JP2005060773A - Special brass and method for increasing strength of the special brass - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an alloy composition of special brass and a method for increasing strength thereof which realize an increase in the strength required to the material for electrical and electronic components such as a connector. <P>SOLUTION: The special brass has a composition comprising, by weight, 18 to 32% zinc, 0.01 to 0.1% phosphorous, 0.6 to 2.5% tin and 0.02 to 0.5% of one or more kinds of metals selected from among iron, nickel and cobalt, and the balance copper with inevitable impurities. In the method for increasing its strength, the special brass is hot-worked, is cold-worked, is heat-treated for distortion removal annealing and precipitation hardening, is further cold-worked, is annealed so as to control the grain size to <3 μm by recrystallization, and is subjected to finish cold working. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an unprecedented high-strength special brass and a method for producing the high-strength special brass. In particular, the high-strength special brass according to the present invention has strength and conductivity suitable as materials for electrical and electronic parts such as connectors and springs.

  Brass is a copper-zinc alloy mainly composed of copper, and is also called brass. The most widespread is an alloy of 30 wt% zinc called 70-30 brass (so-called 7-3 brass), but 60-40 brass (so-called 6) containing 38 wt% to 43 wt% of zinc in a plate or bar. -4 brass) has been widely used.

  In recent years, special brass added with 2 to 3 wt% of lead, tin, iron, nickel, manganese, aluminum, etc. as the third element has been used for the purpose of improving mechanical workability, improving corrosion resistance, and increasing strength. Has come to be.

  Among them, copper alloy strips or wires used for connectors or springs have been required to have particularly high strength because they have become thinner or thinner with the miniaturization of terminals. For example, as disclosed in Non-Patent Document 1 and Non-Patent Document 2, etc., if it is limited to a small and high-density mounting contact material that adopts a cross-sectional contact method such as a fork contact or a crimp terminal, it is generally 700 MPa. A 0.2% proof stress of ˜800 MPa is required, and recently, a 0.2% proof stress of 1000 MPa or more has been required. In the following, documents showing other technical levels are listed.

Journal of Copper Technology Research Vol. 36, No. 1, pp. 21-24 (1997) Journal of Copper Technology Research Vol. 40, No. 1, pp. 22-27 (2001) Copper Products Data Book Japan Copper and Brass Association, page 98 Basics and application of phosphor bronze Nikkan Kogyo Shimbun, pages 81-87 Copper and copper alloys Vol. 41, No. 1, pages 197-203 (2002) Copper and copper alloys Vol. 41, No. 1, pp. 29-34 (2002) JP 2002-88428 A Japanese Patent Publication No.58-21018

  However, brass or phosphor bronze that has been used as a connector material, or phosphor bronze that has been used as a spring material cannot meet the current demand for higher strength. The following is a list of these problems.

  Among them, so-called 7-3 brass, which is representative of brass, is disclosed in Non-Patent Document 3 that the 0.2% proof stress only rises up to 680 MPa even if it is subjected to strong processing with a workability of 90% and work hardening. ing. Moreover, when the plastic deformation is performed with 90% strong processing, the end cracking is severe, and it is not a processing condition that can be adopted industrially. Therefore, it is not wise to adopt the work hardening method to obtain the required mechanical strength for normal brass.

  Phosphor bronze, on the other hand, is known as a high-strength alloy along with beryllium copper among copper alloys, and is widely used as a spring material. In terms of strength, it can clear about 700 MPa with 0.2% proof stress. However, as disclosed in Non-Patent Document 4, the conductivity is as low as about 13%, which is disadvantageous as a material for electronic parts such as contacts.

  Admiralty alloy (C44500) is widely used as a capacitor material, but it is not processed into a strip or wire because it lacks ductility. Furthermore, in recent years, C44250 is disclosed in Non-Patent Document 5 as a new type of this admiralty alloy, but it is still insufficient in terms of increasing the strength.

  Moreover, although it is the copper alloy containing Si, and the thing which precipitated the silicon compound in the crystal | crystallization is disclosed by patent document 1, it is still inadequate in terms of intensity | strength. Furthermore, even the brass containing the Sn component disclosed in Patent Document 2 has a low mechanical strength level because it lacks the tin component. It is unsuitable.

  In view of the above, there has been a demand for inexpensive special brass that achieves the high strength required for materials for electrical and electronic parts such as connectors, and that can survive international price competition.

  Thus, as a result of intensive studies by the inventors of the present invention, the following special brass has been developed. Brass is basically a copper-zinc alloy mainly composed of copper. Therefore, in this invention, the other element added for the purpose of castability, extensibility, and high strength is referred to as the third element, and the alloy is referred to as special brass. Hereinafter, the present invention will be described by being divided into special brass and a strengthening method.

<Special brass according to the present invention>
The special brass according to the present invention is “special brass containing a plurality of third elements, zinc 18 wt% to 32 wt%, phosphorus 0.01 wt% to 0.1 wt%, tin 0.6 wt% to 2.5 wt%. %, And one or more selected from iron, nickel, and cobalt, 0.02 wt% to 0.5 wt%, and the remaining copper and inevitable impurities are special brass.

  First, the zinc content will be described first. Here, the zinc content is 18 wt% to 32 wt%. This zinc amount employs a range of zinc amounts corresponding to three types of brass, four types of brass, and 7-3 brass among practical brasses. Zinc as an alloy element in brass is added to improve castability and workability as an alloy. The range of the amount of zinc adopted here is a range in which the α-solid solution of the face-centered cubic lattice whose crystal structure is rich in the workability of copper and zinc is widely determined as judged from the equilibrium diagram. The special brass according to the present invention is required to have a certain degree of work curability because it is possible to increase the strength at an unprecedented level by applying a strengthening process described later. That is, if the amount of zinc is less than 18 wt%, the work curability necessary for the high-strength treatment cannot be obtained.

  Zinc contributes to an increase in mechanical strength as a special brass and is advantageous in terms of cost because it is inexpensive. However, when the content exceeds 32%, hot workability is achieved by the coexistence of tin described below. May be significantly reduced. Therefore, it is most preferable to adopt a range of 23 wt% to 29 wt% from the viewpoint of ensuring a certain level of mechanical strength and maintaining good hot workability.

  Next, the tin content, which is one of the third elements and is essential in the special brass according to the present invention, will be described. If a person skilled in the art sees the above tin content, it can be understood that the composition of brass containing tin, which is a kind of special brass, is based. If tin is used within a range in which it dissolves in the brass structure, the corrosion resistance is improved and the mechanical strength is improved. The solid solubility limit of tin depends on the zinc content, but the higher the zinc content, the higher the tin content. In general, 7-3 brass can dissolve 1.5 to 2.0 wt% of tin, and 1.0 wt% of tin is called an admiralty alloy having seawater resistance. In the case of 6-4 brass, it is known that 2.5 wt% to 3.0 wt% of solid solution of tin, and 1.0 wt% of tin is called a naval alloy. Therefore, in the present invention, a tin content of 0.6 wt% to 2.5 wt% is employed in relation to the zinc content. If the tin content is less than 0.6 wt%, the corrosion resistance and mechanical strength cannot be improved. On the other hand, when the tin content exceeds 2.5 wt%, tin may not be dissolved, and the mechanical strength starts to deteriorate rather. Moreover, since electrical conductivity falls, so that tin content is high, it is preferable to set it as 2.5 wt%. Furthermore, considering the extremely good hot workability and securing the required electrical conductivity of 20% IACS, it is desirable that the upper limit of tin content is 1.4%. .

  Subsequently, other third elements, such as phosphorus, iron, nickel, and cobalt, will be described. The phosphorus used here adopts a content in the range of 0.01 wt% to 0.1 wt%. And iron, nickel, and cobalt employ | adopt content of the range of 0.02 wt%-0.5 wt% using the 1 type (s) or 2 or more types. In the present invention, the relationship between this phosphorus and the alloy elements of the group of iron, nickel and cobalt plays a very important role.

Phosphorus as an alloy element can be strengthened by coexistence of 10 wt% or less of tin and 0.3 wt% to 1.5 wt% of phosphorus as seen in phosphor bronze for springs. Then, considering the solid solution of phosphorus in the same structure, a small amount of phosphorus dissolves, but as the amount of phosphorus increases, Cu ₃ P, which is a hard and brittle copper phosphide, is generated, and the mechanical strength is reduced. It is not preferable because it deteriorates. That is, in the present invention, the amount of phosphorus necessary for precipitating a phosphide of phosphorus and an alloy element of the group of iron, nickel, and cobalt is secured, and as a range in which a problem that occurs when the amount becomes excessive can be avoided, The content of is determined. In the present invention, when the phosphorus content is less than 0.01 wt%, phosphide formation cannot be performed well in relation to the amount of addition of an alloy element of the iron, nickel, and cobalt group described later, and recrystallized grains Therefore, it cannot be refined and cannot contribute to improvement of mechanical strength. And when phosphorus content exceeds 0.1 wt%, workability will deteriorate and stress corrosion cracking resistance will fall.

  Iron, nickel, and cobalt employ a content in the range of 0.02 wt% to 0.5 wt% using one or more of them. This type of third element has been used in manganese bronze based on 6-4 brass, a representative of high strength brass. Conventionally used are iron, manganese, nickel, aluminum and the like. Among these, iron, manganese, and aluminum refine crystal grains, and in manganese bronze, a fine β layer is deposited to contribute to improvement in mechanical strength and corrosion resistance. Nickel also exhibits the same action, but nickel improves various properties as its content increases, but it is difficult to be an expensive alloy element.

  However, in the special brass according to the present invention, aluminum is excluded from the alloy elements. And what is characteristic is that cobalt can be used as an alloy element. In the special brass according to the present invention, iron, nickel, and cobalt are used to refine the crystal grains and contribute to improvement of mechanical strength and corrosion resistance. These third elements form a fine phosphide with phosphorus, which is an alloy element, and the phosphide is uniformly dispersed in the structure, so that the crystal grains can be made finer.

  Among the above-described iron, nickel, and cobalt, one or more of them can be used. That is, each element has the same effect. And, in the special brass according to the present invention, the phosphide using the iron-based element described here seems to contribute to the refinement of crystal grains by showing the best dispersibility, effectively using the iron-based element. It is preferable to utilize. Therefore, it is preferable to employ a content in the range of 0.02 wt% to 0.5 wt% based on the iron-based alloy element. When the content of these alloy elements is less than 0.02 wt%, a sufficient amount of phosphide cannot be formed, and the effect of refining crystal grains cannot be obtained. On the other hand, when the content of the alloy element exceeds 0.5 wt%, the amount of phosphide dispersed in the structure is excessively increased, and the toughness starts to deteriorate, so that the plastic working performance is deteriorated.

  In addition, since the special brass according to the present invention is brittle and the toughness is impaired when the solid solution amount of the sulfur component is increased, the sulfur component that may be included as an inevitable impurity is desirably 30 ppm or less. is there. Therefore, sufficient consideration should be given to the raw material used in the production of the special brass according to the present invention, and when using the scrap raw material, the incorporation of S should be suppressed as much as possible according to a standard method.

  The special brass described above is provided with performance as a high-strength special brass by the high-strength method described later, while having good conductivity, but in the present invention after high-strength processing Such special brass has the following characteristics.

  In the special brass according to the present invention, since the phosphide is precipitated in an intermediate step, it is easy to obtain a crystal grain refinement effect by processing and heat treatment, and it is easy to adjust the crystal grain size to a desired range. By setting the crystal grain size to a range of less than 3 μm, it is possible to obtain very good workability and to obtain mechanical properties that could not be obtained with conventional special brass.

  In addition, the special brass according to the present invention forms fine phosphides with any of iron, nickel, and cobalt used as alloy elements, and the phosphides are uniformly dispersed in the structure to grow recrystallized grains. Therefore, the crystal grains are made finer.

  When the special brass according to the present invention is specified from the viewpoint of mechanical properties, the processing finish when a tensile test is performed on a sample (hereinafter referred to as “MD sample”) taken in the extending direction after rolling. The 0.2% proof stress can be as high as 760 MPa or higher. Here, “processing finish” means that no heat treatment or the like is performed after the rolling process.

  Furthermore, the special brass according to the present invention has a 0.2% proof stress when subjected to a high strength treatment by rolling under an appropriate heat history, further annealed at a low temperature, and subjected to a tensile test with an MD sample. It can be said that it is a special brass having an extremely high yield strength of 800 MPa or more. Compared to the 0.2% proof stress of the above-described processing, the 0.2% proof stress is improved. In other words, the special brass according to the present invention can be said to be a special brass that can be obtained with extremely efficient crystal grain refinement effects by applying processing under an appropriate thermal history. It can be said that it is a special brass that can easily achieve a crystallization effect.

<Method for strengthening special brass according to the present invention>
Higher strength of brass cannot be achieved simply by the composition of the alloy elements, and in the process of obtaining a product from the ingot, higher mechanical strength is imparted by processing and heat treatment applied to the special brass, Both name and reality become high strength special brass. In order to increase the strength of the special brass described above, it is preferable to employ a method for increasing the strength described below. It should be noted that the special brass described above is obtained by adjusting the amount of alloy elements using a melting casting method, but it is also possible to use a vertical continuous casting method for casting, etc. There is no particular limitation.

  The flow of the high-strength method for special brass according to the present invention is described as follows: “The special brass is hot-worked and then cold-worked, and the strain is removed and the phosphide is precipitated at a temperature of 450 to 550 ° C. Heat treatment for the purpose of, and further cold work, recrystallization annealing at a temperature of 250-320 ℃ so that the grain size of recrystallized grains is less than 3μm, and finish cold work It can be said that the special brass has a high strength. Hereinafter, it demonstrates according to a process.

  First, it starts with hot working a special brass ingot. This hot working is a forming process for turning the ingot into a wire, plate or strip, and the heating temperature during hot working is 900 ° C. or lower. When the said temperature exceeds 900 degreeC, it will become easy to generate | occur | produce a hot crack, More preferably, the temperature of 870 degrees C or less is employ | adopted. Then, after this hot working, it is also useful to chamfer as necessary, and then prevent the occurrence of cracks in the cold working.

  Next, cold working is performed, and this cold working is an operation that can be expected to further deform the product shape and refine the crystal grains by the working. The processing rate of the cold working at this time is desirably 50% or more in order to make the precipitation in the next phosphide precipitation step fine and uniform.

  Next, heat treatment for the purpose of strain removal and precipitation hardening is performed at a temperature of 450 to 550 ° C. The heat treatment at this time employs a temperature range of 450 ° C. to 550 ° C. suitable for precipitation of phosphide. Precipitation of phosphides is unlikely to occur at temperatures below 450 ° C., and if performed at temperatures exceeding 550 ° C., the precipitates of phosphides are coarsened, and not only are distortions removed, but unnecessary crystal grain growth occurs. is there.

  When the heat treatment is completed, cold working is performed again. The cold working at this time is for making the crystal grains plastically deformed and miniaturized, and at the same time, increasing the dislocation density built into the crystal to easily cause recrystallization. Therefore, the processing rate of this cold working is set to 60% or more in order to increase the generation site of recrystallized grains in the next recrystallization process and make the crystal grains after recrystallization fine and uniform. It is desirable. For example, in the case of 7-3 brass having no crystal grains in the crystal structure, if it is attempted to obtain fine crystal grains by the same method, a very high processing rate of 92% is required. Although it is described in 6, in the case of the special brass according to the present invention, strong processing up to that point is not required. As a result, when a rolling process is adopted for the cold working at this stage, it is possible to avoid the occurrence of edge cracking defects.

  When the cold working is completed again, recrystallization annealing is performed. In this recrystallization annealing, a temperature range of 250 ° C. to 320 ° C. is adopted. If the annealing temperature is less than 250 ° C., the annealing time for recrystallization is very long and cannot be used industrially. On the other hand, as the annealing temperature rises, the crystal grain size obtained as recrystallized grains increases, and even when annealing temperature exceeds 320 ° C., the recrystallized grains become 3 μm or more even if annealing is performed for a short time.

  Finally, the finish cold work is performed. This finish cold work is performed in order to give the intended strength to the special brass according to the present invention. The processing rate at this time is determined in consideration of the crystal grain size after recrystallization annealing, and can be said to be a process that can be adjusted according to the crystal grain size after recrystallization annealing. For example, when it can be determined that the recrystallized grains are sufficiently small, since a sufficient mechanical strength is already provided, a processing rate of about 40% is adopted, and the recrystallized grains are considered larger than intended. For example, a processing rate of 70% is adopted. In the case of the method for enhancing the strength of the special brass according to the present invention, the recrystallized grains are suppressed to less than 3 μm in the previous process, and the distortion removal and the refinement of the crystal grains have already been attempted. is there. Therefore, even if a high working rate is adopted in the cold working for the cold working, cracks such as end cracks are hardly generated. With the procedure described above, it is possible to increase the strength of the special brass according to the present invention, and it is particularly suitable as an alloy for connectors.

  In addition, when special ultra brass according to the present invention is used to produce ultra-thin plates and ultra-fine wires while achieving high strength, annealing and cold working may be required in addition to the above steps. However, the conditions used for annealing at this time may be the recrystallization annealing conditions performed between 250 ° C. and 320 ° C. described above.

  When the high-strength special brass subjected to the above-described high-strength method is further strengthened and used as a spring material, it is preferable to further improve the mechanical strength and spring characteristics by performing a low-temperature annealing treatment. This low-temperature annealing treatment employs a temperature range of 150 ° C. to 300 ° C., more preferably 180 ° C. to 250 ° C., as the annealing temperature. Outside the temperature range described here, a sufficient spring characteristic improvement effect cannot be obtained. In addition, when plating treatment is performed for the purpose of rust prevention or the like, annealing treatment may be performed at a temperature of less than 200 ° C. to prevent deterioration of the plating layer, and at a temperature of 200 ° C. or more in other cases. It is desirable.

  The special brass according to the present invention has a remarkable effect of high-strength treatment as compared with conventional tin-containing brass and the like, and has an extremely high 0.2% proof stress. Therefore, the mechanical strength required for miniaturization of electrical and electronic parts such as connectors and the required conductivity are sufficiently satisfied. Moreover, for the special brass according to the present invention, the above-described strengthening method is optimal, and a stable strengthening characteristic can be obtained.

  Hereinafter, examples of the present invention will be shown and compared with comparative examples to explain the enhancement of special brass according to the present invention.

  First, ingots were manufactured by casting special brasses 1 to 4 having an alloy composition shown in Table 1 into a mold having an internal size of 150 mm × 100 mm × 30 mm. The ingot was heated to 850 ° C. and hot-rolled to obtain a 13 mm plate. At the same time, Comparative Examples 1 and 2 are used for comparison using the alloy compositions shown in Table 1.

  When hot rolling was completed, surface polishing was performed, cold rolling with a processing rate of 50% or more was added, and heat treatment was performed at 500 ° C. for 1 hour to precipitate a phosphide in the crystal structure. Then, cold rolling with a processing rate of 70 to 80% was performed, and a recrystallization annealing process was performed. Table 2 shows the recrystallization annealing temperature and the obtained crystal grain size after recrystallization.

  Subsequently, cold rolling was applied as shown in Table 2, and 0.2% yield strength was measured. Table 2 shows the temperature of the low-temperature annealing added as necessary and the measured value of 0.2% proof stress at that time. As will be apparent from the results shown in Table 2, the special brass 1 to the special brass 4 according to the present invention have a high 0.2% yield strength. On the other hand, in the case of the comparative example 1, it turns out that Sn content is low and sufficient 0.2% yield strength cannot be obtained, but it has not been made high-strength. Further, in the case of Comparative Example 2, since the recrystallization temperature is high, the crystal grain after recrystallization becomes as large as 3 μm, and it is considered that the crystal grain refinement effect cannot be obtained and sufficient strength is not obtained. .

  In addition, when the special brass according to the present invention is sampled in a direction perpendicular to the extension direction when cold-rolled (hereinafter referred to as “TD sample”) and subjected to a tensile test, tensile strength and yield strength are obtained. Is higher than that obtained in the parallel direction. For example, as shown in Table 3, there is a large difference between the tensile strength and the 0.2% proof stress between the MD sample and the TD sample in the case of the special brass 1 subjected to low temperature annealing. In addition, the strength of the TD sample is over 1000 MPa. As a brass-based alloy, a tremendous increase in strength has been realized. The electrical conductivity is 23% IACS, which is very good compared to 13% IACS of spring phosphor bronze.

  The special brass according to the present invention described above has a remarkable effect of high-strength treatment, and the 0.2% proof stress is extremely high among conventional special brasses. Therefore, the mechanical strength required for miniaturization of electrical and electronic parts such as connectors and the required conductivity are sufficiently satisfied. Moreover, since an extremely expensive metal is not used in the alloy composition, it can be supplied to the market as an inexpensive special brass while having good conductive properties. Quality can be easily achieved.

  Further, the strengthening method using the special brass according to the present invention is the best strengthening method for the special brass according to the present invention. Moreover, in this high-strength treatment, strengthening by crystal grain refinement by work hardening and recrystallization can be easily obtained without using a special technique.

Claims (7)

Special brass containing a plurality of third elements,
18 wt% to 32 wt% zinc, 0.01 wt% to 0.1 wt% phosphorus, 0.6 wt% to 2.5 wt% tin, and 0.02 wt% to one or more selected from iron, nickel, and cobalt Special brass containing 0.5 wt%, remaining copper and inevitable impurities. The special brass according to claim 1, wherein the crystal grain size is less than 3 µm. The special brass according to claim 1 or 2, wherein a phosphide is precipitated in the crystal structure. The special brass with high strength according to any one of claims 1 to 3, wherein a 0.2% proof stress after processing is 760 MPa or more when a tensile test is performed in the extending direction after rolling. The high strength according to any one of claims 1 to 4, wherein the 0.2% proof stress after low-temperature annealing is 800 MPa or more when subjected to a tensile test in the extending direction after performing a high-strength treatment by a rolling process. Specialized brass. A method for increasing the strength of the special brass according to any one of claims 1 to 5,
Hot working the high-strength special brass, followed by cold working, heat treatment for the purpose of strain relief annealing and phosphide precipitation at a temperature of 450-550 ° C., adding further cold working, 250- A method for enhancing the strength of special brass, characterized in that recrystallization annealing is performed at a temperature of 320 ° C. so that the grain size of the recrystallized grains is less than 3 μm, and finish cold working is performed. A method for enhancing the strength of special brass for a spring material, in which the high strength special brass subjected to the strengthening method according to claim 6 is further subjected to a low temperature annealing treatment to improve mechanical strength and spring characteristics.