Copper alloy for sliding members, castings, sliding members and their manufacturing methods

Abstract

To provide a copper alloy for use in a sliding member that contains tin, sulfur, iron and phosphorus as main components, and offers sliding properties equal to or better than that of the prior art even when containing no iron or having a low iron content, or a method for producing a sliding member by casting.SOLUTION: A copper alloy for use in a sliding member according to the present invention contains tin of 3.0-16.0 mass%, inclusive, sulfur of 0.3-1.0 mass%, inclusive, iron of less than 0.3 mass%, and phosphorus of 0.04-0.5 mass%, inclusive, with the remainder consisting of copper and inevitable impurities.SELECTED DRAWING: None

Description

Technical Field

[0001] This invention relates to a copper alloy for sliding members that does not contain lead as a main component and is used for sliding members.

Background Art

[0002] Conventionally used copper alloys contained a certain amount of lead to improve slidability and machinability, and CAC603 etc. were used as sliding members. However, in recent years, due to the RoHS directive and other requirements for environmental consideration, copper alloys with reduced lead usage or no lead have been developed.

[0003] For example, in Patent Document 1, as a copper alloy for sliding members, in an embodiment, it contains 5.14 mass% or more and 15.54 mass% or less of tin, 0.42 mass% or more and 1.04 mass% or less of sulfur, 0.31 mass% or more and 3.43 mass% or less of iron, and 0.012 mass% or more and 0.033 mass% or less of phosphorus, and the balance is copper and unavoidable impurities, a copper alloy for sliding members is described.

[0004] Also, in Patent Document 2, as a copper alloy with improved machinability, a copper alloy strip containing tin, phosphorus, and sulfur, with the balance being copper and unavoidable impurities, in a cross-section (transverse cross-section) perpendicular to the longitudinal direction of the strip, sulfides with an average diameter of 0.1 to 10 μm are dispersed and contained, and the area ratio of the sulfides is 0.1 to 10%, a copper alloy strip is described.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the copper alloy described in Patent Document 1 had a problem in that its sliding properties were insufficient when the iron content was less than specified.

[0007] Furthermore, while Patent Document 2 describes the machinability effect of copper alloys containing tin, sulfur, and phosphorus in addition to iron, it does not describe the sliding properties. Generally, copper alloys that are suitable for cutting and have good machinability are considered unsuitable for sliding applications.

[0008] Furthermore, copper alloys with a high iron content are prone to casting defects, resulting in a high number of defective products when copper alloys are produced by casting.

[0009] Therefore, the present invention aims to provide a copper alloy for sliding members in which the main components are tin, sulfur, iron, and phosphorus, and which has sliding properties equivalent to or better than those of the prior art, even when it does not contain or contains little iron, and to provide a copper alloy for sliding members that has sliding properties and good castability. [Means for solving the problem]

[0010] To solve the above problems, the copper alloy for sliding members according to the present invention is characterized in that, in the first embodiment, it contains 3.0% to 16.0% by mass of tin, 0.3% to 1.0% by mass of sulfur, less than 0.3% by mass of iron, and 0.04% to 0.5% by mass of phosphorus, with the remainder being copper and unavoidable impurities.

[0011] Furthermore, the copper alloy for sliding members according to the present invention can be further limited to a second embodiment which contains 6.0% to 15.0% by mass of tin and 0.005% to less than 0.3% by mass of iron.

[0012] Furthermore, the copper alloy for sliding members according to the present invention can be further limited to a third embodiment which contains 9.0% to 11.0% by mass of tin, 0.5% to 1.0% by mass of sulfur, and 0.005% to less than 0.05% by mass of iron.

[0013] As the present invention, a casting made of a copper alloy for a sliding member according to any one of the first to third embodiments can be selected.

[0014] As the present invention, a sliding member made of a casting made of a copper alloy for a sliding member according to any one of the first to third embodiments can be selected.

[0015] The method for manufacturing a sliding member according to the present invention is characterized in that it is a method for manufacturing a sliding member by melting and casting to obtain a copper alloy component containing 3.0% by mass or more and 16.0% by mass or less of tin, 0.3% by mass or more and 1.0% by mass or less of sulfur, less than 0.07% by mass of iron, and 0.04% by mass or more and 0.5% by mass or less of phosphorus.

[0016] Furthermore, as the method for manufacturing a sliding member according to the present invention, an embodiment containing 6.0% by mass or more and 15.0% by mass or less of tin and 0.005% by mass or more and less than 0.05% by mass of iron can be selected.

Effect of the Invention

[0017] According to the present invention, even if the iron content is reduced, if the phosphorus content is appropriately adjusted, it is possible to have sliding properties equivalent to or better than those of conventional sliding member copper alloys. Also, in the same metal composition, good casting properties can be achieved.

Brief Description of the Drawings

[0018] [Figure 1A] Cross-sectional photograph of the fracture evaluation of Example 9 in the casting property test [Figure 1B] Cross-sectional photograph of the fracture evaluation of Example 10 in the casting property test [Figure 1C] Cross-sectional photograph of the fracture evaluation of Comparative Example 6 in the casting property test

Modes for Carrying Out the Invention

[0019] The copper alloy for a sliding member according to the present invention will be described below. This copper alloy for a sliding member is a copper alloy containing a predetermined amount of tin, sulfur, iron, and phosphorus, with the balance being composed of copper and inevitable impurities.

[0020] The above copper alloy needs to contain 3.0 mass% or more of tin. Tin has the effect of improving the matrix strength of the copper alloy, improving the wear resistance, and maintaining good sliding characteristics. However, if it is less than 3.0 mass%, these effects will become insufficient. On the other hand, the tin content needs to be 16.0 mass% or less. If it exceeds 16.0 mass%, it may significantly wear the mating material and it may not be possible to obtain good sliding characteristics. Furthermore, in order to obtain a copper alloy with a good balance in terms of the properties required for a sliding member, such as strength, elongation, hardness regarding wear resistance, and wear amount, the tin content is preferably 6.0 mass% or more and 15.0 mass% or less, and more preferably 9.0 mass% or more and 11.0 mass% or less.

[0021] The above copper alloy needs to contain 0.3 mass% or more of sulfur. Sulfur reacts with copper, iron, or both to form sulfides. These sulfides have solid lubricity, reduce the friction coefficient, improve conformity, and impart good sliding characteristics in the sliding state. If sulfur is less than 0.3 mass%, these effects cannot be obtained or will be insufficient, and it is preferably 0.5 mass% or more. On the other hand, the sulfur content needs to be 3.0 mass% or less. This is because if it exceeds 3.0 mass%, there is a high risk that sulfur will reduce the strength. Furthermore, in order to exhibit sufficient sliding performance, the sulfur content is preferably 1.0 mass% or less, and more preferably 0.7 mass% or less.

[0022] The above copper alloy must contain less than 0.3% by mass of iron. If the iron content is 0.3% by mass or more, the hardness of the copper alloy will increase too much, increasing the risk of it attacking and wearing down the mating material when used as a sliding member, or reducing the elongation and thus degrading the product's performance. On the other hand, the less iron there is, the worse the wear resistance tends to be. Iron, together with sulfur, forms Fe-S compounds that improve the sliding properties of the copper alloy, so it is better to include iron in order to form the necessary amount of Fe-S compounds to ensure the required sliding properties. Therefore, in order to obtain a copper alloy with a good balance of hardness and sliding properties, the iron content is preferably 0.005% by mass or more and less than 0.3% by mass, and more preferably 0.005% by mass or more and 0.05% by mass or less.

[0023] Furthermore, the above copper alloy must contain less than 0.3% by mass of iron from the viewpoint of castability. This is because if the iron content is 0.3% by mass or more, the likelihood of casting defects in the cast product increases. In addition, to have sufficient castability, it is preferable that the iron content be 0.07% by mass or less.

[0024] The above copper alloy must contain at least 0.04% by mass of phosphorus. Phosphorus has the effect of increasing the overall hardness of the copper alloy by forming a Cu-P compound with copper. In the copper alloy according to this invention, even if the iron content is reduced, sliding properties can be ensured by including phosphorus within the above range. On the other hand, the phosphorus content must be 0.5% by mass or less. If phosphorus is present in amounts exceeding 0.5% by mass, the overall hardness of the copper alloy increases too much, reducing its resistance to seizing.

[0025] The above copper alloy preferably consists of copper and unavoidable impurities other than the elements mentioned above. The lower the content of the elements included as unavoidable impurities, the better, and it is even better if it is below the detection limit. Examples of such elements include molybdenum and nickel.

[0026] Examples of sliding members using the copper alloy of the present invention include rolling bearings, linear bushings with sliding bearings, and cylinder liners. By using the copper alloy according to the present invention in the parts of these sliding members where sliding performance is required, well-balanced sliding performance can be achieved. Suitable manufacturing methods for producing the sliding members according to the present invention include gravity casting, centrifugal casting, and die casting. Castings obtained by any of these casting methods have reduced casting defects as described above, exhibit a good balance of strength, elongation, wear resistance, hardness, and wear amount, and can be suitably used as the above-mentioned sliding members. [Examples]

[0027] (Mechanical properties test) The raw materials, adjusted so that the composition after casting was the mass percentage of each component of the examples and comparative examples listed in Table 1, with the remainder being copper and unavoidable impurities, were heated to 1200°C and melted, and the copper alloy was cast by gravity casting using a mold.

[0028] (Tensile test and elongation test) The cast copper alloy after the above heat treatment was subjected to a tensile test using a 14A test specimen with a parallel section diameter of 5 mm as specified in JIS Z2241 (Instron 5982, manufactured by Instron Co., Ltd.), and evaluated by the tensile strength and elongation at the time of specimen fracture.

[0029] (Tensile Test Evaluation Criteria) ◎: 300MPa or higher ○: 200 MPa or more and less than 300 MPa △: 100 MPa or more and less than 200 MPa ×: Less than 100 MPa

[0030] (Evaluation criteria for extension test) ◎: 24% or more ○: 16% or more and less than 24% △: 8% or more but less than 16% ×: Less than 8%

[0031] (Hardness test) The cast copper alloy after the above heat treatment was subjected to a Brinell hardness test (BO3, manufactured by Imai Seiki Co., Ltd.) and evaluated according to its Brinell hardness. The test conditions were a test force of 500 kgf, and a 10 mm diameter cemented carbide ball was used as the indenter.

[0032] (Hardness Test Evaluation Criteria) ◎: 80HB or more, less than 120HB ○: 60HB or more, less than 80HB △: 40HB or more and less than 60HB ×: Less than 40HB or 120HB or more

[0033] (Wear amount confirmation test) A disc with an outer diameter of 70 mm and a thickness of 6 mm was prepared from the cast copper alloy after the heat treatment described above by machining. The friction surface was finished with #80 grit waterproof sandpaper.

[0034] Next, friction tests were performed on the disc friction surfaces of each fabricated embodiment using a friction testing machine (UMT-TriboLab, manufactured by Bruker). In the friction test, a 10 mm diameter ball made of high-oxygen chromium bearing steel (SUJ2) was brought into contact with the disc, and the ball was pressed against the contact surface to apply a load of 10 N while the ball was moved back and forth at a friction speed of 20 mm / s for 15 minutes with an amplitude of 2 mm (±1 mm). After the friction test, the amount of wear was calculated from the width and depth of the worn area on the disc friction surface using a 3D shape measuring machine (VR-5200, manufactured by Keyence Corporation).

[0035] (Evaluation criteria for wear amount confirmation test) ◎: 0.15mm 3 below 〇: 0.16mm 3 More than 0.30mm 3 below △: 0.31mm 3 More than 0.45mm 3 below ×: 0.46mm 3 That's all.

[0036] (Comprehensive evaluation criteria for mechanical properties testing) ◎: All ◎ 〇: Contains one or more 〇, others are ◎ △: Contains one or more △ symbols; otherwise, ◎ or 〇. ×: Contains at least one ×

[0037] [Table 1]

[0038] As shown in Table 1, since the content of each component in Examples 1 to 8 is within the range of the present invention, it can be seen that they have good performance in terms of tensile strength, elongation, hardness, and wear resistance, which are necessary for use as sliding members. In particular, from Examples 2, 7, and 8 it can be seen that if the phosphorus content is 0.04% by mass or more, which is greater than the amount described in the examples of Patent Document 1, then even if the iron content is less than 0.05% by mass, they have very good performance.

[0039] Comparative Example 1 has a higher iron content than the range of the present invention, resulting in reduced elongation performance. Similarly, Comparative Example 2 has a lower tin content than the range of the present invention, while Comparative Example 3 has a higher tin content, resulting in reduced hardness performance and reduced elongation and hardness performance, respectively. Furthermore, Comparative Example 4 has a lower sulfur content than the range of the present invention, while Comparative Example 5 has a higher sulfur content, resulting in reduced wear resistance, reduced tensile strength, and reduced elongation performance, respectively.

[0040] (Casting properties test) The raw materials, whose composition after casting was adjusted to consist of the mass percentages of each component in the examples and comparative examples listed in Table 2, with the remainder being copper and unavoidable impurities, were used to prepare tensile test specimens using the same melting, casting, and processing processes as described above. Tensile tests were then conducted under the same conditions. Evaluation was performed by observing the fracture surface after the tensile test.

[0041] (Casting properties test evaluation criteria) ○: No casting defects present on the fracture surface. ×: Casting defects present on the fracture surface

[0042] [Table 2]

[0043] As shown in Table 2, the iron content of Examples 9 and 10 is within the range of the present invention, but the iron content of Comparative Example 6 is higher than the range of the present invention. As a result, as shown in Figures 1A and 1B, Examples 9 and 10 have no casting defects and exhibit good castability, but as shown in Figure 1C, Comparative Example 6 has casting defects and exhibits inferior castability.

[0044] Thus, in copper alloys for sliding members whose main components are tin, sulfur, iron, and phosphorus, by adjusting the iron and phosphorus content—that is, by eliminating iron or reducing the iron content compared to conventional technology while increasing the phosphorus content—it is possible to realize copper alloys for sliding members with sliding properties equal to or better than conventional technology. Furthermore, by reducing the iron content, it is possible to realize a good cast copper alloy for sliding members.

Claims

1. A copper alloy for sliding members containing 6.0% to 15.0% by mass of tin, 0.3% to 1.0% by mass of sulfur, 0.005% to less than 0.3% by mass of iron, and 0.04% to 0.5% by mass of phosphorus, with the remainder being copper and unavoidable impurities.

2. The copper alloy for sliding members according to claim 1, characterized in that it contains 0.17% by mass or less of iron.

3. A casting of a copper alloy for a sliding member according to claim 1 or 2.

4. A sliding member comprising a casting of a copper alloy for sliding members as described in claim 1 or 2.

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