JP3789833B2 - Lead-free free-cutting copper alloy material - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lead-free free-cutting copper alloy material that is rich in machinability without containing lead.
[0002]
[Prior art]
In general, bronze alloys such as JIS H5111 CAC406 and brass alloys such as JIS H3250-C3604 and C3771 are known as copper alloys having excellent machinability. These have improved machinability by containing a considerable amount of lead and ensure industrially satisfactory machinability. In other words, lead does not dissolve in the matrix, disperses in a granular form, and improves the machinability of the copper alloy material by functioning as a chip breaker that melts with cutting heat and finely cuts (shears) the cutting waste. It is something to be made.
[0003]
Since copper alloy materials containing lead are excellent in machinability as described above, they have been useful as constituent materials for various products (for example, faucet fittings for water supply pipes, water supply / drainage fittings, valves, etc.). Has been. However, since lead is a harmful substance that adversely affects the human body and the environment, its use has recently been greatly limited. For example, the metal vapor generated during high-temperature work such as melting or casting of an alloy may contain lead components, or lead components may be eluted from faucet fittings or valves due to contact with drinking water or the like. Yes, there are human and environmental health problems.
[0004]
[Problems to be solved by the invention]
Therefore, recently, in developed countries such as the United States, there is a tendency to significantly limit the lead content in copper alloys, and in Japan, the development of free-cutting copper alloy materials with a reduced lead content as much as possible is strong. It has been requested.
[0005]
The present invention has been made to respond to such global trends and demands, and aims to provide a lead-free free-cutting copper alloy material that has industrially satisfactory machinability without containing lead. To do.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is a copper alloy material having an alloy composition containing 70 to 78% by mass of copper and 3.5 to 7.0% by mass of aluminum, with the balance being zinc. Then, a lead-free free-cutting copper alloy material characterized by forming a metal structure including 95 to 60% α phase and 4 to 20% dispersed fine γ phase in area ratio is proposed.
[0007]
In such a lead-free free-cutting copper alloy material, the metal structure includes fine γ phase and α phase precipitated by β phase transformation, or fine γ phase precipitated by β phase transformation and It is preferably composed of an α phase and a remaining fine β phase that is not transformed . Also, the alloy composition, if desired, may have been the one containing 0.01 to 0.1 wt% boron, or 0.05 to 0.5 weight percent vanadium.
[0008]
Thus, as described above, lead exhibits a chip breaker function that improves the machinability by being dispersed in a granular form without being dissolved in the matrix, but such a melt (lead ) Does not exist, the chip breaker function is exhibited and the machinability is improved because the fine hard phase is dispersed in the matrix. That is, since the hard and fine γ phase is dispersed, the cutting waste is easily broken, and as a result, the cutting waste is finely divided in the cutting process, and the machinability is improved.
[0009]
On the other hand, in the case where a sufficient γ phase is formed to function as a chip breaker, the matrix has a sufficient α phase in order to maintain the original characteristics (workability, etc.) of the copper alloy. It is necessary to be. That is, in order to improve machinability without impairing the original characteristics of the copper alloy, it is preferable that the α phase and the γ phase exist in a predetermined range. Specifically, in the area ratio, it is preferable that the α phase is 95 to 60% and the γ phase is 4 to 20%. However, if the α phase is less than 60% or the γ phase exceeds 20%, the original characteristics of the copper alloy may be impaired. If the γ phase is less than 4%, the effect of improving machinability due to dispersion of the γ phase cannot be expected. On the other hand, if the α phase exceeds 95%, it is difficult to secure a 4 to 20% γ phase.
[0010]
In order to form such α phase and γ phase, it is a necessary condition to specify the alloy composition as described above, but it is not a sufficient condition. In order to secure the α and γ phases necessary and sufficient to improve the machinability while ensuring the original characteristics of the copper alloy, the following structure control by heat treatment is required for those having the above alloy composition. Necessary.
[0011]
That is, high-temperature heat treatment (hereinafter referred to as “primary heat treatment”) at 600 to 800 ° C. for 30 minutes or more on a material (ingot or its hot or cold work material (forged material, extruded material)) having the above-described alloy composition. To form a two-phase microstructure of α phase and β phase, and this primary heat treatment material is subjected to low temperature heat treatment (hereinafter “secondary heat treatment” at 550 to 300 ° C. for 1 hour or more. The β phase is transformed to decompose into a fine γ phase and an α phase, and the fine mixed phase is dispersed in the matrix of the α phase. When the β phase is completely transformed, the mixed phase is composed of fine α phase and γ phase, and when the β phase is not completely transformed, the mixed phase contains the remaining β phase that is not transformed. . Whether or not the mixed phase contains the β phase does not substantially affect the machinability improvement, and the machinability is due to the fact that the fine γ phase in the above range (4 to 20%) is dispersed. It improves. The conditions for the primary heat treatment and the secondary heat treatment are set according to the alloy composition of the material, and even if the heat treatment conditions are the same, the metal structure will be different if the alloy composition is different. Similarly, even if the alloy composition is the same, if the heat treatment conditions are different, the metal structures are different.
[0012]
By the way, the formation of β phase by primary heat treatment is necessary to realize the precipitation of fine γ phase by secondary heat treatment, and when primary heat treatment temperature is less than 600 ° C., there is a strong tendency to become α single phase, and sufficient β If the phase cannot be secured, and the primary heat treatment time is less than 30 minutes, recrystallization is not sufficiently performed, and an appropriate α + β phase cannot be obtained. Further, when the primary heat treatment temperature exceeds 800 ° C., crystal grains grow remarkably, and it becomes difficult to obtain a metal structure necessary for improving the machinability even by the secondary heat treatment. If the secondary heat treatment time is short (for example, less than 1 hour), the formation of the γ phase is not sufficient, and the secondary heat treatment is preferably performed for as long as possible. However, the time until the β phase is completely transformed by the secondary heat treatment (the time to reach the equilibrium state) is extremely long, and the secondary heat treatment under such a long time is difficult to realize industrially. It is. Therefore, in general, the secondary heat treatment time is preferably set within 24 hours. However, when the secondary heat treatment time is within 24 hours, the β phase is not completely transformed, and the mixed phase contains the remaining β phase that is not transformed. In addition, when the secondary heat treatment temperature exceeds 550 ° C., the decomposition of the β phase does not substantially occur, and when it is less than 300 ° C., the reaction rate is slow and the γ phase does not increase to such an extent that the machinability can be improved. .
[0013]
Further, in order to obtain a free-cutting copper alloy material with improved machinability by the above-described structure control without impairing the original characteristics (workability, etc.) of the copper alloy, the constituent elements and their contents are as described above. It is necessary to set.
[0014]
That is, when the content of copper, which is a base constituent element, is less than 70% by mass, the alloy hardness becomes higher than necessary, and the workability decreases. Moreover, when copper content exceeds 78 mass%, an alloy will soften and machinability will fall. Aluminum makes it possible for the β phase to appear, but if its content is less than 3.5% by mass, formation of a fine γ phase due to decomposition of the β phase is not sufficiently performed, and 7.0% by mass. If it is added in excess of, the β single phase is likely to be formed during the primary heat treatment, and the hardness after the secondary heat treatment is increased and the workability is lowered. By the way, although the fracture effect of cutting scraps becomes more remarkable when the structure is refined, boron or vanadium functions as a atomizing agent that promotes the refinement of such a structure. Added. However, when the boron addition amount is less than 0.01% by mass or when the vanadium addition amount is less than 0.05% by mass, the function as the atomizing agent is not sufficiently exhibited. Such functions reach 0.5% by mass for boron and 0.1% by mass for vanadium, and reach saturation, and even if they are added in excess of these amounts, an effect commensurate with the amount added cannot be expected. .
[0015]
【Example】
As an example, an ingot (billet) having the alloy composition shown in Table 1 was hot-extruded into a round bar shape having an outer diameter of 9.5 mm after the head portion was cut out, and the extruded material or this was externally cooled. By applying a primary heat treatment and a secondary treatment to a material drawn into a round bar shape with a diameter of 9.0 mm (drawn material), the fine γ phase is uniformly dispersed in the α phase matrix and the α phase, γ The alloy material No. 1 according to the present invention, in which the area ratio of the phases is controlled to a metal structure having the values shown in Table 1. 1-5 were obtained. In addition, each alloy material No. About 1-5, the structure | tissue control was performed by the following primary heat processing and secondary heat processing. That is, the alloy material No. For No. 1, the extruded material was subjected to a primary heat treatment at 700 ° C. for 1 hour, followed by a secondary heat treatment at 400 ° C. for 3 hours after furnace cooling. Alloy material No. For No. 2, the extruded material was subjected to primary heat treatment at 700 ° C. for 1 hour, and then subjected to secondary heat treatment at 350 ° C. for 3 hours after furnace cooling. Alloy material No. For No. 3, the drawn material was subjected to primary heat treatment at 700 ° C. for 3 hours, and after furnace cooling, secondary heat treatment was performed at 350 ° C. for 5 hours. Alloy material No. For No. 4, the drawn material was subjected to a primary heat treatment at 700 ° C. for 1 hour, and after the furnace cooling, a secondary heat treatment was performed at 350 ° C. for 5 hours. Alloy material No. For No. 5, the drawn material was subjected to a primary heat treatment at 650 ° C. for 3 hours, and after the furnace cooling, a secondary heat treatment was performed at 500 ° C. for 5 hours.
[0016]
As a comparative example, in the same manner as in the example, an ingot (billet) having the alloy composition shown in Table 2 was hot-extruded into a round bar shape having an outer diameter of 9.5 mm after cutting off its head. Alloy material No. 1 in which the metal structure was changed by subjecting the extruded material or a material obtained by cold drawing to a round bar shape with an outer diameter of 9.0 mm (drawn material) to the following heat treatment. 11-16 were obtained. That is, the alloy material No. For Nos. 11 and 12, the extruded material was heat-treated at 700 ° C. for 3 hours, and further subjected to heat treatment at 350 ° C. for 5 hours after furnace cooling. Alloy material No. For No. 13, the extruded material was subjected to heat treatment at 700 ° C. for 3 hours, and further subjected to heat treatment at 400 ° C. for 5 hours after furnace cooling. Alloy material No. For No. 14, the extruded material was heat treated at 700 ° C. for 1 hour, and after air cooling, further heat treated at 350 ° C. for 4 hours. Alloy material No. For No. 15, the drawn material was heat treated at 350 ° C. for 5 hours. Alloy material No. For No. 16, the drawn material was heat-treated at 700 ° C. for 3 hours and cooled with water. Each alloy material no. The area ratio of the α phase and the γ phase in 11 to 16 was as shown in Table 2.
[0017]
And Example alloy material No. 1-5 and comparative alloy material No. 11-16 using a lathe, cutting oil: none, cutting tool: cemented carbide, top rake angle: 0 °, side rake angle: 0 °, front clearance angle: 0 °, side clearance angle: 6 ° , Front cutting edge angle: 15 °, side cutting edge angle: 0 °, nose radius: 0 mm, rotation speed: 785 rpm, feed: 0.1 mm / rev, cutting: 0.5 mm As a result, the machinability was confirmed. The results were as shown in Tables 1 and 2.
[0018]
As shown in Table 1, fine γ phase is dispersed and the area ratio of α phase and γ phase is within the range specified in the present invention (α phase: 95 to 60%, γ phase: 4 to 20%). Example alloy material No. As for 1-5, in all, it was confirmed that the cutting waste is divided within 5 windings and has excellent machinability despite containing no lead. On the other hand, comparative alloy material No. 1 in which at least one of the alloy composition and the area ratio of α phase or γ phase deviates from the range specified in the present invention. As for Tables 11-16, as shown in Table 2, the cutting waste has a continuous curl shape, the machinability is not improved at all, and the machinability is remarkably lowered as compared with the lead-containing alloy. It is clear. Therefore, it is understood that the machinability is greatly improved by controlling the structure of the alloy composition specified in the present invention to the metal structure specified in the present invention without containing lead.
[0019]
[Table 1]
[0020]
[Table 2]
[0021]
【The invention's effect】
As can be easily understood from the above description, the lead-free free-cutting copper alloy of the present invention has extremely high machinability despite the fact that it does not contain lead, which is an element for improving machinability, and contains lead. As a substitute for conventional free-cutting copper alloys, it can be safely used, and there is no environmental hygiene problem including reuse of cutting waste, and lead-containing products are being regulated recently. Can be fully accommodated.

Claims (5)

A copper alloy material comprising 70 to 78% by mass of copper and 3.5 to 7.0% by mass of aluminum, and the balance being zinc alloy composition,
A lead-free free-cutting copper alloy material characterized by forming a metal structure containing 95 to 60% α phase and 4 to 20% dispersed fine γ phase in area ratio . The γ phase, characterized in that it is the ash deposited by transformation β phase, lead-free free-cutting copper alloy material according to claim 1. wherein the forming a metal structure comprising the balance of the fine β-phase which is not transformed with the deposited fine γ phase and α phase by transformation of β-phase, lead-free free-cutting copper alloy material according to claim 1 . The lead-free free-cutting copper alloy material according to claim 1, 2 or 3 , wherein the alloy composition further contains 0.01 to 0.1% by mass of boron. The lead-free free-cutting copper alloy material according to claim 1, 2 or 3 , wherein the alloy composition further comprises 0.05 to 0.5% by mass of vanadium.