Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C9/00—Alloys based on copper
  • C22C9/02—Alloys based on copper with tin as the next major constituent

Definitions

• 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.
• 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.
• high-strength copper alloys such as beryllium copper, titanium copper, Corson-based alloys.
• high-strength copper alloys which are relatively new as copper alloys for electronic parts.
• punching formability and bending formability are particularly important.
• 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.
• 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.
• 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.
• the present inventors have improved the above-described press formability drastically by adjusting components, microstructure and manufacturing conditions of a phosphor bronze strip.
• the invention comprises the following preferred Aspects:
• 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.
• 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/mm 2 or less.
• 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.
• 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.
• 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 ⁇ m or less, a standard deviation of the grain size ( ⁇ GS) is 1 ⁇ 3 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.
• mGS mean grain size
• ⁇ GS standard deviation of the grain size
• 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 ⁇ m or less, a standard deviation of the grain size ( ⁇ GS) of variations in the grain size is 1 ⁇ 3 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.
• mGS mean grain size
• ⁇ GS standard deviation of the grain size
• 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 ⁇ m or less and a variation standard deviation ( ⁇ GS) of 2 ⁇ m or less, and then final cold-rolled with a reduction ratio of 10 to 45%.
• mGS mean grain size
• ⁇ GS variation standard deviation
• 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.
• a crack propagates through the shear deformation part, penetrates the sheet and thereby punching is performed.
• the edges of the punch and the die friction strongly with the surface of the material.
• 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.
• 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.
• Mn, Ca, Mg and Al are mixed in as contaminants in the above-described manufacturing process instead of normal additional element of phosphor bronze.
• containing a total of more 50 ppm of these elements prevents the aforementioned Cu 2 S 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.
• 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.
• 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.
• the amount of Zn added is preferably determined to 100 to 1,000 ppm.
• 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 ⁇ m or less, a standard deviation of the grain size ( ⁇ GS) of 1 ⁇ 3 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.
• mGS mean grain size
• ⁇ GS standard deviation of the grain size
• 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.
• 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.
• 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 ⁇ m or less with a standard deviation of grain size ( ⁇ GS) of 1 ⁇ 3 mGS or less.
• mGS mean grain size
• 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.
• 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 ⁇ m 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 ⁇ m or below, the relationship between tensile strength and bending formability is further improved.
• mGS mean grain size
• ⁇ GS standard deviation of grain size
• Phosphor bronze having characteristics under these conditions is provided with press punching formability combined with bending formability.
• This invention relates to the method of manufacturing a high-strength phosphor bronze strip.
• 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.
• the thickness of the material before cold rolling is set to t o
• the thickness of the material after cold rolling is set to t
• the mean grain size (mGS) after annealing is determined to 3 ⁇ m or less and the standard deviation of the grain size ( ⁇ GS), which is determined to 2 ⁇ m or less because it is necessary to control a heating temperature profile during annealing precisely and make a uniform fine grain microstructure.
• the grain size does not show a normal distribution and when the mean grain size (mGS) is 3 ⁇ m and the standard deviation of the grain size ( ⁇ GS) is 2 ⁇ m, 99% or more of individual grain size is mGS+3 ⁇ , that is, 9 ⁇ m or less.
• a mixture of grains of 8 ⁇ m or greater in size in a recrystallized microstructure is not necessarily desirable, and the standard deviation of the grain size is preferably 1.5 ⁇ m or less.
• 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 TS a ⁇ TS o ⁇ X (reduction ratio of final cold-rolling (%)) where TS o (MPa) is tensile strength before stress relief annealing and TS a (MPa) is tensile strength after stress relief annealing.
• Phosphor bronze and nickel silver, etc. maybe subjected to stress relief annealing.
• 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.
• stress relief annealing is performed on a cold rolled material of tensile strength of TS o (MPa) under the condition of TS a ⁇ TS o ⁇ X, where X % is the reduction ratio of final cold-rolling and TS a (MPa) is tensile strength after stress relief annealing.
• this embodiment shows a lower plastic deformation ratio and better press punching formability.
• TABLE 1 Mn+Ca+Mg+Al Total length of Volume ratio of Plastic Composition S content content etching imprints copper sulfide deformation No.
• 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.
• 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.
• 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.
• 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 ( ⁇ GS) 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 ⁇ n 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 ( ⁇ GS) according to the present invention.
• 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.
• this embodiment Compared to comparative examples (conventional materials), this embodiment has better punching formability and bending formability if the strength is the same.
• 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.
• 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.
• TS tensile strength
• Embodiments No. 39, 41, 43and 45and comparative example No. 27 are materials with tin concentration of 8.0 to 8.2 mass %.
• 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.
• Embodiments No. 40, 42, 44 and46, and comparative example No. 28 are materials with tin concentration of 10.0 to 10.2 mass %.
• 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.
• 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.
• TABLE 6 TS reduced Reduction by stress Plastic ratio of final relief deformation r/t before r/t after Embodiment No. before cold rolling annealing TS ratio stress relief stress relief No.
• 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.

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• 2002
  • 2002-03-29 JP JP2002096387A patent/JP2003293056A/ja active Pending
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