average roughness Ra is 4. Those having a thickness of 0.0 μm or more were evaluated as “x”. The evaluation results are shown in Table 2.

In Comparative Example 1, the cooling rate after hot extrusion was slow, the average crystal grain size D2 in the surface layer region was as large as 130 μm, and the average crystal grain size D1 in the outermost layer region was also as large as 70 μm. Therefore, the surface roughness after the compression test became rough.
In Comparative Example 2, the recrystallization heat treatment temperature was high, and the average crystal grain size D1 in the outermost layer region was as large as 72 μm. Therefore, the surface roughness after the compression test became rough.
In Comparative Example 3, since the surface processing step and the recrystallization heat treatment step were not performed, the average crystal grain size D1 in the outermost layer region was as large as 68 μm. Therefore, the surface roughness after the compression test became rough.
In Comparative Example 4, the cooling rate after hot extrusion was slow, and the average crystal grain size D2 in the surface layer region was as large as 128 μm. The average crystal grain size D1 in the outermost layer region was 35 μm by the surface processing step and the recrystallization heat treatment step, but the surface roughness after the compression test became rough.

On the other hand, in the examples of the present invention in which the average crystal grain size D1 in the outermost layer region was 60 μm or less and the average crystal grain size D2 in the surface layer region was 120 μm or less, the surface roughness after the compression test was The arithmetic average roughness Ra was less than 4.0 μm, and no appearance defect occurred. In particular, in Examples 1 and 2 of the present invention, the surface roughness after the compression test was less than 2.0 μm in arithmetic average roughness Ra.

From the above, it was confirmed that according to the example of the present invention, it is possible to provide a copper rod material capable of suppressing the occurrence of appearance defects even when severe processing is performed.

Claims (1)

It is made of pure copper with a purity of 99.90 mass% or more, and in the cross section orthogonal to the extrusion direction, the average crystal grain size D1 in the outermost layer region from the outer surface to the center is 60 μm or less, from the outer surface to the center. The average crystal grain size D2 in the surface layer region exceeding 200 μm and up to 1000 μm is set to 120 μm or less.
The average crystal grain size D1 in the outermost layer region and the average crystal grain size D2 in the surface layer region have a relationship of D2> D1 .
A copper rod having a diameter of 3 mm or more and 50 mm or less .

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