Title:
Phosphor bronze strip with excellent press formability
Kind Code:
A1


Abstract:
The present invention relates to a high-strength copper alloy used for electronic parts such as terminals and connectors, and more particularly, to a high-strength phosphor bronze strip. The present invention provides a phosphor bronze strip with excellent punching formability characterized in that a total content of S (20 to 100 ppm), Mn, Ca, Mg and Al is 50 ppm or less, a phosphor bronze strip with excellent punching formability characterized in that the sum total of lengths of etching imprints is 5 mm/mm2 or more when a cross-section parallel to the rolling direction is etched, a phosphor bronze strip with excellent punching formability characterized in that a copper sulfide phase exists in a range of 1 to 3% of the microstructure whose cross-section is parallel to the rolling direction and a phosphor bronze strip characterized in that the plastic deformation ratio when subjected to a shearing test with clearance of 4 to 10% is 50% or less.



Inventors:
Fukamachi, Kazuhiko (Koza-gun, JP)
Niimi, Toshihiro (Koza-gun, JP)
Application Number:
10/397259
Publication Date:
10/09/2003
Filing Date:
03/27/2003
Assignee:
FUKAMACHI KAZUHIKO
NIIMI TOSHIHIRO
Primary Class:
International Classes:
C22F1/08; C22C9/00; C22C9/02; C22F1/00; (IPC1-7): C22C9/00
View Patent Images:



Primary Examiner:
IP, SIKYIN
Attorney, Agent or Firm:
EDELL, SHAPIRO & FINNAN, LLC (9801 Washingtonian Blvd. Suite 750, Gaithersburg, MD, 20878, US)
Claims:

What is claimed is:



1. A phosphor bronze strip with excellent punching formability comprising 20 to 100 mass ppm of S, 50 mass ppm or less, in total, of one, two, or more selected from among Mn, Ca, Mg and Al.

2. A phosphor bronze strip with excellent punching formability, wherein the sum total of lengths of etching imprints when a cross-section parallel to rolling direction is etched is 5 mm/mm2 or more.

3. A phosphor bronze strip with excellent punching formability, wherein a copper sulfide phase exists in a range of 1 to 3% of a microstructure of a cross-section parallel to rolling direction.

4. The phosphor bronze strip according to any of claims 1, 2, or 3, wherein a plastic deformation ratio when a shearing test is conducted with clearance of 4 to 10% is 50% or less.

5. A phosphor bronze strip with excellent bending formability and punching formability comprising 20 to 100 mass ppm of S, 50 mass ppm or less, in total, of one, two, or more selected from among Mn, Ca, Mg and Al, 100 to 1,000 mass ppm of Zn.

6. A phosphor bronze strip with excellent bending formability and punching formability, wherein a mean grain size (mGS) after annealing for 10,000 seconds at 425° C. is 5 μm or less, a standard deviation of the grain size (σGS) is ⅓ mGS or less and a difference between tensile strength and 0.2% yield strength of the cold-rolled phosphor bronze strip is within 80 MPa.

7. The phosphor bronze strip with excellent bending formability and punching formability according to any of claims 1, 2, 3, or 5, wherein a mean grain size (mGS) after annealing for 10,000 seconds at 425° C. is5 μm or less, a standard deviation of the grain size (σGS) is ⅓ mGS or less and a difference between tensile strength and 0.2% yield strength of the cold-rolled phosphor bronze strip is within 80 MPa.

8. The phosphor bronze strip with excellent bending formability and punching formability according to claim 4, wherein a mean grain size (mGS) after annealing for 10,000 seconds at 425° C. is 5 μm or less, a standard deviation of the grain size (σGS) is ⅓ mGS or less and a difference between tensile strength and 0.2% yield strength of the cold-rolled phosphor bronze strip is within 80 MPa.

9. A phosphor bronze strip with excellent bending formability and punching formability, wherein a strip subjected to cold-rolling at a reduction ratio of 45% or more is subjected to final recrystallization annealing to a mean grain size (mGS) of 3 μm or less and the extent that standard deviation of the grain size (σGS) of 2 μm or less, and then subjected to final cold rolling at a reduction ratio of 10 to 45%.

10. The phosphor bronze strip with excellent bending formability and punching formability according to any of claims 1, 2, 3, or 5, wherein a strip subjected to cold-rolling at a reduction ratio of 45% or more is subjected to final recrystallization annealing to the extent that the mean grain size (mGS) of 3 μm or less and a standard deviation of the grain size (σGS) of 2 μm or less, and then subjected to final cold rolling at a reduction ratio of 10 to 45%.

11. The phosphor bronze strip with excellent bending formability and punching formability according to claim 4, wherein a strip subjected to cold-rolling at a reduction ratio of 45% or more is subjected to final recrystallization annealing to the extent that the mean grain size (mGS) of 3 μm or less and a standard deviation of the grain size (σGS) of 2 μm or less, and then subjected to final cold rolling at a reduction ratio of 10 to 45%.

12. The phosphor bronze strip with excellent bending formability and punching formability according to any of claims 1, 2, 3, 5, 6, or 9, wherein a cold-rolled material subjected to final cold rolling at a reduction ratio of X (%) with tensile strength of TSo (MPa) is subjected to stress relief annealing until tensile strength TSa (MPa) becomes TSa<TSo−X.

13. The phosphor bronze strip with excellent bending formability and punching formability according to claim 4, wherein a cold-rolled material subjected to final cold rolling at a reduction ratio of X (%) with tensile strength of TSo (MPa) is subjected to stress relief annealing until tensile strength TSa (MPa) becomes TSa<TSo−X.

14. The phosphor bronze strip with excellent bending formability and punching formability according to claim 7, wherein a cold-rolled material subjected to final cold rolling at a reduction ratio of X (%) with tensile strength of TSo (MPa) is subjected to stress relief annealing until tensile strength TSa (MPa) becomes TSa<TSo−X.

15. The phosphor bronze strip with excellent bending formability and punching formability according to claim 8, wherein a cold-rolled material subjected to final cold rolling at a reduction ratio of X (%) with tensile strength of TSo (MPa) is subjected to stress relief annealing until tensile strength TSa (MPa) becomes TSa<TSo−X.

16. The phosphor bronze strip with excellent bending formability and punching formability according to claim 10, wherein a cold-rolled material subjected to final cold rolling at a reduction ratio of X (%) with tensile strength of TSo (MPa) is subjected to stress relief annealing until tensile strength TSa (MPa) becomes TSa<TSo−X.

17. The phosphor bronze strip with excellent bending formability and punching formability according to claim 11, wherein a cold-rolled material subjected to final cold rolling at a reduction ratio of X (%) with tensile strength of TSo (MPa) is subjected to stress relief annealing until tensile strength TSa (MPa) becomes TSa<TSo−X.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a high-strength copper alloys used for electronic parts such as terminals and connectors, and more particularly, to a high-strength phosphor bronze strip.

[0003] 2. Description of the Related Art

[0004] Phosphor bronze such as C5210, C5191 (JIS alloy number) or copper alloy C2600 (JIS alloy number) has excellent formability and mechanical strength, and is therefore widely used as materials for electronic parts such as terminals and connectors. On the other hand, with remarkable progress in the manufacturing of unprecedentedly slimmer, or smaller parts than ever in recent years, there is an increasing demand for high-strength copper alloys such as beryllium copper, titanium copper, Corson-based alloys. However, there are constraints concerning supply and demand or commercialization in the market for these high-strength copper alloys, which are relatively new as copper alloys for electronic parts. For example, there is a problem in a global standard oriented market. Furthermore, the fact that these high-strength copper alloys are more expensive than conventional copper alloys such as phosphor bronze is not desirable. From these standpoints, further improvements have been sought in the aspects of strength and formability of phosphor bronze, which is said to have high mechanical strength among conventional copper alloys.

[0005] With regard to formability, punching formability and bending formability are particularly important. When punch forming is repeated, a punch of the press is worn out by fiction with materials and the shear plane of pressform products deteriorates. Therefore, after presswork is conducted a certain number of times, it is necessary to polish dies and readjust the dies. Since the press speed is also higher from the viewpoint of improving productivity, the importance of a material to make less wear of the dies during punching process is increasing further.

[0006] Furthermore, with miniaturization of contacts, the material is required to have higher strength, and at the same time bending is performed under severe conditions with a small bending radius, which is likely to cause cracking in the bent part. Furthermore, the punching formability and bending formability are mutually contradictory characteristics, and there is a tendency from a sensuous viewpoint that a brittle material is easy to be punched but easy to be cracked, while a ductile material is easy to be bent but hard to be punched causing the dies to wear sooner.

SUMMARY OF THE INVENTION

[0007] It is an object of the present invention to provide a phosphor bronze strip with improved press formability, especially punching formability and bending formability required for pressform of electronic parts such as connector terminals. It is another object of the present invention to provide a technology to achieve higher strength while maintaining the improved press formability.

[0008] The present inventors have improved the above-described press formability drastically by adjusting components, microstructure and manufacturing conditions of a phosphor bronze strip.

[0009] That is, the invention comprises the following preferred Aspects:

[0010] (1) A phosphor bronze strip with excellent punching formability characterized by comprising 20 to 100 mass ppm S, 50 mass ppm or less, in total, of one, two, or more selected from among Mn, Ca, Mg and Al.

[0011] (2) A phosphor bronze strip with excellent punching formability, characterized in that the sum total of lengths of etching imprints when a cross-section parallel to rolling direction is etched is 5 mm/mm2 or less.

[0012] (3) A phosphor bronze strip with excellent punching formability, characterized in that a copper sulfide phase exists in a range of 1 to 3% of a microstructure of a cross-section parallel to rolling direction.

[0013] (4) The phosphor bronze strip according to any of Aspects (1) to (3), characterized in that a plastic deformation ratio when a shearing test is conducted with clearance of 4 to 10% is 50% or less.

[0014] (5) A phosphor bronze strip with excellent bending formability and punching formability, characterized by comprising 20 to 100 mass ppm S, 50 mass ppm or less, in total, of one, two, or more selected from among Mn, Ca, Mg and Al, 100 to 1,000 mass ppm Zn.

[0015] (6) A phosphor bronze strip with excellent bending formability and punching formability, characterized in that a mean grain size (mGS) after annealing for 10,000 seconds at 425° C. is 5 μm or less, a standard deviation of the grain size (σGS) is ⅓ mGS or less and a difference between tensile strength and 0.2% yield strength of the cold-rolled phosphor bronze strip is within 80 MPa.

[0016] (7) The phosphor bronze strip with excellent bending formability and punching formability according to any of Aspects (1) to (5), characterized in that a mean grain size (mGS) after annealing for 10,000 seconds at 425° C. is 5 μm or less, a standard deviation of the grain size (σGS) of variations in the grain size is ⅓ mGS or less and a difference between tensile strength and 0.2% yield strength of the cold-rolled phosphor bronze strip is within 80 MPa.

[0017] (8) A phosphor bronze strip with excellent bending formability and punching formability, characterized in that a cold-rolled strip with a reduction ratio of 45% or more is final recrystallization annealed to the extent that the mean grain size (mGS) of 3 μm or less and a variation standard deviation (σGS) of 2 μm or less, and then final cold-rolled with a reduction ratio of 10 to 45%.

[0018] (9) The phosphor bronze strip with excellent bending formability and punching formability according to any of Aspects (1) to (5), characterized in that a cold rolled strip with a reduction ratio of 45% or more is final recrystallization annealed to the extent that the mean grain size (mGS) of 3 μm or less and a variation standard deviation (σGS) of 2 μm or less, and then final cold rolled with a reduction ratio of 10 to 45%.

[0019] (10) The phosphor bronze strip with excellent bending formability and punching formability according to any of Aspects (1) to (9), characterized in that a cold rolled material with a reduction ratio of X (%) having tensile strength of TSo (MPa) is stress relief annealed until tensile strength TSa (MPa) becomes TSa<TSo−X.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] (1) With punching work, a starting point of crack is formed in a portion to be shear deformed in the process of shearing a sheet material or a strip material using a punch and a die, that is, in a punch stroke step. With this starting point of crack as the starting point, a crack propagates through the shear deformation part, penetrates the sheet and thereby punching is performed. During this period until a crack starts, the edges of the punch and the die friction strongly with the surface of the material. At this time, abrasive wear with the surface of the material and scratch wear by foreign particles occur on the edge of the dies and the edge wears out gradually. Therefore, it is desirable that cracks occur in the shearing process as soon as possible.

[0021] On the other hand, if S exists in phosphor bronze, since the solubility of S into phosphor bronze is low (see phase diagram of Cu-S system), a Cu2S phase appears in the matrix. Since Cu2S phase is more brittle than, the Cu2S phase can become a starting point of crack in the matrix during shearing deformation. Adding 20 ppm or more of S can hasten the starting timing of crack. Basically, the greater the content of S, the better. But if more than 100 ppm of S is added, the bending formability of a sheet and strip products and the rolling formability in the process of manufacturing a sheet and strip products worsen, and so the amount of S to be added is determined to 100 ppm or less.

[0022] By the way, S is not only added as a raw material of copper sulfide, etc., but also included in charcoal carbon that contacts liquid metal during melting or casting of a phosphor bronze raw material and extreme-pressure agent in press oil in a scrap, etc., and therefore it is effective to intentionally control a mix in of S from these materials.

[0023] Mn, Ca, Mg and Al are mixed in as contaminants in the above-described manufacturing process instead of normal additional element of phosphor bronze. However, containing a total of more 50 ppm of these elements prevents the aforementioned Cu2S phase from scattering with functioning as a starting point of crack stably, and therefore it is necessary to control the contents to 50 ppm or less in total.

[0024] (2) On the other hand, when the cross-section of the material is etched using a sulfuric-acid-based etchant reagent, etc., the sulfide phase including copper sulfide is etched preferentially forming fine pit-shaped depressed imprints. When this cross-section is observed as a dark field image using an optical microscope, etching imprints appear scattered as white dots or lines. When a cross-section parallel to the rolling direction is etched with an aqueous solution of sulfuric acid at a normal temperature for a few to 30 seconds and then observed using the above-described method, if the sum total of lengths of the etching imprints observed is 5 mm or more per a cross-section of 1 mm2, the punching formability of the phosphor bronze strip is improved considerably for the same reason as that in (1).

[0025] (3) Furthermore, it is possible to calculate the thickness of the copper sulfide phase from the section parallel to the rolling direction using the following method and estimate the area ratio of the copper sulfide phase. With an EPMA acceleration voltage set to 15 kV and the diameter of an electron beam on the surface of a sample adjusted to 1 μm, a variation of X-ray intensity of sulfur when a beam crosses the copper sulfide phase is measured. The distance measured after the X-ray intensity rises from the background, reaches a peak and returns to the background is defined as the thickness of the copper sulfide phase. The length of the copper sulfide phase was measured from a SEM and the area of the copper sulfide phase was calculated. As a result, it is desirable to determine the total area of the copper sulfide phase to 1 to 3% of the whole area. This is because no improvement in the punching formability would be observed with the area smaller than this, and detriments such as reduction in the bending formability would be questioned with the area greater than this.

[0026] (1) to (3) are identical in attempting to take advantage of the effectiveness of the Cu2S phase in the phosphor bronze as a starting point of crack during shear deformation. However, while they are mutually correlated, they do not always hold a uniquely defined correlation. That is, solubility, shape and size of the copper sulfide phase and distribution statue of the copper sulfide phase in phosphor bronze with the same content of S vary depending on a combination of heat treatment and rolling in the manufacturing process.

[0027] (4) The formability of press punching can also be determined by a plastic deformation rate calculated from the amount of plastic deformation through a shearing test. The amount of plastic deformation refers to a distance of a punch movement after a starting point of crack is formed in the shear deformation part, a crack propagates through the shear deformation part with this starting point of crack as the starting point until the crack penetrates the sheet. The plastic deformation rate is a value (%) obtained by dividing the amount of plastic deformation by the thickness of the sheet and is generally applicable. A shearing test is conducted by attaching an upper die (punch) of a shearing tester to a cross head of a tensile testing machine, letting the upper die down to a material on a lower die (die) to punch out a hole of a certain diameter, measuring the punch stroke at this time using a elongation gauge, measuring the punch load using a load cell of the tensile testing machine and creating a displacement-load curve. The initial linear portion of the displacement-load curve corresponds to an elastic deformation area and the curve then shows a shear deformation and the load descends linearly when rupture takes place. The amount of plastic deformation is a distance between a point of deviation from the straight line of the initial elastic deformation area and a point of deviation from the load descending straight line at the time of rupture. Since clearance has a large influence on the sheet thickness of the material during a measurement of the amount of plastic deformation, it is necessary to select a punch that makes the clearance 4 to 10%. The phosphor bronze strip having an elastic deformation ratio of 50% or less can reduce wear of the dies during high-speed press for manufacturing connector contacts, etc. ps (5) As described above, the phosphor bronze strip characterized by comprising 20 to 100 mass ppm S, 50 mass ppm or less, in total, of one, two, or more selected from among Mn, Ca, Mg and Al has favorable punching formability by scattering the copper sulfide phase into the matrix. Part of the copper sulfide in the phosphor bronze with 100 to 1,000 ppm of Zn changes to zinc sulfide, which promotes a segmentation of the sulfide phase in the reducing thickness process by repeating rolling and annealing. This segmentation of the sulfide phase improves bending formability and provides phosphor bronze, which is excellent in both punching formability and bending formability. When Zn is less than 100 ppm, the copper sulfide changes less to zinc sulfide and bending formability is not improved. When Zn is more than 1,000 ppm, the punching formability deteriorates due to a reduction of the copper sulfide phase, and therefore the amount of Zn added is preferably determined to 100 to 1,000 ppm.

[0028] (6) The phosphor bronze in the present invention is defined as having a mean grain size (mGS) after annealing for 10,000 seconds at 425° C. of 5 μm or less, a standard deviation of the grain size (σGS) of ⅓ mGS or less and a difference between tensile strength and 0.2% yield strength of the cold rolled copper alloy strip of within 80 MPa.

[0029] By the way, in the present invention the grain size is measured using the intercept method based on JTS H 0501. More specifically, the number of crystal grains, which are completely crossed by a straight line segment of a predetermined length, is counted and an average value of the cutting lengths is considered as the grain size. A standard deviation of the grain size, which is an index of the uniformity, is not a standard deviation of the cutting length but a standard deviation of the grain size.

[0030] With a final product subjected to grain boundary strengthening and dislocation strengthening, that is, strengthened by heat treatment and rolling, it is not possible to expose the grain boundary. When a metal strip is deformed by cold working, a difference in local transgranular deformations becomes more remarkable as the deformation progresses and various deformation bands such as shear band and microband appear. These deformation zones make discontinuous the recrystallized gain boundary before cold working and even if its cross-section is etched and observed using an optical microscope, the microstructure remains obscure. Even if the reduction ratio of cold working is about 20%, when the microstructure is observed through a transmission electron microscope image, part of the recrystallized grain boundary before cold working is observed to remain, but it is already covered with a cell structure and it is not possible to determine the grain size precisely. This fact constitutes a great stumbling block in improving the properties of a cold rolling material.

[0031] The present invention has discovered that the behavior of recrystallization after cold working is correlated with the properties of phosphor bronze that is provided with both good bending formability and high strength. This correlation is effective for designing and developing materials.

[0032] That is, the copper alloy of the present invention shows a difference between tensile strength and 0.2% yield strength of 80 MPa or less and at the same time has excellent bending formability, and has a mean grain size (mGS) after annealing for 10,000 seconds at 425° C. of 5 μm or less with a standard deviation of grain size (σGS) of ⅓ mGS or less.

[0033] When cold working is performed after annealing and a reduction ratio is increased, the difference between tensile strength and 0.2% yield strength generally decreases, but ductility also decreases at the same time and cracking is more likely to occur in the bending process.

[0034] However, the present invention has discovered that the reduction in ductility is decreased by adjusting the final annealing condition before the final rolling and cold processing condition before the final annealing. With conventional phosphor bronze, annealing is performed under a condition of 425° C.×10,000 seconds where the grains grows large, and a phosphor bronze product whose mean grain size (mGS) falls below 5 μm is provided with both high strength and excellent bending formability. More preferably, if the mean grain size (mGS) after annealing of 425° C.×10,000 seconds is 3 μm or below, the relationship between tensile strength and bending formability is further improved.

[0035] However, even if the mean grain size (mGS) is 5 μm or below, if grain sizes are not uniform, the effect is reduced. As will be explained later, it is necessary to control the manufacturing method more precisely to make a uniform fine grain microstructure. The allowable range of uniformity should be ⅓ mGS or less as a standard deviation of the grain size. This is because when the standard deviation of grain size (σGS) exceeds ⅓ mGS, the effect of improving bending formability is small.

[0036] Phosphor bronze having characteristics under these conditions is provided with press punching formability combined with bending formability.

[0037] (7) The embodiments in (1) to (4) have improved only the punching formability, and cannot thereby avoid slight deterioration of bending formability. Combining the characteristic in (6) can improve both press punching and bending formability considerably.

[0038] (8) This invention relates to the method of manufacturing a high-strength phosphor bronze strip. With regard to a phosphor bronze strip manufactured by repeating cold rolling and annealing, this embodiment relates to the method of manufacturing a high-strength phosphor bronze strip which determines the final cold-rolling and the preceding final annealing and further the cold rolling process preceding thereto. This embodiment is intended to increase the strength by miniaturization of grains through final annealing.

[0039] The thickness of the material before cold rolling is set to to, the thickness of the material after cold rolling is set to t, and the reduction ratio X of cold rolling defined by X=(to−t)/to×100 (%) is determined to 45% or more because if X is less than 45%, it is difficult to miniaturize the grain size after the final annealing even if the heat treatment condition of final annealing is adjusted. Furthermore, the mean grain size (mGS) after annealing is determined to 3 μm or less and the standard deviation of the grain size (σGS), which is determined to 2 μm or less because it is necessary to control a heating temperature profile during annealing precisely and make a uniform fine grain microstructure. To be accurate, the grain size does not show a normal distribution and when the mean grain size (mGS) is 3 μm and the standard deviation of the grain size (σGS) is 2 μm, 99% or more of individual grain size is mGS+3σ, that is, 9 μm or less.

[0040] Moreover, a mixture of grains of 8 μm or greater in size in a recrystallized microstructure is not necessarily desirable, and the standard deviation of the grain size is preferably 1.5 μm or less.

[0041] The higher the reduction ratio of cold rolling before final annealing, the smaller the recrystallized grain after the final annealing is likely to become, but at the same time the behavior of nucleation and subsequent secondary recrystallization varies a great deal, increasing the likelihood to produce duplex grain structure. This tendency is particularly strong with a copper alloy having a pure copper type recrystallization structure with high copper concentration. On the contrary, with phosphor bronze containing 4 mass % or more of Sn, recrystallized gains after relatively strong working are more likely to be made uniform. It is necessary to optimize the annealing condition, that is, temperature, time and temperature profile for each alloy system considering these aspects, and create the above-described recrystallization structure. If either the specification of the mean grain size of 3 μm or less or the specification of its standard deviation of the grain size of 2 μm or less is not observed, it is not possible to achieve a high work hardening property during final cold rolling.

[0042] When final cold working at a reduction ratio of 10 to 45% is performed under conditions with an mean grain size of 3 μm or less and its standard deviation of the grain size of 2 μm or less, a copper alloy with high strength and excellent bending formability results. At a reduction ratio of less than 10%, even a conventional copper alloy whose mean grain size after final annealing is approximately 10 μm has good bending formability and has a small effect of miniaturization of grains. Furthermore, at a reduction ratio greater than 45%, bending formability deteriorates and the range of application as a metallic material such as bent contacts becomes narrower.

[0043] (9) By improving only punching formability, the embodiments in (1) to (4) cannot avoid slight reduction of bending formability. Combining the characteristic in (8) makes it possible to improve both punching formability and bending formability considerably.

[0044] (10) This embodiment performs stress relief annealing after final rolling on the above-described copper alloy and specifies the amount of reduction in tensile strength with the stress relief annealing, and this specification is TSa<TSo−X (reduction ratio of final cold-rolling (%)) where TSo (MPa) is tensile strength before stress relief annealing and TSa (MPa) is tensile strength after stress relief annealing.

[0045] Phosphor bronze and nickel silver, etc., maybe subjected to stress relief annealing. Unlike recrystallization annealing applied before final rolling, stress relief annealing is generally practiced on, for example, phosphor bronze for springs (C5210: JIS H 3130), etc., for the purpose of recovering the ductility (formability) which has been reduced by cold working and improving spring properties together. This stress relief annealing can be applied through a tension annealing line, etc., after final rolling as required. That is, even after stress relief annealing, the phosphor bronze according to the above-described embodiment has higher strength and better bending formability than phosphor bronze manufactured using a conventional technology. Furthermore, when an annealing material of a small grain size is subjected to cold rolling, it is effective to perform stress relief annealing according to the final reduction ratio to recover ductility. In order to improve bending formability in particular, stress relief annealing is performed on a cold rolled material of tensile strength of TSo (MPa) under the condition of TSa<TSo−X, where X % is the reduction ratio of final cold-rolling and TSa (MPa) is tensile strength after stress relief annealing. For example, in the case of a cold rolled material manufactured and hardened up to 800 MPa at a final reduction ratio of 50%, if this material is subjected to stress relief annealing until its tensile strength falls below 750 MPa, it is possible to obtain a material with good bending formability.

[0046] Having now generally described the invention, the same will be more readily understood through reference to the following Embodiments, which are provided by way of illustration, and are not intended to be limiting of the present invention, unless specified.

[0047] (1) Embodiment 1

[0048] This is related to the embodiments according to Aspects 1 to 4.

[0049] Using the phosphor bronze of the composition shown in Table 1 as a base, S, Mn, Ca, Mg and Al were added thereto, the phosphor bronze is melted covered with charcoal in the atmosphere, and casted into an ingot measuring W 100 mm×t 40 mm×L 150 mm. This ingot was annealed for homogenizing in an atmosphere of 75% N2+25% H2 at 700° C. for one hour, a tin segregation layer formed on the surface was ground and removed using a grinder and then a chemical analysis was performed. Then, cold rolling and recrystallization annealing were repeated a plurality of times as required and a sheet of 0.2 mm in thickness was obtained. Adjustments were made so as not to produce differences in the work history by equalizing the reduction ratio of cold rolling before final annealing, grain size at final recrystallization annealing and the reduction ratio of final cold rolling, etc. Composition, the sum total of lengths of etching imprints measured by etching the cross-section of the sheet, area ratio of copper sulfide phase measured by EPMA and plastic deformation ratio obtained by a shearing test are shown in Table 1.

[0050] In contrast to comparative examples, this embodiment shows a lower plastic deformation ratio and better press punching formability. 1

TABLE 1
Mn+Ca+Mg+AlTotal length ofVolume ratio ofPlastic
CompositionS contentcontentetching imprintscopper sulfidedeformation
No.(mass %)(ppm)(ppm)(mm/mm2)phase (%)ratio (%)
Embodiments
1Cu-4.5Sn-0.15P31446.81.741
2Cu-6.2Sn-0.13P33377.21.840
3Cu-8.0Sn-0.14P30357.31.842
4Cu-10.0Sn-0.15P32417.21.742
5Cu-8.2Sn-0.14P21364.81.246
6Cu-8.2Sn-0.15P22355.30.944
7Cu-8.0Sn-0.16P56429.4233
8Cu-8.1Sn-0.14P934811.42.631
Comparative examples
1Cu-4.2Sn-0.13P14383.80.457
2Cu-6.2Sn-0.15P114220.358
3Cu-8.0Sn-0.14P22875.10.855
4Cu-10.0Sn-0.15P16603.61.159
Zn 23 20 ppm
Grain size: 5 to 10 μm
Rolled material at reduction ratio of final cold working of 25%

[0051] (2) Embodiment 2

[0052] This is the embodiment according to Aspect 5.

[0053] This embodiment is composed of a phosphor bronze composition as a base and S, Mn, Ca, Mg, Al and Zn as added elements, and a test piece was adjusted using the same method as that in Embodiment 1 so as not to produce differences in the work history by equalizing the reduction ratio of cold-rolling before final annealing, grain size at final recrystallization annealing and the reduction ratio of final cold-rolling, etc. With regard to bending formability (r/t), a test piece measuring W 10 mm×L 100 mm was prepared perpendicular to the rolling direction, subjected to a W-bending test (JIS H 3110) with various bending radiuses and a minimum bending radius ratio (r (bending radius)/t (thickness of test piece)) without cracking was found. The bending axis for the W-bending test was parallel to the rolling direction.

[0054] Among comparative examples, those with a low plastic deformation ratio have a large r/t and those with a small r/t have a high plastic deformation ratio. This embodiment has a low plastic deformation ratio and a small r/t, and is therefore excellent in both press punching formability and bending formability.

[0055] The results are shown in Table 2. 2

TABLE 2
Mn+Ca+Mg+AlPlastic
CompostitionS contentcontentZn contentdeformation
No(mass %)(ppm)(ppm)(ppm)ratio (%)r/t
Embodiments
9Cu-4.0Sn-0.14P3044220440.5
10Cu-6.1Sn-0.15P3137228420.5
11Cu-8.0Sn-0.13P3335217420.5
12Cu-9.9Sn-0.14P3241202440.5
13Cu-8.2Sn-0.16P2136107490.5
14Cu-7.9Sn-0.15P2435334470.5
15Cu-8.0Sn-0.13P5542820351.0
16Cu-8.1Sn-0.16P9048730311.5
Comparative examples
5Cu-4.2Sn-0.13P1535212550.5
6Cu-6.2Sn-0.15P1440300540.5
7Cu-8.0Sn-0.14P2481185520.5
8Cu-10.0Sn-0.15P1663108561.0
9Cu-4.1Sn-0.13P25381200590.5
10Cu-6.0Sn-0.14P804266321.5
11Cu-8.0Sn-0.15P24351070570.5
12Cu-10.0Sn-0.15P904575302.0

[0056] (3) Embodiment 3

[0057] This is the embodiment according to Aspect 6.

[0058] With the phosphor bronze of the composition shown in Table 3, a test piece was adjusted using the same method as that in Embodiment 1 without adding S, Mn, Ca, Mg, Al and Zn. However, in Embodiment 3, the reduction ratio of cold rolling before final annealing, grain size at final recrystallization annealing and the reduction ratio of final cold rolling, etc., were adjusted to produce differences in the work history. The mechanical properties are shown in Table 3.

[0059] Tensile strength (TS: MPa) and 0.2% yield strength (YS: Mpa) were obtained by preparing a No. 13 B test piece (JIS Z 2201) in parallel to the rolling direction and carrying out a tensile test (JIS Z 2241) on the test piece.

[0060] With regard to the grain size, the number of grains completely cut by a line segment of a predetermined length according to the intercept method (JIS H 0501) is counted and an average value of the cutting lengths is considered as the grain size. The standard deviation of the grain size (σGS) is a standard deviation of the grain size. That is, a cross-sectional microstructure perpendicular to the rolling direction is magnified using a scanning electron microscope (SEM image) 4,000times, a value obtained by dividing a straight line segment of 50 μn in length by a value obtained by subtracting 1 from the number of intersections between the line and grain boundary is considered as the grain size. An average of the respective grain size obtained by measuring 10 line segments is considered as a mean grain size (mGS) and a standard deviation of the respective grain size is considered as the standard deviation of the grain size (σGS) according to the present invention.

[0061] Compared to comparative examples (conventional materials), this embodiment has better punching formability and bending formability if the strength is the same. 3

TABLE 3
After
annealing of
425° C. ×Plastic
10,000deform-
secondsation
CompositionmGSσGSTS-YSTSratio
No(mass %)(μm)(μm)(M Pa)(M Pa)(%)r/t
Embodiments
17Cu-4.2Sn-0.13P4.90.811606410.5
18Cu-6.2Sn-0.13P4.00.714730401.0
19Cu-8.0Sn-0.13P3.90.68874361.5
20Cu-10.0Sn-0.13P3.50.611868361.0
21Cu-4.2Sn-0.13P3.30.68650380.5
22Cu-6.2Sn-0.13P3.50.78760350.5
23Cu-8.0Sn-0.13P3.60.55906311.0
24Cu-10.0Sn-0.13P3.50.511914331.0
Comparative examples
13Cu-4.2Sn-0.13P6.51.325590521.5
14Cu-6.2Sn-0.13P7.02.522667512.0
15Cu-8.0Sn-0.13P5.01.813805463.5
16Cu-10.0Sn-0.13P6.01.524855442.0

[0062] (4) Embodiment 4

[0063] This is the embodiment according to Aspect 7.

[0064] For the coils of the compositions 1 to 16 of the embodiments shown in Tables 1 and 2, the test piece was prepared using the same method as that in Embodiment 3 by adjusting the reduction ratio of cold rolling before final annealing, grain size at final recrystallization annealing and the reduction ratio of final cold rolling, etc., to produce differences in the work history.

[0065] Compared to comparative examples (conventional materials), this embodiment has better punching formability and bending formability if the strength is the same.

[0066] The results are shown in Table 4. 4

TABLE 4
After annealling ofPlastic
Mn+Ca+Mg+Al425° C. × 10,000 secondsdeformation
CompositionS contentcontentmGSσGSTS-YSTSratio
No(mass %)(ppm)(ppm)(μm)(μm)(M Pa)(M Pa)(%)r/t
Embodiments
25Cu-4.2Sn-0.15P31444.50.713601391.0
(alloy of Embodiment 1)
26Cu-6.2Sn-0.13P333740.614725381.5
(alloy of Embodiment 2)
27Cu-8.0Sn-0.14P30353.60.611870362.0
(alloy of Embodiment 3)
28Cu-10.0Sn-0.15P32413.20.515865341.5
(alloy of Embodiment 4)
29Cu-4.2Sn-0.15P31443.30.68644380.5
(alloy of Embodiment 1)
30Cu-6.2Sn-0.13P33373.30.57767330.5
(alloy of Embodiment 2)
31Cu-8.0Sn-0.14P303530.47901301.0
(alloy of Embodiment 3)
32Cu-10.0Sn-0.15P32412.90.411905301.0
(alloy of Embodiment 4)
Comparative Examples
17Cu-4.2Sn-0.15P31447.2227588522.0
(alloy of Embodiment 1)
18Cu-6.2sn-0.13P333772.325660522.5
(alloy of Embodiment 2)
19Cu-8.0sn-0.14P30356.31.620811453.0
(alloy of Embodiment 3)
20Cu-10.0Sn-0.15P32415.01.825872453.0
(alloy of Embodiment 4)

[0067] (5) Embodiment 5

[0068] The embodiment according to Aspect 8 was verified.

[0069] Table 5 shows the result.

[0070] Comparative examples are conventional examples with the reduction ratio of cold rolling before final annealing, and mean grain size at final annealing deviating from the present invention. Compared to conventional materials, which are comparative examples, this embodiment has higher strength and lower r/t and better bending formability. 5

TABLE 5
Reduction ratio of
cold rolling beforeAfter recrystallizationReduction
recrystallizationanneallingratio of final
CompositionannealingmGS(σm)cold rollingTS
No(mass %)(%)(μm)(μm)(%)(M Pa)r/t
Embodiments
33Cu-4.2Sn-0.13P482.01306231.5
34Cu-6.2Sn-0.13P501.81.2257101.0
35Cu-8.0Sn-0.13P501.61257461.5
36Cu-10.0Sn-0.13P601.20.73595040
Comparative examples
17Cu-4.2Sn-0.13P4062.1356022.0
18Cu-6.2Sn-0.13P408.22.3306501.0
19Cu-8.0Sn-0.13P4452.2256822.0
20Cu-10.0Sn-0.13P404.22.1358804.0
21Cu-8.0Sn-0.13P402.81.9257102.0
22Cu-8.0Sn-0.13P502.82.1257152.0
23Cu-8.0Sn-0.13P502.71.355500
24Cu-8.0Sn-0.13P505.02.3105601.0

[0071] (6) Embodiment 6

[0072] The effect of stress relief annealing according to Aspect 10 was tested.

[0073] Table 6 shows the result of the test.

[0074] The test pieces prepared in Embodiments 3 to 5 were subjected to stress relief annealing under various conditions and their mechanical properties were evaluated. The amount of reduction of tensile strength (TS) due to stress relief annealing is also shown.

[0075] Embodiments No. 39, 41, 43and 45and comparative example No. 27 are materials with tin concentration of 8.0 to 8.2 mass %. In contrast to the tensile strength (TS) of 721 to 850 MPa and bending formability (r/t) of 0.5 in this embodiment, the comparative example demonstrates a tensile strength (TS) of 755 MPa and r/t of 1, which shows that the present invention has higher strength and better bending formability. Furthermore, Embodiments No. 40, 42, 44 and46, and comparative example No. 28 are materials with tin concentration of 10.0 to 10.2 mass %. In contrast to the tensile strength (TS) of 820 to 859 MPa and bending formability (r/t) of 0.5 in this embodiment, the comparative example demonstrates a tensile strength (TS) of 830 MPa and r/t of 1.5, which shows that the present invention has higher strength and better bending formability as well.

[0076] By applying stress relief annealing as shown above, the material according to the present invention has clearly high strength and improved bending formability compared to the conventional materials shown in the comparative examples. That is, the present invention improves bending formability if the strength is at a comparable level. Furthermore, stress relief annealing provides a drastic increase in the strength if the bending formability is at a comparable level. 6

TABLE 6
TS reduced
Reductionby stressPlastic
ratio of finalreliefdeformationr/t beforer/t after
Embodiment No. beforecold rollingannealingTSratiostress reliefstress relief
No.stress relief annealing(%)(M Pa)(M Pa)(%)annealingannealing
Embodiments
37Embodiment 1730355714150
38Embodiment 1830307004060
39Embodiment 1940658093780.5
40Embodiment 2030488203660.5
41Embodiment 2340568503150.5
42Embodiment 243055859334.50.5
43Embodiment 2740468243570.5
44Embodiment 2830358303460.5
45Embodiment 3525257214140
46Embodiment 36351008503560.5
Comparative examples
25Comparative example 1330205705270.5
26Comparative example 1430426255280.5
25Comparative example 15405075547101.0
28Comparative example 1630258304481.5

[0077] Effects of the Invention

[0078] The present invention can improve strength of phosphor bronze without sacrificing bending formability and provide high-level mechanical properties required of a copper alloy as terminals and connectors for electronic parts. Furthermore, with high tin phosphor bronze (Cu-10 mass %, Sn-P: CDA52400), the present invention has made it possible to make its way into the filed of high-strength copper alloys, which is the market monopolized by beryllium copper, etc., into which phosphor bronze has been conventionally unable to make its way because of its inferiority in bending formability.

[0079] All publications and patents mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. This application hereby incorporates by reference the disclosure of Japanese Patent Application No. 2002-096387.

[0080] While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifications and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth.