JP2007297675A - Lead-free copper alloy for casting superior in machinability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lead-free copper alloy for casting, which shows excellent machinability and pressure resistance even without containing such lead as to cause the degradation of water quality, is superior in mechanical properties such as strength and elongation, and is useful as a base material of water tap fittings, faucets for contact with water and the like. <P>SOLUTION: The lead-free alloy for casting includes 0.05-1.5% S (by mass%, hereafter the same), 3.5% or less Bi (excluding 0%), 0.5% or less Fe (excluding 0%) and/or 3.0% or less Ni (excluding 0%); and has sulfides dispersed therein. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a copper alloy for castings excellent in machinability, and in particular, exhibits excellent machinability and pressure resistance without containing lead harmful to the human body, and has a machine such as strength and elongation. The present invention relates to a lead-free copper alloy for castings having excellent mechanical properties.

  Copper alloys have been widely used as materials for various electric parts and the like since they are excellent in electrical conductivity and thermal conductivity. Among the copper alloys, various copper alloys for casting are defined in JIS H5120, and are planned to be used for various purposes such as valve bodies, water taps, and bearings.

  By the way, a copper alloy for casting is generally used for water faucet fittings for general water supply and sewerage and water pipes for general piping, and among those specified in the above JIS H5120, a brass system such as CAC203 alloy (Cu -Zn-based) copper alloys and bronze-based (Cu-Sn-Zn-based, Cu-Sn-Pb-Zn-based) such as CAC403 and 406 are known as materials.

  When used for faucet fittings and water faucets as described above, in addition to pressure resistance, wear resistance, castability, mechanical properties (strength and hardness), machinability (cutability) However, it is well known that lead (Pb) is contained as a means for improving the machinability. Among the above-mentioned copper alloys for casting, CAC406 contains 4 lead. The machinability is improved by adding about 6%. Moreover, it is known that inclusion of lead is also useful in improving the pressure resistance of a copper alloy (for example, Non-Patent Document 1).

  However, if a faucet fitting or water faucet is manufactured using a copper alloy for casting containing lead, harmful lead contained in the faucet elutes in the drinking water, causing water quality deterioration and adversely affecting the human body. It has been pointed out. In particular, in Japan, the water quality standard for lead has been strengthened to 1/5 of the conventional level since fiscal 2003, and as a result, the regulation of lead in copper alloys for castings used for faucets and faucets has become stricter. ing.

  For these reasons, various copper alloys for casting that improve the machinability without actively containing lead have been proposed. In order to improve machinability, copper alloys to which Bi or Se is added as a substitute for lead have been developed mainly in Europe and the United States, and are registered as CDA (Copper Development Association) standards (for example, Non-Patent Document 2). It is also known to contain Sb together with Bi (Non-Patent Document 1).

  These copper alloys contain Bi, Se, Sb, etc. instead of lead as free-cutting elements, and the development of such technology can maintain relatively good machinability while preventing harm from lead. It was.

However, lead-free copper alloys that have been developed so far are more prone to casting defects, which are likely to deteriorate the pressure resistance of conventional standard copper alloys. The actual situation is that improvement is desired.
“Materia”, Vol. 43, No. 8 (2004), pp. 647-650 “Shape Material”, August 2003, Issued by the Shape Materials Center, pages 7-14

  The present invention has been made under such circumstances, and its purpose is to exhibit excellent machinability and pressure resistance without containing lead that causes deterioration of water quality, and mechanical properties such as strength and elongation. Another object of the present invention is to provide a lead-free copper alloy for castings that is excellent as a material for faucets and water faucets.

  The lead-free copper alloy for castings of the present invention that can achieve the above-mentioned object is S: 0.05 to 1.5% (meaning of mass%, the same shall apply hereinafter) and Bi: 3.5% or less (0% Not contained), Fe: not more than 0.5% (not including 0%) and / or Ni: not more than 3.0% (not including 0%), and sulfide was dispersed It has a gist in that it is a thing. In this copper alloy, the S content is preferably about 0.05 to 0.8%.

  The lead-free copper alloy for castings of the present invention may contain (a) Sn: 10% or less (not including 0%), (b) Zn: 10% or less (not including 0%), etc. as necessary. Is also effective, and the properties of the copper alloy are improved depending on the components contained.

  In the copper alloy of the present invention, by containing Fe and Ni together with S and Bi, sulfides can be effectively dispersed in the copper matrix, and excellent pressure resistance without containing lead that causes water quality deterioration and A lead-free copper alloy for castings that has excellent machinability and excellent mechanical properties such as strength could be realized. This copper alloy is useful as a material for water faucets and water faucets.

  The present inventors have studied from various angles to realize a copper alloy for castings that exhibits excellent pressure resistance and machinability without containing lead. As a result, copper containing sulfur (S) and bismuth (Bi) as essential components, adjusting the content of Fe and Ni to an appropriate range, and forming and dispersing sulfide in the metal structure In the case of alloys, the inventors have found that the above object can be achieved brilliantly and completed the present invention.

  It is known that S is a machinability improving element in the field of steel materials. However, in the case of a copper alloy, S is not employed as a machinability improving element. This is because, in dissolved copper, S forms sulfides at an early stage, floats and separates on the surface of the dissolved copper, and it is considered difficult to disperse sulfides in the copper matrix itself. It was.

  On the other hand, in a copper alloy, it is also known to contain Bi as a free-cutting element instead of lead. However, in a lead-free copper alloy containing Bi, a “cast hole” that is a casting defect is likely to occur. As a result, the pressure resistance deteriorated compared with the conventional standard copper alloy.

  In the copper alloy containing Bi useful as a free-cutting element, the inventors of the present invention can realize good machinability and pressure resistance if sulfides can be effectively dispersed in a copper matrix. I have studied further under the idea. As a result, in the state where a predetermined amount of Fe or Ni coexists, the activity of S is suppressed, and the sulfide is formed at a stage where the temperature is relatively low (that is, a stage immediately before completion of solidification of copper). Thus, it has been found that sulfide can be effectively dispersed in the copper matrix. In addition, in the copper alloy in which sulfide is dispersed, the occurrence of a casting hole due to Bi is suppressed, good pressure resistance is exhibited, and the mechanical characteristics can be maintained well.

  Although not all of the reasons why the above-described effects can be obtained by the copper alloy for castings of the present invention can be considered as follows.

  When the copper alloy for castings solidifies, dendrites (dendrites) are formed, and solidification is completed while leaving minute voids (bubbles) between the dendrites (final solidification region), which becomes the casting cavity. It is known. In the copper alloy of the present invention, the formation of sulfide is suppressed to a relatively low temperature by coexisting Fe and Ni together with S and Bi. It is in a liquid state. Then, this eutectic melt flows into the bubbles that cause the cast hole to form sulfides. As a result, it was considered that the occurrence of a cast hole was suppressed and good pressure resistance was exhibited, and mechanical properties such as strength were improved. In addition, when sulfides are eutectic or finely dispersed between dendrites, each sulfide plays the role of a chip breaker that divides cutting chips (chips become finer), and the sulfide itself is a solid lubricant. It was considered that the machinability was improved by contributing as an agent.

  In addition to containing S and Bi as essential components, the lead-free copper alloy of the present invention contains a predetermined amount of Fe or Ni. The reasons for limiting these ranges are as follows.

[S: 0.05 to 1.5%]
S combines with Cu or Bi to form a Cu ₂ S compound (ZnS compound when Zn is contained) or Bi ₂ S ₃ compound, and the pressure resistance, machinability and mechanical strength of the copper alloy are increased. It is an element useful for improvement. In order to exert such effects, the S content needs to be at least 0.05%, but if it exceeds 1.5% and excessively contained, the pressure resistance and mechanical properties will decrease. Should be less than 1.5%. In addition, the upper limit with preferable S content is about 0.8%, and even if it does not contain Sn mentioned later with this content, favorable intensity | strength is securable. However, when applied to a member (for example, a bearing member) that does not require so much strength, even if the S content is more than 0.8% to about 1.5%, Sn may not be contained. .

[Bi: 3.5% or less (excluding 0%)]
Bi is an element useful for combining with S to form a Bi ₂ S ₃ compound and improving the pressure resistance, machinability and mechanical strength of the copper alloy. Such an effect increases as its content increases. However, if the content exceeds 3.5%, the Bi phase becomes excessive and the mechanical properties are lowered. Bi is preferably contained in an amount of 0.05% or more in order to exhibit the above effects. Moreover, the upper limit with preferable Bi content is 3.0%, It is good to set it as 2.0% or less more preferably.

[Fe: 0.5% or less (not including 0%) and / or Ni: 3.0% or less (not including 0)]
Fe and Ni are elements necessary for forming a sulfide (Cu ₂ S, Bi ₂ S ₃ , ZnS, etc.) at a low temperature and dispersing the sulfide in the copper matrix. Such an effect increases as the content thereof increases. However, if the content is excessive, the flowability of the molten metal deteriorates and the castability deteriorates. For these reasons, Fe is defined as 0.5% or less, and Ni is defined as 3.0% or less. In addition, the minimum with preferable Fe content is 0.1%, It is good to set it as 0.2% or more more preferably. Moreover, the upper limit with preferable Fe content is 0.4%, More preferably, it is good to set it as 0.3% or less. On the other hand, the preferable lower limit of the Ni content is 0.5%, more preferably 1.0% or more. Moreover, the upper limit with preferable Ni content is 2.5%, It is good to set it as 2.0% or less more preferably.

  The basic chemical composition of the copper alloy of the present invention is as described above, and the balance is substantially made of copper (Cu), but it is also effective to contain Sn, Zn or the like if necessary. The reasons for limiting the range when these are contained are as follows. In addition, “substantially copper” means that the copper alloy of the present invention can contain trace elements (allowable components) to the extent that they do not impede their properties in addition to Cu. Examples of such allowable components include Sb, Examples thereof include elements such as P and Si, and inevitable impurities such as Al and Mn. Of the above basic components, S may be inevitably mixed, but when it is contained in less than 0.05%, it is treated as an unavoidable impurity.

[Sn: 10% or less (excluding 0%)]
Sn is an element effective for improving the strength (tensile strength) of the copper alloy. In particular, by containing S, it is effective to compensate for the decreasing strength by containing Sn. For example, when S is contained in an amount of more than 0.8% to about 1.5%, the strength tends to decrease, but the strength is improved while maintaining the machinability improvement effect by containing S. It is an effective element for securing These effects increase as the content increases, but if excessively contained, the mechanical properties deteriorate (see FIG. 5 below), and should be 10% or less. In order to exert such an effect, the preferable lower limit of the Sn content is 2.0%. Moreover, the upper limit with preferable Sn content is about 7.6%, More preferably, it is good to set it as 6.0% or less. Sn may be inevitably mixed, but if it is 0.1% or less, it is treated as an unavoidable impurity.

[Zn: 10% or less (excluding 0%)]
Zn is an element useful for further improving the pressure resistance, machinability and mechanical strength of a copper alloy by forming a ZnS compound. Such effects increase as the content increases, but it is preferable to contain at least 3.0% or more. However, if Zn is excessively contained, the elution amount of Zn increases, so that it is preferably 10% or less, more preferably 8.0% or less.

  The copper alloy of the present invention exhibits the above effect by dispersing sulfides in the metal structure (copper matrix). Such sulfides have a content of S, Bi, Fe, Ni. It is inevitably formed by appropriately adjusting and dissolving and solidifying. Moreover, when manufacturing a casting using the copper alloy of this invention, the methods generally performed until now, such as sand casting, metal mold casting, centrifugal casting, and precision casting, can be adopted.

  Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are not intended to limit the present invention, and any design changes in accordance with the gist of the preceding and following descriptions are technical aspects of the present invention. It is included in the range.

Example 1
Each copper alloy having chemical composition shown in Table 1 below was melted and cast according to a conventional method. The machinability of the obtained copper alloy casting was investigated. The cutting conditions at this time are as follows. Then, after cutting the test piece with φ23 mm → φ22 mm → 21 mm, cutting resistance was measured by cutting with φ20 mm, and machinability was evaluated by a machinability index obtained by the following equation (1). In addition, the value (content) of each component other than S shown in Table 1 is a value measured by a fluorescent X-ray analyzer [Element Analyzer JSX-3202 (trade name: manufactured by JEOL Ltd.)] S is a value obtained by the combustion method.

[Cutting conditions]
NC lathe: OKUMA LP25C (trade name: manufactured by Okuma Corporation)
Tip: Igetaroy cutting dynamometer: KISER 9257B (trade name: manufactured by Nippon Kistler Co., Ltd.)
Cutting oil: Oil-based cutting speed: 100 m / min
Feeding speed: 0.1mm / rev
Cutting depth: 0.5 mm or 1.0 mm
Test piece diameter: φ23mm
Processing diameter: φ20mm
Machinability index = (cutting resistance value of CAC406 / cutting resistance value of each test piece)
× 100 ... (1)

  The results (relationship between S content and machinability index) are shown in FIG. As is clear from this result, it is understood that the machinability tends to improve as the S content increases. This is considered to be due to the fact that the sulfide was uniformly dispersed.

(Example 2)
For each copper alloy casting shown in Table 1 above, various mechanical properties (tensile strength and elongation) were investigated. The measurement results (relationship between S content and mechanical properties) are shown in FIG. 2 (n = 2 average values). The tensile strength of CAC406 referring to JIS is 195 MPa, and the elongation is 15%. This result can be considered as follows. First, when the S content exceeds 0.3%, the tensile strength tends to decrease slightly, but it is understood that the tensile strength is better than that of the conventional copper alloy (CAC406). In addition, about the thing of each copper alloy (No. 1-3) of this invention, when the structure | tissue was observed with the scanning electron microscope (SEM), it has confirmed that the sulfide was disperse | distributing to the last solidification area | region.

(Example 3)
Each copper alloy shown in Table 1 was examined for pressure resistance. The test method of the pressure resistance was carried out in accordance with “9.1 pressure resistance test of valve box” in “JIS B 2062 tap water gate valve” (water pressure: 3 MPa, 2 minutes). Each test piece is tested 24 times (n = 24), the presence or absence of water leakage is observed with the naked eye, and when “leakage” is confirmed, it is determined as a defective product, and the occurrence rate (defective rate = The pressure resistance was evaluated by the number of defective products / 24).
As a result, no. In the copper alloys shown in 1 to 3, the defect rate was extremely low (4% or less), and it was confirmed that good pressure resistance was exhibited.

Example 4
Each copper alloy having chemical composition shown in Table 2 below was melted and cast according to a conventional method. Various mechanical properties (tensile strength and elongation) of the obtained copper alloy casting were investigated.

  The measurement results (relationship between Bi content and mechanical properties) are shown in FIG. 3 (n = 2 average values), and can be considered as follows from this result. First, it can be seen that when the Bi content is about 2%, the tensile strength is maintained high while suppressing the decrease in elongation. However, when the Bi content exceeds 3%, the mechanical properties tend to be lowered.

(Example 5)
About each copper alloy casting shown in the said Table 2, it carried out similarly to Example 1, and investigated machinability. The results (relationship between Bi content and machinability index) are shown in FIG. As is clear from this result, it can be seen that the machinability tends to improve as the Bi content increases.

(Example 6)
Each copper alloy having chemical composition shown in Table 3 below was melted and cast according to a conventional method. Various mechanical properties (tensile strength and elongation) of the obtained copper alloy casting were investigated.

  The measurement results (relationship between Sn content and mechanical properties) are shown in FIG. 5 (n = 2 average values), and can be considered as follows from this result. First, when the Sn content is up to about 7.6%, the tensile strength is improved while suppressing the decrease in elongation. Especially when the Sn content is 6% or more, it is comparable to the conventional copper alloy (CAC406). I understand. This can be considered to be due to the solid solution strengthening of Sn.

(Example 7)
About each copper alloy casting which shows a chemical component composition in following Table 4, it carried out similarly to Example 1, and investigated machinability (machinability index). The result is shown in FIG. 6, and it can be seen that even if Fe, Ni, Sn, Zn, and the like are contained, good machinability is exhibited.

(Example 8)
For each copper alloy casting shown in Table 3 and the copper alloy casting (No. 19) having chemical components shown in Table 5 below, the machinability (cutability index) was investigated in the same manner as in Example 1. The result (relationship between Sn content and machinability index) is shown in FIG. 7, but it has sufficient machinability even when it does not contain Sn, and even if the Sn content increases, the machining by S It can be seen that the effect of improving the performance is exhibited.

It is the graph which showed the S content and the machinability in the copper alloy of this invention. It is the graph which showed the relationship between S content and the mechanical characteristic in the copper alloy of this invention. It is the graph which showed the relationship between Bi content and the mechanical characteristic in the copper alloy of this invention. It is the graph which showed the Bi content and the machinability in the copper alloy of this invention. It is the graph which showed the relationship between Sn content and the mechanical characteristic in the copper alloy of this invention. It is the graph which compared and showed the machinability (cutability index) in various copper alloys. It is the graph which showed the relationship between Sn content and machinability in the copper alloy of this invention.

Claims (4)

  S: 0.05 to 1.5% (meaning of mass%, the same shall apply hereinafter) and Bi: 3.5% or less (excluding 0%) and Fe: 0.5% or less (0% And / or Ni: 3.0% or less (excluding 0%), and sulfides dispersed therein. Lead-free copper alloy for casting with excellent machinability .   The lead-free copper alloy for castings according to claim 1, wherein the content of S is 0.05 to 0.8%.   The lead-free copper alloy for castings according to claim 1 or 2, further comprising Sn: 10% or less (not including 0%).   The lead-free copper alloy for castings according to any one of claims 1 to 3, further comprising Zn: 10% or less (not including 0%).

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