Cu-Zn-Si-Pb-P-BASED ALLOY CONTINUOUS CASTING WIRE ROD MATERIAL

Abstract

To provide a high-quality Cu-Zn-Si-Pb-P-based alloy continuous wire rod material having excellent strength, elongation and machinability, and less defect.SOLUTION: A wire rod material contains Cu of more than 60.0 mass% and less than 65.0 mass%, Si within the range of 0.40 mass% or more and 1.20 mass% or less, Pb within the range of 0.002 mass% or more and 0.250 mass% or less, and P within the range of 0.040 mass% or more and 0.190 mass% or less, and contains Bi of 0.001 mass% or more and 0.100 mass% or less as an arbitrary element, where the balance consists of Zn and impurities, the total content of Fe, Mn, Co and Cr being impurities is 0.450 mass% or less, the total content of Sn and Al is 0.30 mass% or less, and on a cross section orthogonal to casting direction, an area proportion of phase α and phase β is α:β=40 to 70:60 to 30, an area ratio of phase γ is 0.1% or less, and an area ratio of fine phase α having a particle diameter 10 μm or less is 30% or more and 60% or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a continuously cast wire rod of a Cu-Zn-Si-Pb-P alloy used for automotive parts, electrical and electronic equipment parts, mechanical parts, stationery, toys, sliding parts, instrument parts, precision mechanical parts, medical parts, beverage utensils and parts, drainage utensils and parts, industrial piping parts, and parts related to liquids and gases such as drinking water, industrial water, drainage, and hydrogen. Specific part names include valves, joints, cocks, faucets, gears, shafts, bearings, shafts, sleeves, spindles, sensors, bolts, nuts, flare nuts, pen tips, insert nuts, bag nuts, nipples, spacers, screws, etc. The present invention relates to a continuously cast wire rod of a Cu-Zn-Si-Pb-P alloy used for parts subjected to such cutting.

Background Art

[0002] Conventionally, for drinking water, utensils and parts related to sanitary facilities, automotive parts, electrical and household appliance parts, mechanical parts, stationery, instrument parts, medical parts, and utensils and parts related to liquids and gases such as drinking water, industrial water, drainage, and hydrogen, specific part names include water faucet fittings, faucets, mixing faucets, stop valves, valves, cocks, joints, valves, water meters, etc. For these utensils and parts, a Cu-Zn-Pb alloy (so-called free-cutting brass rod, forging brass, casting brass) or a Cu-Sn-Zn-Pb alloy (so-called bronze casting (leaded red brass)) having excellent machinability has generally been used. Here, the composition of the Cu-Zn-Pb alloy contains, for example, 56 to 70 mass% of Cu and 1 to 4 mass% of Pb, and the balance is Zn. The composition of the Cu-Sn-Zn-Pb alloy contains, for example, 80 to 88 mass% of Cu, 1 to 8 mass% of Sn, and 1 to 8 mass% of Pb, and the balance is Zn.

[0003] However, in recent years, concerns have been raised about the impact of Pb on the human body and the environment, and regulatory activities regarding Pb have been active in various countries. For example, in the state of California, USA, since January 2010, regulations have been in effect that limit the Pb content in drinking water appliances, etc. to 0.25 mass% or less. Even in countries other than the USA, the regulatory movement is rapid, and the development of copper alloy materials that can meet the Pb content regulations is required.

[0004] In addition, in other industrial fields such as the automotive, electrical and electronic equipment, and machinery industries, for example, in the European ELV Directive and RoHS Directive, the Pb content of free-cutting copper alloys is exceptionally allowed up to 4 mass%, but similar to the drinking water field, the strengthening of Pb content regulations, including the abolition of exceptions, is actively being discussed. Therefore, in order to ensure excellent machinability even when the Pb content is limited to 0.25 mass% or less, Cu-Zn-Si alloys (see, for example, Patent Document 1), Cu-Zn-Si-Pb-P alloys (see, for example, Patent Document 2), etc. have been proposed, which have a crystal structure controlled to have excellent machinability performance instead of Pb.

[0005] By the way, when manufacturing the above-mentioned various parts using copper alloy as a material, bars and wires with various cross-sections may be used as processing materials. When manufacturing bars and wires, usually, a large ingot is hot-extruded or hot-rolled to form a bar, and this bar is then subjected to plastic processing such as wire drawing to manufacture it. However, when manufacturing a bar by extrusion or rolling, it is necessary to perform many processes, including a casting process for manufacturing a large ingot, a heating process for heating the ingot, and an extrusion process or rolling process for extruding the heated ingot, which requires a large manufacturing cost and manufacturing time.

[0006] Therefore, as a method for efficiently manufacturing a metal bar or wire at low cost, for example, as disclosed in Patent Documents 3-6, a continuous casting method is provided in which a mold is installed in a casting furnace storing a molten metal, and a rod-shaped ingot is continuously cast. In the above-mentioned mold, a mold having self-lubricity such as graphite is usually used.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Summary of the Invention

Problems to be Solved by the Invention

[0008] By the way, when continuously casting a Cu-Zn-Si-Pb-P alloy as described in Patent Documents 3-6, there were the following problems. (1) Problems on the casting surface such as the occurrence of shrinkage cavities during casting. (2) The presence of coarse dendrites and the deterioration of cold workability due to the formation of more γ-phase than necessary by heat treatment. (2) Deterioration of mechanical properties (elongation, strength) due to the remaining casting structure and coarse grains at the final wire diameter. (3) Segregation of Sn, etc. (4) Intergranular cracking due to Pb and Bi segregated at grain boundaries. (5) Since the solidification temperature range is wide, casting defects such as shell breakage during casting are likely to occur. (6) Since it contains Zn, Si, etc., the thermal conductivity decreases, making it easy for the cooling during casting to be insufficient and for casting defects to easily occur. (7) Increase in casting skin cracking due to a decrease in mold heat extraction by casting of Zn and an increase in the restraint force during drawing.

[0009] Because there is a risk of various problems as described above, it has been difficult to stably and continuously cast a high-quality wire rod made of a Cu-Zn-Si-Pb-P alloy with few defects. Also, in the Cu-Zn-Si-Pb-P alloy, more than ever, improvement in mechanical properties (strength, elongation) and machinability is required.

[0010] The present invention has been made against the background of the above circumstances, and aims to provide a high-quality Cu-Zn-Si-Pb-P alloy continuous wire rod that is excellent in strength, elongation, and machinability and has few defects.

Means for Solving the Problems

[0011] In order to solve the above problems, the Cu-Zn-Si-Pb-P alloy continuous wire rod of Aspect 1 of the present invention contains Cu exceeding 60.0 mass% and less than 65.0 mass%, Si in the range of 0.40 mass% or more and 1.20 mass% or less, Pb in the range of 0.002 mass% or more and 0.250 mass% or less, P in the range of 0.040 mass% or more and 0.190 mass% or less, contains Bi as an optional element in the range of 0.001 mass% or more and 0.100 mass% or less, the balance being composed of Zn and impurities, and among the impurities, the total content of Fe, Mn, Co, and Cr is 0.450 mass% or less, and the total content of Sn and Al is 0.30 mass% or less. In a cross-section orthogonal to the casting direction, the area ratio of the α phase and the β phase is α:β = 40 to 70:60 to 30, the area ratio of the γ phase is 0.1% or less, and the area ratio of the fine α phase with a particle size of 10 μm or less is 30% or more and 60% or less.

[0012] In the Cu-Zn-Si-Pb-P series alloy continuous wire rod of Aspect 1 of the present invention, the component composition is defined as described above. In a cross-section orthogonal to the casting direction, the area ratio of the α-phase to the β-phase is α:β = 40 - 70:60 - 30, the area ratio of the γ-phase is 0.1% or less, and the area ratio of the fine α-phase with a particle size of 10 μm or less is 30% or more and 60% or less. Therefore, it has excellent mechanical properties (strength, elongation) and machinability, with few manufacturing defects and excellent quality. Also, it can be stably manufactured by continuous casting.

[0013] The Cu-Zn-Si-Pb-P series alloy continuous wire rod of Aspect 2 of the present invention is characterized in that, in the Cu-Zn-Si-Pb-P series alloy continuous wire rod of Aspect 1 of the present invention, the tensile strength is 450 MPa or more and 600 MPa or less, and the elongation is 12% or more and 35% or less. According to the Cu-Zn-Si-Pb-P series alloy continuous wire rod of Aspect 2 of the present invention, the tensile strength is 450 MPa or more and 600 MPa or less, and the elongation is 12% or more and 35% or less, and it is excellent in strength and ductility. Therefore, it is particularly suitable as a material for various parts.

[0014] The Cu-Zn-Si-Pb-P series alloy continuous wire rod of Aspect 3 of the present invention is, in the Cu-Zn-Si-Pb-P series alloy continuous wire rod of Aspect 1 or Aspect 2 of the present invention, when cutting on the circumference of a test material with a diameter of 14 mm that has been cut under the conditions of rake angle: 0°, nose radius: 0.4 mm, relief angle: 6°, cutting speed: 40 m / min, cutting depth: 1.0 mm, feed rate: 0.11 mm / rev. (under dry conditions) using a lathe equipped with a carbide tool with an ISO classification symbol of K10, the cutting resistance calculated by the following formula (1) from the measured value by a dynamometer attached to the tool is a machinability index that is a relative value with the cutting resistance of commercially available free-cutting brass rod C3604 made of Zn-59 mass% Cu-3 mass% Pb-0.2 mass% Fe-0.3 mass% Sn alloy as 100 and is 90 or more. (1) Formula: Cutting resistance = ((main cutting force) 2 +(feed cutting force) 2 +(back cutting force) 2 ) 1 / 2 According to the Cu-Zn-Si-Pb-P series alloy continuous wire rod of Embodiment 3 of the present invention, since the machinability index, which is the relative value with the cutting resistance of C3604 taken as 100, is 90 or more, it is excellent in machinability.

[0015] The Cu-Zn-Si-Pb-P series alloy continuous wire rod of Embodiment 4 of the present invention is any one of the Cu-Zn-Si-Pb-P series alloy continuous wire rods of Embodiments 1 to 3 of the present invention. When cutting on the circumference of a test material with a diameter of 14 mm that has been machined under the conditions of rake angle: 0°, nose radius: 0.4 mm, relief angle: 6°, cutting speed: 110 m / min, depth of cut: 1.0 mm, feed rate: 0.21 mm / rev. (under dry conditions) using a lathe equipped with a cemented carbide tool with an ISO classification symbol of K10, the cutting resistance calculated by the following formula (1) from the measured value by a dynamometer attached to the tool is such that the machinability index, which is the relative value with the cutting resistance of a commercially available free-cutting brass rod C3604 made of Zn-59 mass% Cu-3 mass% Pb-0.2 mass% Fe-0.3 mass% Sn alloy taken as 100, is 60 or more. (1) Formula: Cutting resistance = ((main cutting force) 2 + (feed force) 2 + (back cutting force) 2 ) 1 / 2 According to the Cu-Zn-Si-Pb-P series alloy continuous wire rod of Embodiment 4 of the present invention, even when machined under severe conditions, since the machinability index, which is the relative value with the cutting resistance of C3604 taken as 100, is 60 or more, it is sufficiently excellent in machinability.

[0016] The Cu-Zn-Si-Pb-P series alloy continuous wire rod of Embodiment 5 of the present invention is any one of the Cu-Zn-Si-Pb-P series alloy continuous wire rods of Embodiments 1 to 4 of the present invention. After performing a heat treatment of holding at 450 °C for 120 minutes and then air-cooling, in the constituent phases of the metal structure, the area ratio of the γ phase is 0.1% or less, and the area ratio of the fine α phase with a particle size of 10 μm or less is 30% or more and 60% or less. According to the Cu-Zn-Si-Pb-P series alloy continuous wire rod of Aspect 5 of the present invention, even when a heat treatment of holding at 450°C for 120 minutes and then air-cooling is carried out, the area ratio of the γ phase is limited to 0.1% or less, and the area ratio of the fine α phase with a particle size of 10 μm or less is 30% or more and 60% or less. Therefore, it is sufficiently excellent in heat resistance and ductility.

[0017] The Cu-Zn-Si-Pb-P series alloy continuous wire rod of Aspect 6 of the present invention is any one of the Cu-Zn-Si-Pb-P series alloy continuous wire rods of Aspects 1 to 5 of the present invention. After carrying out a heat treatment of holding at 475°C for 120 minutes and then air-cooling, the tensile strength is 400 MPa or more and 550 MPa or less, and the elongation is 14% or more and 38% or less. According to the Cu-Zn-Si-Pb-P series alloy continuous wire rod of Aspect 6 of the present invention, even when a heat treatment of holding at 475°C for 120 minutes and then air-cooling is carried out, the γ tensile strength is 400 MPa or more and 550 MPa or less, and the elongation is 14% or more and 38% or less. Therefore, it is sufficiently excellent in heat resistance and mechanical properties.

[0018] The Cu-Zn-Si-Pb-P series alloy continuous wire rod of Aspect 7 of the present invention is any one of the Cu-Zn-Si-Pb-P series alloy continuous wire rods of Aspects 1 to 6 of the present invention. After carrying out a heat treatment of holding at 475°C for 120 minutes and then air-cooling, when cutting on the circumference of a test material with a diameter of 14 mm under the conditions of rake angle: 0°, nose radius: 0.4 mm, relief angle: 6°, cutting speed: 40 m / min, cutting depth: 1.0 mm, feed rate: 0.11 mm / rev. (under dry conditions) using a lathe equipped with a carbide tool of ISO classification symbol K10, the cutting resistance calculated by the following formula (1) from the measured value by a dynamometer attached to the tool is such that the machinability index, which is the relative value with the cutting resistance of commercially available free-cutting brass rod C3604 made of Zn-59 mass% Cu-3 mass% Pb-0.2 mass% Fe-0.3 mass% Sn alloy as 100, is 80 or more. (1) Formula: Cutting resistance = ((main cutting force) 2 +(feed force) 2 +(back cutting force) 2 ) 1 / 2 According to the Cu-Zn-Si-Pb-P series alloy continuous wire rod of Aspect 7 of the present invention, even when a heat treatment of holding at 475°C for 120 minutes and then air-cooling is carried out, since the above-mentioned machinability index is 80 or more, it is sufficiently excellent in heat resistance and machinability.

[0019] The Cu-Zn-Si-Pb-P series alloy continuous wire rod of Aspect 8 of the present invention is any one of the Cu-Zn-Si-Pb-P series alloy continuous wire rods of Aspects 1 to 7 of the present invention, and after carrying out a heat treatment of holding at 475°C for 120 minutes and then air-cooling, the maximum possible cold drawing reduction ratio until wire breakage is 50% or more. According to the Cu-Zn-Si-Pb-P series alloy continuous wire rod of Aspect 8 of the present invention, even when a heat treatment of holding at 475°C for 120 minutes and then air-cooling is carried out, since the maximum possible cold drawing reduction ratio until wire breakage is 50% or more, it is sufficiently excellent in heat resistance and workability.

[0020] The Cu-Zn-Si-Pb-P series alloy continuous wire rod of Aspect 9 of the present invention is any one of the Cu-Zn-Si-Pb-P series alloy continuous wire rods of Aspects 1 to 8 of the present invention, and after carrying out a heat treatment of holding at 600°C for 120 minutes and then air-cooling, in the cross-section orthogonal to the casting direction, the area ratio of the fine α-phase with a particle size of 10 μm or less is 10% or more and 20% or less. According to the Cu-Zn-Si-Pb-P series alloy continuous wire rod of Aspect 9 of the present invention, even when a heat treatment of holding at 600°C for 120 minutes and then air-cooling is carried out, in the cross-section orthogonal to the casting direction, since the area ratio of the fine α-phase with a particle size of 10 μm or less is 10% or more and 20% or less, it is further excellent in heat resistance and strength.

[0021] The Cu-Zn-Si-Pb-P series alloy continuous wire rod of aspect 10 of the present invention is any one of the Cu-Zn-Si-Pb-P series alloy continuous wire rods of aspects 1 to 9 of the present invention. In a cross-section orthogonal to the casting direction, the average crystal grain size of the β phase is 500 μm or less, and it has a crystal structure in which dendrites and columnar crystals are fragmented. Taking the location with the maximum length of the α phase as the major axis and the location with the maximum length orthogonal to the major axis as the minor axis, the ratio L1 / L2 of the major axis length L1 to the minor axis length L2 is in the range of 1 or more and 4 or less, and it is characterized by being non-circular, elliptical or polygonal. According to the Cu-Zn-Si-Pb-P series alloy continuous wire rod of aspect 10 of the present invention, since the β phase and the α phase are defined as described above, it is further excellent in strength, ductility, and machinability.

[0022] The Cu-Zn-Si-Pb-P series alloy continuous wire rod of aspect 11 of the present invention is any one of the Cu-Zn-Si-Pb-P series alloy continuous wire rods of aspects 1 to 10 of the present invention, and is characterized in that the oscillation mark depth is less than 50 μm. According to the Cu-Zn-Si-Pb-P series alloy continuous wire rod of aspect 11 of the present invention, since the oscillation mark depth is less than 50 μm, there are few defects during casting and the quality is excellent.

[0023] The Cu-Zn-Si-Pb-P series alloy continuous wire rod of aspect 12 of the present invention is any one of the Cu-Zn-Si-Pb-P series alloy continuous wire rods of aspects 1 to 11 of the present invention. In a cross-section orthogonal to the casting direction, the cross-sectional area is 12 mm 2 or more and 227 mm 2 or less. According to the Cu-Zn-Si-Pb-P series alloy continuous wire rod of aspect 12 of the present invention, since the cross-sectional area of the cross-section orthogonal to the casting direction is in the range of 12 mm 2 or more and 227 mm 2 or less, various parts can be efficiently manufactured.

Effects of the Invention

[0024] According to the present invention, it is possible to provide a high-quality Cu-Zn-Si-Pb-P-based alloy continuous wire rod that is excellent in strength, elongation, machinability, and has few defects.

Brief Description of the Drawings

[0025]

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Figure 10

Modes for Carrying Out the Invention

[0026] Hereinafter, the Cu-Zn-Si-Pb-P-based alloy continuous wire rod according to the embodiment of the present invention will be described. The Cu-Zn-Si-Pb-P series alloy continuous wire rod according to the embodiment of the present invention is used as a material for various parts such as faucets, mixing faucets, stop valves, valves, cocks, joints, water meters, gears, sensors, nuts, screws, etc., for drinking water, instruments and equipment related to sanitary facilities, musical instruments, tableware, parts of electric, household and electronic devices, automotive parts, mechanical parts, stationery, precision mechanical parts, medical parts, and instruments and parts related to liquids and gases such as industrial water, wastewater, and hydrogen.

[0027] The Cu-Zn-Si-Pb-P series alloy continuous wire rod of this embodiment has a composition in which the Cu content is in the range of more than 60.0 mass% and less than 65.0 mass%, the Si content is in the range of 0.40 mass% or more and 1.20 mass% or less, the Pb content is in the range of 0.002 mass% or more and 0.250 mass% or less, the P content is in the range of 0.040 mass% or more and 0.190 mass% or less, Bi is in the range of 0.001 mass% or more and 0.100 mass% or less as an optional element, and the balance is composed of Zn and impurities. Also, among the impurities, the total content of Fe, Mn, Co and Cr is 0.450 mass% or less, and the total content of Sn and Al is 0.30 mass% or less. And in the cross section perpendicular to the casting direction, the area ratio of the α phase and the β phase is α:β = 40 - 70:60 - 30, the area ratio of the γ phase is 0.1% or less, and the area ratio of the fine α phase with a particle size of 10 μm or less is 30% or more and 60% or less.

[0028] Also, in this embodiment, in the cross section perpendicular to the casting direction, the average crystal grain size of the β phase is 500 μm or less, and it has a crystal structure in which dendrites and columnar crystals are segmented. Taking the location with the maximum length of the α phase as the long axis and the location with the maximum length perpendicular to the long axis as the short axis, the ratio L1 / L2 of the long axis length L1 to the short axis length L2 is in the range of 1 or more and 4 or less, and it preferably has a non-circular shape, an elliptical shape or a polygonal shape.

[0029] Further, in the present embodiment, it is preferable that the tensile strength is in the range of 450 MPa or more and 600 MPa or less, and the elongation is in the range of 12% or more and 35% or less.

[0030] Furthermore, in the present embodiment, when cutting on the circumference of a test material with a diameter of 14 mm under the conditions of using a lathe equipped with a cemented carbide tool with an ISO classification symbol K10, rake angle: 0°, nose radius: 0.4 mm, relief angle: 6°, cutting speed: 40 m / min, depth of cut: 1.0 mm, feed rate: 0.11 mm / rev. (under dry conditions), the cutting resistance calculated by the following formula (1) from the measured value by a dynamometer attached to the tool is preferably 90 or more in terms of the relative value with the cutting resistance of a commercially available free-cutting brass bar C3604 made of a Zn-59 mass% Cu-3 mass% Pb-0.2 mass% Fe-0.3 mass% Sn alloy being 100. (1) Formula: Cutting resistance = ((main cutting force) 2 + (feed force) 2 + (back cutting force) 2 ) 1 / 2

[0031] Also, in the present embodiment, when cutting under severe conditions of cutting speed: 110 m / min and feed rate: 0.11 mm / rev., it is preferably that the above-mentioned machinability index is 60 or more.

[0032] Furthermore, in the present embodiment, after performing a heat treatment of holding at 450°C for 120 minutes and then air-cooling, it is preferable that the area ratio of the γ phase is 0.1% or less. Also, after performing a heat treatment of holding at 450°C for 120 minutes and then air-cooling, in a cross-section perpendicular to the casting direction, it is preferable that the area ratio of the fine α phase with a particle size of 10 μm or less is 30% or more and 60% or less. Furthermore, in the present embodiment, after performing a heat treatment of holding at 600°C for 120 minutes and then air-cooling, in a cross-section perpendicular to the casting direction, it is preferable that the area ratio of the fine α phase with a particle size of 10 μm or less is 10% or more and 20% or less.

[0033] In addition, in this embodiment, after performing the heat treatment of holding at 475°C for 120 minutes and then air-cooling, it is preferable that the tensile strength is 400 MPa or more and 550 MPa or less, and the elongation is 14% or more and 38% or less. Furthermore, in this embodiment, after performing the heat treatment of holding at 475°C for 120 minutes and then air-cooling, when cutting under the conditions of rake angle: 0°, nose radius: 0.4 mm, flank angle: 6°, cutting speed: 40 m / min, depth of cut: 1.0 mm, feed rate: 0.11 mm / rev. (dry condition), it is preferable that the above-mentioned machinability index is 80 or more. In addition, in this embodiment, after performing the heat treatment of holding at 475°C for 120 minutes and then air-cooling, it is preferable that the maximum possible cold drawing ratio until wire breakage is 50% or more.

[0034] Furthermore, in this embodiment, it is preferable that the oscillation mark depth is less than 50 μm. In addition, in this embodiment, the cross-sectional area of the cross-section orthogonal to the casting direction is 12 mm 2 or more and 227 mm 2 or less.

[0035] Below, the composition, metallographic structure, mechanical properties and machinability of the continuous casting wire rod, the metallographic structure after heat treatment, and the mechanical properties and machinability after heat treatment will be described for the reasons defined as above.

[0036] (Cu) When the Cu content is less than 60.00 mass%, depending on the contents of Si, Zn, P, Pb and the manufacturing process, the proportion of the β phase may exceed 80%, and the ductility may decrease. Also, by increasing the Cu content, the dezincification corrosion resistance, stress corrosion cracking resistance and cold workability can be improved. Furthermore, when the Cu content is low, the thermal conductivity of the alloy decreases, leading to a decrease in coolability and possibly causing casting defects. On the one hand, when the Cu content is more than 65.00 mass%, although it depends on the contents of Si, Zn, P, Pb and the manufacturing process, the proportion of the β phase decreases and the proportion of the γ phase increases. However, excessive addition of Cu will reduce the hot workability and strength. Therefore, in the present embodiment, the Cu content is set within the range of 60.00 mass% or more and 65.00 mass% or less. In addition, the lower limit of the Cu content is preferably 62.15 mass% or more, and more preferably 62.40 mass% or more. On the other hand, the upper limit of the Cu content is preferably 63.05 mass% or less, and more preferably 63.00 mass% or less.

[0037] (Si) Si affects the formation of metal phases such as κ phase, γ phase, μ phase, and β phase. Also, Si has the effect of improving the machinability, strength, hot workability, wear resistance, and stress corrosion cracking resistance of the alloy of the present embodiment. Furthermore, since the α phase and β phase are solid-solution strengthened by the inclusion of Si, the alloy is strengthened, which also affects the ductility and toughness of the alloy. And the inclusion of Si lowers the conductivity of the α phase, but improves the conductivity of the alloy due to the formation of the β phase. Furthermore, Si lowers the viscosity of the molten metal, improves the flowability of the molten metal, and improves the castability. The higher the Si concentration in the alloy, the higher the Si concentration contained in the β phase, and the machinability and strength are improved. Regarding hot workability, the inclusion of Si increases the hot workability of the α phase and β phase in the temperature range exceeding 500 °C, lowers the hot deformation resistance, and as a result, increases the hot workability of the alloy and lowers the deformation resistance. In particular, when Si is contained in an amount exceeding 0.400 mass%, the effect is remarkably exhibited. On the one hand, if the Si content is too high, the γ phase will be excessive. The γ phase is inferior in ductility and toughness to the β phase, reducing the ductility of the alloy and, in some cases, increasing the cutting resistance. When the γ phase is excessive, the thrust of drill cutting deteriorates. Although it depends on the manufacturing process and Cu concentration, when the Si content is 1.20 mass% or less, by reducing the amount of the γ phase and increasing the proportion of the β phase, excellent machinability can be maintained and the balance between strength and ductility can be improved. Also, increasing the Si content reduces the electrical conductivity of the alloy, leading to a decrease in the cooling property during casting and causing casting defects such as shell breakage. Furthermore, although it depends on the combination of Cu and Zn, if Si is too much, the solidification temperature range becomes wider and the castability deteriorates. Moreover, as the temperature range of the solid-liquid coexistence phase becomes wider, Si reacts with the mold, and Si-containing deposits are formed on the inner wall of the mold. The formation of these deposits reduces the heat extraction property of the mold. Therefore, in this embodiment, the Si content is set within the range of 0.40 mass% or more and 1.20 mass% or less. Note that the lower limit of the Si content is preferably 0.90 mass% or more, and more preferably 0.93 mass% or more. On the other hand, the upper limit of the Si content is preferably 1.00 mass% or less, and more preferably 0.97 mass% or less.

[0038] (Pb) By containing a small amount of Pb and having a small amount of Pb particles present in the metal structure, the machinability is further improved. In the composition of this embodiment, about 0.002 mass% of Pb is dissolved in the matrix, and the amount of Pb exceeding that does not dissolve in the matrix and functions as a so-called chip breaker by dispersing as Pb particles with a diameter of about 0.1 to about 3 μm, improving the machinability. Even a trace amount of Pb is effective for machinability. On the other hand, when Pb is contained more than necessary, the cutting surface becomes rough, the workability in the hot state (for example, forging property) deteriorates, and the ductility in the cold state also decreases. Also, intergranular cracking starting from Pb segregated at the grain boundaries is likely to occur during casting. Furthermore, since Pb has low strength, it causes a decrease in strength and fatigue resistance. Therefore, in this embodiment, the Pb content is set within the range of 0.002 mass% or more and 0.250 mass% or less. Note that the lower limit of the Pb content is preferably 0.055 mass% or more, and more preferably 0.080 mass% or more. On the other hand, the upper limit of the P content is preferably 0.200 mass% or less, and more preferably 0.150 mass% or less.

[0039] (P) P is dissolved in the β phase, and as the amount increases, the machinability of the β phase, that is, the chip breakability (chip segmentation property) of the β phase, can be enhanced, the cutting resistance can be reduced, and excellent machinability as an alloy can be obtained. Furthermore, depending on the P content and the manufacturing process, compounds containing P with an average size of about 0.5 to 3 μm in diameter are formed within the β phase. These compounds reduce the three cutting forces, namely the main cutting force, feed force, and back force, in the case of peripheral cutting, and particularly reduce the torque in the case of drill cutting. The three cutting forces during peripheral cutting, the torque during drill cutting, and the chip shape are interrelated. The smaller the three cutting forces and torque, the more the chips are segmented. That is, the machinability index is improved. Here, as the P content increases, the critical cooling rate for the formation of P-containing compounds increases, facilitating the formation of P-containing compounds. Furthermore, P has the effect of refining the crystal grains of the α phase, and by refining the α phase, the machinability of the copper alloy casting is improved. Also, P, when co-added with Si, has the function of making it easier for Bi-containing particles to exist within the α phase, contributing to the improvement of the machinability of the α phase. On the other hand, if P is contained more than necessary, not only do the precipitates coarsen and the effect on machinability saturate, but also the Si concentration in the β phase decreases, resulting in worse machinability, as well as a decrease in ductility and toughness. In addition, the solidification temperature range becomes wider, the castability decreases, cracks are likely to occur on the surface or inside during ingot formation, and wire breakage is likely to occur during processing. Furthermore, P reacts with the carbon mold, causing deterioration of the castability (such as deterioration of the casting surface). Therefore, in this embodiment, the P content is set within the range of 0.040 mass% or more and 0.190 mass% or less. Note that the lower limit of the P content is preferably 0.055 mass% or more, and more preferably 0.070 mass% or more. On the other hand, the upper limit of the P content is preferably 0.150 mass% or less, and more preferably 0.100 mass% or less.

[0040] (Zn) Zn is an element necessary for enhancing machinability, strength, high-temperature properties, and castability. On the other hand, when Zn adheres to the inner wall of the mold, the self-lubricity of the graphite mold is inhibited, and seizure of the solidified shell tends to occur. Furthermore, the adhered Zn may reduce the heat extraction property of the mold, increasing the likelihood of casting defects. Therefore, in the present embodiment, although Zn is the balance, the lower limit of the Zn content is preferably 34.00 mass% or more, more preferably 34.80 mass% or more, and even more preferably 35.50 mass% or more. On the other hand, the upper limit of the Zn content is preferably 41.00 mass% or less, more preferably 36.80 mass% or less, and even more preferably 36.00 mass% or less.

[0041] (Optional element: Bi) Bi is contained as an optional element and is not an essential element. Bi mainly takes the place of Pb. When Bi is contained in the presence of Pb, in many cases, Pb and Bi exist together, and the particles in which Pb and Bi coexist have an effect on machinability that is not impaired compared to Bi particles and Pb particles. The environmental and human impacts of Bi are unknown at present, but it is considered to be smaller than that of Pb. By reducing the amount of Pb by containing Bi, the impact on the environment and the human body can be reduced. Further, due to the action of Si, particles containing Bi can be preferentially present in the α phase, improving the machinability of the α phase and making it possible to improve the machinability of copper alloy castings by another means. That is, when the frequency of particles containing Bi existing in the α phase increases, the machinability of the α phase is improved, and the effect of improving the machinability by particles containing Bi exceeds the effect of improving the machinability by Pb particles. On the one hand, Bi has the property of embrittling copper alloy castings. The upper limit of Bi needs to take into account the impact on the environment and the human body, the reduction in the ductility and toughness of copper alloy castings, and the problem of cracking during casting production. In addition, intergranular cracking starting from Bi segregated at grain boundaries is likely to occur during casting. Since Bi has low strength, it causes a decrease in strength and fatigue resistance. Therefore, in the present embodiment, when Bi is contained to further improve machinability, the content of Bi is set within the range of 0.001 mass% or more and 0.100 mass% or less. Of course, since Bi is an optional element, even when the content of Bi is less than 0.001 mass%, it is within the scope of the present invention. Note that the lower limit of the content of Bi is preferably 0.020 mass% or more, and more preferably 0.025 mass% or more. On the other hand, the upper limit of the content of Bi is preferably 0.040 mass% or less, and more preferably 0.030 mass% or less.

[0042] (Impurities: Fe, Mn, Co, Cr) Fe, Mn, Co, and Cr dissolve into the α-phase, β-phase, and γ-phase of the Cu-Zn alloy up to a certain concentration. However, when Si is present at that time, they easily combine with Si, and in some cases, they bind to Si, which may consume Si effective for machinability. And Fe, Mn, Co, and Cr combined with Si form Fe-Si compounds, Mn-Si compounds, Co-Si compounds, and Cr-Si compounds in the metal structure. Since these intermetallic compounds are very hard, they reduce ductility. Furthermore, there is a risk of increasing cutting resistance and shortening the tool life. Therefore, in the present embodiment, the total content of Fe, Mn, Co, and Cr, which are impurities, is less than 0.450 mass%. Note that the total content of Fe, Mn, Co, and Cr, which are impurities, is preferably less than 0.30 mass%, and more preferably less than 0.20 mass%.

[0043] (Impurities: Sn, Al) Sn and Al, which are mixed in from free-cutting brass, plated waste products, etc., promote the formation of the γ phase in the alloy of the present embodiment and may seem useful for machinability at first glance. However, Sn and Al also change the original properties of the γ phase formed by Cu, Zn, and Si. In addition, Sn and Al are distributed more in the β phase than in the α phase, changing the properties of the β phase. As a result, there is a risk of reducing the ductility and toughness of the alloy and the machinability. If the content of Sn is too high, the segregation of Sn becomes significant, resulting in poor ductility during hot working, and also causing a decrease in workability and ductility during cold working. Furthermore, the solidification temperature range widens as the Sn addition amount increases. As a result, the castability decreases (cracking, shrinkage cavities, and porosity occur), and the hot workability and cold workability deteriorate. Also, if the content of Al is too high, the elongation decreases. Therefore, in the present embodiment, the total content of Sn and Al, which are impurities, is set to less than 0.300 mass%. Note that the total content of Sn and Al, which are impurities, is preferably less than 0.20 mass%, and more preferably less than 0.10 mass%. Also, the content of Sn is preferably less than 0.300 mass%, and the content of Al is preferably less than 0.200 mass%.

[0044] (Impurities: Others) Examples of other impurities other than the elements described above include Ag, B, Ca, Sc, rare earth elements (excluding Y and Sc), V, Nb, Ta, Mo, W, Re, Ru, Os, Rh, Ir, Ni, Pd, Pt, Au, Cd, Hg, Al, Ga, In, Ge, Sn, As, Sb, Tl, Be, N, C, Li, H, O, etc. Since these impurities may reduce various properties, the total content of these impurities is preferably less than 0.20 mass%, more preferably less than 0.15 mass%, and even more preferably 0.10 mass% or less.

[0045] (Ratio of α phase and β phase) Since the α-phase is soft, it has high ductility and toughness but low machinability. Even when the α-phase is contained at an area ratio of about 50%, the soft α-phase itself serves as a cushioning material. During cutting, the boundary with the hard β-phase becomes a stress concentration source and breaks the chips, so the excellent machinability of the β single-phase alloy is maintained, and in some cases, the machinability is considered to be improved. On the other hand, the β-phase has high machinability but low ductility and toughness. Also, good conductivity can be obtained. Therefore, it is necessary to consider the ductility, toughness, and balance between ductility and strength of the alloy. Therefore, in this embodiment, the area ratio of the α-phase and the β-phase in the cross-section orthogonal to the casting direction is set to α:β = 40~70:60~30.

[0046] (Area ratio of the γ-phase) Since the γ-phase is hard and brittle, when a small amount of the γ-phase is contained, the improvement effect on machinability is large, but the improvement effect on machinability decreases even if the amount of the γ-phase is increased. Also, as a demerit of the γ-phase, dezincification occurs starting from the γ-phase. Since it causes the generation of holes in applications such as water pipe uses starting from dezincification, it is preferable that the ratio of the γ-phase is small. Therefore, in order to achieve an excellent balance between ductility and strength, the γ-phase must be significantly restricted. Therefore, in this embodiment, the area ratio of the γ-phase is set to 0.1% or less. Note that the area ratio of the γ-phase is preferably 0.08% or less. Also, if the γ-phase does not exist, the machinability and strength are inferior, so the area ratio of the phase is preferably 0.01% or more.

[0047] (Area ratio of the fine α-phase) The finer the crystal grain size of the α-phase crystal grains, the better the machinability and mechanical properties. When the α-phase crystal grains are granular and fine, the distribution of the α-phase becomes uniform, and the β-phase is also segmented. For this reason, in terms of cutting and strength / ductility, the α-phase serves as a good cushioning material, or the phase boundary between the α-phase and the β-phase serves as a stress concentration source for chip segmentation, and the chip is segmented rather than a single-phase β-alloy. Therefore, as the proportion of granular and fine α-phase crystal grains increases, the strength increases and the machinability improves. On the other hand, considering the balance between strength and ductility, if the area ratio of fine α-phase with a crystal grain size of 10 μm or less is too large, it will cause excessive elongation and a decrease in ductility. Therefore, in this embodiment, the area ratio of the fine α-phase with a particle size of 10 μm or less is set within the range of 30% or more and 60% or less. Note that the lower limit of the area ratio of the fine α-phase with a particle size of 10 μm or less is preferably 40% or more. The upper limit of the area ratio of the fine α-phase with a particle size of 10 μm or less is preferably 50% or less.

[0048] (Shape of fine α-phase and β-phase) Regarding the shape, distribution of the α-phase, and distribution of the β-phase that affect the machinability and mechanical properties of the alloy, when the shape of the α-phase crystal grains is needle-shaped (ellipse with an aspect ratio of the crystal grains exceeding 4), the dispersion of the α-phase deteriorates, and the needle-shaped α-phase with a large long side becomes an obstacle during cutting. Then, the crystal grains of the β-phase around the α-phase become larger, and the degree of dispersion of the β-phase also deteriorates. Therefore, the strength of the alloy decreases. Therefore, in this embodiment, taking the location of the maximum length of the α-phase as the major axis and the location of the maximum length perpendicular to the major axis as the minor axis, the ratio L1 / L2 of the major axis length L1 to the minor axis length L2 is within the range of 1 or more and 4 or less, and it preferably has a non-circular shape, elliptical shape, or polygonal shape. Also, the β-phase preferably has an average crystal grain size of 500 μm or less and a structure in which dendrites and columnar crystals are segmented.

[0049] (Strength, elongation) There are strong demands for thinning and weight reduction for members and parts targeted for use in this embodiment, starting with automotive parts. As for the required strength, tensile strength is emphasized, and the balance with ductility is also considered important. Also, by increasing the strength of the material, the weight reduction of the parts can be achieved. Furthermore, if the strength and elongation are too low, the cold drawing property is poor. The cold drawing property is important in terms of the balance between strength and elongation, and generally, strength and ductility (cold drawing property) are in opposition. If the strength is too high, the elongation, which is important for cold drawing property, decreases. Therefore, in this embodiment, the tensile strength is set within the range of 450 MPa or more and 600 MPa or less, and the elongation is set within the range of 12% or more and 35% or less.

[0050] (Machinability) In this embodiment, as described above, the machinability is evaluated by the machinability index, which is a relative value with the cutting resistance of commercially available free-cutting brass bar C3604 (Zn - 59 mass% Cu - 3 mass% Pb - 0.2 mass% Fe - 0.3 mass% Sn alloy) set to 100. Here, the higher the machinability index, the higher the machinability, leading to a longer tool life. In this embodiment, when cutting under the conditions of rake angle: 0°, nose radius: 0.4 mm, relief angle: 6°, cutting speed: 40 m / min, cutting depth: 1.0 mm, feed rate: 0.11 mm / rev. (dry cutting) using a lathe equipped with a cemented carbide tool of ISO classification symbol K10, it is preferable that the machinability index is 90 or more. Also, under more severe conditions, when the cutting speed is 110 m / min and the feed rate is 0.21 mm / rev., it is preferable that the machinability index is 60 or more.

[0051] (Metallographic structure after heat treatment) In this embodiment, after performing heat treatment of holding at 450°C for 120 minutes and then air-cooling, in the constituent phases of the metal structure, it is preferable that the area ratio of the γ phase is 0.1% or less, and the area ratio of the fine α phase with a particle size of 10 μm or less is 30% or more and 60% or less. Even when heat treatment of holding at 450°C for 120 minutes is performed, the metal structure does not change significantly, and properties such as strength, elongation, and machinability are maintained. Therefore, it is particularly suitable as a material for parts used in a high-temperature environment with excellent heat resistance. Also, after performing heat treatment of holding at 600°C for 120 minutes and then air-cooling, in the cross-section orthogonal to the casting direction, it is preferable that the area ratio of the fine α phase with a particle size of 10 μm or less is 10% or more and 20% or less. Even when held under higher temperature conditions, the area ratio of the fine α phase with a particle size of 10 μm or less is ensured, and it becomes possible to ensure certain properties.

[0052] (Strength, elongation, and machinability index after heat treatment) In this embodiment, even when heat-treated at 475°C for 120 minutes, it preferably has a strength of 400 - 550 MPa, an elongation of 14 - 38%, a machinability index of 80 under the conditions of a cutting speed of 40 m / min and 0.11 mm / rev, and a maximum possible cold drawing ratio of 50% until wire breakage. When heat-treated, the strength decreases and the elongation increases. In this embodiment, due to limiting the components, it is difficult to form the γ phase (hard and brittle) even after heat treatment, so it is possible to improve the elongation and cold workability without increasing the strength more than necessary.

[0053] (Oscillation mark depth) In this embodiment, it is preferable that the oscillation mark depth is less than 50 μm. The thinner the oscillation mark depth, the better the castability and particularly the surface quality. Also, when surface cutting to remove the oscillation marks, it is possible to reduce the cutting cost.

[0054] (Cross-sectional area of the cross-section orthogonal to the casting direction) In this embodiment, the cross-sectional area of the cross-section orthogonal to the casting direction is 12 mm 2 or more and 227 mm2 It is preferably within the following range. The cross-sectional area of the cross-section orthogonal to the casting direction is 12 mm 2 By setting it to or more, the cooling rate during casting does not become too fast, and the α-phase can be sufficiently generated. On the other hand, by setting the cross-sectional area of the cross-section orthogonal to the casting direction to 227 mm 2 or less, the cooling rate during casting does not become too slow, and the α-phase can be sufficiently refined. Also, sufficient solidification shell strength can be ensured, and it is possible to suppress the oscillation marks from becoming large due to the drawing stress applied during casting, and continuous casting can be stably performed.

[0055] Next, an example of a method for manufacturing the Cu-Zn-Si-Pb-P-based alloy continuous casting wire rod according to the present embodiment will be described. In the Cu-Zn-Si-Pb-P-based alloy continuous casting wire rod according to the present embodiment, it is continuously cast using a continuous casting apparatus. Any of a vertical continuous casting apparatus that draws the continuous casting wire rod downward, a horizontal continuous casting apparatus that draws the continuous casting wire rod horizontally, and an upward-drawing type continuous casting apparatus that draws the continuous casting wire rod upward can be applied.

[0056] Here, in the vertical continuous casting apparatus and the horizontal continuous casting apparatus, a large site is required for equipment introduction. Also, when switching the product type during casting, the molten metal in the crucible must be discarded. On the other hand, in the upward-drawing type continuous casting apparatus, since the upper space can be utilized and the equipment is compact, there is no need to create a large site or underground, and product type switching only requires moving the mold to another crucible, so multi-product casting is possible and it has an advantage in terms of production.

[0057] Therefore, in the present embodiment, it will be described as being continuously cast using the upward-drawing type continuous casting apparatus 10 shown in FIG. 1. The continuous casting apparatus 10 shown in FIG. 1 includes a casting furnace 11, a continuous casting mold 20 connected to the casting furnace 11, and a pinch roll 17 that draws out the cast wire 1 produced from the continuous casting mold 20.

[0058] The casting furnace 11 heats and melts the melting raw materials to produce and hold a copper melt of a predetermined composition, and includes a crucible 12 for holding the melting raw materials and the copper melt, and a heating means (not shown) for heating the crucible 12. The pinch rolls 17 sandwich the cast wire rod 1 produced from the continuous casting mold 20 and pull it in the pulling direction F. In the present embodiment, the cast wire rod 1 is configured to be pulled intermittently.

[0059] The continuous casting mold 20 includes a cylindrical mold 21 into which the supplied copper melt is poured, and a cooling unit 28 for cooling the mold 21. Here, in the present embodiment, as shown in FIG. 1, the continuous casting mold 20 is disposed on the copper melt in the casting furnace 11 via a refractory heat insulating material 15, and is configured to pull the cast wire rod 1 upward.

[0060] The mold 21 has a substantially cylindrical shape, and is provided with a casting hole 24 that penetrates from one side to the other side. The cooling unit 28 is a water-cooled jacket disposed on the outer peripheral side of the mold 21, and is configured to cool the mold 21 by circulating cooling water.

[0061] First, the melting raw materials are charged into the crucible 12 from the raw material inlet of the casting furnace 11. As the raw materials, Cu single body, Zn single body, Sn single body, Cu-Zn master alloy, Cu-Sn master alloy, etc. can be used. Further, raw materials containing Zn and Sn may be melted together with the copper raw materials. Further, recycled materials and scrap materials of this alloy may be used.

[0062] Next, the melting raw materials charged into the crucible 12 are heated and melted by the heating means to produce a copper melt prepared with the above-described component composition. This copper melt is heated and held in the crucible 12 to a predetermined casting temperature. Then, this copper melt is supplied to the continuous casting mold 20.

[0063] The molten copper supplied into the mold 20 for continuous casting is cooled and solidified in the mold 21 to form the cast wire 1. By intermittently pulling out the cast wire 1 with the pinch roll 17, the cast wire 1 is continuously manufactured.

[0064] Here, the cooling rate during casting (the cooling rate until the molten metal (1000 °C) is cooled to room temperature (25 °C)) is preferably in the range of 22 °C / sec or more and 75 °C / sec or less. By setting the cooling rate to 22 °C / sec or more, the growth or coalescence of the α-phase can be suppressed, and the α-phase can be refined. On the other hand, by setting the cooling rate to 75 °C / sec or less, the α-phase can be surely generated.

[0065] Also, the casting speed is preferably in the range of 0.6 m / min or more and 3.3 m / min or less. By setting the casting speed to 0.6 m / min or more, the cooling rate does not become too large, and the α-phase can be surely generated. Also, it is possible to suppress the solid phase ratio of the molten metal from becoming high during pulling and the fluidity from decreasing, and it is possible to suppress the occurrence of poor molten metal circulation, deep oscillation marks, internal defects, and the formation of a deep altered layer. On the other hand, by setting the casting speed to 3.3 m / min or less, the cooling rate does not become too small, and the α-phase can be surely refined and generated. Also, it is possible to suppress the molten metal supply from becoming insufficient during pulling, and the occurrence of deep oscillation marks and internal defects. Also, the frictional force between the mold and the solidified shell during pulling does not become too large, and it is possible to suppress the breakage of the solidified shell and the formation of deep oscillation marks during pulling.

[0066] According to the Cu-Zn-Si-Pb-P series alloy continuous casting wire rod with the above-described configuration of this embodiment, the Cu content is in the range exceeding 60.0 mass% and less than 65.0 mass%, the Si content is in the range of 0.40 mass% or more and 1.20 mass% or less, the Pb content is in the range of 0.002 mass% or more and 0.250 mass% or less, the P content is in the range of 0.040 mass% or more and 0.190 mass% or less, Bi is in the range of 0.001 mass% or more and 0.100 mass% or less as an optional element, the balance consists of Zn and impurities, among the impurities, the total content of Fe, Mn, Co, and Cr is 0.450 mass% or less, and the total content of Sn and Al is 0.30 mass% or less. In the constituent phases of the metal structure, the area ratio of the γ phase is 0.1% or less, and the area ratio of the fine α phase with a particle size of 10 μm or less is 30% or more and 60% or less. Therefore, it is excellent in mechanical properties (strength, elongation) and machinability, and has few manufacturing defects and excellent quality. Also, it can be stably manufactured by continuous casting.

[0067] In this embodiment, when the area ratio of the α phase and the β phase in the cross section perpendicular to the casting direction is α:β = 40~70:60~30, the ductility and toughness, and the strength and machinability can be improved in a well-balanced manner.

[0068] In this embodiment, when the tensile strength is 450 MPa or more and 600 MPa or less, and the elongation is 12% or more and 35% or less, it is excellent in strength and ductility. Therefore, it is particularly suitable as a material for various parts.

[0069] In this embodiment, when the machinability index during cutting is 90 or more under the conditions of cutting speed: 40 m / min, feed rate: 0.11 mm / rev. (dry condition), even if the Pb content is limited to 0.190 mass% or less, it is possible to ensure sufficient machinability.

[0070] In this embodiment, when the machinability index during cutting is 60 or more under the conditions of cutting speed: 110 m / min and feed rate: 0.21 mm / rev. (dry cutting), even under more severe conditions, cutting can be performed well.

[0071] In this embodiment, after performing heat treatment of holding at 450°C for 120 minutes and then air cooling, when in the constituent phases of the metal structure, the area ratio of the γ phase is 0.1% or less and the area ratio of the fine α phase with a particle size of 10 μm or less is 30% or more and 60% or less, the heat resistance and various properties are sufficiently excellent.

[0072] In this embodiment, after performing heat treatment of holding at 475°C for 120 minutes and then air cooling, when the tensile strength is 400 MPa or more and 550 MPa or less and the elongation is 14% or more and 38% or less, the heat resistance and mechanical properties are sufficiently excellent.

[0073] In this embodiment, after performing heat treatment of holding at 475°C for 120 minutes and then air cooling, when the machinability index during cutting is 80 or more under the conditions of cutting speed: 40 m / min and feed rate: 0.11 mm / rev. (dry cutting), the heat resistance and machinability are sufficiently excellent.

[0074] In this embodiment, after performing heat treatment of holding at 475°C for 120 minutes and then air cooling, when the maximum possible cold drawing processing rate until wire breakage is 50% or more, the heat resistance and workability are sufficiently excellent.

[0075] In this embodiment, after performing heat treatment of holding at 600°C for 120 minutes and then air cooling, when in the cross-section perpendicular to the casting direction, the area ratio of the fine α phase with a particle size of 10 μm or less is 10% or more and 20% or less, the heat resistance and strength are further excellent.

[0076] In this embodiment, in a cross-section orthogonal to the casting direction, the average crystal grain size of the β phase is 500 μm or less, and it has a crystal structure in which dendrites and columnar crystals are segmented. Taking the location of the maximum length of the α phase as the major axis and the location of the maximum length orthogonal to the major axis as the minor axis, when the ratio L1 / L2 of the major axis length L1 to the minor axis length L2 is in the range of 1 or more and 4 or less and it has a non-circular shape, an elliptical shape, or a polygonal shape, it is further excellent in strength, ductility, and machinability.

[0077] In this embodiment, when the oscillation mark depth is less than 50 μm, there are few defects during casting and the quality is excellent.

[0078] In this embodiment, when the cross-sectional area of the cross-section orthogonal to the casting direction is 12 mm 2 or more and 227 mm 2 or less, various parts can be efficiently manufactured.

[0079] The Cu-Zn-Si-Pb-P-based alloy continuous casting wire rod, which is an embodiment of the present invention, has been described above. However, the present invention is not limited to this, and can be appropriately changed without departing from the technical idea of the invention. For example, in this embodiment, it has been described as an upward-drawing continuous casting wire rod manufactured using the upward-drawing type continuous casting apparatus shown in FIG. 1. However, it is not limited to this, and it may be manufactured using a horizontal-drawing type continuous casting apparatus that draws out a continuous casting wire rod in the horizontal direction.

[0080] Also, in this embodiment, it has been described as manufacturing a continuous casting wire rod with a circular cross-section and a cross-sectional area in the range of 12 mm 2 or more and 227 mm 2 or less. However, it is not limited to this, and it may be a continuous casting wire rod with a polygonal cross-section, or a continuous casting wire rod with a tubular cross-section. Also, it may be a continuous casting wire rod with a special-shaped cross-section having convex and concave portions. Also, there is no particular limitation on the cross-sectional area of the cross-section orthogonal to its longitudinal direction.

Examples

[0081] The results of the confirmation experiments conducted to confirm the effects of the present invention will be described below. Melting raw materials were prepared so as to have the compositions shown in Tables 1 and 2. The prepared melting raw materials were charged into the crucible 12 of the casting furnace 11 shown in FIG. 1 in an amount of 500 kg and melted by heating with a heating means. As a mold, one for producing a cast wire rod having a circular cross section with an outer diameter of 6 mm (cross-sectional area of 28.26 mm in the cross section perpendicular to the drawing direction) was prepared. Also, for the machinability evaluation, one for producing a cast wire rod having a circular cross section with an outer diameter of 17 mm (cross-sectional area of 226.87 mm in the cross section perpendicular to the drawing direction) was prepared. 2 ) was prepared. 2 ) was prepared. Then, the casting conditions were set so as to have the cooling conditions shown in Tables 1 and 2, and the cast wire rod was drawn to perform casting of 300 kg.

[0082] The obtained cast wire was cut in a direction perpendicular to the casting direction to obtain a sample for microstructural observation. Also, it was cut along the center line parallel to the casting direction to create a sample for microstructural observation for evaluating the oscillation mark depth and the discolored part. The above various samples were subjected to emery polishing in the order of #240, 400, 800, and 1500 for 1000 s each at a pressure of 100 N and a speed of 100 r / min. Next, buff polishing was performed in the order of particles of 9 μm, 3 μm, and 1 μm for 1000 s each at a pressure of 30 N and a speed of 100 r / min. Thereafter, it was immersed in an etching solution (a mixed solution of hydrogen peroxide water and ammonia water) at 30 to 40 °C and subjected to ultrasonic cleaning for 30 to 60 s. Next, it was immersed in normal temperature water, subjected to ultrasonic cleaning for 30 to 60 s, and then dried.

[0083] (Microstructure of the cross section perpendicular to the casting direction) The cross section of the cast wire rod perpendicular to the casting direction was observed with an optical microscope at a magnification of 500 times to obtain a tissue image of a region of 219 μm in width and 275 μm in length. An example of the overall microstructural observation result of the cross section of the cast wire rod is shown in FIG. 2.

[0084] (Area ratio of γ phase) The tissue image obtained as described above was imported into the image analysis software ImageJ Fiji, and the image was binarized so that the γ-phase portion was white and the rest was black. An example of the binarized image is shown in Fig. 3. The area ratio of the γ-phase was calculated from the binarized image.

[0085] (Area ratio of fine α-phase with a particle size of 10 μm or less) From the tissue image obtained as described above, α-phase grains with a two-dimensional shape having an aspect ratio of 1:1 to 1:4 and being substantially circular, elliptical, or polygonal were extracted. For each of the extracted α-phase grains, as shown in Fig. 4, the distance of the line with the longest distance among the lines connecting two points on the grain boundary of the same crystal was defined as the crystal grain size. Fine α-phase grains with a particle size of 10 μm or less were extracted, and the area ratio was calculated using the image analysis software ImageJ Fiji.

[0086] (Area ratio of α-phase and β-phase) The tissue image obtained as described above was imported into the image analysis software ImageJ Fiji, and the image was binarized so that the α-phase portion was white and the rest (β-phase and γ-phase) was black. Examples of the observed image and the binarized image are shown in Fig. 5. The area ratio of the α-phase was calculated from the binarized image. For example, when the area ratio of the α-phase is 50 and the area ratio of the γ-phase is 0.01, the area ratio of the β-phase is 100 - 50 - 0.01 = 49.99. Therefore, the area ratio of α and β is 50:49.99.

[0087] (Mechanical properties) The obtained φ6 mm continuous casting wire rod was cut into lengths of 150 mm, and a tensile test was performed using a tensile testing machine AG-100kNX under the conditions of a gripping distance of 70 mm, a gauge distance of 50 mm, and a tensile speed of 15 MPa / sec to evaluate the tensile strength and elongation.

[0088] (Machinability) Evaluation was performed by a cutting test using a lathe. For a φ17 mm continuous casting wire rod (cast material), cutting was performed to make a test material with a diameter of 14 mm. For the extruded material of Comparative Example 9, after directly processing it to φ25 mm by extrusion on a prototype machine, it was cut to Φ14 to produce a sample. A machinability test was conducted on this sample.

[0089] A K10 carbide tool (tip) without a chip breaker was attached to a lathe. Using this lathe, under dry conditions, with a rake angle of 0°, a nose radius of 0.4 mm, a relief angle of 6°, a cutting speed of 40,110 m / min, a cutting depth of 1.0 mm, and a feed rate of 0.11, 0.21 mm / rev., the circumference of a test material with a diameter of 14 mm was cut.

[0090] The signal emitted from a three-component dynamometer (manufactured by Sanbao Electric Co., Ltd., AST type tool dynamometer AST-TL1003) attached to the tool was converted into an electrical voltage signal and recorded by a recorder. Next, these signals were converted into cutting resistances (main component force, feed component force, back component force, N). In order to suppress the influence of chip wear, the cutting test was carried out 2 times for the reciprocation of A→B→C→···C→B→A, and each sample was measured 4 times. The cutting resistance was obtained by the following formula. Cutting resistance (resultant force of main component force, feed component force, and back component force) = ((main component force) 2 +(feed component force) 2 +(back component force) 2 ) 1 / 2

[0091] Note that each sample was measured 4 times, and the average value was adopted. Taking the cutting resistance of a commercially available free-cutting brass bar C3604 made of a Zn-59 mass% Cu-3 mass% Pb-0.2 mass% Fe-0.3 mass% Sn alloy as 100, the relative value (machinability index) of the cutting resistance of the sample was calculated for relative evaluation. The higher the machinability index, the better the machinability. The description of "three-component forces" refers to the resultant force of the main component force, feed component force, and back component force, and indicates the machinability index. The machinability index was obtained as follows. Index of the cutting test result of the sample (machinability index) = (cutting resistance of C3604 / cutting resistance of the sample) × 100

[0092] (Heat treatment) The obtained continuously cast wire rod was heat-treated under an oxygen atmosphere at 450 °C for 120 minutes using a muffle furnace and then air-cooled, and the phase ratio of the α-phase, β-phase, and γ-phase and the area ratio of the fine α-phase were measured by the above-described procedure. An example of the microstructure observation result after the heat treatment is shown in Fig. 6. Also, an example of the binarized image is shown in Fig. 7, where the γ-phase part is white and the rest is black.

[0093] Further, the obtained continuously cast wire rod was heat-treated under an oxygen atmosphere at 475 °C for 120 minutes using a muffle furnace and then air-cooled, and the strength, elongation, and machinability (cutting index) were measured by the above-described procedure. Furthermore, the obtained continuously cast wire rod was heat-treated under an oxygen atmosphere at 600 °C for 120 minutes using a muffle furnace and then air-cooled, and the area ratio of the fine α-phase was measured by the above-described procedure.

[0094] (Cold drawing processing rate until fracture) For the φ6 cast wire, cold drawing tests were conducted in the order of drawing with a 6.0 inner diameter die (processing rate 0%) → removing the skin by 50 μm each with a 5.8 inner diameter peeling die → drawing with a 5.5 inner diameter die (processing rate 10% from the 5.8 inner diameter wire) → drawing with a 5.2 inner diameter die (processing rate 20% from the 5.8 inner diameter wire) → drawing with a 4.8 inner diameter die (processing rate 32% from the 5.8 inner diameter wire) → drawing with a 4.45 inner diameter die (processing rate 41% from the 5.8 inner diameter wire) → drawing with a 4.0 inner diameter die (processing rate 52% from the 5.8 inner diameter wire) → drawing with a 3.8 inner diameter die (processing rate 57% from the 5.8 inner diameter wire) → drawing with a 3.6 inner diameter die (processing rate 61% from the 5.8 inner diameter wire). For example, when wire breakage occurs during drawing with a 3.8 inner diameter die, since drawing was possible up to the previous die (4.0 inner diameter), the cold drawing processing rate until fracture is 52%. The cold drawing processing rate until fracture is determined in such a way.

[0095] (Oscillation mark depth) The obtained cast wire rod was cut into 10 mm lengths along the center line parallel to the drawing direction. Emery polishing was performed in the order of #240, 400, 800, and 1500 for 1000 s each at a pressure of 100 N and a speed of 100 r / min. Next, buff polishing was performed in the order of 9 μm, 3 μm, and 1 μm particles for 1000 s each at a pressure of 30 N and a speed of 100 r / min. Thereafter, it was immersed in an etching solution (a mixed solution of hydrogen peroxide water and ammonia water) at 30 to 40 °C and subjected to ultrasonic cleaning for 30 to 60 s. Next, it was immersed in normal temperature water, subjected to ultrasonic cleaning for 30 to 60 s, and then dried. Observation of the microstructure was carried out at a magnification of 100 times using an optical microscope. An example of the observation results is shown in Fig. 8. As shown in Fig. 8, continuous dents and cracks from the surface end part to the center part side of the cast wire sample were defined as oscillation marks. The starting position of the oscillation mark at the surface end part was set as the 0 mm position, and a line perpendicular to the drawing direction was drawn from the 0 mm position so as to intersect with the ending position of the oscillation mark on the center part side. The length of that line was defined as the oscillation mark depth. When the oscillation mark depth was less than 50 μm, it was evaluated as "〇", and when it exceeded 50 μm, it was evaluated as "×".

[0096] (Discolored part) A φ6 cast wire was cut into 10 mm lengths, and further cut horizontally in the direction perpendicular to the casting direction so as to pass through the center part of the cast wire. The total length of the discolored part was measured for both long sides (10 mm each, a total length of 20 mm) of the cast wire cut in this way (the cut surface is a rectangle of 6 mm × 10 mm). An example of the observation results is shown in Fig. 9. In Fig. 9, the total length of the discolored part is 2.4 mm (although only two examples of the images for measuring the length of the discolored part are shown below, actually, the total length of the discolored part is obtained from more observation images).

[0097] (Average crystal grain size of β phase) Observation of the microstructure was carried out at a magnification of 100 times using an optical microscope. An example of the observation results is shown in Fig. 10. Note that (a) is Example 11 of the present invention and (b) is Comparative Example 1. In FIG. 10, for Comparative Example 1, the β phase has a columnar crystal shape. Further, when the distance of the line connecting two points on the grain boundary of the same crystal with the longest distance is defined as the crystal grain size, the grain size also exceeds 500 μm. On the other hand, for the example ○○ of the present invention, it has a granular structure in which the columnar crystals are segmented. Those with a grain boundary of the β phase of 500 μm or less are marked as "〇" and those exceeding 500 μm are marked as "×" and described in the table.

[0098]

Table 1

[0099]

Table 2

[0100]

Table 3

[0101]

Table 4

[0102] In Comparative Example 1, the Cu content was low (the Zn content was high), the ratio of the α phase was low (the ratio of the β phase was high) in the area ratio of the α phase and the β phase, and the cold drawing processing rate until fracture was low and workability could not be ensured. Also, the cutting property index was low and the machinability was insufficient. Further, the evaluation of the oscillation mark depth and the discolored part became "×". In Comparative Example 2, the Cu content was high (the Zn content was low), the area ratio of the γ phase exceeded 0.1%, and the cold drawing processing rate until fracture was low and workability could not be ensured. Also, the evaluation of the discolored part became "×".

[0103] In Comparative Example 3, the Si content was low, the cold extraction processing rate until fracture was low, and workability could not be ensured. Also, the cutting property index was low and the machinability was insufficient. Furthermore, the evaluation of the oscillation mark depth was "×". In Comparative Example 4, the Si content was high, the area ratio of the γ phase exceeded 0.1%, the cold extraction processing rate until fracture was low, and workability could not be ensured. Also, the cutting property index was low and the machinability was insufficient. Furthermore, the evaluations of the oscillation mark depth and the discolored part were "×".

[0104] In Comparative Example 5, it did not contain Pb, the cutting property index was low, and the machinability was insufficient. Also, the evaluation of the discolored part was "×". In Comparative Example 6, the Pb content was high and the strength decreased. Also, the cold extraction processing rate until fracture was low and workability could not be ensured. Furthermore, the evaluations of the oscillation mark depth and the discolored part were "×".

[0105] In Comparative Example 7, the P content was low, the cutting property index was low, and the machinability was insufficient. Also, the cold extraction processing rate until fracture was low and workability could not be ensured. Furthermore, the evaluation of the discolored part was "×". In Comparative Example 8, the P content was high, the cutting property index was low, and the machinability was insufficient. Also, the cold extraction processing rate until fracture was low and workability could not be ensured. Furthermore, the evaluations of the oscillation mark depth and the discolored part were "×".

[0106] On the other hand, according to the example of the present invention, it was excellent in strength and elongation. Also, the cutting property index was high and the machinability was excellent. Furthermore, the cold extraction processing rate until fracture was high and workability could be ensured. Also, the evaluations of the oscillation mark depth and the discolored part were "〇", and continuous casting could be stably performed. Furthermore, even after heat treatment, it was excellent in strength, elongation, and machinability.

[0107] As described above, according to the example of the present invention, it was confirmed that it is possible to provide a high-quality Cu-Zn-Si-Pb-P-based alloy continuous wire rod excellent in strength, elongation, machinability, and having few defects.

Claims

1. The alloy contains Cu of more than 60.0 mass% and less than 65.0 mass%, Si of 0.40 mass% or more and 1.20 mass% or less, Pb of 0.002 mass% or more and 0.250 mass% or less, and P of 0.040 mass% or more and 0.190 mass% or less, and contains Bi of 0.001 mass% or more and 0.100 mass% or less as an optional element, with the balance being Zn and impurities, and among the impurities, the total content of Fe, Mn, Co and Cr is 0.450 mass% or less, and the total content of Sn and Al is 0.30 mass% or less, A Cu-Zn-Si-Pb-P based alloy continuous cast wire rod, characterized in that in a cross section perpendicular to the casting direction, the area ratio of α phase to β phase is α:β=40-70:60-30, the area ratio of γ phase is 0.1% or less, and the area ratio of fine α phase having a grain size of 10 μm or less is 30% to 60%.

2. 2. The Cu-Zn-Si-Pb-P based alloy continuous cast wire rod according to claim 1, characterized in that the tensile strength is in the range of 450 MPa or more and 600 MPa or less, and the elongation is in the range of 12% or more and 35% or less.

3. The Cu-Zn-Si-Pb-P alloy continuous cast wire rod according to claim 1 or 2, characterized in that when a lathe equipped with a carbide tool of ISO classification symbol K10 is used to cut a circumference of a test material having a diameter of 14 mm under the conditions of a rake angle of 0 °, a nose radius of 0.4 mm, a clearance angle of 6 °, a cutting speed of 40 m / min, a cutting depth of 1.0 mm, and a feed rate of 0.11 mm / rev. (dry condition), the cutting resistance calculated from the measurement value by a dynamometer attached to the tool using the following formula (1) is 90 or more, which is a relative value with respect to the cutting resistance of a commercially available free-cutting brass rod C3604 made of Zn-59 mass% Cu-3 mass% Pb-0.2 mass% Fe-0.3 mass% Sn alloy, taken as 100. (1) Formula: Cutting resistance = ((main component force) ２ + (Send り force) ２ +(Back force) ２ ) １／２

4. The Cu-Zn-Si-Pb-P alloy continuous cast wire rod according to claim 1 or 2, characterized in that when a lathe equipped with a carbide tool of ISO classification symbol K10 is used to cut a circumference of a test material having a diameter of 14 mm under the conditions of a rake angle of 0 °, a nose radius of 0.4 mm, a clearance angle of 6 °, a cutting speed of 110 m / min, a cutting depth of 1.0 mm, and a feed rate of 0.21 mm / rev. (dry condition), the cutting resistance calculated from the measurement value by a dynamometer attached to the tool using the following formula (1) is 60 or more, the machinability index being a relative value with respect to the cutting resistance of a commercially available free-cutting brass rod C3604 made of Zn-59 mass% Cu-3 mass% Pb-0.2 mass% Fe-0.3 mass% Sn alloy being taken as 100. (1) Formula: Cutting resistance = ((main component force) ２ + (Send り force) ２ +(Back force) ２ ) １／２

5. 3. The Cu-Zn-Si-Pb-P alloy continuous cast wire rod according to claim 1 or 2, characterized in that after heat treatment is performed by holding at 450°C for 120 minutes and then air-cooling, the area ratio of the γ phase in the constituent phases of the metal structure is 0.1% or less, and the area ratio of fine α phases having a grain size of 10 μm or less is 30% to 60%.

6. 3. The Cu-Zn-Si-Pb-P based alloy continuous cast wire rod according to claim 1, characterized in that after carrying out a heat treatment of holding at 475° C. for 120 minutes and then air-cooling, the wire rod has a tensile strength of 400 MPa or more and 550 MPa or less and an elongation of 14% or more and 38% or less.

7. After performing a heat treatment at 475°C for 120 minutes and then air cooling, The Cu-Zn-Si-Pb-P alloy continuous cast wire rod according to claim 1 or 2, characterized in that when a lathe equipped with a carbide tool of ISO classification symbol K10 is used to cut a circumference of a test material having a diameter of 14 mm under the conditions of a rake angle of 0 °, a nose radius of 0.4 mm, a clearance angle of 6 °, a cutting speed of 40 m / min, a cutting depth of 1.0 mm, and a feed rate of 0.11 mm / rev. (dry condition), the cutting resistance calculated from the measurement value by a dynamometer attached to the tool using the following formula (1) is 80 or more, which is a relative value with respect to the cutting resistance of a commercially available free-cutting brass rod C3604 made of Zn-59 mass% Cu-3 mass% Pb-0.2 mass% Fe-0.3 mass% Sn alloy, taken as 100. (1) Formula: Cutting resistance = ((main component force) ２ + (Send り force) ２ +(Back force) ２ ) １／２

8. After performing a heat treatment at 475°C for 120 minutes and then air cooling, 3. A Cu-Zn-Si-Pb-P alloy continuously cast wire rod according to claim 1, wherein the maximum possible cold drawing reduction ratio before breakage is 50% or more.

9. 3. The Cu-Zn-Si-Pb-P based alloy continuous cast wire rod according to claim 1, characterized in that after carrying out a heat treatment in which the wire rod is held at 600° C. for 120 minutes and then air-cooled, the area ratio of fine α phases having a grain size of 10 μm or less is 10% or more and 20% or less.

10. In a cross section perpendicular to the casting direction, the average crystal grain size of the β phase is 500 μm or less, and the dendrites and columnar crystals are separated, 3. The Cu-Zn-Si-Pb-P based alloy continuous cast wire rod according to claim 1 or 2, characterized in that the ratio L1 / L2 of the major axis length L1 to the minor axis length L2, where the major axis is the maximum length of the α phase and the minor axis is the maximum length of the α phase perpendicular to the major axis, is within a range of 1 or more and 4 or less, and the wire rod has a substantially circular, elliptical or polygonal shape.

11. 3. The Cu-Zn-Si-Pb-P alloy continuously cast wire rod according to claim 1, wherein the depth of oscillation marks is less than 50 μm.

12. The cross-sectional area of ​​the cross section perpendicular to the casting direction is 12 mm ２ 227mm or more ２ 3. The Cu-Zn-Si-Pb-P based alloy continuous cast wire rod according to claim 1, wherein the Cu-Zn-Si-Pb-P based alloy continuous cast wire rod has a composition within the following range:

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