JP2005097638A - High-strength copper alloy superior in bending workability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To further improve a strength of a copper-titanium alloy, while respecting the essence of the strengthening mechanism and maintaining the superior characteristics of the alloy. <P>SOLUTION: The high-strength copper alloy superior in bending workability is a copper-base alloy which comprises 2.0-4.0 mass% Ti and 0.01-0.50 mass% one or more third elements among Fe, Co, Ni, Si, Cr, V, Zr, B, and P, and contains a secondary phase particle having the area of 0.01 μm<SP>2</SP>or more when the cross section of the alloy is observed with a microscope, in an amount of 10/μm<SP>2</SP>or less by average particle density. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a copper alloy used for a connector material or the like, and in particular, provides a copper alloy manufacturing technique that simultaneously realizes excellent bending workability and high strength.

A copper alloy containing titanium (hereinafter referred to as “titanium copper”) is used for connector materials and the like. In recent years, as electronic devices have become lighter, thinner and shorter, the need for higher strength and superior bending workability for connector materials is increasing, and various research and development has been carried out on titanium copper. Some conventional copper alloys include Ni and Al added to titanium copper (see, for example, Patent Document 1). Further, there is a titanium copper to which Al and Mg are added (for example, see Patent Document 2). Further, there is a titanium copper to which Sn, Ni, and Co are added (for example, see Patent Document 3). In recent years, a technique for adding Cr, Zr, Ni, and Fe to titanium copper has been proposed (see, for example, Patent Document 4). In addition, a technique related to crystal grain refinement is also disclosed (see, for example, Patent Document 5). Furthermore, a technique for adding Zn, Cr, Zr, Fe, Ni, Sn, In, P, and Si to titanium copper has been proposed (see, for example, Patent Document 6).
When titanium copper forms a supersaturated solid solution by solution treatment and is subjected to low-temperature aging from this state, a modulated structure that is a metastable phase develops and hardens significantly at a certain stage of the development stage. If this develops too much, it will be in a so-called overaging state, and eventually TiCu ₃ which is a stable phase will precipitate, and if this phase increases, it will soften conversely.

In this series of aging processes, a modulation structure exhibiting high strength is a change that can occur from an unstable supersaturated solid solution, and cannot change from a stable phase of TiCu ₃ phase to a metastable phase of a modulation structure. On the other hand, when the solution treatment is insufficient, titanium that has not been solid-solved in the matrix phase remains as deposited as TiCu ₃ . Therefore, in order to maximize the hardening by aging, it is necessary to completely eliminate the TiCu ₃ phase in the solution treatment in the previous step, in other words, it is necessary to completely dissolve titanium in the matrix phase. It is necessary to heat to a temperature at which the solid solubility limit of titanium exceeds the titanium content. For example, when 3% of titanium is contained in copper, in order to completely dissolve titanium, it is necessary to perform a solution treatment by heating to a temperature of 800 ° C. or higher.

Japanese Patent No. 1045416 Japanese Patent No. 1047328 Japanese Patent No. 1456429 JP-A-6-248375 JP 2001-303158 A JP 2002-356726 A

On the other hand, in the high temperature region where titanium is completely dissolved, the crystal grains are likely to become coarser. Therefore, in order to improve the yield strength by refining the crystal grains with the conventional technology, compared with the high temperature region where titanium is completely dissolved. Solution treatment must be performed on the low temperature side. For example, in an alloy containing 3% titanium in copper, the crystal grains are not refined at 800 ° C., so that the crystal grains are refined by solution treatment at 750 to 775 ° C. . For this reason, when the crystal grain of titanium copper is refined by the prior art, the solid solution of titanium is not sufficient, and TiCu ₃ which is a stable phase is precipitated. As described above, TiCu ₃ precipitated at the grain boundary at this time has a drawback that it does not contribute to hardening due to aging in the post-process but also deteriorates bending workability.

  In addition, in the prior art aimed at precipitation hardening by adding a third element group (Fe, Co, Ni, Cr, V, Zr, B or P) to titanium copper, and precipitating a second phase containing those components, If the amount of addition is sufficient to obtain sufficient precipitation hardening, there is a drawback that the formation of the modulation structure is hindered. In addition, since the solution conditions and aging conditions for maximizing the precipitation hardening of these elements are different from the solution conditions and aging conditions for maximizing the strengthening by the modulation structure inherent to titanium copper, The precipitation hardening of the three element group and the development of the modulation structure of titanium-copper could not be sufficiently achieved. Thus, in the prior art, it has been difficult to obtain high strength by fully utilizing the excellent strength characteristics of titanium copper.

The present invention has been made in view of the above requirements, and realizes excellent bending workability by suppressing the precipitation of TiCu ₃ , respects the essence of the strengthening mechanism of titanium copper, and sufficiently exhibits its excellent characteristics. The purpose of this is to further improve the strength.

As a result of intensive studies aimed at improving the bending workability with the strength of the copper alloy, the inventors have focused on the existence density of second phase particles having a specific size or more present in the crystal grains, and have completed the present invention. did.
That is, the present invention provides (1) a copper-based alloy containing 2.0 to 4.0% by mass of Ti, from among Fe, Co, Ni, Si, Cr, V, Zr, B, and P as the third element. 1st type or 2 types or more containing 0.01-0.50 mass%, an average crystal grain diameter is 1.0-10.0 micrometers, and the ^2nd more than area | region 0.01 micrometer ² observed by cross-sectional microscopy High-strength copper alloy excellent in bending workability, characterized in that the average particle density of phase particles is 10 particles / μm ² or less,
(2) In a copper-based alloy containing 2.0 to 4.0% by mass of Ti, one or two of Fe, Co, Ni, Si, Cr, V, Zr, B, and P as the third element A second phase containing 0.01 to 0.50 mass% of the above, having an average crystal grain size of 1.0 to 10.0 μm, and an area of 0.01 μm ² or more observed in the crystal grains by cross-sectional microscopy A high-strength copper alloy excellent in bending workability, characterized in that the proportion of crystal grains having a particle density of 10 particles / μm ² or less is 70% or more of the entire crystal grains,
It is.

  According to the present invention, excellent bendability is achieved by optimizing the content of Ti, optimizing the content of the third element group, and optimizing the generation of second phase particles existing at the grain boundaries. And the achievement of strength improvement can be realized at a high level at the same time. Therefore, the present invention is promising in that a copper alloy suitable for a connector material or the like can be manufactured.

Hereinafter, the reasons for limitation of the present invention will be described.
In the present invention, Ti is set to 2.0 to 4.0% by mass. However, when Ti is less than 2.0% by mass, sufficient strength cannot be obtained. Conversely, when Ti exceeds 4.0% by mass, precipitates are formed. Bending workability deteriorates because it tends to be coarse. The most preferable range of Ti is 2.5 to 3.5% by mass.

  Further, in the present invention, the addition of the third element is specified, but the effect of these elements is that the crystal grains are easily fine even if solution treatment is performed at a temperature at which Ti is sufficiently dissolved by addition of a small amount. It is to become. When these elements are contained in an amount of 0.01% by mass or more, the effect appears. However, if too much is added, the solid solubility limit of Ti is narrowed and coarse second-phase particles are easily precipitated. That is, when too much is added, strength is improved, but bending workability is deteriorated. When the amount exceeds 0.5% by mass, this adverse effect becomes remarkable.

  Furthermore, in the present invention, the refinement of crystal grains is prescribed, but if the average crystal grain size is less than 1.0 μm, the bending workability deteriorates, and if it exceeds 10.0 μm, the predetermined strength cannot be obtained. is there.

  In the present invention, as a necessary condition for obtaining excellent bending workability, the existence density of second phase particles having a specific size or more existing in crystal grains is defined. The second phase particles include foreign inclusions such as furnace materials during melting, reaction products generated during melting, crystallized products generated during solidification, and precipitates formed during annealing. In the alloy system targeted by the present invention, most of the second phase particles as shown in FIG. 1 are precipitates.

When a large number of second phase particles having an area of 0.01 μm ² or more are present as shown in FIG. 1, the continuity of deformation during plastic working is lost, and conversely, cracks are likely to propagate, and in particular bending workability decreases. . That is, a local strain is generated around the second phase particles during the plastic working, which acts like a tear line and facilitates the propagation of cracks. In bending work in which a sudden internal stress change occurs in the thickness direction, stress concentration tends to occur around the coarse non-metallic inclusions on the outer surface, and cracks are generated starting from this, through neighboring second phase particles. Cracks propagate into the plate. Even if an initial crack is generated, if it does not propagate to the inside of the plate, a new surface is generated and the crack is not caused. In bending, the ease of crack propagation affects the ease of cracking rather than the ease of initial cracking.

Among the various factors, the distribution of the second phase particles has the most influence on the bending workability, and the higher the density of the large second phase particles, the easier the crack propagates. Specifically, if the area of the second phase particles is less than 0.01 μm ² , the effect is small no matter how much it is present, but if the area is more than that, it cannot be ignored due to its distribution. That is, the average number of second phase particles having an area of 0.01 μm ² or more in the field of view observed by cross-sectional microscopy exceeds 10 particles / μm ² , and the area is 0 in the observed crystal grains. the average number of .01Myuemu ² or more second phase particles of crack propagation becomes significant in the case of 10 / [mu] m ² more than the crystal grains exceeds 30% of the total grains.

In order to prevent the coarsening of the second phase particles in the crystal grains, it is necessary to increase the temperature rising rate in the solution treatment and to surely heat to a temperature region where the second phase particles are completely dissolved. The longer the heating time at this temperature, the more the generation of coarse second phase particles can be suppressed. However, if the structure before the solution treatment is sufficiently homogeneous, the heating time for the solution treatment may be relatively short. Rather, if the heating time of the solution treatment is too long, the crystal grains are likely to become coarse, which is not preferable.
Furthermore, generation | occurrence | production of coarse 2nd phase particle | grains can be suppressed, so that the cooling rate after solution treatment is quick, the subsequent cold rolling work degree is small, and final aging temperature is low. Until now, the aging treatment was performed before the solution treatment, and fine second phase particles were precipitated, and the effect of suppressing the growth of crystal grains during the solution treatment was expected. As a result, the precipitate is likely to be coarsened, and a large amount of precipitate remains if the solution treatment is not sufficiently performed. When the steel is cold-rolled with a large amount of precipitate remaining and subjected to the final aging treatment, the precipitate further grows. Therefore, it is preferable that the structure after the solution treatment should have no second phase particles as much as possible. Therefore, it is better not to perform the aging treatment before the solution treatment.

The steps will be sequentially described as embodiments of the present invention.
1) Ingot manufacturing process 0.01 to 0.50 mass% of one or more elements selected from Fe, Co, Ni, Si, Cr, V, Zr, B, and P as a third element group is added to an appropriate amount of Cu. After sufficiently holding, 2 to 4% by mass of Ti is added, and casting is performed after Ti is dissolved.
In order to eliminate the undissolved residue in order for the third element group to act effectively, it is necessary to keep it sufficiently, and since Ti is more easily dissolved in Cu than the third element group, it may be added after the third element group is dissolved. .

2) Process after the ingot manufacturing process After this ingot manufacturing process, it is desirable to perform homogenization annealing for 1 hour or more at 950 degreeC or more. This is because the segregation is eliminated and the precipitation of the second phase particles is finely and uniformly dispersed in the solution treatment described later, which is also effective in preventing mixed grains. Thereafter, hot rolling is performed, and cold rolling and annealing are repeated to perform a solution treatment that is one of the basic processes of titanium copper.
When an annealing process is performed in the middle, it is desirable to carry out according to the solution treatment conditions described later. That is, the rate of temperature rise and the rate of cooling should be sufficiently high without TiCu ₃ being precipitated, and the temperature may be 800 ° C. if it is ordinary titanium copper to which the third element group is not added. The titanium copper to which the element group is added preferably has a temperature of 900 ° C. or higher. That is, in the prior art, the temperature, the heating rate, and the cooling rate were strictly managed only in the final solution treatment, but it is important to manage so that the second phase particles do not precipitate even during the annealing process. is there. Furthermore, in cold rolling immediately before the solution treatment, the higher the degree of processing, the more uniform and fine the precipitation of the second phase particles in the solution treatment. In addition, in order to precipitate fine 2nd phase particle | grains before solution treatment, after the above-mentioned cold rolling, aging before solution treatment should not be performed. If this is done, in the final solution treatment, the second phase particles will remain as a stable phase unless sufficient heating time is taken. In the final solution treatment, a fine and homogeneous structure can be obtained by proceeding simultaneously with recrystallization and precipitation of second phase particles from a completely solid solution state.

3) Solution treatment before the final cold rolling process The generation and coarsening of the second phase particles can be suppressed by rapidly heating to a temperature at which Ti is completely dissolved and increasing the cooling rate. Since sufficient solution is achieved by annealing in the upper process, the heating time may be short. Since the second phase particles generated at this point grow with the final aging, the second phase particles at this point are as small as possible and preferably smaller.

4) Final cold rolling work degree / final aging treatment After the solution treatment step, cold rolling and aging treatment are performed. For cold rolling, a working degree of 50% or less is desirable. This is because the higher the degree of processing, the easier the grain boundary precipitation occurs in the next aging treatment. The aging treatment is performed at 300 to 450 ° C. depending on the third element to be added. Although the strength is improved by aging, when the aging is excessive, the second phase particles are coarsened and bending workability is lowered. Preferably, it is 400 degreeC x 1h-400 degreeC x 3h.

Next, examples will be described.
When manufacturing the copper alloy of the present invention example, Ti, which is an active metal, is added as the second component, so a vacuum melting furnace was used for melting. In addition, in order to prevent unexpected side effects due to mixing of impurity elements other than the elements defined in the present invention, raw materials having a relatively high purity were carefully selected and used.

  First, for Examples 1 to 10 and Comparative Examples 11 to 20, Fe, Co, Ni, Si, Cr, V, Zr, B and P were added to Cu in the compositions shown in Table 1, respectively. Ti having the composition shown was added. After sufficient consideration was given to the retention time after the addition so that there was no undissolved residue of the added elements, these were injected into the mold in an Ar atmosphere to produce about 2 kg of ingots.

The ingot was coated with an antioxidant, dried at room temperature for 24 hours, heated at 980 ° C. for 12 hours, and hot-rolled to obtain a plate having a thickness of 10 mm. Next, in order to suppress segregation, after applying an antioxidant again, it was heated at 980 ° C. for 2 hours and cooled with water. The reason for water cooling here is to make the solution as much as possible, and the reason why the antioxidant is applied is that the grain boundary oxidation and the internal oxidation in which the oxygen entering from the surface reacts with the additive element component to become inclusions are performed. This is to prevent as much as possible. Each hot-rolled sheet was cold-rolled to a sheet thickness of 0.2 mm after descaling by pickling and mechanical polishing, respectively. Thereafter, the cold-rolled rolled material is inserted into an annealing furnace capable of rapid heating, and for the present invention, the temperature at which the solid solubility limit of Ti becomes larger than the addition amount at a heating rate of 50 ° C./second or more ( For example, it was heated to 800 ° C. when the addition amount of Ti was 3% by mass, held for 2 minutes, and then cooled with water. At this time, the average crystal grain size (GS) was measured by a cutting method.
Thereafter, pickling, descaling, cold rolling, and aging under the conditions shown in Table 1 in an inert gas atmosphere gave a test piece of the present invention.

Table 1 shows the MBR / t value, which is the ratio of the minimum radius (MBR) to the thickness (t) at which cracks do not occur by performing a W-bending test on the test piece manufactured as an example of the present invention and the test piece prepared as a comparative example. While measuring, 0.2% yield strength was measured and the effectiveness of the invention example was verified.
As for the distribution state of the second phase particles, a field of view of 100 μm × 100 μm is observed with a field emission scanning electron microscope (FE-SEM) and an image processing apparatus attached thereto, and an area existing per unit area of 0.01 μm ² or more. The number of second phase particles (A value) was determined. Similarly, 100 crystal grains are selected at random, and the number density of second phase particles having an area of 0.01 μm ² or more existing in each crystal grain is counted to obtain the number density, which is 10 / μm ^2. The number of crystal grains (B value) as follows was determined. Table 2 shows the A value, B value, crystal grain size (GS), 0.2% yield strength, and MBR / t of the inventive examples and comparative examples.

  As shown in Table 2, in the examples of the present invention, the 0.2% proof stress is 850 MPa or more and the MBR / t value is 1.0 or less. In particular, Example No. In 3 to 10, since Ti is in a preferable range, the 0.2% proof stress is further improved and has a value of 870 MPa or more. No. Nos. 4 to 6 are P in addition to Fe, Co and Ni, respectively. Since Nos. 9 to 10 have B added to V and Zr, the crystal grains are further refined, and a 0.2% yield strength of 880 MPa or more is obtained. Further, it can be seen that those satisfying the A value substantially satisfy the B value. Further, FIG. 2 shows a state in which the density of the second phase particles is suppressed as prescribed, but the number of second phase particles is smaller than that in FIG.

  On the other hand, Comparative Example No. No. 11 has a Ti content of less than 2.0% by mass, so a sufficient 0.2% yield strength is not obtained. Conversely, Comparative Example No. Since No. 12 contains 4.0 mass% or more of Ti, bending workability is deteriorated. Comparative Example No. In No. 13, since the third element defined in the present invention is not added, the crystal grains are not refined and sufficient 0.2% yield strength is not obtained. Further, since the crystal grains are coarsened, the bending workability is also inferior. Conversely, Comparative Example No. In Nos. 14 to 17, since the total value of the third elements exceeds 0.5% by mass, the second phase particles are precipitated more than necessary, and the bending workability is deteriorated. In particular, Comparative Example No. Nos. 16 to 17 are subjected to an aging treatment that is believed to have a conventional effect before the final solution treatment, so that Ti in the parent phase is lost due to precipitation of excessive second-phase particles, so that age hardening ability can be obtained. As a result, sufficient 0.2% yield strength is not obtained.

Comparative Example No. In No. 18, the rate of temperature increase to a temperature at which Ti was completely dissolved by solution treatment was slow, so the amount of the third element added was in an appropriate range, but precipitation of TiCu ₃ particles increased, resulting in aging. Hardening was hindered, and sufficient 0.2% yield strength and bending workability were not obtained. Comparative Example No. In No. 19, since the final cold rolling work degree was too high, precipitation of second phase particles increased in the final aging treatment, and sufficient 0.2% yield strength and bending workability were not obtained. Comparative Example No. No. 20 was overheated for a long time in the final aging treatment, so the second phase particles precipitated too much, and sufficient 0.2% yield strength and bending workability were not obtained.

It is an image which shows the state which the 2nd phase particle precipitated more than regulation. It is an image which shows the state by which the 2nd phase particle density was suppressed as prescribed.

Claims (2)

In a copper base alloy containing 2.0 to 4.0% by mass of Ti, one or more of Fe, Co, Ni, Si, Cr, V, Zr, B, and P is used as the third element. The average particle density of the second phase particles containing 0.01 to 0.50% by mass, having an average crystal grain size of 1.0 to 10.0 μm, and an area of 0.01 μm ² or more as observed by a surface microscope. A high-strength copper alloy excellent in bending workability characterized by being 10 pieces / μm ² or less. In a copper base alloy containing Ti: 2.0 to 4.0% by mass, one or more of Fe, Co, Ni, Si, Cr, V, Zr, B, and P is used as the third element. .01 to 0.50 mass% of the second phase particles having an average crystal grain size of 1.0 to 10.0 μm and an area of 0.01 μm ² or more observed in the crystal grains by cross-sectional microscopy A high-strength copper alloy excellent in bending workability, wherein the proportion of crystal grains having a particle density of 10 particles / μm ² or less is 70% or more of the entire crystal grains.