Copper alloy sheet material, method for producing same, and current-carrying component

Abstract

[Problem] To provide a sheet material having excellent strength and electrical conduction property and also having an increased bending workability level in a Cu-Fe-P-based copper alloy. [Solution] A copper alloy sheet material, having a chemical composition containing, in mass%, Fe: 0.05 to 1.10%, P: 0.02 to 0.50%, Mg: 0 to 0.50%, Ni: 0 to 0.80%, Sn: 0 to 0.80%, Zn: 0 to 0.80%, and elements other than Fe, P, Mg, Ni, Sn, Zn, and Cu: 0 to 0.10% in total, with a balance including Cu, in which a crystallite size, as determined using a Halder-Wagner method based on an integral width of a peak in an X-ray diffraction pattern using Cu-Kα radiation on a sheet surface, is 30 nm or less, and a 0.2% proof stress in a direction perpendicular to a rolling direction is 450 N / mm2 or more.

Description

Technical Field

[0001] The present invention relates to a Cu-Fe-P-based copper alloy sheet material suitable for a connector that connects a board to a board (sometimes called "B to B" or "BTB"), and a method for producing the same. The invention also relates to a current-carrying component formed using the copper alloy sheet material.Background Art

[0002] As a material using relatively inexpensive additive elements among copper alloys applied to a current-carrying component such as a connector, there is a Cu-Fe-P-based copper alloy that can utilize strengthening by an Fe-P-based precipitate.

[0003] PTL 1 describes a Cu-Fe-P-based copper alloy material that combines strength, an electrical conduction property, and drawing workability by enhancing the orientation of a {220} plane. It is described that the material is produced by a process in which cold rolling and recrystallization annealing are repeated after hot rolling, and distortion relief annealing is performed after final cold rolling.Citation ListPatent Literature

[0004] PTL 1: JP5467163BSummary of InventionTechnical Problem

[0005] In a connector, conduction between paired pins (current-carrying components) is ensured by fitting the bent portions of both pins together. A board-to-board connector is formed of many pins, and each pin has been subjected to complex bending. When a board-to-board connector is inserted and removed, large stress may be applied to some pins depending on slight misalignment between the boards or the insertion and removal operation method (handling method). For this reason, it is extremely important that the bent portion of each pin is quality controlled in a sound state without cracking. It is also important to have a high strength and a high electrical conduction property.

[0006] In recent years, with the reduction in size and height and the increase in electrical current of a board-to-board connector, a material used therefor is required to combine even higher levels of strength, an electrical conduction property, and bending workability than ever before.

[0007] According to the technique of PTL 1, it is possible to obtain a Cu-Fe-P-based copper alloy sheet material having excellent strength and electrical conduction property. However, since there is generally a trade-off relationship between strength and bending workability, there is still room for improvement in terms of providing excellent bending workability that can meet the recent strict requirement for a board-to-board connector.

[0008] An object of the invention is to provide a sheet material having excellent strength and electrical conduction property and also having an increased bending workability level in a Cu-Fe-P-based copper alloy.Solution to Problem

[0009] In order to achieve the above object, the present description discloses the following invention. [1] A copper alloy sheet material, having a chemical composition containing, in mass%, Fe: 0.05 to 1.10%, P: 0.02 to 0.50%, Mg: 0 to 0.50%, Ni: 0 to 0.80%, Sn: 0 to 0.80%, Zn: 0 to 0.80%, and elements other than Fe, P, Mg, Ni, Sn, Zn, and Cu: 0 to 0.10% in total, with a balance including Cu, in which a crystallite size, as determined using a Halder-Wagner method based on an integral width of a peak in an X-ray diffraction pattern using Cu-Kα radiation on a sheet surface, is 30 nm or less, and a 0.2% proof stress in a direction perpendicular to a rolling direction is 450 N / mm 2< or more. [2] The copper alloy sheet material according to the above [1], in which a number density of precipitate particles having a major axis of 10 to 100 nm is 50 particles / µm 2< or more in an observation plane parallel to a sheet surface. [3] The copper alloy sheet material according to the above [1] or [2], in which an electrical conductivity is 50% IACS or more. [4] The copper alloy sheet material according to any one of the above [1] to [3], in which MBR / t being a ratio of a minimum bending radius MBR without cracking to a sheet thickness t in a 90° L bending test with a bending axis parallel to a rolling direction (B.W.) is 0.7 or less. The copper alloy sheet material according to the above [1] to [4] can be produced by the following method. [5] A method for producing a copper alloy sheet material, including, in the following order: a hot rolling step of subjecting a cast slab having a chemical composition containing, in mass%, Fe: 0.05 to 1.10%, P: 0.02 to 0.50%, Mg: 0 to 0.50%, Ni: 0 to 0.80%, Sn: 0 to 0.80%, Zn: 0 to 0.80%, and elements other than Fe, P, Mg, Ni, Sn, Zn, and Cu: 0 to 0.10% in total, with a balance including Cu to rolling at a rolling reduction rate of 70% or more in a temperature range of 950°C or lower and 650°C or higher, and then rolling at a rolling reduction rate of 60% or more in a temperature range of lower than 650°C and 350°C or higher; an intermediate cold rolling step of performing cold rolling at a rolling reduction rate of 30% or more; an intermediate heat treatment step of subjecting the material obtained in the intermediate cold rolling step to a heat treatment of holding the material at a temperature of 400°C or higher and 700°C or lower for 1 hour or more; a finish cold rolling step of subjecting the material obtained in the intermediate heat treatment step to cold rolling at a rolling reduction rate of 80% or more; and a finish heat treatment step of subjecting the material obtained in the finish cold rolling step to a heat treatment of heating the material in a temperature range of 180°C or higher and 500°C or lower. [6] The method for producing a copper alloy sheet material according to the above [5], in which in the finish heat treatment step, a material having a crystallite size, as determined using a Halder-Wagner method based on an integral width of a peak in an X-ray diffraction pattern using Cu-Kα radiation on a sheet surface, of 30 nm or less is obtained. Further, the following invention is provided. [7] A current-carrying component formed using the copper alloy sheet material according to any one of the above [1] to [4].

[0010] In the present description, the notation "n1 to n2" indicating a numerical range means "n1 or more and n2 or less". Here, n1 and n2 are numerical values satisfying n1 < n2. The "sheet material" means a sheet-shaped metal material that is formed by utilizing the malleability of a metal. A thin sheet-shaped metal material is sometimes called "foil", and such a "foil" is also included in the "sheet material" as used herein. A long sheet-shaped metal material wound into a coil shape is also included in the "sheet material". In the present description, the thickness of the sheet-shaped metal material is referred to as "sheet thickness". The "sheet surface" is a surface perpendicular to the sheet thickness direction of a sheet material. The "sheet surface" is sometimes called "rolled surface". The "major axis" of a particle is defined as the diameter of the smallest circle surrounding the particle. The "number density of precipitate particles having a major axis of 10 to 100 nm" can be determined as follows.[Method for Determining Number Density of Precipitate Particles]

[0011] An observation plane obtained by electrolytically polishing a sheet surface under the following electrolytic polishing conditions, and then performing ultrasonic cleaning in ethanol for 20 minutes using an ultrasonic cleaner is observed using an FE-SEM (field emission scanning electron microscope) at an acceleration voltage of 15 kV and a magnification of 100,000 times, and an observation field in which a part or the whole of a particle having a major axis of 1.0 µm or more is not included in the visual field is randomly set. In the observation field, the number of precipitate particles having a major axis of 10 to 100 nm among particles whose entire particle outline is seen is counted. This operation is performed for a plurality of observation fields with no overlapping regions so that the total observation area is 10 to 100 µm 2< in total, and a value obtained by dividing the total number obtained by the counting in all observed visual fields by the total area of the observation fields is defined as the number density of precipitate particles (particles / µm 2< ).(Electrolytic Polishing Conditions)

[0012] · Electrolytic solution: a solution obtained by mixing distilled water, phosphoric acid, ethanol, and 2-propanol at a volume ratio of 10:5:5:1 · Liquid temperature: 20°C · Voltage: 15 V · Electrolysis time: 20 seconds

[0013] The rolling reduction rate in a certain step is determined by the following formula (1). t 0 : a sheet thickness before rolling in that step (mm) t 1 : a sheet thickness after rolling in that step (mm) Advantageous Effects of Invention

[0014] According to the invention, a sheet material that combines high levels of strength, an electrical conduction property, and bending workability in a Cu-Fe-P-based copper alloy could be achieved. This sheet material uses relatively inexpensive additive elements and can be produced by steps that do not require a solution treatment or repeated cold rolling and recrystallization annealing, and therefore it becomes advantageous also in the production cost as compared with the same type of copper alloy-based or other types of copper alloy-based high-strength sheet materials. The invention particularly contributes to the improvement of the performance and the reduction in the cost of a board-to-board connector which is becoming increasingly miniaturized.Brief Description of Drawings

[0015] [FIG. 1] FIG. 1 is a laser micrograph of an outer surface of a bent portion subjected to a 90° L bending test in B.W. with R / t of about 0.6 with respect to a sheet material sample (intermediate product) after finish cold rolling at a mid-production stage of Inventive Example No. 2. [FIG. 2] FIG. 2 is a laser micrograph of an outer surface of a bent portion subjected to a 90° L bending test in B.W. with R / t of about 0.6 with respect to a sheet material sample (finished product) after a finish heat treatment obtained in Inventive Example No. 2. Description of Embodiments[Chemical Composition]

[0016] The invention is directed to a Cu-Fe-P-based copper alloy. Hereinafter, the symbol "%" regarding the alloy components means "mass%" unless otherwise specified.

[0017] Fe (iron) forms a compound with P and precipitates finely in a matrix (a metal base of a copper alloy) to contribute to the improvement of the strength. In order to fully exhibit this effect, an Fe content of 0.05% or more is ensured. Excessive incorporation of Fe causes a decrease in electrical conductivity, and therefore the Fe content is set in the range of 1.10% or less. The Fe content is more preferably 0.90% or less, and still more preferably 0.50% or less, and may be set to 0.30% or less.

[0018] P (phosphorus) generally contributes as a deoxidizer for a copper alloy, but in the invention, P forms a fine precipitate of an Fe-P-based compound or even a Mg-P-based compound to contribute to the improvement of the strength. In order to fully exhibit this effect, a P content of 0.02% or more is ensured. The P content is more preferably 0.03% or more, and still more preferably 0.05% or more. When the P content increases, hot cracking becomes more likely to occur, and therefore the P content is set in the range of 0.50% or less. The P content is more preferably 0.30% or less, and may be controlled to 0.15% or less.

[0019] In the Cu-Fe-P-based copper alloy, one or more types of Mg (magnesium), Ni (nickel), Sn (tin), and Zn (zinc) can be contained as needed.

[0020] Mg forms a compound with P and contributes to the improvement of the strength in the same manner as Fe. When Mg is contained, it is more effective to set the content to 0.03% or more. When the Mg content increases, inclusion of Mg oxide is likely to occur during hot rolling, and therefore the Mg content is set in the range of 0.50% or less. The Mg content is more preferably 0.30% or less, and still more preferably 0.20% or less. Further, the Mg content is preferably set so that the total content of Fe and Mg is 1.10% or less. The (Fe + Mg) / P ratio, which represents the mass ratio of the total content of Fe and Mg to the P content, is preferably in the range of 0.4 to 13.0, and more preferably in the range of 0.5 to 12.5.

[0021] Ni, Sn, and Zn are solid-dissolved in a matrix and contribute to the improvement of the heat resistance. When one or more types of these elements are contained, from the viewpoint of maintaining a high electrical conduction property, the content of each of Ni, Sn, and Zn is permitted up to 0.80%, and the content of each element is more preferably set in the range of 0.50% or less, and may be controlled in the range of 0.30% or less, respectively. When one or more types of Ni, Sn, and Zn are contained, it is effective to set the content of each of these elements to be contained to 0.001% or more, and more effective to set the content to 0.002% or more.

[0022] The other elements to be contained are permitted to the extent that the object of the invention (to combine high levels of strength, an electrical conduction property, and bending workability) is not impaired. Specifically, the total content of elements other than Fe, P, Mg, Ni, Sn, Zn, and Cu (copper) may be controlled to 0.10% or less. For example, depending on the application, one or more types of of Al (aluminum), B (boron), Co (cobalt), Cr (chromium), Mn (manganese), Pb (lead), S (sulfur), Si (silicon), Te (tellurium), Ti (titanium), Zr (zirconium), and the like can be contained so that the total content of these elements is 0.10% or less. In addition, for example, when one or more types of Al, B, Co, Cr, Mn, Pb, S, Si, Te, Ti, and Zr are contained, examples of the content of each of these elements to be contained can include the range of 0.001% or more.

[0023] One aspect of an alloy composition when the total content of elements other than Fe, P, Mg, Ni, Sn, Zn, and Cu is 0.10% or less can be exemplified by "a chemical composition containing, in mass%, Fe: 0.05 to 1.10%, P: 0.02 to 0.50%, Mg: 0 to 0.50%, Ni: 0 to 0.80%, Sn: 0 to 0.80%, Zn: 0 to 0.80%, and Al, B, Co, Cr, Mn, Pb, S, Si, Te, Ti, and Zr: 0 to 0.10% in total, with a balance including Cu and unavoidable impurities". In this case, the unavoidable impurities refer to elements that are unavoidably mixed in production and refer to those other than the elements listed above.[Crystallite Size]

[0024] The inventors found that by reducing the crystallite size, the bending workability can be significantly improved while maintaining a high strength and a high electrical conduction property. Specifically, it is extremely effective that the crystallite size, as determined using a Halder-Wagner method based on an integral width of a peak in an X-ray diffraction pattern using Cu-Kα radiation on a sheet surface, is 30 nm or less, and more preferably 25 nm or less. The lower limit of the crystallite size is not particularly specified, and according to previous studies, it is considered that the crystallite size may be adjusted, for example, in the range of 10 to 30 nm, and the crystallite size may be controlled in the range of 15 to 25 nm.

[0025] The Halder-Wagner method is a method in which, based on an integral width β of each of a plurality of diffraction peaks in an X-ray diffraction pattern, plotting is performed on a coordinate with β / (tanθ × sinθ) on the horizontal axis and (β / tanθ) 2< on the vertical axis, and an approximate straight line of the following formula (2) is drawn for the plots, and the crystallite size D is determined from the slope Kλ / D of the straight line. β / tanθ 2 = Kλ / D × β / tanθ × sinθ + 16 ε 2

[0026] Here, β denotes an integral width of a diffraction peak, θ denotes a Bragg angle of the diffraction peak, K denotes a Scherrer constant, λ denotes an X-ray wavelength (nm), D denotes a crystallite size (nm), and ε denotes a lattice distortion.

[0027] Here, the integral width β is measured for four diffraction peaks derived from each of the crystal planes (111), (200), (220), and (311) with a diffraction angle 2θ in the range of 30 to 150°, and the Halder-Wagner method is applied.[Number Density of Precipitate Particles]

[0028] Precipitate particles having a major axis of 10 to 100 nm contribute to the improvement of the strength of a copper alloy sheet material. The number density of the precipitate particles having a major axis of 10 to 100 nm is preferably 50 particles / µm 2< or more. The upper limit of the number density is not particularly limited, and the number density is usually 200 particles / µm 2< or less, and may be controlled to 150 particles / µm 2< or less.[0.2% Proof Stress]

[0029] In order to meet the needs for miniaturization and thinning of a current-carrying component, it is important to maintain the strength level high. In consideration of the application to a board-to-board connector, the 0.2% proof stress in a direction perpendicular to a rolling direction (TD) of the copper alloy sheet material is desirably 450 N / mm 2< or more, and more desirably 500 N / mm 2< or more. It is also possible to adjust the 0.2% proof stress to 550 N / mm 2< or more. The 0.2% proof stress of the copper alloy sheet material to which the invention is directed may be adjusted in the range of usually 900 N / mm 2< or less, and may be controlled to 700 N / mm 2< or less.[Electrical Conductivity]

[0030] In consideration of the application to a current-carrying component such as a connector, the electrical conductivity of the copper alloy sheet material is desirably 50% IACS or more, and more desirably 65% IACS or more. It is also possible to adjust the electrical conductivity to 70% IACS or more. In the copper alloy sheet material having the above-mentioned composition range, the electrical conductivity is usually 90% IACS or less, and may be controlled to 85% IACS or less.[Bending Workability]

[0031] In consideration of the application to a board-to-board connector to be subjected to complex bending, MBR / t being a ratio of a minimum bending radius MBR without cracking to a sheet thickness t in a 90° L bending test with a bending axis parallel to the rolling direction (B.W.) of the copper alloy sheet material is desirably 0.7 or less, and more desirably 0.5 or less. According to the production method described later, it is also possible to adjust the above MBR / t to an extremely excellent bending workability level for a Cu-Fe-P-based copper alloy, such as 0.3 or less.[Production Method]

[0032] The copper alloy sheet material described above can be obtained, for example, by the following production steps. Melting and casting → hot rolling → intermediate cold rolling → an intermediate heat treatment → finish cold rolling → a finish heat treatment

[0033] Although the description is omitted in the above-mentioned steps, surface grinding is performed as needed after hot rolling, and after each heat treatment, pickling, polishing, or further degreasing is performed as needed. Hereinafter, the respective steps will be described.[Melting and Casting]

[0034] A copper alloy having the above-mentioned chemical composition is melted to obtain a cast slab. As a casting method, a known method such as a semi-continuous casting method or a continuous casting method can be applied. An ingot (cast ingot) obtained by an ingot making method is also included in the "cast slab" as used herein.[Hot Rolling]

[0035] The cast slab is heated and then subjected to hot rolling. The heating temperature of the cast slab is preferably set to 850 to 1,000°C. The holding time in the above-mentioned temperature range is preferably set to 0.3 hours or more, and more preferably set to 0.5 to 10 hours. This heating and holding allows homogenization of the cast structure (relaxation of solidification segregation) to proceed and also allows solid dissolution of a coarse Fe-P-based compound or a Mg-P-based compound to proceed.

[0036] The heated cast slab is taken out from the furnace and hot rolling is started. The hot rolling is performed according to a pass schedule in which hot rolling at a rolling reduction rate of 70% or more is performed in a temperature range of 950°C or lower and 650°C or higher, and thereafter hot rolling at a rolling reduction rate of 60% or more is performed in a temperature range of lower than 650°C and 350°C or higher. The rolling temperature at each rolling pass can be monitored based on the surface temperature of the material immediately after the material comes out from between the work rolls of a hot rolling mill. The clause "hot rolling at a rolling reduction rate of 70% or more is performed in a temperature range of 950°C or lower and 650°C or higher" means that the rolling reduction rate represented by [(h 0 - h 1 ) / h 0 ] × 100 (%) when the sheet thickness (cast slab thickness) before the start of the first rolling pass in which the rolling temperature is 950°C or lower is denoted by h 0 (mm) and the sheet thickness after the completion of the final rolling pass in which the rolling temperature is 650°C or higher is denoted by h 1 (mm) is 70% or more. Further, the clause "hot rolling at a rolling reduction rate of 60% or more is performed in a temperature range of lower than 650°C and 350°C or higher" means that the rolling reduction rate represented by [(h 1 - h 2 ) / h 1 ] × 100 (%) when the sheet thickness before the start of the first rolling pass in which the rolling temperature is lower than 650°C is denoted by h 1 (mm) and the sheet thickness after the completion of the final rolling pass in which the rolling temperature is 350°C or higher is denoted by h 2 (mm) is 60% or more.

[0037] In a temperature range of 950°C or lower and 650°C or higher, dynamic recrystallization is likely to occur. In order to obtain a structure formed of fine and highly uniform crystal grains from a coarse and non-uniform cast structure, it is extremely effective to set the rolling reduction rate in the temperature range of 950°C or lower and 650°C or higher to 70% or more, and even more effective to set the rolling reduction rate to 80% or more. The rolling reduction rate in the temperature range of 950°C or lower and 650°C or higher may be adjusted in the range of, for example, 92% or less. On the other hand, in the temperature range of lower than 650°C and 350°C or higher, an Fe-P-based compound or a Mg-P-based compound is likely to precipitate. In order to generate many precipitation nuclei of an Fe-P-based compound or a Mg-P-based compound, it is extremely effective to set the rolling reduction rate in the temperature range of lower than 650°C and 350°C or higher to 60% or more. The rolling reduction rate in the temperature range of lower than 650°C and 350°C or higher may be set in the range of, for example, 85% or less, and may also be set in the range of 75% or less. By bringing the material (hot-rolled sheet) after completion of hot rolling into a structure state in which a large amount of precipitation nuclei of the above-mentioned compound or ultrafine precipitates derived therefrom are present, in the intermediate heat treatment step described below, which is performed without going through a solution treatment step, it becomes possible to quickly and sufficiently generate fine precipitates of an Fe-P-based compound or a Mg-P-based compound. The sheet thickness after hot rolling may be adjusted, for example, in the range of 5 to 20 mm depending on the final target sheet thickness.[Intermediate Cold Rolling]

[0038] The material after hot rolling is subjected to cold rolling at a rolling reduction rate of 30% or more, more preferably 35% or more, and still more preferably 55% or more. The upper limit of the cold rolling reduction rate can be set according to the target sheet thickness and the milling power of a cold rolling mill. Usually, the rolling reduction rate may be set to 95% or less, and may be set in the range of 85% or less. This intermediate cold rolling may be performed on a material having a sheet thickness reduced by performing cold rolling and annealing one or more times as needed to the extent that the structure state in which a large amount of precipitation nuclei of an Fe-P-based compound or a Mg-P-based compound formed by hot rolling or ultrafine precipitates derived therefrom are contained is maintained.[Intermediate Heat Treatment]

[0039] The material obtained by the intermediate cold rolling is subjected to a heat treatment of holding the material at a temperature of 400°C or higher and 700°C or lower for 1 hour or more. A large amount of precipitation nuclei of an Fe-P-based compound or a Mg-P-based compound or ultrafine precipitates derived therefrom are formed by the above-mentioned hot rolling, and cold working distortion is added by the above-mentioned intermediate cold rolling, and therefore precipitates formed of an Fe-P-based compound or a Mg-P-based compound can be quickly and abundantly formed by heating and holding the material in a temperature range of 400°C or higher and 700°C or lower. Specifically, the density of precipitates having a particle diameter of 10 to 100 nm can be adjusted to 50 particles / µm 2< or more. In addition, a fine and highly uniform recrystallized structure can be obtained. When the highest reached temperature of the material exceeds 700°C, the recrystallized grains may become coarse. The upper limit of the holding time at 400°C or higher and 700°C or lower is not particularly specified, and it is usually sufficient to perform the step within 24 hours.[Finish Cold Rolling]

[0040] The material obtained by the intermediate cold rolling is subjected to cold rolling at a rolling reduction rate of 80% or more to adjust the final sheet thickness and further improve the strength. By setting the rolling reduction rate to 80% or more, a large amount of dislocations can be introduced, which is advantageous for obtaining a structure with a small crystallite size in the finish heat treatment described below. It is more effective to set the rolling reduction rate to 90% or more, and still more effective to set the rolling reduction rate to 95% or more. The upper limit of the rolling reduction rate may be set in the range of, for example, 99% or less depending on the milling power.[Finish Heat Treatment]

[0041] The material obtained by the finish cold rolling is subjected to a heat treatment of heating the material in the temperature range of 180°C or higher and 500°C or lower. Since cold working distortion is introduced by the finish cold rolling, even if the time of holding the material in the temperature range of 180°C or higher and 500°C or lower is short, for example, about a few seconds, reduction in the crystallite size by rearrangement of dislocations can be made to occur. As specific heat treatment conditions, the above-mentioned optimum conditions under which a material having a crystallite size of 30 nm or less can be obtained may be applied according to a heat treatment furnace. However, the highest reached temperature is set in the range of 180°C or higher and 500°C or lower. As the heat treatment furnace, either a continuous heat treatment furnace or a batch-type heat treatment furnace may be used. In the case of a continuous heat treatment furnace, the time during which the material's temperature is 180°C or higher and 500°C or lower (hereinafter referred to as "heat treatment time") is easily set in the range of, for example, 3 to 120 seconds. In the case of a batch-type heat treatment furnace, the heat treatment time is easily set in the range of, for example, 10 minutes or more. The upper limit of the heat treatment time is not particularly specified, and can be set in the range of, for example, 5 hours or less.

[0042] The mechanism for being able to obtain a structure state in which the crystallite size is small by the finish heat treatment has not been fully elucidated, but it is presumed that a large amount of precipitates having a particle diameter of 10 to 100 nm are formed at a density of 50 particles / µm 2< or more by the intermediate heat treatment, and a large amount of dislocations are introduced by the finish cold rolling, so that when heating is performed in the temperature range of 180 to 500°C, a pinning effect is exhibited by the finely dispersed precipitates, and rearrangement of dislocations occurs in a form advantageous to miniaturization of the crystallite size. When the heating temperature is 180°C or higher, it is thought that rearrangement of dislocations can be caused, and as a result, the crystallite size can be miniaturized. It is thought that by controlling the highest reached temperature of the material to 500°C or lower, the dislocations introduced by the finish cold rolling can be left sufficiently, and as a result, softening can be prevented.

[0043] In this manner, a Cu-Fe-P-based copper alloy sheet material having excellent strength, electrical conduction property, and bending workability can be obtained. The sheet thickness of the sheet material can be set, for example, in the range of 0.02 to 2.0 mm, preferably 0.04 to 0.8 mm. It is possible to produce a current-carrying component such as a connector, for example, by punching or bending using this Cu-Fe-P-based copper alloy sheet material as a material.Examples

[0044] Copper alloys having a chemical composition shown in Table 1 was melted and cast slabs having a thickness of 215 mm, a width of about 500 mm, and a length of about 5,500 mm were obtained. Samples collected from the cast slabs were quantitatively analyzed using the method shown below. As a result, it was found that in all examples, the requirement of "elements other than Fe, P, Mg, Ni, Sn, Zn, and Cu: 0 to 0.10 mass% in total" was satisfied.(Elemental Analysis Method)

[0045] O (oxygen) and N (nitrogen) were quantified using an oxygen / nitrogen / hydrogen analyzer (ONH-836, manufactured by LECO Corporation), H (hydrogen) was quantified using a hydrogen analyzer (EMGA-921, manufactured by Horiba, Ltd.), C (carbon) and S (sulfur) were quantified using a carbon / sulfur analyzer (model: CS844, manufactured by LECO Corporation), elements in periods 2 to 6 (excluding C, N, O, elements in group XVII, elements in group XVIII, Tc (technetium), Po (polonium), and Pm (promethium)) were quantified using ICP-MS (7900, manufactured by Agilent Technologies, Inc.), and F (fluorine), Cl (chlorine), and Br (bromine) were quantified using a combustion ion chromatography system (DIONEX ICS-1600, manufactured by Thermo Fisher Scientific, Inc.). These measurements enable quantification of substantially all elements that may be contained in the copper alloy.

[0046] The obtained cast slabs were held at 950°C for 4 hours, taken out from the furnace, and then subjected to hot rolling. The rolling temperature at each rolling pass was recorded by monitoring the material surface temperature at the work roll exit side of the hot rolling mill. With the exception of some examples (Comparative Examples No. 33 and 39), the pass schedule was set so that the rolling reduction rate at a rolling temperature of 950°C or lower and 650°C or higher was 87%, and the rolling reduction rate at a rolling temperature of lower than 650°C and 350°C or higher was 63 to 68%. In No. 39, the pass schedule was set so that the rolling reduction rate at a rolling temperature of 950°C or lower and 650°C or higher was 87%, and the rolling reduction rate at a rolling temperature of lower than 650°C and 350°C or higher was 50%. The total rolling reduction rate thereof was 95.1 to 95.8%, and in all examples, the rolling temperature of the final pass was 350°C or higher. In this manner, hot-rolled sheets having a sheet thickness of 9.5 to 11.0 mm were obtained. In No. 33, cracking occurred in the material during hot rolling, and therefore the steps thereafter were stopped.

[0047] With the exception of some examples (Comparative Example No. 35), the surface oxide film of the obtained hot-rolled sheet was removed by mechanical polishing (surface grinding), and then cold rolling was performed at a rolling reduction rate of about 67 to 98% (intermediate cold rolling step). In No. 35, there were many inclusions of Mg oxide in the hot-rolled sheet, and therefore proceeding to the step after hot rolling was stopped.

[0048] The material after the cold rolling was subjected to a heat treatment of holding the material at a holding temperature set in the range of 500 to 600°C for 5 to 9 hours using a batch-type heat treatment furnace (intermediate heat treatment step).

[0049] Subsequently, with the exception of some examples (Comparative Example No. 41), cold rolling was performed at a rolling reduction rate of about 87 to 98% so that the sheet thickness was 0.06 to 0.08 mm (finish cold rolling step). In No. 41, cold rolling was performed at a rolling reduction rate of about 60% so that the sheet thickness was 0.10 mm.

[0050] Subsequently, with the exception of some examples (Comparative Example No. 40), a heat treatment was performed in a continuous heat treatment furnace or a batch-type heat treatment furnace under conditions that the highest reached temperature was 200 to 430°C and a time (heat treatment time) required for the material temperature to reach 180°C or higher and the highest reached temperature or lower was 13 seconds to 30 minutes (final heat treatment step). In No. 40, this heat treatment was omitted.

[0051] In this manner, test materials having a final sheet thickness of 0.06 to 0.10 mm were obtained. The production conditions are shown in Table 2. The obtained test materials were subjected to the following studies.(Number Density of Precipitate Particles)

[0052] The number density (particles / µm 2< ) of precipitate particles having a major axis of 10 to 100 nm was determined according to the above-mentioned "Method for Determining Number Density of Precipitate Particles". As an electrolytic polishing apparatus, ElectroMet 4 manufactured by Buehler Ltd. was used, as an ultrasonic cleaner, BRANSONIC M2800-J was used, and as FE-SEM, JSM-7200F manufactured by JEOL Ltd. was used.(Crystallite Size)

[0053] With respect to the sheet surface of the test material, an X-ray diffraction pattern was measured using an X-ray diffractometer (RINT-2000, manufactured by Rigaku Corporation) by a 2θ / θ method under conditions of CuKα radiation (λ = 0.1542 nm), a tube voltage of 40 kV, and a tube current of 40 mA. An analysis was performed using an analytical software (PDXL 2, manufactured by Rigaku Corporation) without separating Kα1 radiation and Kα2 radiation, and the integral width β was measured for four diffraction peaks derived from each of the crystal planes (111), (200), (220), and (311) with 2θ in the range of 30 to 150°, plotting was performed on a coordinate with β / (tanθ × sinθ) on the horizontal axis and (β / tanθ) 2< on the vertical axis, and each plot was fitted with a straight line to obtain a function (Halder-Wagner formula) represented by the above-mentioned formula (2), and a crystallite size D (nm) was calculated from the slope of the function Kλ / D (K: Scherrer constant, λ: X-ray wavelength, D: crystallite size). Here, 0.94 was adopted as the value of the Scherrer constant K.(0.2% Proof Stress)

[0054] A tensile test piece (JIS No. 5) in a direction perpendicular to a rolling direction (TD) was collected from each test material and subjected to a tensile test in accordance with JIS Z 2241 to measure the 0.2% proof stress. One having a 0.2% proof stress of 450 N / mm 2< or more was determined to be acceptable.(Electrical Conductivity)

[0055] The electrical conductivity was determined in accordance with JIS H 0505. One having an electrical conductivity of 50% IACS or more was determined to be acceptable.(Bending Workability)

[0056] A test piece having a width of 0.3 mm with its longitudinal direction perpendicular to the rolling direction was cut out from the test material, and subjected to a 90° L bending test with the bending axis parallel to the rolling direction (B.W.), and MBR / t being a ratio of a minimum bending radius MBR without cracking to a sheet thickness t was determined. One having an MBR / t of 0.7 or less was determined to be acceptable.

[0057] The results are shown in Table 3.[Table 1]

[0058] Table 1CategoryExample No.Chemical composition (mass%)CuFePMgNiSnZnOthersInventive Example1Balance0.180.07-----2Balance0.210.080.110.0030.0050.002Cr:0.0023Balance0.230.08-0.1510.0680.018Pb:0.01,Mn:0.014Balance0.800.07---Zr:0.01,S:0.0015Balance0.070.06---Co:0.005,Si:0.0086Balance0.180.28---B:0.0027Balance0.180.04---Ti:0.0058Balance0.180.07---Al:0.005,Te:0.001Comparative Example31Balance1.200.07----32Balance0.030.03----33Balance0.180.62----34Balance0.180.01----35Balance0.180.070.80---36Balance0.180.07-1.20--37Balance0.180.07--1.20-38Balance0.200.07---1.24-39Balance0.180.07----40Balance0.210.080.11---41Balance0.210.080.11---Underline: outside the range specified in the invention [Table 2]

[0059] Table 2CategoryExample No.Hot rollingIntermediate cold rollingIntermediate heat treatmentFinish cold rollingFinish heat treatmentFinal sheet thickness (mm)Rolling reduction rate at 950°C or lower and 650°C or higher (%)Rolling reduction rate at lower than 650°C and 350°C or higher (%)Total rolling reduction rate (%)Hot-rolled sheet thickness (mm)Rolling reduction rate (%)Temperature (°C)Time (h)Rolling reduction rate (%)Highest reached temperature (°C)Heat treatment time [*1]Inventive Example1876595.310.57655079743013s0.082876595.310.57655079743013s0.083876395.111.07755059743013s0.084876595.310.56755099843013s0.085876595.310.58955079543013s0.066876895.89.59450098743018s0.087876595.310.57660059720030min0.088876595.310.57655079743013s0.08Comparativ,-Example31876595.310.57655079743013s0.0832876595.310.57655079743013s0.0833(Cracking occurred during hot rolling, and steps were stopped)34876595.310.57655079743013s0.0835876595.310.5(Many inclusions of Mg oxide occurred in hot-rolled sheet, and steps were stopped)36876595.310.57655079743013s0.0837876595.310.57655079743013s0.0838876595.310.57655079743013s0.0839915095.310.57655079743013s0.0840876595.310.576550797(omitted)0.0841876595.310.59855076020024min0.10Underline: outside the range specified in the invention *1: The time during which the material's temperature is 180°C or higher and the highest reached temperature or lower [Table 3]

[0060] Table 3CategoryExample No.Number density of precipitate particles of 10 to 100 nm (particles / µm 2< )Crystallite size (nm)0.2% Proof stress (N / mm 2< )Electrical conductivity (% IACS)B.W. 90° L bending MBR / tInventive Example17321519730.128820562780.136824517770.146924618660.655722511720.267120507640.078221534680.387520521720.1Comparative Example317223584460.5325420421780.033-----343246438420.135-----367222511470.4376824520440.4386625517460.4392653426440.1406735547780.9417328415720.0Underline: outside the range specified in the invention

[0061] All of the Cu-Fe-P-based copper alloy sheet materials of the Inventive Examples had a high number density of precipitate particles, exhibited a structure state in which the crystallite size is small, and combined excellent strength, electrical conduction property, and bending workability.

[0062] On the other hand, in Comparative Examples, the following results were obtained.

[0063] In No. 31, the Fe content was too high, and therefore the electrical conduction property was poor.

[0064] In No. 32, the Fe content was too low, and therefore the strength was low.

[0065] In No. 33, the P content was too high, and therefore cracking occurred during hot rolling.

[0066] In No. 34, the P content was too low, and therefore the number density of precipitate particles was insufficient, resulting in poor strength and electrical conduction property. In addition, it is presumed that the amount of finely dispersed precipitates was small, and therefore the pinning effect was not fully exhibited, and rearrangement of dislocations did not occur sufficiently in a form advantageous to miniaturization of the crystallite size. Note that the material was soft, and therefore the bending workability was good.

[0067] In No. 35, the Mg content was too high, and therefore a hot-rolled sheet with many inclusions of Mg oxide was obtained, and the steps thereafter were stopped.

[0068] In No. 36, the Ni content was too high, and therefore the electrical conduction property was poor.

[0069] In No. 37, the Sn content was too high, and therefore the electrical conduction property was poor.

[0070] In No. 38, the Zn content was too high, and therefore the electrical conduction property was poor.

[0071] In No. 39, the rolling reduction rate in the temperature range of lower than 650°C and 350°C or higher in the hot rolling was low, and therefore the number density of precipitate particles was insufficient in the end, resulting in poor strength and electrical conduction property. Since the dislocation density was low, the miniaturization of the crystallite size was not achieved even if the finish heat treatment was performed. Note that the material was soft, and therefore the bending workability was good.

[0072] In No. 40, the finish heat treatment was omitted, and therefore the miniaturization the crystallite size could not be achieved, and the bending workability was poor.

[0073] In No. 41, the rolling reduction rate in the finish cold rolling was low, and therefore, although the crystallite size was small, the introduction of dislocations was insufficient and the strength level was low.(Test for Verifying Effect of Finish Heat Treatment)

[0074] With respect to a sheet material sample (an intermediate product having a sheet thickness of 0.08 mm) at the time of completing the finish cold rolling of the above No. 2 which is an Inventive Example, and a sheet material sample (a finished product having a sheet thickness of 0.08 mm) obtained by performing a finish heat treatment in which the highest reached temperature was 430°C and the time during which the material's temperature was 180°C or higher and the highest reached temperature or lower was 13 seconds, a test example in which the crystallite size and the 0.2% proof stress were measured by the above-mentioned methods, and a 90° L bending test in B.W. was performed under the conditions: a bending radius R = 0.05 mm, a sheet thickness t = 0.08 mm, and R / t = 0.05 / 0.08 ≈ 0.6, and the properties of both samples were compared is shown.

[0075] The results are shown in Table 4.

[0076] For reference, laser micrographs of the outer surface of a bent portion after the 90° L bending test with R / t ≈ 0.6 with respect to the sheet material samples after the finish cold rolling and after the finish heat treatment are shown in FIG. 1 and FIG. 2, respectively. The breadth of each of these photographs corresponds to about 0.26 mm.[Table 4]

[0077] Table 4Inventive Example No. 2After finish cold rollingAfter finish heat treatmentCrystallite size (nm)35200.2% Proof stress (N / mm 2< )547562Electrical conductivity (% IACS)7878With or without cracking in 90° L bending in B.W. with R / t ≈ 0.6With crackingWithout cracking

[0078] No difference was observed in electrical conduction property before and after the finish heat treatment, but by performing the finish heat treatment, the strength was improved, and also the bending workability was improved. Although it has generally been said that there is a trade-off relationship between strength and bending workability, the reason why both properties could be simultaneously improved by the finish heat treatment is presumed to be due to the effect derived from the fact that rearrangement of dislocations by the finish heat treatment proceeded, and the crystallite size was miniaturized in a state where the precipitates were finely dispersed by the production step according to the invention.

Claims

1. A copper alloy sheet material, having a chemical composition comprising, in mass%, Fe: 0.05 to 1.10%, P: 0.02 to 0.50%, Mg: 0 to 0.50%, Ni: 0 to 0.80%, Sn: 0 to 0.80%, Zn: 0 to 0.80%, and elements other than Fe, P, Mg, Ni, Sn, Zn, and Cu: 0 to 0.10% in total, with a balance including Cu, wherein a crystallite size, as determined using a Halder-Wagner method based on an integral width of a peak in an X-ray diffraction pattern using Cu-Kα radiation on a sheet surface, is 30 nm or less, and a 0.2% proof stress in a direction perpendicular to a rolling direction is 450 N / mm2 or more.

2. The copper alloy sheet material according to claim 1, wherein a number density of precipitate particles having a major axis of 10 to 100 nm is 50 particles / µm2 or more in an observation plane parallel to a sheet surface.

3. The copper alloy sheet material according to claim 1, wherein an electrical conductivity is 50% IACS or more.

4. The copper alloy sheet material according to claim 1, wherein MBR / t being a ratio of a minimum bending radius MBR without cracking to a sheet thickness t in a 90° L bending test with a bending axis parallel to a rolling direction (B.W.) is 0.7 or less.

5. A method for producing a copper alloy sheet material, comprising, in the following order: a hot rolling step of subjecting a cast slab having a chemical composition containing, in mass%, Fe: 0.05 to 1.10%, P: 0.02 to 0.50%, Mg: 0 to 0.50%, Ni: 0 to 0.80%, Sn: 0 to 0.80%, Zn: 0 to 0.80%, and elements other than Fe, P, Mg, Ni, Sn, Zn, and Cu: 0 to 0.10% in total, with a balance including Cu to rolling at a rolling reduction rate of 70% or more in a temperature range of 950°C or lower and 650°C or higher, and then rolling at a rolling reduction rate of 60% or more in a temperature range of lower than 650°C and 350°C or higher; an intermediate cold rolling step of performing cold rolling at a rolling reduction rate of 30% or more; an intermediate heat treatment step of subjecting a material obtained in the intermediate cold rolling step to a heat treatment of holding the material at a temperature of 400°C or higher and 700°C or lower for 1 hour or more; a finish cold rolling step of subjecting a material obtained in the intermediate heat treatment step to cold rolling at a rolling reduction rate of 80% or more; and a finish heat treatment step of subjecting a material obtained in the finish cold rolling step to a heat treatment of heating the material in a temperature range of 180°C or higher and 500°C or lower.

6. The method for producing a copper alloy sheet material according to claim 5, wherein in the finish heat treatment step, a material having a crystallite size, as determined using a Halder-Wagner method based on an integral width of a peak in an X-ray diffraction pattern using Cu-Kα radiation on a sheet surface, of 30 nm or less is obtained.

7. A current-carrying component formed using the copper alloy sheet material according to any one of claims 1 to 4.

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