Free-machining copper alloy casting and method for producing free-machining copper alloy casting

Abstract

This free-machining copper alloy casting is characterized in that: prescribed amounts of Cu, Si, Pb, and P are contained, with the remainder including Zn and unavoidable impurities; the total content of Fe, Mn, Co, and Cr among the unavoidable impurities is less than a prescribed amount; the content of Al among the unavoidable impurities is less than a prescribed amount; the composition relational expression f1 defined from the composition of elements and the structure relational expressions f2, f3, and f4 defined from area ratios of constituent phases of the metal structure are respectively within prescribed ranges; and a grain boundary of a modified β1 phase is observable when etched with a liquid mixture of hydrogen peroxide and aqueous ammonia.

Description

Free-cutting copper alloy casting, and method for producing free-cutting copper alloy casting

[0001] The present invention relates to a free-cutting copper alloy casting having high corrosion resistance, particularly dezincification corrosion resistance and strength, and a significantly reduced Pb content, and a method for producing the free-cutting copper alloy casting. It relates to a free-cutting copper alloy casting used for utensils and parts used in drinking water consumed daily by humans and animals, utensils and parts used in sanitary facilities such as kitchens, bathrooms, and toilets, water meters, musical instruments, tableware, drainage utensils and parts, industrial piping parts, electrical and electronic equipment parts, automobile parts, machine parts, stationery, toys, sliding parts, instrument parts, precision machine parts, medical parts, parts related to liquids and gases such as hydrogen, and specifically, faucet, mixing faucet, faucet fitting, stopcock, valve, joint, valve, shower head, cock, gear, shaft, bearing, shaft, sleeve, spindle, sensor, bolt, nut, flare nut, pen tip, insert nut, bag nut, nipple, spacer, screw, etc. for parts to be cut, and a method for producing the free-cutting copper alloy casting. This application claims priority based on Japanese Patent Application No. 2024-192019 filed in Japan on October 31, 2024, and Japanese Patent Application No. 2024-192034 filed in Japan on October 31, 2024, and incorporates the contents herein.

[0002] Conventionally, for parts such as faucet, mixing faucet, stopcock, valve, cock, joint, gear, sensor, nut, screw, etc. used in drinking water, utensils and parts related to sanitary facilities, water meters, musical instruments, tableware, electrical, household appliances, and electronic equipment parts, automobile parts, machine parts, stationery, precision machine parts, medical parts, and utensils and parts related to liquids and gases such as industrial water, drainage, and hydrogen, Cu-Zn-Pb alloys (so-called free-cutting brass bars, forging brass, casting brass) containing 56 to 65 mass% of Cu and 1 to 4 mass% of Pb, with the balance being Zn, or Cu-Sn-Zn-Pb alloys (so-called bronze castings: gunmetal) containing 80 to 88 mass% of Cu, 2 to 8 mass% of Sn, and 1 to 8 mass% of Pb, with the balance being Zn, which have excellent machinability, antibacterial properties, and good corrosion resistance, have generally been used.

[0003] However, in recent years, concerns have arisen regarding the effects of lead (Pb) on human health and the environment, leading to increased regulatory efforts in various countries. For example, in California, USA, regulations limiting the Pb content in drinking water equipment to 0.25 mass% or less have been in effect since January 2010. Regulations are also rapidly advancing in countries other than the United States, creating a demand for the development of copper alloy materials that comply with Pb content regulations.

[0004] Furthermore, in other industrial sectors such as electrical and electronic equipment, automobiles, and machinery, for example, the European RoHS Directive and ELV Directive exceptionally allow Pb content up to 4 mass% in free-cutting copper alloys. However, similar to the drinking water sector, there is active discussion about strengthening regulations on Pb content, including the elimination of these exceptions.

[0005] Amidst the trend of stricter Pb regulations for free-cutting copper alloys, as an alternative to Pb-containing free-cutting copper alloys containing 56-65 mass% Cu, 1-4 mass% Pb, and the remainder being Zn, particularly free-cutting brass containing 3 mass% Pb (JIS standard: C3604, ASTM standard: C36000, EN standard: CW614N), which is the most widely used free-cutting copper alloy worldwide, (1) Bi, which has machinability properties, is used instead of Pb, and in some cases Therefore, various alloys have been proposed, including (1) Cu-Zn-Bi alloys and Cu-Zn-Bi-Se alloys containing Se in addition to Bi, (2) Cu-Zn alloys containing a high concentration of Zn and increasing the β phase to improve machinability, (3) Cu-Zn-Si alloys containing a large amount of γ phase and κ phase which have excellent machinability instead of Pb, and (4) Cu-Zn-Si-Pb alloys in which the machinability of the β phase is improved by the inclusion of Si. For example, in Patent Document 1, 0.5 to 2.5 mass% of Bi is added to a Cu-Zn alloy, and since the β phase has poor resistance to dezincification corrosion, the β phase is reduced to improve resistance to dezincification corrosion.

[0006] However, alloys containing Bi instead of Pb have many problems, including the fact that Bi is inferior to Pb in terms of machinability, may be harmful to the environment and human health like Pb, is a rare metal and therefore has resource problems, and makes copper alloy materials brittle. Furthermore, as shown in Patent Document 2, the β phase of Cu-Zn alloys has conventionally had poor resistance to dezincification corrosion, and as a measure to improve this, it is practically necessary to reduce the β phase and perform annealing to separate the β phase with the α phase.

[0007] Furthermore, while Cu-Zn binary alloys containing a large amount of β phase contribute to improved machinability, the β phase has inferior machinability compared to Pb, and is also inferior in dezincification corrosion resistance and stress corrosion cracking resistance. Therefore, it cannot possibly replace Pb-containing free-machining copper alloys. For this reason, Cu-Zn-Si alloys containing Si instead of Pb have been proposed as free-machining copper alloys, for example, in Patent Documents 3 to 9.

[0008] Patent documents 3 to 8 state that the Cu content is approximately 58 to 65 mass%, and the Si content is approximately 0.2 to 1.5 mass%, and that the machinability is improved by the presence of Si contained in the β phase and fine P compounds formed by P and Zn, and that by specifying the area ratio of the β phase and γ phase, excellent machinability is achieved in combination with the presence of P compounds and a small amount of Pb. However, it is a well known fact that the β phase of Cu-Zn alloys has poor dezincification resistance, as disclosed in Patent Document 2. For this reason, no specific data related to dezincification resistance is disclosed in Patent Documents 2 to 7, and it is presumed that the dezincification resistance, which is a technical problem of the β phase of conventional Cu-Zn alloys, has not been improved.

[0009] Patent Document 9 describes how, by specifying the total surface area of ​​the γ and κ phases, which have excellent machinability properties and are formed in alloys with high Cu and Si concentrations, with a Cu content of 71.5 to 78.5 mass% and a Si content of 2.0 to 4.5 mass%, excellent machinability is achieved with a small amount of Pb content of 0.02 mass% or less. Furthermore, by including Sn and Al in amounts of 0.1 mass% or more each, a large amount of γ phase is formed, further improving machinability and corrosion resistance.

[0010] Furthermore, Patent Document 10 describes a Cu-Zn-Sn alloy containing small amounts of Si, Pb, P, or Fe, and containing 0.5 mass% or less of Pb. By devising a manufacturing method, Pb-enriched particles are dispersed in the matrix, and the number density of Pb-enriched particles present in the α phase is increased, thereby obtaining excellent machinability. Patent Document 9 states that a finish heat treatment of 400 to 600°C is substantially necessary to improve resistance to dezincification corrosion.

[0011] Patent document 11 relates to a technology for manufacturing near-net cavity hot forged products using a hollow material in a Cu-Zn-Si-Pb-P alloy, and proposes a copper alloy in which the area ratios of the β phase, γ phase, and μ phase are limited. Patent document 12 proposes a copper alloy casting in a Cu-Zn-Zr-P alloy in which Si, Pb, and Sn are selectively contained, and the crystal grains are refined by the action of Zr and P. Patent document 13 proposes a copper alloy in a Cu-Zn-Sn-Al alloy in which Si and Pb are selectively contained, and the area ratios of the γ phase and β phase are limited, resulting in excellent discoloration resistance. Patent document 14 proposes a copper alloy casting in a Cu-Zn-Si-Sn-Al-P alloy that does not contain Pb.

[0012] Patent document 15 states that in Cu-Zn-Si-Sn-Al alloys, the apparent Zn content is important for improving corrosion resistance, and proposes a copper alloy in which machinability is improved by substantially containing a large amount of Pb or Bi. Patent document 16 describes a copper alloy casting in a Cu-Zn-Si alloy that contains 65 mass% or more of Cu, has good castability and mechanical strength, does not contain Pb, and whose machinability is improved by the γ phase, and describes an example containing large amounts of Sn, Al, Mn, Ni, and Sb.

[0013] Patent documents 17 to 19 state that the Cu content is approximately 58 to 66 mass%, and the Si content is approximately 0.04 to 1.2 mass%, and that machinability is improved by specifying the size and number of fine P compounds formed by P and Zn, etc., with respect to the Si contained in the alloy. They also state that by specifying the area ratio of the β phase, excellent machinability is achieved in combination with the presence of P compounds. However, it is a well known fact that the β phase of Cu-Zn alloys has poor dezincification resistance, as disclosed in Patent Document 2. Therefore, no specific data related to dezincification resistance is disclosed in Patent Documents 17 to 19, and it is presumed that the dezincification resistance, which is a technical problem of the β phase of conventional Cu-Zn alloys, has not been improved.

[0014] Japanese Patent Publication No. 4397963, Japanese Unexamined Patent Publication No. 2002-003967, Japanese Unexamined Patent Publication No. 2021-042461, Japanese Unexamined Patent Publication No. 2021-042459, Japanese Unexamined Patent Publication No. 2021-042460, International Publication No. 2020 / 261666, Japanese Unexamined Patent Publication No. 2021-042462, International Publication No. 2021 / 117528, International Publication No. 2007 / 034571, Japanese Unexamined Patent Publication No. 2016-194 Publication No. 123, International Publication No. 2013 / 065830, International Publication No. 2006 / 016630, International Publication No. 2015 / 046421, Japanese Patent Publication No. 2010-133006, Japanese Patent Publication No. 2018-048398, Japanese Patent Publication No. 2019-508584, Publication DE102022002927B4, DE102022002928B4, International Publication No. 2024 / 032925

[0015] As shown in these Patent Documents 1 to 19, there has been no fundamental improvement in the dezincification corrosion resistance of the β phase present in Cu-Zn alloys, which has been a major technical challenge in the past.

[0016] The present invention has been made to solve the problems of the prior art, and aims to provide a free-machining copper alloy casting that has good resistance to dezincification corrosion despite containing a large amount of β phase (modified β1 phase), high strength, and a significantly reduced Pb content, as well as a method for manufacturing a free-machining copper alloy casting.

[0017] In order to solve the above-mentioned problems and achieve the above-mentioned objectives, the inventors diligently conducted research and obtained the following findings. In this specification, unless otherwise specified, the β phase includes the β' phase, the γ phase includes the γ' phase, and the α phase includes the α' phase. The β1 phase is a modified β phase and is distinct from the β phase and the β' phase. The β1 phase is characterized by the observation of grain boundaries within the β1 phase when observed with a metallurgical microscope using hydrogen peroxide and aqueous ammonia as etching solutions. Here, grain boundaries refer to linear patterns that penetrate within the β1 phase crystal grains, as shown in Figure 1A.

[0018] The β phase present in common Cu-Zn alloys, Cu-Zn-Bi alloys, and Cu-Zn-Si alloys does not exhibit grain boundaries even when etched with hydrogen peroxide and ammonia water. Therefore, the β phase and the β1 phase can be clearly distinguished. P compounds refer to compounds of P and mainly Zn and / or Si. Cold workability refers to the performance of cold processing such as drawing, wire drawing, rolling, riveting, and bending. Good or excellent machinability, unless otherwise specified, refers to low cutting resistance and good or excellent chip breaking when drilling with a drill. Conductivity refers to electrical conductivity, thermal conductivity, and electrical conductivity. Cooling rate refers to the average cooling rate over a certain temperature range.

[0019] In the aforementioned Patent Document 9, it is stated that in Cu-Zn-Si alloys, the β phase contributes little to, or rather inhibits, the machinability of the copper alloy. In Patent Documents 11, 12, and 13, the amount of the β phase is also significantly limited. In Patent Document 2, as a method to improve the dezincification corrosion resistance of the β phase, it is necessary to reduce the β phase and perform an annealing process at 350 to 550°C so that the β phase is separated by the α phase. In Patent Document 10, in order to improve the dezincification corrosion resistance of the β phase, it is necessary to have a higher Sn content than Si, and to heat the alloy to a temperature of 700 to 850°C, hot extrude it, and then perform a finish heat treatment by holding it at 400 to 600°C for 30 minutes or more, with an average cooling rate of 0.2 to 10°C / second from 400 to 200°C.

[0020] On the other hand, Patent Documents 3 to 8 describe the discovery that, in Cu-Zn-Si alloys, first, incorporating a certain amount of Si into the β phase has a significant effect on the machinability of the β phase itself. Furthermore, it is stated that the presence of fine P compounds, the inclusion of small amounts of Pb, and in some cases Bi, work synergistically to obtain excellent machinability in the alloy. However, in order to include P compounds, it is preferably necessary to cool the alloy at an average rate of approximately 0.1°C / min to approximately 70°C / min in the temperature range from approximately 530°C to approximately 450°C after hot working. Incidentally, Patent Documents 3 to 8 do not disclose any data related to dezincification corrosion resistance. Nor do they mention any modification of the β phase itself. In other words, it is presumed that there is no improvement in the dezincification corrosion resistance of the β phase present in Cu-Zn-Si alloys, nor any further improvement in machinability.

[0021] The inventors further worked on modifying the β phase itself in Cu-Zn-Si alloys. As a result of diligent research, they found that even without the presence of P compounds, the modified β phase, i.e., the β1 phase, possesses excellent machinability without requiring the inclusion of Bi, and significantly improves the dezincification corrosion resistance of the β phase, which had been a long-standing issue for Cu-Zn alloys. In addition, alloys containing the β1 phase instead of the β phase showed further increased strength without impairing ductility. This β1 phase is obtained by first solid-solving a certain amount of Si and P within the β phase, maintaining the β phase state at 500-700°C, and increasing the cooling rate when cooling to room temperature, thereby bringing the high-temperature metallic state down to room temperature (maintaining the high-temperature metallic state down to room temperature).

[0022] Incidentally, the β1 phase can be easily distinguished and identified from the β phase of Cu-Zn alloys. The surface is polished to a mirror finish and etched with a mixture of hydrogen peroxide and ammonia water. For etching, an aqueous solution is used, which is a mixture of 3 mL of 3 vol% hydrogen peroxide and 22 mL of 14 vol% ammonia water. When the polished surface of the metal is immersed in this aqueous solution for about 2 to 10 seconds at room temperature of about 15 to 25°C and observed with a metal microscope at 200 to 1000x magnification, grain boundary patterns can be seen in the β1 phase, but grain boundaries cannot be seen in the β phase of a normal Cu-Zn alloy. The use of this etching solution is also disclosed in Patent Documents 3 to 8, 11, and 12, and the metal structure is shown.

[0023] The conditions for obtaining the β1 phase are that the molten metal is poured into the mold, and after solidification, the casting maintains a high temperature of over 500°C, i.e., a β phase state between 500°C and 700°C, until it reaches room temperature. Specifically, to obtain the β1 phase, during the cooling process after solidification, the cooling process must begin at a temperature below 700°C and above 500°C, the casting must be cooled at a cooling rate exceeding 300°C / min when it reaches 500°C, i.e., in the temperature region just above 500°C, and in the subsequent cooling process, the average cooling rate in the temperature region from 500°C to 300°C must be at least 300°C / min. In this specification, unless otherwise specified, the cooling process refers to controlling the cooling rate by water cooling or a similar method, rather than natural cooling.

[0024] Patent documents 3 to 8 state that in order to obtain a compound containing fine P particles, the casting or hot-worked material must be cooled at an average cooling rate of approximately 0.1°C / min to approximately 70°C / min in the temperature range from approximately 530°C to approximately 450°C after casting or hot working. In other words, it is clear that this embodiment and patent documents 3 to 8 are moving in opposite directions (giving opposite instructions). However, for example, if the cooling rate around 520°C after casting is 60°C / min, and the average cooling rate in the temperature range from 520°C to 500°C (the starting temperature of the cooling process) exceeds 300°C / min, then in this embodiment as well, an alloy containing both the β1 phase and the P compound may exist. However, in this embodiment, the P compound is not important, so the presence of the P compound is not required.

[0025] The modification from the β phase to the β1 phase in this application, even without the P compounds disclosed in Patent Documents 3 to 8, promotes a reduction in cutting resistance and chip fragmentation through the synergistic effect of the β1 phase and fine Pb particles. More importantly, the unresolved and significant problem of dezincification corrosion resistance in conventional β phases is greatly improved and resolved by the modification from the β phase to the β1 phase. Furthermore, the mechanical properties inherit the high strength of the conventional β phase, resulting in a material with high strength. As a result, we have invented a copper alloy casting that has machinability close to that of conventional free-cutting brass, and which has better dezincification corrosion resistance and higher strength compared to conventional free-cutting brass.

[0026] The free-machining copper alloy casting of embodiment 1 of the present invention contains Cu in an amount greater than 58.0 mass% and less than 63.5 mass%, Si in an amount greater than 0.05 mass% and less than 0.50 mass%, Pb in an amount greater than 0.002 mass% and less than 0.20 mass%, and P in an amount greater than 0.01 mass% and less than 0.40 mass%, with the remainder being Zn and unavoidable impurities, wherein the total content of Fe, Mn, Co and Cr among the unavoidable impurities is less than 0.40 mass%, and the content of Al is less than 0.30 mass%, and the Cu content is [Cu] mass%, the Si content is [Si] mass%, and the Pb content is When the P content is [Pb] mass%, the P content is [P] mass%, and the relationship 57.5 ≤ f1 = [Cu] - 4.6 × [Si] + 0.5 × [Pb] + 0.5 × [P] ≤ 61.5 holds. In the constituent phases of the metallic structure excluding nonmetallic inclusions, when the area ratio of the α phase is (α)%, the area ratio of the γ phase is (γ)%, and the area ratio of the modified β phase, the β1 phase, is (β1)%, the relationships 10 ≤ f2 = (α) < 80, 20 < f3 = (β1) ≤ 90, and 0 ≤ f4 = (γ) < 4 hold. Furthermore, when etched with a mixture of hydrogen peroxide and ammonia water, grain boundaries can be observed inside the β1 phase.

[0027] The free-machining copper alloy casting of embodiment 2 of the present invention contains 58.8 mass% to 63.0 mass% of Cu, 0.08 mass% to 0.48 mass% of Si, 0.01 mass% to 0.10 mass% of Pb, and 0.03 mass% to 0.20 mass% of P, with the remainder being Zn and unavoidable impurities, wherein the total content of Fe, Mn, Co and Cr among the unavoidable impurities is less than 0.30 mass%, and the content of Al is less than 0.15 mass%, with the Cu content being [Cu] mass%, the Si content being [Si] mass%, and the Pb content being [ When the Pb content is [P]mass%, the relationship 58.0 ≤ f1 = [Cu] - 4.6 × [Si] + 0.5 × [Pb] + 0.5 × [P] ≤ 61.0 holds, and in the constituent phases of the metallic structure excluding nonmetallic inclusions, when the area ratio of the α phase is (α)%, the area ratio of the γ phase is (γ)%, and the area ratio of the modified β phase, the β1 phase, is (β1)%, the relationships 15 ≤ f2 = (α) < 75, 25 < f3 = (β1) ≤ 85, 0 ≤ f4 = (γ) < 1 hold, and grain boundaries can be observed inside the β1 phase when etched with a mixture of hydrogen peroxide and ammonia water.

[0028] The free-machining copper alloy casting of embodiment 3 of the present invention contains Cu in amounts exceeding 58.0 mass% and less than 63.5 mass%, Si in amounts exceeding 0.05 mass% and less than 0.50 mass%, Pb in amounts of 0.002 mass% or more and less than 0.20 mass%, and P in amounts exceeding 0.01 mass% and less than 0.40 mass%, and as an optional element, Sn in amounts exceeding 0.01 mass% and less than 0.90 mass%, and 0.0001 ma It contains Bi in an amount greater than ss% and less than 0.20 mass%, Sb in an amount of 0.01 mass% or more and 0.12 mass%, and As in an amount of 0.01 mass% or more and 0.12 mass%, with the remainder being Zn and unavoidable impurities, wherein the total content of Fe, Mn, Co and Cr among the unavoidable impurities is less than 0.40 mass%, and the content of Al is less than 0.30 mass%, and the content of Cu is When the content of Cu is [Cu] mass%, the content of Si is [Si] mass%, the content of Pb is [Pb] mass%, the content of P is [P] mass%, the content of Bi is [Bi] mass%, and the content of Sn is [Sn] mass, the relationship 57.5 ≤ f1 = [Cu] - 4.6 × [Si] + 0.5 × ([Pb] + [Bi]) + 0.5 × [P] - 1.0 × [Sn] ≤ 61.5 holds true for nonmetallic inclusions. In the constituent phases of the metal structure excluding the specified phase, when the area ratio of the α phase is (α)%, the area ratio of the γ phase is (γ)%, and the area ratio of the modified β phase, the β1 phase, is (β1)%, the following relationships exist: 10 ≤ f2 = (α) < 80, 20 < f3 = (β1) ≤ 90, 0 ≤ f4 = (γ) < 4, and grain boundaries can be observed inside the β1 phase when etched with a mixture of hydrogen peroxide and ammonia water.

[0029] The free-machining copper alloy casting of embodiment 4 of the present invention contains 58.8 mass% to 63.0 mass% of Cu, 0.08 mass% to 0.48 mass% of Si, 0.01 mass% to 0.10 mass% of Pb, and 0.03 mass% to 0.20 mass% of P, and as an optional element, 0.05 mass% to 0.85 mass% of Sn, 0.001 mass It contains Bi in an amount of % or more and 0.10 mass% or less, Sb in an amount of 0.012 mass% or more and 0.08 mass% or less, As in an amount of 0.025 mass% or more and 0.08 mass% or less, with the remainder being Zn and unavoidable impurities, wherein the total content of Fe, Mn, Co and Cr among the unavoidable impurities is less than 0.30 mass%, and the content of Al is less than 0.15 mass%, and the content of Cu is When the content of Cu is [Cu] mass%, the content of Si is [Si] mass%, the content of Pb is [Pb] mass%, the content of P is [P] mass%, the content of Bi is [Bi] mass%, and the content of Sn is [Sn] mass, the relationship 58.0 ≤ f1 = [Cu] - 4.6 × [Si] + 0.5 × ([Pb] + [Bi]) + 0.5 × [P] - 1.0 × [Sn] ≤ 61.0 holds true for nonmetallic inclusions. In the constituent phases of the metal structure excluding the specified phase, when the area ratio of the α phase is (α)%, the area ratio of the γ phase is (γ)%, and the area ratio of the modified β phase, the β1 phase, is (β1)%, the following relationships exist: 15 ≤ f2 = (α) < 75, 25 < f3 = (β1) ≤ 85, 0 ≤ f4 = (γ) < 1, and grain boundaries can be observed inside the β1 phase when etched with a mixture of hydrogen peroxide and ammonia water.

[0030] The free-machining copper alloy casting of embodiment 5 of the present invention is characterized in that, in any one of embodiments 1 to 4 of the present invention, the electrical conductivity is 17.0% IACS or higher, the Vickers hardness is 95 HV or higher, and the maximum dezincification corrosion depth in the dezincification corrosion test results according to ISO 6509 is 400 μm or less.

[0031] The free-machining copper alloy casting of embodiment 6 of the present invention is characterized in that, in any one of embodiments 1 to 5 of the present invention, it is used for appliances and parts related to drinking water and sanitary equipment, valves, cocks, industrial piping parts, water meters, musical instruments, automobile parts, electrical and electronic equipment parts, machine parts, stationery, toys, sliding parts, instrument parts, precision machine parts, and medical parts.

[0032] The method for producing a free-machining copper alloy casting according to embodiment 7 of the present invention comprises Cu in an amount greater than 58.0 mass% and less than 63.5 mass%, Si in an amount greater than 0.05 mass% and less than 0.50 mass%, Pb in an amount greater than 0.002 mass% and less than 0.20 mass%, and P in an amount greater than 0.01 mass% and less than 0.40 mass%, with the remainder being Zn and unavoidable impurities, wherein among the unavoidable impurities, Fe, Mn, C If the total content of oxygen and Cr is less than 0.40 mass%, and the content of Al is less than 0.30 mass%, and the content of Cu is [Cu] mass%, the content of Si is [Si] mass%, the content of Pb is [Pb] mass%, and the content of P is [P] mass%, then the relationship is 57.5 ≤ f1 = [Cu] - 4.6 × [Si] + 0.5 × [Pb] + 0.5 × [P] ≤ 61.5. A method for producing a free-machining copper alloy casting using a copper alloy having the following characteristics, wherein in the former casting process, the starting temperature for the cooling process in the final casting process is set to a temperature higher than 500°C and lower than 700°C; in the latter heat treatment process, in the final heat treatment process, the casting is heated at a temperature between 520°C and 650°C for 1 minute to 5 hours; and in the cooling process after the heat treatment, the cooling process is started when the temperature of the casting exceeds 500°C; and in both the former and latter cooling processes, the cooling rate when the temperature of the casting reaches 500°C exceeds 300°C / min, and the average cooling rate in the temperature range from 500°C to 300°C exceeds 300°C / min.

[0033] The method for producing a free-machining copper alloy casting according to aspect 8 of the present invention comprises 58.8 mass% to 63.0 mass% of Cu, 0.08 mass% to 0.48 mass% of Si, 0.01 mass% to 0.10 mass% of Pb, and 0.03 mass% to 0.20 mass% of P, with the remainder being Zn and unavoidable impurities, of which Fe, Mn, and Co If the total content of Cr is less than 0.30 mass%, and the content of Al is less than 0.15 mass%, and the content of Cu is [Cu] mass%, the content of Si is [Si] mass%, the content of Pb is [Pb] mass%, and the content of P is [P] mass%, then the relationship is 58.0 ≤ f1 = [Cu] - 4.6 × [Si] + 0.5 × [Pb] + 0.5 × [P] ≤ 61.0. A method for producing a free-machining copper alloy casting using a copper alloy having the following characteristics, wherein in the former casting process, the starting temperature for the cooling process in the final casting process is set to a temperature higher than 500°C and lower than 700°C; in the latter heat treatment process, in the final heat treatment process, the casting is heated at a temperature between 520°C and 650°C for 1 minute to 5 hours; and in the cooling process after the heat treatment, the cooling process is started when the temperature of the casting exceeds 500°C; and in both the former and latter cooling processes, the cooling rate when the temperature of the casting reaches 500°C exceeds 300°C / min, and the average cooling rate in the temperature range from 500°C to 300°C exceeds 300°C / min.

[0034] The method for producing a free-machining copper alloy casting according to aspect 9 of the present invention comprises Cu in amounts exceeding 58.0 mass% and less than 63.5 mass%, Si in amounts exceeding 0.05 mass% and less than 0.50 mass%, Pb in amounts of 0.002 mass% or more and less than 0.20 mass%, and P in amounts exceeding 0.01 mass% and less than 0.40 mass%, with optional elements including Sn in amounts exceeding 0.01 mass% and less than 0.90 mass%, Bi in amounts exceeding 0.0001 mass% and less than 0.20 mass%, and 0.01 mass% or more and 0.12 mass. It contains ss% or less of Sb, 0.01 mass% to 0.12 mass% of As, with the remainder being Zn and unavoidable impurities, wherein the total content of Fe, Mn, Co, and Cr among the unavoidable impurities is less than 0.40 mass%, and the content of Al is less than 0.30 mass%, with Cu content being [Cu] mass%, Si content being [Si] mass%, Pb content being [Pb] mass%, P content being [P] mass%, Bi content being [Bi] mass%, and Sn A method for producing a free-machining copper alloy casting using a copper alloy having the relationship 57.5 ≤ f1 = [Cu] - 4.6 × [Si] + 0.5 × ([Pb] + [Bi]) + 0.5 × [P] - 1.0 × [Sn] ≤ 61.5, where the content of [Sn] is [Sn] mass%, wherein the manufacturing process includes one or more casting steps, or one or more casting steps and a heat treatment step, wherein in the former casting step, in the cooling process of the final casting step, the cooling treatment start temperature is higher than 500°C and 70 The temperature is set to a temperature lower than 0°C. In the latter heat treatment process, in the final heat treatment process, the casting is heated under conditions of being held at a temperature between 520°C and 650°C for 1 minute to 5 hours. In the cooling process after heat treatment, the cooling process is started when the temperature of the casting exceeds 500°C. In both the former and latter cooling processes, the cooling rate when the temperature of the casting reaches 500°C exceeds 300°C / min, and the average cooling rate in the temperature range from 500°C to 300°C exceeds 300°C / min.

[0035] The method for producing a free-machining copper alloy casting according to embodiment 10 of the present invention comprises 58.8 mass% to 63.0 mass% of Cu, 0.08 mass% to 0.48 mass% of Si, 0.01 mass% to 0.10 mass% of Pb, and 0.03 mass% to 0.20 mass% of P, and as optional elements, 0.05 mass% to 0.85 mass% of Sn, 0.001 mass% to 0.10 mass% of Bi, and 0.012 mass% to 0.08 mass% of Ma. It contains ss% or less of Sb, 0.025 mass% to 0.08 mass% of As, with the remainder being Zn and unavoidable impurities, wherein the total content of Fe, Mn, Co and Cr among the unavoidable impurities is less than 0.30 mass%, and the content of Al is less than 0.15 mass%, with Cu content being [Cu] mass%, Si content being [Si] mass%, Pb content being [Pb] mass%, P content being [P] mass%, Bi content being [Bi] mass%, and Sn A method for producing a free-machining copper alloy casting using a copper alloy having the relationship 58.0 ≤ f1 = [Cu] - 4.6 × [Si] + 0.5 × ([Pb] + [Bi]) + 0.5 × [P] - 1.0 × [Sn] ≤ 61.0, where the content of [Sn] is [Sn] mass%, by a manufacturing process having one or more casting steps, or by a manufacturing process having one or more casting steps and a heat treatment step, wherein in the former casting step, in the cooling process of the final casting step, the cooling treatment start temperature is higher than 500°C and 70 The temperature is set to a temperature lower than 0°C. In the latter heat treatment process, in the final heat treatment process, the casting is heated under conditions of being held at a temperature between 520°C and 650°C for 1 minute to 5 hours. In the cooling process after heat treatment, the cooling process is started when the temperature of the casting exceeds 500°C. In both the former and latter cooling processes, the cooling rate when the temperature of the casting reaches 500°C exceeds 300°C / min, and the average cooling rate in the temperature range from 500°C to 300°C exceeds 300°C / min.

[0036] According to one aspect of the present invention, it is possible to provide a free-machining copper alloy casting that has good resistance to dezincification corrosion despite containing a large amount of β phase (modified β1 phase), high strength, and a significantly reduced Pb content, as well as a method for producing a free-machining copper alloy casting.

[0037] This is a photograph of the metallographic structure of a copper alloy in an embodiment, where the copper alloy was obtained by subjecting alloy No. S03 to process No. B1. In process No. B1, raw materials were melted in a predetermined ratio in the laboratory, the molten metal at approximately 950°C was poured into an iron mold with an inner diameter of 40 mm and a depth of 200 mm, and the material, which had been cooled to room temperature, was subjected to another heat treatment at 570°C for 20 minutes, and the cooling process was started at 565°C, with both the cooling rate at 500°C and the average cooling rate in the temperature range from 500°C to 300°C being 1200°C / min. This is a photograph of the metallographic structure of a copper alloy in an embodiment, where the copper alloy was obtained by subjecting alloy No. S03 to process No. A11H. In A11H, the raw materials were melted in a predetermined ratio in the laboratory, and the molten metal at approximately 950°C was poured into an iron mold with an inner diameter of 40 mm and a depth of 200 mm. The average cooling rate in the temperature range from 500°C to 300°C was set to 40°C / min. Figure 2A shows the results of a dezincification corrosion test performed according to the ISO 6509 test method, and is a cross-sectional metallographic photograph including the area showing the maximum corrosion depth.

[0038] The following describes a free-machining copper alloy casting and a method for manufacturing a free-machining copper alloy casting according to an embodiment of the present invention. Applications of the free-machining copper alloy casting according to an embodiment of the present invention include equipment and fixtures related to drinking water and sanitary facilities, musical instruments, tableware, electrical, home appliance and electronic equipment components, automobile parts, machine parts, stationery, precision machine parts, medical parts, and equipment and parts related to liquids and gases such as industrial water, wastewater, and hydrogen. Specific examples of parts include water taps, mixing taps, stopcocks, valves, cocks, fittings, water meters, gears, sensors, nuts, screws, etc.

[0039] Herein, in this specification, element symbols enclosed in parentheses, such as [Zn], indicate the content (mass%) of that element. In this embodiment, using this method of indicating content, the composition relation f1 is defined as follows: Composition relation f1 = [Cu] - 4.6 × [Si] + 0.5 × ([Pb] + [Bi]) + 0.5 × [P] - 1.0 × [Sn]. If Sn is not included, or if Bi is not included, then [Sn] and [Bi] in f1 are 0.

[0040] Furthermore, in this embodiment, in the constituent phases of the metallic microstructure excluding nonmetallic inclusions, the area ratio of the α phase is (α)%, the area ratio of the γ phase is (γ)%, the area ratio of the unmodified β phase is (β)%, and the area ratio of the modified β phase, the β1 phase, is (β1)%. The area ratio of each phase is also called the amount of each phase, the proportion of each phase, or the percentage occupied by each phase. In this embodiment, several microstructure relation equations are defined as follows: Microstructure relation equation f2 = (α) Microstructure relation equation f3 = (β1) Microstructure relation equation f4 = (γ)

[0041] The free-machining copper alloy casting according to the first embodiment of the present invention contains Cu in an amount greater than 58.0 mass% and less than 63.5 mass%, Si in an amount greater than 0.05 mass% and less than 0.50 mass%, Pb in an amount greater than 0.002 mass% and less than 0.20 mass%, and P in an amount greater than 0.01 mass% and less than 0.40 mass%, with the remainder being Zn and unavoidable impurities, wherein the total content of Fe, Mn, Co and Cr among the unavoidable impurities is less than 0.40 mass%, and the content of Al is less than 0.30 mass%, with the Cu content being [Cu] mass%, the Si content being [Si] mass%, and the Pb content being When the amount is [Pb] mass%, and the P content is [P] mass%, the relationship 57.5 ≤ f1 = [Cu] - 4.6 × [Si] + 0.5 × [Pb] + 0.5 × [P] ≤ 61.5 holds, and in the constituent phases of the metallic structure excluding nonmetallic inclusions, when the area ratio of the α phase is (α)%, the area ratio of the γ phase is (γ)%, and the area ratio of the modified β phase, the β1 phase, is (β1)%, the relationships 10 ≤ f2 = (α) < 80, 20 < f3 = (β1) ≤ 90, and 0 ≤ f4 = (γ) < 4 hold, and when etched with a mixture of hydrogen peroxide and ammonia water, grain boundaries can be observed inside the β1 phase.

[0042] The free-machining copper alloy casting according to the second embodiment of the present invention contains 58.8 mass% to 63.0 mass% of Cu, 0.08 mass% to 0.48 mass% of Si, 0.01 mass% to 0.10 mass% of Pb, and 0.03 mass% to 0.20 mass% of P, with the remainder being Zn and unavoidable impurities, wherein the total content of Fe, Mn, Co and Cr among the unavoidable impurities is less than 0.30 mass%, and the content of Al is less than 0.15 mass%, with the Cu content being [Cu] mass%, the Si content being [Si] mass%, and the Pb content being When the content of Pb is [Pb] mass%, and the content of P is [P] mass%, the relationship 58.0 ≤ f1 = [Cu] - 4.6 × [Si] + 0.5 × [Pb] + 0.5 × [P] ≤ 61.0 holds, and in the constituent phases of the metallic structure excluding nonmetallic inclusions, when the area ratio of the α phase is (α)%, the area ratio of the γ phase is (γ)%, and the area ratio of the modified β phase, the β1 phase, is (β1)%, the relationships 15 ≤ f2 = (α) < 75, 25 < f3 = (β1) ≤ 85, and 0 ≤ f4 = (γ) < 1 hold, and when etched with a mixture of hydrogen peroxide and ammonia water, grain boundaries can be observed inside the β1 phase.

[0043] The free-cutting copper alloy casting according to the third embodiment of the present invention contains Cu exceeding 58.0 mass% and less than 63.5 mass%, Si exceeding 0.05 mass% and less than 0.50 mass%, Pb of 0.002 mass% or more and less than 0.20 mass%, and P exceeding 0.01 mass% and less than 0.40 mass%. As optional elements, it contains Sn exceeding 0.01 mass% and less than 0.90 mass%, Bi exceeding 0.0001 mass% and less than 0.20 mass%, Sb of 0.01 mass% or more and 0.12 mass% or less, and As of 0.01 mass% or more and 0.12 mass% or less. The balance consists of Zn and inevitable impurities. Among the inevitable impurities, the total content of Fe, Mn, Co, and Cr is less than 0.40 mass%, and the content of Al is less than 0.30 mass%. When the content of Cu is [Cu] mass%, the content of Si is [Si] mass%, the content of Pb is [Pb] mass%, the content of P is [P] mass%, the content of Bi is [Bi] mass%, and the content of Sn is [Sn] mass%, it has the relationship of 57.5 ≦ f1 = [Cu] - 4.6 × [Si] + 0.5 × ([Pb] + [Bi]) + 0.5 × [P] - 1.0 × [Sn] ≦ 61.5. In the constituent phases of the metal structure excluding non-metallic inclusions, when the area ratio of the α-phase is (α)%, the area ratio of the γ-phase is (γ)%, and the area ratio of the β1-phase, which is the modified β-phase, is (β1)%, it has the relationships of 10 ≦ f2 = (α) < 80, 20 < f3 = (β1) ≦ 90, 0 ≦ f4 = (γ) < 4. When etched with a mixed solution of hydrogen peroxide and ammonia water, grain boundaries can be observed inside the β1-phase.

[0044] The free-machining copper alloy casting according to the fourth embodiment of the present invention contains 58.8 mass% to 63.0 mass% of Cu, 0.08 mass% to 0.48 mass% of Si, 0.01 mass% to 0.10 mass% of Pb, and 0.03 mass% to 0.20 mass% of P, and as an optional element, 0.05 mass% to 0.85 mass% of Sn, 0.001 It contains Bi in mass% to 0.10 mass%, Sb in mass% to 0.012 mass%, and As in mass% to 0.08 mass%, with the remainder being Zn and unavoidable impurities, wherein the total content of Fe, Mn, Co, and Cr among the unavoidable impurities is less than 0.30 mass%, and the content of Al is less than 0.15 mass%, and the content of Cu is When the amount is [Cu] mass%, the Si content is [Si] mass%, the Pb content is [Pb] mass%, the P content is [P] mass%, the Bi content is [Bi] mass%, and the Sn content is [Sn] mass, the relationship 58.0 ≤ f1 = [Cu] - 4.6 × [Si] + 0.5 × ([Pb] + [Bi]) + 0.5 × [P] - 1.0 × [Sn] ≤ 61.0 holds true for nonmetallic inclusions. In the constituent phases of the metal structure excluding the specified phase, when the area ratio of the α phase is (α)%, the area ratio of the γ phase is (γ)%, and the area ratio of the modified β phase, the β1 phase, is (β1)%, the following relationships exist: 15 ≤ f2 = (α) < 75, 25 < f3 = (β1) ≤ 85, 0 ≤ f4 = (γ) < 1. Furthermore, when etched with a mixture of hydrogen peroxide and ammonia water, grain boundaries can be observed within the β1 phase.

[0045] The following explains the reasons for defining the component composition, compositional relationship formula f1, microstructure relationship formulas f2, f3, and f4, and the metal structure as described above.

[0046] <Composition> (Cu)Cu is the main element of the free-cutting copper alloy casting of the present embodiment. In order to overcome the problems of the present invention, it is necessary to contain Cu in an amount exceeding at least 58.0 mass%. When the Cu content is 58.0 mass% or less, depending on the contents of Si, Zn, P, Pb, Sn, and the manufacturing process, the proportion of the β1 phase exceeds 90%, and the ductility decreases. Also, the modification of the β phase becomes insufficient, and the dezincification corrosion resistance deteriorates. Therefore, the lower limit of the Cu content is more than 58.0 mass%, preferably 58.8 mass% or more, more preferably 59.4 mass% or more, and optimally 60.0 mass% or more. On the other hand, when the Cu content is 63.5 mass% or more, depending on the contents of Si, Zn, P, Pb, Sn, and the manufacturing process, the proportion of the β1 phase decreases. As a result, excellent machinability cannot be obtained, and the strength also decreases. Therefore, the Cu content is less than 63.5 mass%, preferably 63.0 mass% or less, more preferably 62.5 mass%, and optimally 62.0 mass% or less.

[0047] (Si) Si is a main element of the free-cutting copper alloy casting of the present embodiment. Si contributes to the formation of metal phases such as κ phase, γ phase, μ phase, β phase, β1 phase, and ζ phase. By containing Cu, Zn, Si, and P in the amounts within the above ranges and adding an appropriate process, the β phase is modified, and the β1 phase is generated through a predetermined cooling process described later. The β1 phase (modified β phase) improves the machinability and at the same time significantly improves the dezincification corrosion resistance, which was a drawback of the conventional β phase.

[0048] In the composition range of the present embodiment, the machinability of the α phase is slightly improved by the inclusion of Si, and the dezincification corrosion resistance of the α phase is improved by the inclusion of Si. The modified β1 phase and the improved α phase improve the dezincification corrosion resistance of the alloy as a whole. Note that a certain amount of the α phase is required for the modification of the β phase. For example, when the α phase is completely absent, the β phase is insufficiently modified. In order to improve the dezincification corrosion resistance, ductility, and machinability of the alloy, the α phase needs to be 10% or more in area ratio, preferably 15% or more, more preferably 20% or more, and optimally 30% or more.

[0049] Si is an essential element for modifying the β phase to the β1 phase. The higher the amount of Si, the more the β phase is modified, resulting in a β1 phase with superior properties. To modify the β phase and create a more modified β1 phase, the Si content must exceed 0.05 mass%. The Si content is preferably 0.08 mass% or more, more preferably 0.13 mass% or more, and optimally 0.20 mass% or more. On the other hand, if the Si content is too high, the conductivity will decrease. For these reasons, the Si content is less than 0.50 mass%, preferably 0.48 mass% or less, and more preferably 0.46 mass%.

[0050] (Zn) Zn, along with Cu and Si, is a major constituent element of the free-machining copper alloy casting of this embodiment, and is an element necessary to improve machinability, strength, high-temperature properties, and castability. Although Zn is described as the remainder, if we were to specify, the Zn content is less than approximately 42.0 mass%, preferably less than 41.5 mass%, and more than approximately 35.0 mass%, preferably more than 35.5 mass%.

[0051] (P) Like Si, P is an essential element for modifying the β phase to the β1 phase. After solidification, P dissolves in the β phase together with Si, and during the cooling process after solidification, the β1 phase is obtained by cooling at a rate exceeding 300°C / min when the casting temperature reaches 500°C and in the temperature range from 500°C to 300°C. The modification from the β phase to the β1 phase improves machinability and significantly improves the dezincification corrosion resistance and stress corrosion cracking resistance, which were problems with the conventional β phase. Incidentally, compounds of P and Zn or Si reduce cutting resistance and improve chip fragmentation, but when the cooling process is started at a temperature exceeding approximately 550°C or approximately 530°C and cooled at a rate exceeding 300°C / min, compounds containing P are absent or present in only small amounts. Regarding machinability, the effect of modifying from the β phase to the β1 phase outweighs the effect when a β phase containing Si and a compound of P are present. Furthermore, the inclusion of P improves the dezincification corrosion resistance of the α phase, leading to a significant improvement in the dezincification corrosion resistance of the alloy consisting of the β1 phase and the α phase.

[0052] To modify the β phase to the β1 phase, the lower limit of the P content must be at least 0.01 mass%. Considering the superior modification to the β1 phase, as well as the amount of unavoidable impurities described later, the cooling treatment start temperature, and the cooling rate after the start of the cooling treatment, the P content is preferably 0.03 mass% or more, more preferably 0.04 mass%, and optimally 0.06 mass% or more. Note that P readily forms compounds with Zn, Si, Mn, Fe, Cr, Co, Al, etc. When P forms compounds and the amount of P dissolved in the β phase of the alloy after casting decreases, the modification from the β phase to the β1 phase is inhibited. The formation of compounds between Zn, Si, and P, which are the main elements of the alloy in this embodiment, begins at about 550°C, and the amount of P compounds increases as the cooling rate slows down. The formation of compounds between P and the unavoidable impurities Mn, Fe, Cr, Co begins at temperatures above approximately 550°C, and the formation of P compounds is further promoted as their amounts increase. In other words, the presence of Mn, Fe, Cr, and Co hinders the modification from the β phase to the β1 phase, resulting in increased cutting resistance of the alloy, poor chip fragmentation, and reduced resistance to dezincification corrosion. Therefore, the total content of Fe, Mn, Co, and Cr must be kept below 0.40 mass%, preferably below 0.30 mass%.

[0053] The formation of compounds of P, Zn, and Si positively impacts machinability, but the modification from the β phase to the β1 phase and the presence of these compounds are contradictory. As mentioned above, the formation of the β1 phase requires starting the cooling process at a temperature between 500°C and 700°C after solidification, and accelerating the cooling rate in the temperature range from the cooling start temperature to 300°C. In contrast, as described in Patent Documents 3 to 8, sufficient formation of compounds of P, Zn, and Si requires slow cooling in the temperature range of approximately 530°C to 450°C. Therefore, when a large amount of P compounds are formed, the modification of the β phase is somewhat insufficient. On the other hand, even if P is included in an amount of 0.40 mass% or more, the effect of forming the β1 phase is already saturated, and conversely, the influence of P dissolved in the β1 phase reduces ductility, cold workability, and electrical conductivity. Therefore, the P content is less than 0.40 mass%, preferably 0.20 mass% or less, more preferably 0.18 mass% or less, and optimally 0.16 mass% or less.

[0054] (Pb) In this embodiment, good machinability is obtained as an alloy by the β1 phase containing Si and P, but the machinability is further improved by the inclusion of a small amount of Pb. In the composition of this embodiment, about 0.001 mass% of Pb is solid-dissolved in the matrix, and the amount of Pb exceeding that exists as fine Pb particles with a diameter of about 0.1 to about 2 μm. Generally, it is considered that the inclusion of about 0.1 mass% of Pb contributes almost nothing to improving machinability. For example, the ASM Specialty Handbook, Copper and Copper Alloys, first edition, published August 2001, p. 267, Fig. 6, shows the relationship between Pb content and machinability, with the machinability of a Cu-Zn-Pb alloy containing 62-65 mass% Cu, approximately 3.2 mass% Pb, and the remainder being Zn, set at 100%. It shows that a Pb content of 0.1 mass% only improves machinability by a mere 5%, from approximately 25% to approximately 30% in terms of machinability index.

[0055] On the other hand, in this embodiment, even a small amount of Pb has a significant effect on machinability, and exhibits its effect at a content of 0.002 mass% or more. The Pb content is preferably 0.003 mass% or more, and more preferably 0.01 mass% or more. Furthermore, when cutting conditions become more severe, such as when the cutting speed is high, the feed rate is high, the depth of cut is high, or the drill hole diameter is large, the Pb content is preferably 0.03 mass% or more, and the machinability of the alloy is greatly improved by the β1 phase with significantly improved machinability and the inclusion of a small amount of Pb.

[0056] It is a well-known fact that Pb improves the machinability of copper alloys, and for this purpose, approximately 3 mass% of Pb is required in a Cu-Zn binary alloy, as exemplified by the free-cutting brass rod C3604. In this embodiment, an alloy with excellent machinability is completed by having a β1 phase containing Si and P, and a small amount of Pb particles, or Pb and Bi particles as described later, within the metal structure. On the other hand, since Pb is harmful to the human body, the upper limit of Pb is set to less than 0.20 mass%. Furthermore, the Pb content is preferably 0.10 mass% or less, and optimally, it is 0.08 mass% or less, considering the impact on the human body and the environment.

[0057] (Bi) Similar to Pb, Bi is dissolved in the matrix in an amount of approximately 0.0001 mass%, and any amount of Bi exceeding this exists as particles with a diameter of approximately 0.1 to 2 μm. When both Pb and Bi are added, they mostly exist as a mixture of Pb and Bi particles with a diameter of approximately 0.1 to 2 μm. In this embodiment, it was found that by including Bi together with Pb in the presence of the β1 phase, machinability equivalent to or better than that obtained when Pb and Bi are included individually is obtained. Incidentally, Bi worsens the stress corrosion cracking resistance of brass, but when it exists as a mixture of Pb and Bi particles, or when the amount of Bi is small, the effect on stress corrosion cracking is almost eliminated.

[0058] When Bi is included, at least 0.0001 mass% of Bi is required for the alloy to have good machinability. The Bi content is preferably 0.001 mass% or more, more preferably 0.002 mass% or more. The effects of Bi on the human body are currently unknown, but it is preferable that the amount of Bi be less than 0.20 mass%, preferably 0.10 mass% or less, and even more preferably 0.08 mass% or less. In this embodiment, as described above, Bi can adequately substitute for Pb, the effects of Bi on the human body are unknown, Bi is one of the rare metals and has an impact on the environment, and on the other hand, it is included in the raw material as an unavoidable impurity, so Bi is included as an optional element and may or may not be included. Thus, in this embodiment, the amount of Pb, which is harmful to the human body, is limited to less than 0.20 mass%, including Bi in some cases, and the goal is to achieve excellent machinability.

[0059] (Sn) When Sn is present, it is found in the β1 phase and, by solid dissolving in the β1 phase, it further improves the dezincification corrosion resistance of the β1 phase and enhances the dezincification corrosion resistance of the alloy. When Sn is present, in order to obtain this effect, the amount of Sn must be greater than 0.01 mass%, preferably 0.05 mass% or more, and more preferably 0.10 mass% or more. Incidentally, Sn is originally distributed more in the β phase and β1 phase than in the α phase, and even a small amount of Sn improves dezincification corrosion resistance, but as the Sn concentration increases, the γ phase is more likely to form, and ductility decreases. The formation of the γ phase not only leads to a decrease in ductility of the alloy, but also reduces machinability and worsens dezincification corrosion resistance. While it is related to the amount of Si, the Sn content must be kept below 0.90 mass%, preferably 0.85 mass% or less, and more preferably 0.80 mass% or less.

[0060] (Sb, As) Both Sb and As, like P and Sn, have the effect of further improving dezincification corrosion resistance in particularly harsh environments, and therefore may be included as optional elements. In order to improve the corrosion resistance of the alloy by including Sb, it is necessary to include 0.01 mass% or more of Sb, and it is preferable to include 0.012 mass% or more of Sb. On the other hand, even if the amount of Sb exceeds 0.12 mass%, the effect of improving corrosion resistance saturates, and the γ phase increases instead, so the Sb content is 0.12 mass% or less, preferably 0.08 mass% or less, and more preferably 0.07 mass% or less. Furthermore, in order to improve the corrosion resistance of the alloy by including As, it is necessary to include 0.01 mass% or more of As, and it is preferable to include 0.025 mass% or more of As. On the other hand, even if the As content exceeds 0.12 mass%, the effect of improving corrosion resistance saturates, so the As content is 0.12 mass% or less, preferably 0.08 mass% or less, and more preferably 0.07 mass% or less.

[0061] (Unavoidable impurities, especially Fe, Mn, Co and Cr / Al) Examples of unavoidable impurities in this embodiment include Mn, Fe, Al, Ni, Mg, Se, Te, Sn, Bi, Co, Ca, Zr, Cr, Ti, In, W, Mo, B, Ag and rare earth elements. Conventionally, free-cutting copper alloys, especially free-cutting brass containing about 30 mass% or more of Zn, do not use high-quality raw materials such as electrolytic copper or electrolytic zinc as the main raw material, but rather recycled copper alloys as the main raw material. In the downstream processes (processing processes) of this field, most components and parts are subjected to cutting, and a large amount of copper alloy is discarded at a ratio of 40 to 80 parts by mass per 100 parts by mass of material.

[0062] Examples include chips, scraps, burrs, sprues, and products containing manufacturing defects. These discarded copper alloys become the main raw materials. If the sorting of cutting chips and scraps is insufficient, Pb, Fe, Mn, Si, Se, Te, Sn, P, Sb, As, Bi, Ca, Al, Zr, Ni, and rare earth elements may be mixed in as raw materials from free-cutting brass with added Pb, free-cutting copper alloys that do not contain Pb but have Bi added, or special brass alloys containing Si, Mn, Fe, Al, and other copper alloys. Cutting chips also contain Fe, W, Co, Mo, etc., which are mixed in from the tools. Since recycled waste products include plated products, Ni, Cr, and Sn may be mixed in. Furthermore, pure copper scrap used as a substitute for electrolytic copper may contain Mg, Sn, Fe, Cr, Ti, Co, In, Ni, Se, and Te. Brass scrap used as a substitute for electrolytic copper or electrolytic zinc is often plated with Sn, and therefore contains Sn.

[0063] From the standpoint of resource reuse and cost considerations, scrap containing these elements is used as raw material, at least to the extent that it does not adversely affect its properties. In the case of free-cutting brass rod C3604 with added Pb according to JIS standard (JIS H 3250), the essential element Pb is contained in an amount of approximately 3 mass%, and further, impurities such as Fe are permitted up to 0.5 mass%, and Fe + Sn (total amount of Fe and Sn) up to 1.0 mass%. In practice, high concentrations of Fe and Sn are sometimes found in free-cutting brass rods.

[0064] Fe, Mn, Co, and Cr dissolve in the α and β phases of Cu-Zn alloys up to certain concentrations. However, if Si or P is present, these compounds readily combine with Si and P, potentially consuming the Si and P necessary for modifying the β phase. Fe, Mn, Co, and Cr that combine with Si then form Fe-Si compounds, Mn-Si compounds, Co-Si compounds, Cr-Si compounds, etc., in the metal structure. Similarly, Fe, Mn, Co, and Cr that combine with P form Fe-P compounds, Mn-P compounds, Co-P compounds, Cr-P compounds, etc., in the metal structure. These intermetallic compounds are extremely hard, not only increasing cutting resistance but also shortening tool life. Therefore, the amounts of Fe, Mn, Co, and Cr must be limited, and the content of each is preferably less than 0.30 mass%, more preferably less than 0.20 mass%, and even more preferably 0.15 mass% or less. In particular, the total content of Fe, Mn, Co, and Cr must be less than 0.40 mass%, preferably less than 0.30 mass%, more preferably less than 0.25 mass%, and even more preferably 0.20 mass% or less.

[0065] On the other hand, Al mixed in from special brass rods, brass castings, etc., affects the modification of the β phase if the content is high, and since Al forms compounds with P or Si, it needs to be limited. In the alloy of this embodiment, the Al content needs to be less than 0.30 mass%, preferably less than 0.15 mass%, and more preferably 0.10 mass% or less.

[0066] Among other major unavoidable impurity elements, Ni is empirically often found to be mixed in from scrap and other sources. Although Ni has a relatively small impact on mechanical properties such as machinability, it needs to be limited in consideration of its effects on the human body. The Ni content is preferably less than 0.20 mass%, and more preferably less than 0.10 mass%. As for Ag, Ag is generally considered to be Cu and has almost no impact on various properties, so there is no need to particularly limit it, but the Ag content is preferably less than 0.05 mass%. Te and Se are elements that are free-machining themselves and may be mixed in in large quantities, although rarely. Considering their impact on ductility and impact properties, the content of Te and Se, respectively, is preferably less than 0.10 mass%, more preferably less than 0.05 mass%, and even more preferably 0.02 mass% or less.

[0067] The content of other elements such as Mg, Ca, Zr, Ti, In, W, Mo, B, and rare earth elements is preferably less than 0.05 mass%, more preferably less than 0.03 mass%, and even more preferably 0.02 mass% or less. The content of rare earth elements is the total amount of one or more of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Tb, and Lu. In addition, the total amount of unavoidable impurities other than Fe, Mn, Co, Cr, and Al is preferably less than 0.70 mass%, and more preferably less than 0.50 mass%.

[0068] (Composition relation formula f1) Composition relation formula f1 = [Cu] - 4.6 × [Si] + 0.5 × ([Pb] + [Bi]) + 0.5 × [P] - 1.0 × [Sn]. If Sn is not included or Bi is not included, then [Sn] and [Bi] in f1 are 0. f1 is an expression that represents the relationship between composition and metal structure. Even if the amount of each element is within the range specified above, if this composition relation formula f1 is not satisfied, the properties targeted by this embodiment cannot be satisfied. If the composition relation formula f1 is less than 57.5, the proportion of β phase and β1 phase increases, the modification of the β phase becomes insufficient, and ductility and dezincification corrosion resistance deteriorate. Therefore, the lower limit of the composition relation formula f1 is 57.5 or higher, preferably 58.0 or higher, and more preferably 58.2 or higher. As the composition relation f1 falls within a more favorable range, the proportion of the α phase increases, the modification of the β phase becomes sufficient, and excellent machinability is maintained, along with good resistance to dezincification corrosion, resulting in good ductility and cold workability. On the other hand, the upper limit of the composition relation f1 affects the proportions of the β phase and the β1 phase. If the composition relation f1 is greater than 61.5, the proportion of the β1 phase decreases, resulting in poor machinability and lower strength. Therefore, f1 is 61.5 or less, preferably 61.0 or less, and more preferably 60.5 or less.

[0069] Furthermore, if Bi is included, since Bi is an optional element that substitutes for the function of Pb, it is preferable that the relationship 0.003 ≤ [Pb] + [Bi] < 0.20 is satisfied. That is, at this stage, the effects of Bi on the human body are unknown, and considering that Bi is one of the rare metals and has an impact on the environment, it is necessary to limit the total amount of Pb and Bi. If Bi is included, the total amount of Pb and Bi should be less than the upper limit of the amount of Pb, which is 0.20 mass%, and preferably less than 0.10 mass%. On the other hand, in order to obtain good machinability, if Bi is included, the total amount of Pb and Bi must be 0.003 mass% or more, preferably 0.004 mass% or more, and more preferably 0.005 mass% or more.

[0070] The free-machining copper alloy casting of this embodiment contains a large amount of the conventional β phase, and in this embodiment, the β1 phase, while possessing good resistance to dezincification corrosion and mechanical properties. It also possesses machinability that requires a certain degree of brittleness, which finely breaks up chips during cutting, and ductility, which are completely contradictory properties. In order to obtain these good corrosion resistance, machinability, and mechanical properties, it is possible to provide an alloy that is better suited to the purpose and application by specifying in detail not only the composition of each component, but also the composition relation formula f1, the microstructure relation formulas f2 to f4 described later, and the requirements of the metallic structure. Note that Fe, Mn, Co, Cr, Al, and separately defined unavoidable impurities are not specified in the composition relation formula f1 because their influence on the composition relation formula f1 is small as long as they are within the range treated as unavoidable impurities.

[0071] (Comparison with Patent Documents) Here, Table 1-3 shows the results of comparing the composition of the Cu-Zn-Si alloy described in Patent Documents 1 to 19 above with the alloy of this embodiment.

[0072]

[0073]

[0074]

[0075] This embodiment and Patent Document 9 differ in the content of the main elements Si and Cu, this embodiment and Patent Document 10 differ in the content of the main element Si, and this embodiment and Patent Document 16 differ in the content of the main element Cu. Patent Documents 2, 14, and 16 state that Pb is not included, and therefore the Pb content differs. In Patent Documents 9, 11, 12, and 13, the β phase in the metal structure is significantly limited from the viewpoint of machinability, resistance to dezincification corrosion, and corrosion resistance. The β1 phase of this embodiment is different from the β phase of Patent Documents 9, 11, 12, and 13, but the β phase is set to 5% or less, 25% or less, 15% or less, and 0.9% or less, respectively.

[0076] Patent document 11 relates to a near-net-shape tubular hot forged product and specifies the use of a tubular material. Patent documents 2 and 10 state that heat treatment is performed at a temperature of 350 to 550°C or 400 to 600°C in order to reduce or break up the β phase. Patent document 10 contains 0.2 mass% or more of Sn, and contains Sn and Si to improve the dezincification corrosion resistance of the β phase. Hot extrusion at a temperature of 700°C or higher is required to improve machinability, and heat treatment at 400 to 600°C is required to improve corrosion resistance. The proportion of the β phase is generally 5 to 20%, which differs from this embodiment, which requires more than 20% of the β1 phase.

[0077] Patent documents 13, 14, and 15 state that Al is essential to improve discoloration resistance, castability, and dezincification corrosion resistance. Patent document 15 states that in order to improve dezincification corrosion resistance, Sn and Al should be included in amounts of at least 0.1 mass% each, and that a large amount of Pb and Bi is necessary to obtain excellent machinability. Patent document 16 states that Pb is not included, a γ phase is required, and by including 65 mass% or more of Cu and Si, along with trace amounts of Al, Sb, Sn, Mn, Ni, B, etc., a corrosion-resistant copper alloy casting with good mechanical properties and castability is obtained.

[0078] Patent documents 3 to 8 all describe a cooling process after hot working in which the average cooling rate in the temperature range from approximately 530°C to approximately 450°C is approximately 0.1°C / min or more and approximately 70°C / min or less. Patent documents 17 to 19 describe a cooling process after hot working in which the average cooling rate in the temperature range from approximately 550°C to approximately 350°C is approximately 30°C / min or more and approximately 60°C / min or less, and require that the resulting P compound be present in the metal structure. Furthermore, there is no mention of β phase modification, and there is no disclosure of data regarding dezincification resistance. In this embodiment, the cooling process after hot working is initiated at a temperature lower than 700°C and higher than 500°C, and the cooling rate at 500°C, as well as the average cooling rate in the temperature range from 500°C to 300°C, exceeds 300°C / min, which is basically the opposite of the cooling described in patent documents 3 to 8 and 17 to 19.

[0079] The most significant and clear difference between this embodiment and Patent Documents 3-8, 10, and 17-19 is that none of the Patent Documents mention the modification of the β phase or the modified β phase, i.e., the β1 phase. The β1 phase is formed under the following conditions: During hot working, a β phase is formed in which a certain amount of Si and P are dissolved. Then, a cooling process is started at a temperature higher than 500°C, and during the cooling process, the cooling rate at 500°C exceeds 300°C / min, and the average cooling rate in the temperature range from 500°C to 300°C exceeds 300°C / min. The β1 phase is formed by the above. When etching is performed with a mixture of hydrogen peroxide and ammonia water, grain boundaries can be observed within the β1 phase if the β phase is modified into the β1 phase, but even if a certain amount of Si and P is present, if the β phase remains as it was before modification, no grain boundaries can be observed within the β phase. Patent documents 3 to 8 disclose metal structures etched with a mixture of hydrogen peroxide and aqueous ammonia, but in all cases, no grain boundaries are observed within the β phase.

[0080] <Metal Structure> Cu-Zn-Si alloys have more than 10 different phases, and complex phase transitions occur. Therefore, the desired properties cannot necessarily be obtained by simply looking at the composition range and elemental relationships. Ultimately, the desired properties can be obtained by identifying and determining the types of phases present in the metal structure and the range of their area ratios. For this reason, the microstructure relationships are defined as follows: 10 ≤ f2 = (α) < 80, 20 < f3 = (β1) ≤ 90, where the β1 phase is the modified β phase. 0 ≤ f4 = (γ) < 4

[0081] (β1 phase) The microstructure of this embodiment, excluding nonmetallic inclusions, consists of α phase, β1 phase, and, in some cases, a small amount or 0% of γ phase. The difference between the β phase and the β1 phase is that when the β1 phase is etched with a mixture of hydrogen peroxide and aqueous ammonia, grain boundary patterns are observed within the β1 phase, whereas in the case of an unmodified, ordinary β phase, no grain boundaries are observed within the β phase.

[0082] In this embodiment, the β1 phase is obtained by maintaining a high temperature of over 500°C, i.e., approximately 500-700°C, in a β phase with a certain amount or more of Si and P dissolved in it after solidification, and then performing a cooling treatment from that temperature range (cooling at a rate of at least 300°C / min, both at 500°C and the average cooling rate from 500°C to 300°C, and continuing to cool to near room temperature), thereby bringing the metallic structure at 500-700°C down to room temperature. Specifically, the cooling rate is increased rapidly in the temperature range from the cooling treatment start temperature of 500-700°C to 300°C to cool to room temperature of 100°C or less. This brings the metallic structure at 500-700°C down to room temperature. As a result, the β1 phase is obtained. The β1 phase cannot be obtained by performing the same cooling treatment on the β phase of a Cu-Zn alloy that does not contain both predetermined amounts of Si and P. Similarly, if an alloy containing predetermined amounts of Si and P is cooled at a cooling rate of 300°C / min or less at 500°C, the β1 phase will not be obtained. The β1 phase will not be obtained if the temperature range from 500°C to 300°C is cooled at an average cooling rate of 300°C / min or less. The β1 phase will not be obtained if the cooling treatment is performed at a temperature lower than 500°C, for example, from 450°C. Furthermore, the degree of modification of the β phase is also affected by the amount of Si and P, the amount of unavoidable impurities such as Fe and Al, the cooling rate at 500°C, the average cooling rate from 500°C to 300°C, and the starting temperature of the cooling treatment. Improving the degree of modification of the β phase, that is, if the β1 phase is more modified, a material with better machinability and better resistance to dezincification corrosion can be obtained.

[0083] The β1 phase (modified β phase) overcomes the drawback of the β phase in Cu-Zn alloys, which has been a major challenge: the alloy's resistance to dezincification corrosion. Specifically, to give a concrete example, it can reduce the progression of dezincification corrosion by approximately 50%. As described in Patent Document 2, dezincification corrosion of Cu-Zn alloys containing the β phase is a major problem, and since dezincification corrosion occurs along the β phase, the amount of β phase is limited to 25% or less or 20% or less, and further heat treatment at 350 to 550°C is applied to reduce the amount of β phase and fragment the β phase.

[0084] (β1 phase, microstructure relationship formula f3) In the Cu-Zn-Si-P-Pb alloy that constitutes the free-machining copper alloy casting of this embodiment, in order to achieve good machinability while keeping the Pb content to a minimum, the area ratio of the β1 phase must be at least 20%. Furthermore, in order to improve machinability and strength, the area ratio of the β1 phase is preferably 25% or more, and more preferably 30% or more. On the other hand, if the β1 phase exceeds 90%, the modification of the β phase becomes insufficient. If the β1 phase exceeds 90% and the modification of the β phase is insufficient, the alloy's resistance to dezincification corrosion and ductility will be reduced. Based on the above, after diligent research, it has been found that the area ratio of the β1 phase must be set to 90% or less, preferably 85% or less, more preferably 80% or less, and optimally 70% or less.

[0085] (α phase, microstructure relationship formula f2) This embodiment is basically composed of α phase and β1 phase, and a treatment is carried out to modify the β phase into β1 phase, but the α phase is hardly affected by this treatment. If there is too much β1 phase, there is a problem with the ductility of the alloy, and an appropriate amount of ductile α phase is necessary, while conversely, if there is too much α phase the strength will be low. Also, the α phase containing Si has only a slight improvement in machinability compared to the α phase without Si, so the amount of α phase is limited from the viewpoint of machinability as well. As a result of diligent research on the modification of the β phase, the dezincification corrosion resistance of the alloy, machinability and mechanical properties, it has been found that the amount of α phase should be 10% or more, preferably 15% or more, more preferably 20% or more, and optimally 30% or more. On the other hand, the upper limit of the α phase is less than 80%, preferably less than 75%, and more preferably 70% or less.

[0086] (γ phase, microstructure relationship formula f4) As described in Patent Documents 9 and 11, the γ phase is a phase that contributes to machinability in Cu-Zn-Si alloys with a Cu concentration of about 69 to about 80 mass% and a Si concentration of about 2 to about 4 mass%. In Patent Document 16, the γ phase is essential in Cu-Zn-Si alloys that do not contain Pb, and further, in Patent Documents 3 to 7, it is stated that both the β phase containing Si and the γ phase containing Si have good machinability. In this embodiment, the γ phase impairs the machinability and ductility of the alloy and worsens its resistance to dezincification corrosion. In Cu-Zn-Si alloys, the appearance of the γ phase is sometimes unavoidable, but it must be at least limited. That is, the proportion (area ratio) of the γ phase should be less than 4%, preferably less than 2%, more preferably less than 1%, and optimally, the γ phase should not be present.

[0087] As shown in Figure 1A, in samples where the cast material has undergone appropriate cooling treatment, grain boundary patterns, i.e., crystal grain boundaries, are observed in metallurgical microscope images, along with α-phase crystal grain boundaries, within the β1 phase. Here, a crystal grain boundary refers to a linear pattern that penetrates the β1 phase crystal grains, as observed within the β1 phase, as shown in Figure 1A. Thus, grain boundaries are recognized within the modified β phase, i.e., the β1 phase. On the other hand, no crystal grain boundaries penetrating the β phase crystal grains are observed in Figure 2A, indicating that the β phase in Figure 2A has not been modified into the β1 phase. Instead, in Figure 2A, granular precipitates of approximately 0.5 to 3 μm, which appear black, are mainly present within the β phase and at the phase boundary between the β and α phases. The granular precipitates are mainly P compounds, but also include Pb particles, mixed particles of Pb and Bi, compounds such as Fe, oxides, and sulfides. These can be identified under a microscope, but are somewhat difficult to distinguish in printed photographs.

[0088] From these findings, whether the β phase is modified into the β1 phase and whether grain boundaries exist in the β1 phase depends on whether the cooling treatment start temperature is higher or lower than approximately 500°C, the cooling rate at 500°C, and whether the average cooling rate in the temperature range from 500°C to 300°C exceeds 300°C / min. The results of the dezincification corrosion test of these alloys according to ISO 6509 are shown in Figures 1B and 2B. The maximum corrosion depth of the sample in which grain boundaries were observed within the β1 phase (Figure 1B) was less than 350 μm, while the maximum corrosion depth of the sample in which grain boundaries were not observed within the β1 phase (Figure 2B), i.e., the sample in which the β1 phase was absent, was approximately 500 μm, showing a difference of approximately 1.5 times in corrosion depth. In all cases, the form of dezincification corrosion was selective corrosion of the β1 phase and the β phase. Even in the β1 and β phases, dezincification corrosion is preferentially carried out in those phases, but the β1 phase can slow down the progression of dezincification corrosion to about two-thirds or less than that of the β phase.

[0089] <Characteristics> (Strength at room temperature, hardness) Hardness is considered important as a strength required in various fields, including valves, fixtures, fittings, and piping for drinking water, as well as valves and fittings for automobiles. For this reason, in order for copper alloy castings to have high hardness, it is preferable that the material is a high-strength material with a Vickers hardness of 95 HV or higher at room temperature. The Vickers hardness at room temperature is more preferably 100 HV or higher, even more preferably 110 HV or higher, and optimally 115 HV or higher. There is no particular upper limit to the Vickers hardness at room temperature, but in reality, 160 HV or lower is preferable.

[0090] (Electrical Conductivity) Applications of this embodiment include electrical and home appliance components, automobile parts, etc., and it is a substitute material for brass castings CAC203 and bronze castings CAC406 with added Pb. Currently, phosphor bronze (JIS standards, C5191, C5210) containing 6 mass% or 8 mass% of Sn in the above applications is widely used, and its electrical conductivity is about 14% IACS and about 12% IACS, respectively, while the electrical conductivity of CAC203 and CAC406 is about 24% IACS and about 15% IACS, respectively. Therefore, if the electrical conductivity of the copper alloy of this embodiment is 17.0% IACS or higher, there will be no problems regarding electrical conductivity. Preferably it is 18.0% IACS or higher, and more preferably 19.0% IACS or higher. Furthermore, there is no upper limit on conductivity, as improved conductivity rarely poses practical problems. However, in reality, a value of 28.0% IACS or less is preferable. Here, %IACS stands for International Annealed Copper Standard, and the volume resistivity of annealed standard soft copper is 1.7241 × 10⁻⁶. －２ This value is expressed as a ratio with μΩm representing 100% IACS.

[0091] (Castability) The fundamental premise of the free-machining copper alloy casting of this embodiment is that a sound casting can be obtained. First, the inclusion of Si suppresses Zn vapor during melting, resulting in good melting and casting. Furthermore, the inclusion of Si and the restriction of Cu, Zn, and f1 result in good molten metal flowability, allowing the molten metal to reach even thin-walled areas, enabling casting of complex shapes and minimizing the occurrence of defects in the casting, such as porous shrinkage cavities. Moreover, the casting must not crack. Regarding casting cracks, the first point is whether or not low-melting-point metals exist as a molten state at high temperatures after solidification. If low-melting-point metals are present, the amount and whether or not the matrix is ​​ductile at high temperatures determine the outcome. In this embodiment, during the solidification and cooling process of the casting, the total amount of low-melting-point metals Pb and Bi present as a molten state in the matrix is ​​preferably limited to less than 0.20 mass%, making it less likely to lead to casting cracks. Furthermore, if the composition and various relational equations of this embodiment are satisfied, it contains a large amount of β1 phase, which has excellent ductility at high temperatures, so the adverse effects of the small amount of low-melting-point metal can be covered, and there is no problem of casting cracking.

[0092] (Maximum Dezincification Corrosion Depth) In dezincification corrosion tests conducted according to ISO 6509, it is preferable that the maximum dezincification corrosion depth is 400 μm or less. When tested according to ISO 6509, a maximum corrosion depth of 400 μm or less is considered to be at a level that does not pose a problem in terms of practical corrosion resistance. That is, in dezincification corrosion tests conducted according to ISO 6509, it is preferable that the maximum dezincification corrosion depth is 400 μm or less, more preferably 300 μm or less, and optimally 200 μm or less. It is desirable that the dezincification corrosion depth be as small as possible, and there is no particular lower limit, but the practical range for measurement is 1 μm or more.

[0093] <Manufacturing Process> Next, a method for manufacturing a free-machining copper alloy casting according to an embodiment of the present invention will be described. The metallic structure of the free-machining copper alloy casting of this embodiment changes not only with its composition but also with the manufacturing process. There are various casting methods for manufacturing castings, such as molds, sand molds, continuous casting, die casting, and lost wax casting. The thickness and shape of the casting, the material and thickness of the mold or sand mold, etc., roughly determine the cooling rate of the casting after solidification. The cooling rate can be changed by means of the cooling method, such as heat retention, water cooling, oil cooling, and forced air cooling. On the other hand, various changes in the metallic structure occur during the cooling process after solidification, and the metallic structure changes significantly depending on the cooling rate. Changes in metallic structure refer to significant changes in the types of constituent phases and the amount (area ratio) of those constituent phases. As a result of diligent research on the cooling process after solidification, it has been found that the cooling rate at 500°C and the average cooling rate in the temperature range from 500°C to 300°C are the most important during the cooling process, and that they greatly affect the dezincification corrosion resistance and machinability.

[0094] (Melting and Casting) Depending on the casting method, melting is carried out at a temperature of approximately 950 to 1200°C, which is about 100 to 300°C higher than the melting point (liquidus temperature) of the alloy in this embodiment. Molten metal at a temperature of approximately 900 to 1150°C, which is about 50 to 250°C higher than the melting point, is poured into a predetermined mold such as a metal mold, sand mold, or other mold, and then cooled. After solidification, the constituent phases change in various ways.

[0095] (Casting and Solidification) The cooling rate after casting and solidification varies depending on the weight, thickness, and thermal conductivity of the cast copper alloy, as well as the material of the mold, such as a sand mold or metal mold. In conventional copper alloy casting, when cast into a mold made of copper alloy or iron, i.e., in the case of mold casting, after casting, the casting is removed from the mold at a temperature of approximately 750°C or lower, and then air-cooled or slowly cooled, cooling in the temperature range of 500°C to 300°C at an average cooling rate of approximately 10 to 200°C / min. In the case of copper alloy casting, since most contain 1 mass% or more of Pb or Bi, it is rare for them to be cooled at a cooling rate of 300°C / min or higher in the temperature range above approximately 300°C or 250°C, where Pb or Bi solidify. This is because, at temperatures above 300°C, the Pb or Bi particles are in a molten state, and if the cooling rate is too fast, thermal contraction may cause cracks in the casting.

[0096] In continuous casting, the cooling process is roughly the same as in die casting. The casting rods that emerge from the iron mold are generally air-cooled, and the cooling rate is primarily determined by the cross-sectional area of ​​the continuous casting rod and the casting speed. For a continuous casting rod with a diameter of 20 mm, it is cooled in the temperature range from 500°C to 300°C at an average cooling rate of approximately 40 to 100°C / min. On the other hand, in sand casting, the copper alloy cast into the sand mold is cooled in the temperature range from 500°C to 300°C at an average cooling rate of approximately 0.6 to 60°C / min, depending on the size of the casting and the material and size of the sand mold. When the temperature drops below approximately 300°C or approximately 250°C, the casting is either removed from the sand mold and air-cooled, or left in the sand mold until it reaches near room temperature. The cooling rate of these castings at 500°C is roughly the same as, or slightly faster than, the average cooling rate in the temperature range from 500°C to 300°C.

[0097] In the free-machining copper alloy casting of this embodiment, after casting and solidification, the metal structure is a single β phase at a high temperature of, for example, 800°C. Subsequent cooling forms various phases such as α and γ phases. In the free-machining copper alloy casting of this embodiment, during the cooling process after solidification, the cooling rate exceeds 300°C / min when the casting temperature reaches 500°C, and by adjusting the average cooling rate from 500°C to 300°C to exceed 300°C / min, the β phase is modified to a β1 phase. The cooling process is then continued even at temperatures below 300°C.

[0098] As a cooling method, it is necessary to start the cooling process in the temperature range of 700°C to 500°C during the cooling process after solidification. The average cooling rate from the start of the cooling process to 500°C is roughly the same as the average cooling rate from 500°C to 300°C. After the casting temperature reaches 300°C, the cooling process continues even at temperatures below 300°C, and although the average cooling rate is slightly slower than that from 500°C to 300°C, it is roughly the same. Through the above cooling process, the β phase is modified into the β1 phase, and when etched with a mixture of hydrogen peroxide and ammonia, grain boundaries appear within the β1 phase, and it is modified and replaced by a β1 phase with different properties from the conventional β phase. As a result, machinability is improved, and the dezincification corrosion resistance, which was a problem with the conventional β phase, is significantly improved.

[0099] The degree of modification of the β phase is influenced by the amounts of Si and P, the amounts of Al, Fe, and Sn, the value of the compositional relation f1, and further by the average cooling rate from 500°C to 300°C during the cooling process after solidification, the cooling rate at 500°C, and the cooling treatment start temperature. If the cooling treatment start temperature is 700°C or higher, the proportion of the β phase increases, which may result in insufficient modification of the β phase. The cooling treatment start temperature should be lower than 700°C, and more preferably 650°C or lower. On the other hand, if the cooling rate is 300°C / min or lower when the casting temperature is 500°C, or if the cooling treatment start temperature is 500°C or lower, the β phase will not be modified. If the cooling treatment is started at a temperature of 500°C or higher, preferably 530°C or higher, and more preferably 550°C or higher, the β phase will be more modified, improving the alloy's resistance to dezincification corrosion and machinability.

[0100] Furthermore, if the average cooling rate from 500°C to 300°C is 300°C / min or less after the start of the cooling process, the β phase will not be modified. The average cooling rate in the temperature range from 500°C to 300°C should be at least 300°C / min, preferably 600°C / min, and more preferably 900°C / min or more. Cooling at a preferred rate results in a more modified β phase, which has better resistance to dezincification corrosion and better machinability. The upper limit of the cooling rate at 500°C and the average cooling rate in the temperature range from 500°C to 300°C can be achieved with normal production equipment and is not specifically defined, but if mentioned, a cooling rate of approximately 9000°C / min or less is preferred. In addition, ingots made from castings may be used as raw materials for castings, but the modification of the β phase is not affected by the thermal history of the raw materials used, and whether or not the β phase is modified is determined during the cooling process after the final solidification of the casting.

[0101] (Heat Treatment) In the production of castings, it can be difficult to achieve a cooling rate exceeding 300°C / min at 500°C and an average cooling rate exceeding 300°C / min from 500°C to 300°C after casting. In such cases, the β phase can be modified by applying heat treatment again to the casting after it has cooled to room temperature. Specifically, the casting is heated at a temperature higher than 520°C and lower than 650°C for 1 minute to 5 hours, and the cooling process is started at a temperature lower than 650°C and higher than 500°C. When the casting temperature reaches 500°C, the cooling rate exceeds 300°C / min, and the β phase can be modified to the β1 phase by cooling in the temperature range from 500°C to 300°C at an average cooling rate exceeding 300°C / min.

[0102] When the heat-treated casting of this embodiment is polished to a mirror finish and etched with a mixture of hydrogen peroxide and ammonia, grain boundaries can be observed within the β phase, indicating that the β phase has been replaced by a β1 phase with properties different from the conventional β phase. The heating temperature during heat treatment and the cooling start temperature are preferably 530°C or higher, and more preferably 550°C or higher. On the other hand, if the cooling start temperature is higher than 700°C, the proportion of the β1 phase increases, worsening the dezincification corrosion resistance and impact properties, so 650°C or lower is preferable. Furthermore, a faster cooling rate at 500°C and the average cooling rate from 500°C to 300°C is preferable as it further modifies the β phase, preferably exceeding 600°C / min, and more preferably cooling at 900°C / min or higher. The cooling rate at 500°C and the upper limit of the average cooling rate in the temperature range from 500°C to 300°C can be sufficiently achieved with normal production equipment, and are not specifically defined. However, if we were to mention it, a cooling rate of approximately 9000°C / min or less is preferable.

[0103] Furthermore, even if the β1 phase is formed by the heat treatment described above, if additional heat treatment that does not satisfy the above conditions is applied, or if the casting is reheated to 300°C or higher, the modification of the β phase is lost, and the β1 phase returns to the normal β phase. When heat of 300°C or higher is applied to the casting that has undergone the final predetermined cooling treatment, the modification of the β phase is lost, and the β1 phase that was present in the predetermined casting returns to the normal β phase. As a result, when the metal structure is observed, the grain boundaries that were present in the β1 phase are no longer observed.

[0104] According to the free-machining alloy casting of the present invention configured as described above, the alloy composition, compositional relationship formula, metal structure, and microstructure relationship formula are defined as described above, so even with a low Pb content, excellent machinability can be obtained, it has good resistance to dezincification corrosion, high strength, and an excellent balance between strength and ductility.

[0105] Although embodiments of the present invention have been described above, the present invention is not limited thereto, and can be modified as appropriate without departing from the technical requirements of the invention.

[0106] The following shows the results of verification experiments conducted to confirm the effects of this embodiment. Note that the following examples are for illustrative purposes only, and the constituent elements, processes, and conditions described in the examples do not limit the technical scope of this embodiment.

[0107] We fabricated prototype copper alloy mold castings using laboratory equipment. Furthermore, some samples were heat-treated in the laboratory. The alloy compositions are shown in Tables 4 and 5. The manufacturing process is shown in Tables 6 and 7.

[0108]

[0109]

[0110]

[0111]

[0112] Process A: Laboratory Manufacturing, Mold Casting (Process No. A1, A11H) In the laboratory, the raw materials were melted in a predetermined ratio. The molten metal at approximately 950°C was then poured into an iron mold with an inner diameter of 40 mm and a depth of 200 mm. Considering actual casting, when the casting reached approximately 750°C, the sample was removed from the mold and cooled at a cooling rate of approximately 60°C / min. Then, the cooling process was started at 550°C. The average cooling rate in the temperature range from 500°C to 300°C was set to 1200°C / min, and the sample was cooled to room temperature. The cooling rate at 500°C, i.e., the average cooling rate from 550°C or the start temperature of the cooling process to 500°C, was adjusted to be approximately the same as the average cooling rate from 500°C to 300°C. Process No. In A11H, the average cooling rate from the time of removal of the casting up to 550°C was 60°C / min, and the average cooling rate from 500°C to 300°C was adjusted to 40°C / min. For temperature measurement, the temperature of the casting was measured using both an infrared thermometer and a contact thermometer, and the average cooling rate in each temperature range was adjusted to a predetermined value. The resulting mold castings were then subjected to metallurgical microscopy observation, cutting tests, dezincification corrosion tests, hardness tests, and conductivity measurements.

[0113] Process B: Heat Treatment (Process No. B1, B11H, B12H) Process B involved further heat treatment of the mold castings manufactured in Process A11H. Using the mold castings obtained in Process No. A11H, heating was carried out in all cases under the condition of holding at 570°C for 20 minutes. In Process No. B1, after heating, the cooling process was started at 565°C, and the average cooling rate from 550°C to 500°C and from 500°C to 300°C was the same at 1200°C / min. In Process No. B11H, the starting temperature for the cooling process was 565°C, the average cooling rate from 565°C to 500°C was 250°C / min, and the average cooling rate from 500°C to 300°C was also 250°C / min. Process No. In the case of B12H, after heat treatment at 570°C, no special cooling treatment was performed, and the cooling was carried out from 500°C to 300°C at an average rate of 40°C / min. These heat-treated materials were subjected to metallurgical microscopy observation, cutting tests, dezincification corrosion tests, hardness tests, and conductivity measurements.

[0114] The above-mentioned test material was evaluated for the following items. The evaluation results are shown in Tables 8 and 9. The area ratio of the β phase, i.e., the unmodified β phase, was distinguished from the area ratio of the β1 phase (f3) as f3A and is listed in each table.

[0115] (Observation of Metal Microstructure) The metal microstructure was observed using the following method, and the area percentage (%) of each phase, such as the α phase, β phase, and γ phase, was measured by image analysis. When grain boundaries were observed within the β phase, it was classified as the β1 phase and distinguished from the normal β phase. The α', β', and γ' phases were included in the α, β, and γ phases, respectively. The α phase exhibits a granular, elliptical shape and is often accompanied by twinning. The β and β1 phases exist around this granular, elliptical α phase. This distinguishes the α, β, and β1 phases. The rods and forgings of each test material were cut parallel to the longitudinal direction or parallel to the flow direction of the metal microstructure. The cut surfaces were then polished to a mirror finish and etched with a mixture of hydrogen peroxide and ammonia water. For etching, an aqueous solution of 3 mL of 3 vol% hydrogen peroxide and 22 mL of 14 vol% ammonia water was used. At room temperature of approximately 15 to 25°C, the polished metal surface was immersed in this aqueous solution for approximately 2 to 10 seconds. Note that in the presence of the β1 phase, corrosion resistance was improved compared to the presence of the β phase, so the etching immersion time needed to be longer, approximately 5 to 10 seconds.

[0116] Using a metallurgical microscope, the microstructure was observed at 500x magnification, and the proportion of each phase was determined. Depending on the condition of the microstructure, observation was performed at 1000x magnification to confirm the phases and compounds. In the five fields of view microscope images, each phase (α phase, β phase, β1 phase, γ phase) was manually filled in using the image processing software "Photoshop CC". For the distinction between the β phase and the β1 phase, if one or more grain boundaries were observed within the β phase in a single field of view, the entire β phase in that field of view was filled in as the β1 phase. Next, the images were binarized using the image analysis software "WinROOF2013," and the area percentage of each phase was determined. In detail, the average of the area percentages in the five fields was calculated for each phase, and this average was used as the area percentage of each phase. Compounds containing P and Si, precipitates, oxides, Pb or Bi particles, sulfides, and crystals were excluded, and the sum of the area percentages of all constituent phases was set to 100%.

[0117] If phase identification is difficult, the phase may be identified using a field emission scanning electron microscope (FE-SEM) with the EBSD (Electron Back Scattering Diffracton Pattern) method at a magnification of 1000x. In this case, the α phase is identified, and the remaining phase is designated as the β phase or β1 phase. For the areas identified as the β phase or β1 phase by EBSD, the β phase or β1 phase is distinguished by whether or not grain boundaries are observed inside the β phase using a metallurgical microscope. In this embodiment, the presence or absence of grain boundaries in the β phase is not determined by the EBSD method. The β phase or β1 phase is distinguished solely by whether or not grain boundaries (linear patterns penetrating the β phase crystal grains as shown in Figure 1A) are observed inside the β phase when etched with the etching solution using a metallurgical microscope.

[0118] When the metal structure is observed with a metallurgical microscope using the etching solution described above, if the β phase is modified, grain boundary patterns, i.e., crystal grain boundaries, can be observed within the β phase. In this embodiment, when crystal grain boundaries are observed within the β phase, that β phase is designated as the β1 phase and distinguished from the normal β phase. Here, a crystal grain boundary refers to a linear pattern that penetrates within the β1 phase crystal grains, as shown in Figure 1A. In addition to the phases, compounds and precipitates of P and Si may be present in the metal structure. Compounds of P and Zn or Si can be observed as blackish-gray particles of about 0.5 to 2 μm under a 500x metallurgical microscope, mainly within the β phase, β1 phase, and at the phase boundary between the β phase and α phase. Compounds of Fe, Mn, Cr, and P or Si can be seen as light blue particles of about 1 to 5 μm. Pb or Bi particles, and particles formed by the combination of Pb and Bi, exist as fine black particles of 2 μm or less. These compounds can be roughly distinguished under a metallurgical microscope. In the characterization table, when grain boundaries were observed within the β phase in the metal structure, that β phase was designated as the β1 phase, and the presence of grain boundaries within the β1 phase was indicated as "B" (present). When no grain boundaries were observed within the β phase, it was indicated as "D" (absent).

[0119] (Conductivity) Conductivity was measured using a conductivity measuring device (SIGMATEST D2.068) manufactured by Nippon Förster Co., Ltd. In this specification, the terms "electrical conductivity" and "conductivity" are used interchangeably. Furthermore, since thermal conductivity and electrical conductivity are strongly correlated, higher conductivity indicates better thermal conductivity.

[0120] (Vickers hardness test) The Vickers (HV) hardness (load 49N) of the cross-sections of the castings and heat-treated castings was measured using a Vickers hardness tester (HV-114) manufactured by Mitutoyo Corporation. The test method was measured in accordance with the method specified in JIS Z2244-1.

[0121] (Dezincification Corrosion Test: ISO 6509 Dezincification Corrosion Test) The dezincification corrosion test was evaluated using the ISO 6509 dezincification corrosion test method. This test method is adopted in many countries and is also specified in the JIS standard JIS H 3250. The procedure for the dezincification corrosion test is as follows: First, the test material is embedded in a phenolic resin material, specifically, the exposed sample surface is embedded in the phenolic resin material so that it is perpendicular to the extrusion direction of the extruded material. The sample surface is polished with emery paper up to 1200 grit, then ultrasonically cleaned in pure water and dried. The exposed surface of each sample is treated with 1.0% cupric chloride dihydrate (CuCl ２ ・2H ２ The sample was immersed in an aqueous solution of O) (12.7 g / L) and held at a temperature of 75°C for 24 hours. After that, the sample was removed from the aqueous solution. The sample was re-embedded in a phenolic resin material so that the exposed surface remained perpendicular to the extrusion direction, longitudinal direction, or forging flow direction. Next, the sample was cut so that the cross section of the corroded area was obtained as the longest cut section. Subsequently, the sample was polished. Using a metallurgical microscope, the corrosion depth was observed at 10 locations in the field of view of the microscope at a magnification of 100 to 500 times. The deepest corrosion point was recorded as the maximum dezincification corrosion depth.

[0122] Furthermore, when tested according to ISO 6509, a maximum corrosion depth of 400 μm or less is considered to be at a level that does not pose a problem in terms of practical corrosion resistance. When superior corrosion resistance is required, the maximum corrosion depth is preferably 200 μm or less. In this test, a maximum corrosion depth exceeding 400 μm was evaluated as unacceptable (evaluation: D, poor). A maximum corrosion depth between 300 μm and 400 μm was evaluated as acceptable (evaluation: C, fair), and a maximum corrosion depth between 200 μm and 300 μm was evaluated as good (evaluation: B, good). A maximum corrosion depth of 200 μm or less was evaluated as excellent (evaluation: A, excellent).

[0123] (Drill Cutting Test) Using a φ3.5 mm high-speed steel JIS standard drill, a 10 mm deep drill was drilled dry on a drill press under the conditions of rotational speed: 1250 rpm and feed rate: 0.17 mm / rev. Voltage changes were collected in the circumferential and axial directions using an AST type tool dynamometer during drilling, and chips were collected during drilling. Machinability was evaluated based on the chip shape. Problems in practical cutting are chip entanglement with the tool and chip bulkiness. For this reason, a chip shape with an average of less than one turn was evaluated as good ("A"). A chip shape with one or more turns but less than three turns was evaluated as fair ("B"), indicating that drilling is possible, although there are some practical problems. A chip shape with three or more turns was evaluated as poor ("D"). Note that the initial chips generated were excluded. To minimize the effects of drill wear, for each sample, a single back-and-forth pass was performed (X→Y→Z→...Z→Y→X) for samples numbered X, Y, and Z, and measurements were taken twice.

[0124]

[0125]

[0126] It was confirmed that by satisfying the composition of this embodiment and the composition relation f1, the metal structure relation formulas f2, f3, and f4, and the requirements of the metal structure, castings with good machinability, good dezincification corrosion resistance, high electrical conductivity of 17.0% IACS or higher, and strength of HV hardness of 95 or higher can be obtained with a small amount of Pb content. It was confirmed that the dezincification corrosion resistance, which was a major problem of conventional β phases, could be significantly improved by modifying the β phase to the β1 phase, as shown below (alloy Nos. S01 to S08). On the other hand, even if the composition of this embodiment was satisfied and the composition relation formula f1 was satisfied, if the metal structure relation formula f3 = 0, that is, if grain boundaries were not observed inside the β1 phase, which is a requirement of the metal structure, the dezincification corrosion resistance was poor (alloy Nos. S01, S03, S05, S09, processes A11H, B11, B12H).

[0127] By including more than 0.05 mass% of Si and more than 0.01 mass% of P, the β phase was modified into the β1 phase, and grain boundaries were observed within the β1 phase. As a result, dezincification corrosion resistance improved. When the amount of Si was 0.08 mass% or more and the amount of P was 0.03 mass% or more, dezincification corrosion resistance improved further. That is, it is considered that the β phase was further modified (alloy No. S02).

[0128] When Sn content exceeded 0.01 mass%, dezincification corrosion resistance improved. When Sn content exceeded 0.10 mass%, dezincification corrosion resistance improved even further compared to materials without Sn, and dezincification corrosion resistance improved to less than 100 μm in the ISO 6509 test (alloys No. S07, S08).

[0129] After casting, when the starting temperature for the cooling process exceeded 500°C, and the cooling rate at 500°C, as well as the average cooling rate in the temperature range from 500°C to 300°C, exceeded 300°C / min, the β phase was modified, and grain boundaries were observed within the β1 phase. When the β phase was modified, the resistance to dezincification corrosion improved (alloy Nos. S01, S03, S05, process A1).

[0130] When the average cooling rate in the temperature range from 500°C to 300°C was less than 300°C, no grain boundaries were observed within the β1 phase. As a result, the resistance to dezincification corrosion deteriorated (alloys No. S01, S03, process B11H).

[0131] This embodiment does not require a P compound, but even if a P compound is present, the dezincification corrosion resistance is poor, and the presence of a P compound has no effect on dezincification corrosion resistance (Figure 2A, Alloy No. S03, Process A11H).

[0132] Even if a predetermined cooling treatment is not performed after casting, the cast material can be annealed at a temperature above 520°C but below 630°C for 1 minute to 5 hours. After annealing, the cooling treatment is started at a temperature above 500°C, and the cooling rate at 500°C, as well as the average cooling rate in the temperature range from 500°C to 300°C, exceeds 300°C / min. This process modifies the β phase to the β1 phase, and it has been confirmed that, in particular, the resistance to dezincification corrosion is significantly improved (Alloy Nos. S01 to S08, Process No. B1).

[0133] In the comparative example, when etching was performed with a mixture of hydrogen peroxide and ammonia water, the β1 phase was not observed, the dezincification corrosion depth exceeded 400 μm, and the corrosion resistance was insufficient. In contrast, in the present invention example, when etching was performed with a mixture of hydrogen peroxide and ammonia water, the β1 phase was observed, the dezincification corrosion depth was 370 μm or less, and the corrosion resistance was excellent.

[0134] From the above, alloys of this embodiment, in which the content and compositional relationships of each additive element and each microstructure relationship are within an appropriate range, exhibit good mechanical properties and resistance to dezincification corrosion. Furthermore, excellent properties can be obtained in alloys of this embodiment by setting the manufacturing conditions in casting and the heat treatment conditions within an appropriate range.

[0135] The free-machining copper alloy casting of this embodiment has a low Pb content, excellent machinability, high strength, and an excellent balance of strength and elongation. For this reason, the free-machining copper alloy casting of this embodiment is suitable for appliances and parts related to drinking water and sanitation equipment, food appliances, electrical and electronic equipment parts, automobile parts, machine parts, stationery, toys, musical instruments, sliding parts, instrument parts, precision machine parts, medical parts, drinking appliances and parts, water meters, and parts related to liquids and gases such as industrial water, wastewater, and hydrogen. Specifically, it can be suitably applied as a component material for items used in the above fields, such as water taps, stopcocks, mixing taps, shower heads, valves, fittings, cocks, gears, shafts, bearings, trumpets, shafts, sleeves, spindles, sensors, bolts, nuts, flare nuts, pen tips, insert nuts, cap nuts, nipples, spacers, and screws.

Claims

1. Containing Cu in an amount greater than 58.0 mass% and less than 63.5 mass%, Si in an amount greater than 0.05 mass% and less than 0.50 mass%, Pb in an amount of 0.002 mass% or more and less than 0.20 mass%, and P in an amount greater than 0.01 mass% and less than 0.40 mass%, with the remainder being Zn and unavoidable impurities, wherein the total content of Fe, Mn, Co, and Cr among the unavoidable impurities is less than 0.40 mass%, and the content of Al is less than 0.30 mass%, and when the Cu content is [Cu] mass%, the Si content is [Si] mass%, the Pb content is [Pb] mass%, and the P content is [P] mass%, A free-cutting copper alloy casting characterized by having the relationship 57.5 ≤ f1 = [Cu] - 4.6 × [Si] + 0.5 × [Pb] + 0.5 × [P] ≤ 61.5, and in the constituent phases of the metallic structure excluding nonmetallic inclusions, when the area ratio of the α phase is (α)%, the area ratio of the γ phase is (γ)%, and the area ratio of the modified β phase, the β1 phase, is (β1)%, the relationships 10 ≤ f2 = (α) < 80, 20 < f3 = (β1) ≤ 90, 0 ≤ f4 = (γ) < 4, and grain boundaries being observable within the β1 phase when etched with a mixture of hydrogen peroxide and ammonia water.

2. Containing Cu in an amount of 58.8 mass% to 63.0 mass%, Si in an amount of 0.08 mass% to 0.48 mass%, Pb in an amount of 0.01 mass% to 0.10 mass%, and P in an amount of 0.03 mass% to 0.20 mass%, with the remainder being Zn and unavoidable impurities, wherein the total content of Fe, Mn, Co, and Cr among the unavoidable impurities is less than 0.30 mass%, and the content of Al is less than 0.15 mass%, and when the Cu content is [Cu] mass%, the Si content is [Si] mass%, the Pb content is [Pb] mass%, and the P content is [P] mass%, A free-cutting copper alloy casting characterized by having the relationship 58.0 ≤ f1 = [Cu] - 4.6 × [Si] + 0.5 × [Pb] + 0.5 × [P] ≤ 61.0, and in the constituent phases of the metallic structure excluding nonmetallic inclusions, when the area ratio of the α phase is (α)%, the area ratio of the γ phase is (γ)%, and the area ratio of the modified β phase, the β1 phase, is (β1)%, the relationships 15 ≤ f2 = (α) < 75, 25 < f3 = (β1) ≤ 85, 0 ≤ f4 = (γ) < 1, and when etched with a mixture of hydrogen peroxide and ammonia water, grain boundaries can be observed inside the β1 phase.

3. Containing Cu in amounts exceeding 58.0 mass% and less than 63.5 mass%, Si in amounts exceeding 0.05 mass% and less than 0.50 mass%, Pb in amounts between 0.002 mass% and less than 0.20 mass%, and P in amounts exceeding 0.01 mass% and less than 0.40 mass%, and as optional elements, containing Sn in amounts exceeding 0.01 mass% and less than 0.90 mass%, Bi in amounts exceeding 0.0001 mass% and less than 0.20 mass%, Sb in amounts between 0.01 mass% and 0.12 mass%, and As in amounts between 0.01 mass% and 0.12 mass%, with the remainder being Zn and unavoidable impurities. If the total content of Fe, Mn, Co, and Cr among the aforementioned unavoidable impurities is less than 0.40 mass%, and the content of Al is less than 0.30 mass%, and the content of Cu is [Cu] mass%, the content of Si is [Si] mass%, the content of Pb is [Pb] mass%, the content of P is [P] mass%, the content of Bi is [Bi] mass%, and the content of Sn is [Sn] mass, then the relationship 57.5 ≤ f1 = [Cu] - 4.6 × [Si] + 0.5 × ([Pb] + [Bi]) + 0.5 × [P] - 1.0 × [Sn] ≤ 61.5 holds. A free-cutting copper alloy casting characterized in that, in the constituent phases of the metallic structure excluding nonmetallic inclusions, when the area ratio of the α phase is (α)%, the area ratio of the γ phase is (γ)%, and the area ratio of the modified β phase, the β1 phase, is (β1)%, the following relationships exist: 10 ≤ f2 = (α) < 80, 20 < f3 = (β1) ≤ 90, 0 ≤ f4 = (γ) < 4, and grain boundaries can be observed inside the β1 phase when etched with a mixture of hydrogen peroxide and ammonia water.

4. Containing 58.8 mass% to 63.0 mass% of Cu, 0.08 mass% to 0.48 mass% of Si, 0.01 mass% to 0.10 mass% of Pb, and 0.03 mass% to 0.20 mass% of P, and as optional elements, containing 0.05 mass% to 0.85 mass% of Sn, 0.001 mass% to 0.10 mass% of Bi, 0.012 mass% to 0.08 mass% of Sb, and 0.025 mass% to 0.08 mass% of As, with the remainder being Zn and unavoidable impurities. If, among the aforementioned unavoidable impurities, the total content of Fe, Mn, Co, and Cr is less than 0.30 mass%, and the content of Al is less than 0.15 mass%, and the content of Cu is [Cu] mass%, the content of Si is [Si] mass%, the content of Pb is [Pb] mass%, the content of P is [P] mass%, the content of Bi is [Bi] mass%, and the content of Sn is [Sn] mass, then the relationship 58.0 ≤ f1 = [Cu] - 4.6 × [Si] + 0.5 × ([Pb] + [Bi]) + 0.5 × [P] - 1.0 × [Sn] ≤ 61.0 holds. A free-machining copper alloy casting characterized in that, in the constituent phases of the metallic structure excluding nonmetallic inclusions, when the area ratio of the α phase is (α)%, the area ratio of the γ phase is (γ)%, and the area ratio of the modified β phase, the β1 phase, is (β1)%, the following relationships exist: 15 ≤ f2 = (α) < 75, 25 < f3 = (β1) ≤ 85, 0 ≤ f4 = (γ) < 1, and grain boundaries can be observed inside the β1 phase when etched with a mixture of hydrogen peroxide and ammonia water.

5. A free-machining copper alloy casting according to any one of claims 1 to 4, characterized in that it has an electrical conductivity of 17.0% IACS or higher, a Vickers hardness of 95 HV or higher, and a maximum dezincification corrosion depth of 400 μm or less in a dezincification corrosion test according to ISO 6509.

6. A free-machining copper alloy casting according to any one of claims 1 to 4, characterized in that it is used in appliances and parts related to drinking water and sanitation facilities, valves, cocks, industrial piping parts, water meters, musical instruments, automobile parts, electrical and electronic equipment parts, machine parts, stationery, toys, sliding parts, instrument parts, precision machine parts, and medical parts.

7. Containing Cu in amounts exceeding 58.0 mass% and less than 63.5 mass%, Si in amounts exceeding 0.05 mass% and less than 0.50 mass%, Pb in amounts between 0.002 mass% and less than 0.20 mass%, and P in amounts exceeding 0.01 mass% and less than 0.40 mass%, with the remainder being Zn and unavoidable impurities. A method for producing a free-machining copper alloy casting using a copper alloy having the relationship 57.5 ≤ f1 = [Cu] - 4.6 × [Si] + 0.5 × [Pb] + 0.5 × [P] ≤ 61.5, wherein the total content of Fe, Mn, Co, and Cr among the aforementioned unavoidable impurities is less than 0.40 mass%, the content of Al is less than 0.30 mass%, and when the content of Cu is [Cu] mass%, the content of Si is [Si] mass%, the content of Pb is [Pb] mass%, and the content of P is [P] mass%, the manufacturing process having one or more casting steps, or the manufacturing process having one or more casting steps and a heat treatment step, wherein A method for manufacturing free-machining copper alloy castings, characterized in that, in the former casting process, the starting temperature for the cooling process in the final casting process is set to a temperature higher than 500°C and lower than 700°C; in the latter heat treatment process, in the final heat treatment process, the casting is heated under conditions of being held at a temperature above 520°C and below 650°C for 1 minute to 5 hours; and in the cooling process after heat treatment, the cooling process is started when the temperature of the casting exceeds 500°C; and in both the former and latter cooling processes, the cooling rate when the temperature of the casting reaches 500°C exceeds 300°C / min, and the average cooling rate in the temperature range from 500°C to 300°C exceeds 300°C / min.

8. Containing Cu in an amount of 58.8 mass% to 63.0 mass%, Si in an amount of 0.08 mass% to 0.48 mass%, Pb in an amount of 0.01 mass% to 0.10 mass%, and P in an amount of 0.03 mass% to 0.20 mass%, with the remainder being Zn and unavoidable impurities, wherein the total content of Fe, Mn, Co, and Cr among the unavoidable impurities is less than 0.30 mass%, and the content of Al is less than 0.15 mass%, and when the Cu content is [Cu] mass%, the Si content is [Si] mass%, the Pb content is [Pb] mass%, and the P content is [P] mass%, A method for producing a free-machining copper alloy casting using a copper alloy having the relationship 58.0 ≤ f1 = [Cu] - 4.6 × [Si] + 0.5 × [Pb] + 0.5 × [P] ≤ 61.0, wherein the manufacturing process comprises one or more casting steps, or one or more casting steps and a heat treatment step, wherein in the former casting step, the starting temperature for the cooling process of the final casting step is set to a temperature higher than 500°C and lower than 700°C, and in the latter heat treatment step, the final heat treatment step is heated at a temperature above 520°C and lower than 650°C for 1 minute to 5 hours, and in the cooling process after heat treatment, the cooling process is started when the temperature of the casting exceeds 500°C. A method for manufacturing free-machining copper alloy castings, characterized in that, in both the former and latter cooling treatments, the cooling rate at a casting temperature of 500°C exceeds 300°C / min, and the average cooling rate in the temperature range from 500°C to 300°C exceeds 300°C / min.

9. Containing Cu in amounts exceeding 58.0 mass% and less than 63.5 mass%, Si in amounts exceeding 0.05 mass% and less than 0.50 mass%, Pb in amounts of 0.002 mass% or more and less than 0.20 mass%, and P in amounts exceeding 0.01 mass% and less than 0.40 mass%, and as optional elements, containing Sn in amounts exceeding 0.01 mass% and less than 0.90 mass%, Bi in amounts exceeding 0.0001 mass% and less than 0.20 mass%, Sb in amounts of 0.01 mass% or more and less than 0.12 mass%, and As in amounts of 0.01 mass% or more and less than 0.12 mass%, the remainder being Zn and unavoidable impurities. A method for producing a free-machining copper alloy casting using a copper alloy having the following relationship: 57.5 ≤ f1 = [Cu] - 4.6 × [Si] + 0.5 × ([Pb] + [Bi]) + 0.5 × [P] - 1.0 × [Sn] ≤ 61.5, wherein the total content of Fe, Mn, Co, and Cr among the aforementioned unavoidable impurities is less than 0.40 mass%, and the content of Al is less than 0.30 mass%, and the content of Cu is [Cu] mass%, the content of Si is [Si] mass%, the content of Pb is [Pb] mass%, the content of P is [P] mass%, the content of Bi is [Bi] mass%, and the content of Sn is [Sn] mass, wherein the relationship is 57.5 ≤ f1 = [Cu] - 4.6 × [Si] + 0.5 × ([Pb] + [Bi]) + 0.5 × [P] - 1.0 × [Sn] ≤ 61.5, by a manufacturing process having one or more casting steps, or by a manufacturing process having one or more casting steps and a heat treatment step, A method for manufacturing free-machining copper alloy castings, characterized in that, in the former casting process, the starting temperature for the cooling process in the final casting process is set to a temperature higher than 500°C and lower than 700°C; in the latter heat treatment process, in the final heat treatment process, the casting is heated under conditions of being held at a temperature above 520°C and below 650°C for 1 minute to 5 hours, and in the cooling process after heat treatment, the cooling process is started when the temperature of the casting exceeds 500°C; and in both the former and latter cooling processes, the cooling rate when the temperature of the casting reaches 500°C exceeds 300°C / min, and the average cooling rate in the temperature range from 500°C to 300°C exceeds 300°C / min.

10. Containing 58.8 mass% to 63.0 mass% of Cu, 0.08 mass% to 0.48 mass% of Si, 0.01 mass% to 0.10 mass% of Pb, and 0.03 mass% to 0.20 mass% of P, and as optional elements, containing 0.05 mass% to 0.85 mass% of Sn, 0.001 mass% to 0.10 mass% of Bi, 0.012 mass% to 0.08 mass% of Sb, and 0.025 mass% to 0.08 mass% of As, with the remainder being Zn and unavoidable impurities. A method for producing a free-machining copper alloy casting using a copper alloy having the following relationship: 58.0 ≤ f1 = [Cu] - 4.6 × [Si] + 0.5 × ([Pb] + [Bi]) + 0.5 × [P] - 1.0 × [Sn] ≤ 61.0, wherein the total content of Fe, Mn, Co, and Cr among the aforementioned unavoidable impurities is less than 0.30 mass%, and the content of Al is less than 0.15 mass%, and the content of Cu is [Cu] mass%, the content of Si is [Si] mass%, the content of Pb is [Pb] mass%, the content of P is [P] mass%, the content of Bi is [Bi] mass%, and the content of Sn is [Sn] mass, wherein the relationship is 58.0 ≤ f1 = [Cu] - 4.6 × [Si] + 0.5 × ([Pb] + [Bi]) + 0.5 × [P] - 1.0 × [Sn] ≤ 61.0, by a manufacturing process having one or more casting steps, or by a manufacturing process having one or more casting steps and a heat treatment step, A method for manufacturing free-machining copper alloy castings, characterized in that, in the former casting process, the starting temperature for the cooling process in the final casting process is set to a temperature higher than 500°C and lower than 700°C; in the latter heat treatment process, in the final heat treatment process, the casting is heated under conditions of being held at a temperature above 520°C and below 650°C for 1 minute to 5 hours, and in the cooling process after heat treatment, the cooling process is started when the temperature of the casting exceeds 500°C; and in both the former and latter cooling processes, the cooling rate when the temperature of the casting reaches 500°C exceeds 300°C / min, and the average cooling rate in the temperature range from 500°C to 300°C exceeds 300°C / min.

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