JP2010242184A - Lead-free, free-machining brass excellent in castability and corrosion resistance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide brass containing no lead (Pb) and is excellent in cutting property, castability, corrosion resistance, mechanical properties, etc. <P>SOLUTION: The brass comprises 62-75 wt.% Cu, 0.3-1.5 wt.% Bi, 0.1-0.5 wt.% Sn, 0.15-0.5 wt.% P, 0.1-1.0 wt.% Al, 0.0005-0.0035 wt.% B, 0.5-1.0 wt.% Si, 37.5-40.0% of apparent Zn and the balance substantially being Zn and unavoidable impurities. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a so-called lead-free brass that does not contain lead, and more specifically, because it does not contain lead, it is preferably used for faucet fittings and the like, and has excellent machinability, castability, corrosion resistance, mechanical properties, etc. About.

  The faucet fitting is generally manufactured from brass or bronze, and lead (Pb) is added in an amount of 2 to 3 wt% for brass and 4 to 6 wt% for bronze in order to improve the machinability. However, in recent years, there has been a concern about the influence of Pb on the human body and the environment, and the movement of regulations concerning Pb has been activated in each country. For example, in California in the United States, a regulation to make the Pb content of the faucet 0.25 wt% or less came into effect from January 2010. Further, it is said that the amount of Pb leaching will be regulated to about 5 ppm in the future. Even in countries other than the United States, the movement of the regulation is remarkable, and the development of materials corresponding to the regulation of the Pb content or the Pb leaching amount is required.

  Since bismuth (Bi) exhibits similar behavior to Pb in brass, brass added with Bi instead of Pb has been proposed (for example, Patent Document 1). In addition, it is disclosed that boron (B), nickel (Ni), or the like is added to improve the machinability in a system to which Bi is added (for example, Patent Document 2). Furthermore, the knowledge that a crystal | crystallization can be refined | miniaturized by adding iron (Fe) in the system which added Bi is disclosed (for example, patent document 3). However, the systems disclosed by these prior arts leave room for improvement in castability, particularly cracking during casting. Therefore, it can be said that there is still a need for brass that does not contain Pb and has excellent castability, machinability, mechanical properties, and the like.

  In addition, since the faucet fitting is used around water, one of the basic characteristics is to maintain corrosion resistance. In order to maintain corrosion resistance, brass that prevents dezincification corrosion and selective corrosion by adding Sn in the range of 0.2% to 4% and P in the range of 0.001 to 0.5% has been proposed. (For example, Patent Document 4). In addition, brass with improved dezincification corrosion resistance by adding Sn, Al, Sb, Ni or the like has been proposed (Patent Document 5). However, these elements, which are added as corrosion resistance improving elements, are closely related to castability, such as increasing the sensitivity of casting cracks and reducing sink performance. For this reason, there is almost no conventional technology that has excellent corrosion resistance that can be used without any problem even in an environment containing a low pH and high free carbonic acid concentration, which easily corrodes copper alloys, and also maintains castability. .

JP 7-310133 A JP 2005-290475 A JP 2001-59123 A JP 2001-64742 A Japanese Patent No. 2793041

In the present invention, the present invention has developed a corrosion resistance improvement effect by adding Sn, P and Al, which have an effect of improving corrosion resistance, in a range in which castability is not impaired in brass added with Bi instead of Pb, and machinability. The inventors have obtained knowledge that brass having excellent mechanical properties can be obtained. The present invention is based on such knowledge.
Accordingly, an object of the present invention is to provide brass that does not contain Pb and is excellent in machinability, castability, corrosion resistance, mechanical properties, and the like.

And the brass according to the present invention is
Cu is 62 wt% or more and 75 wt% or less,
Bi is 0.3 wt% or more and 1.5 wt% or less,
Sn 0.1 wt% to 0.5 wt% P 0.15 wt% to 0.5 wt% Al 0.1 wt% to 1.0 wt% B 0.0005 wt% to 0.0035 wt% Si 0.5 wt% or more and 1.0 wt% or less The apparent Zn content is 37.5% or more and 40.0% or less, and the balance is substantially composed of Zn and inevitable impurities.

  The present invention can provide brass that does not contain Pb and is excellent in machinability, castability, corrosion resistance, mechanical properties, and the like.

It is a figure which shows the shape of the metal mold | die 1 used for the both-ends restraint type | mold test method which evaluates casting cracking property. It is a figure which shows sectional drawing of the test piece which evaluates a sink test.

Definitions In the present invention, “inevitable impurities” means an element in an amount of less than 0.1 wt% unless otherwise specified. However, Sb, As, Mg, Se, Te, Fe, Co, Zr, Cr, and Ti are included in the inevitable impurities, but the amount is allowed to be added in the amount separately defined in this specification. . The amount of this inevitable impurity is preferably less than 0.05 wt%.
Brass according to α-phase · beta phase present invention, the total ratio of the α phase and the beta phase is 95% or more, preferably 98% or more. By making the crystal structure mainly composed of α phase and β phase, brass having good castability can be realized. Further, in the present invention, it is preferable to avoid dendritic crystallization of the primary α phase, and further excellent corrosion resistance can be obtained by performing heat treatment to reduce the β phase ratio. In the present invention, the total ratio of the α phase and the β phase is based on the area ratio in the crystal cross section. For example, the crystal structure photograph taken with an optical microscope is subjected to image processing to obtain the α phase and the β phase. And the total area ratio.

Bi
The brass according to the present invention contains Bi in a range of 0.3 wt% to 1.5 wt%. Since Bi shows a behavior similar to Pb in brass, it gives a machinability equivalent to that instead of Pb. In the present invention, Bi is set to 0.3 wt% or more in order to obtain good machinability. On the other hand, if Bi is excessive, Bi tends to agglomerate, and the agglomerated portion may be a starting point for casting cracks. Further, the addition of an element for improving corrosion resistance increases the sensitivity to casting cracks. Therefore, in the present invention, the upper limit is 1.5 wt%. According to a preferred aspect of the present invention, the preferred lower limit value of Bi is 0.5 wt% or more, and more preferably 1.0 wt% in consideration of machinability.

  In addition, according to this invention, even if it does not contain Pb at all, favorable machinability is implement | achieved. Pb is preferably not included at all, and even if it is included, it is only allowed to exist as an inevitable impurity. Specifically, it is 0.5 wt% or less, preferably 0.1 wt% or less in consideration of the human body and the environment.

B and Si
In the present invention, B promotes refinement of crystals (particularly the primary β phase), and as a result, Bi is finely dispersed and cracks during casting can be effectively prevented. Further, it is presumed that Si has a function of dissolving in the β phase and relaxing the fracture at the interface between Bi and β phase, which is the starting point of casting crack. In addition, the brass according to the present invention exhibits good performance in terms of mechanical properties as a result of the miniaturization.

  If B is added in a large amount, it forms an intermetallic compound with Fe, Cr, etc., forms a hard spot, and there is a risk of causing problems during surface processing of the molded product after casting. Therefore, as in the present invention, in the case of obtaining smoothness on the surface, it is preferable to reduce the addition amount of B and / or to reduce the content of Fe, Cr and the like. It is preferably 0.0025 wt% or less, more preferably 0.0015 wt% or less, and Fe, Cr, etc. are preferably less than 0.1 wt%.

  In addition, as will be described later, the Zn equivalent of Guillet is 10 as Si will be described, and as the amount added increases, the apparent Zn content increases, and different phases such as γ phase and κ phase appear in the crystal structure. There is a risk of precipitation. Moreover, corrosion resistance falls by making many solid solution. Therefore, according to one aspect of the present invention, the amount of Si added is 1.0 wt% or less, and preferably the upper limit is 0.8 wt% or less.

In the present specification, the apparent Zn content means an amount calculated by the following formula proposed by Guillet. This formula is based on the idea that additive elements other than Zn show the same tendency as Zn addition.
Apparent Zn content (%) = [(B + tq) / (A + B + tq)] × 100
In the formula, A = Cuwt%, B = Znwt%, t is the Zn equivalent of the additive element, and q is the additive amount wt% of the additive element. And the Zn equivalent of each element is Si = 10, Al = 6, Sn = 2, Pb = 1, Fe = 0.9, Mn = 0.5, Ni = -1.3. The Zn equivalent of Bi is not yet clearly defined, but in the present specification, it is calculated as 0.6 in consideration of the literature. In addition, other elements were added in a very small amount, and the influence on the value of the Zn equivalent was small.

Cu, Zn, and Other Components The brass according to the present invention comprises 62 wt% or more and 75 wt% or less of copper (Cu). When Cu exceeds the above range, there is a concern about the generation of cracks due to dendritic crystallization of the primary α phase. Moreover, when Cu is less than the above range, it is difficult to be influenced by the α phase, but there is a concern that the performance of brass is deteriorated. According to a preferred embodiment of the present invention, the preferred lower limit for Cu is 62 wt%, and the preferred upper limit is 70 wt%.

  If the apparent Zn content is adjusted to 37.5-40% and the crystal phase can be adjusted to an α + β phase ratio of 95% or more, the Cu content can be used even in the upper limit of the above range, so the upper limit of Cu content is large. It has become.

  In the brass according to the present invention, the remainder of the portion composed of the above-described components is substantially composed of zinc (Zn). The brass according to the present invention can contain various additive components in order to modify the properties of the brass. Further, in the present invention, the presence of inevitable impurities is not excluded, but it is preferable that they be as few as possible.

  According to one aspect of the present invention, Sn is added to improve corrosion resistance. However, in the brass according to the present invention, casting cracks and sink marks may be easily generated. In order to improve the corrosion resistance by adding Sn, 0.1 wt% or more of Sn is added. On the other hand, excessive Sn may cause casting cracks or sink marks, so the upper limit is preferably 0.5 wt%. It is as follows. By coexisting with P, the corrosion resistance effect is drastically improved, and excellent corrosion resistance can be imparted with a smaller amount of Sn, so that the casting performance can be improved.

  Moreover, according to one aspect of the present invention, P is added to improve corrosion resistance. However, in the brass according to the present invention, there is a risk that casting cracks and sink marks are likely to occur as in the case of Sn. In order to effectively improve the corrosion resistance by adding P, 0.15 wt% or more of P is added. On the other hand, excessive addition of P may cause pressure resistance and intergranular corrosion in addition to casting cracks and sink marks. Therefore, the upper limit is preferably 0.5 wt% or less.

  Furthermore, according to one aspect of the present invention, Al is added to improve corrosion resistance. However, in the brass according to the present invention, casting cracks and sink marks may be easily generated. In order to effectively improve the corrosion resistance by adding Al, 0.1 wt% or more of Al is added. On the other hand, excessive addition of Al may cause casting cracks or sink marks, or when coexisting with P May form an Al—P compound and impair mechanical properties, so the upper limit is preferably 1.0 wt% or less.

  Moreover, according to another aspect of the present invention, Al can be added for improving the hot metal flowability and casting surface properties in addition to improving the corrosion resistance. In order to more effectively improve the corrosion resistance, hot metal flow, and casting surface properties by adding Al, preferably 0.3 wt% or more of Al is added.

  In the brass according to the present invention, when Mn is added to improve the strength, an intermetallic compound of Mn and Si is generated and Si is consumed, which may cause casting cracks. In the case where Mn is not used, the upper limit is made less than 0.3 wt% in order to suppress the influence on casting cracking property.

  The brass according to the present invention includes other components such as Sb that contributes to the improvement of corrosion resistance when added in a small amount, Fe that can improve casting cracking properties and can be expected to improve strength as a refiner, depending on the purpose. May be selected and added.

Applications Brass according to the present invention does not contain Pb, while its machinability, castability, corrosion resistance, and mechanical properties are equivalent to or better than those of brass containing Pb. . Specifically, it is preferably used as a material for water supply fittings, drainage fittings, valves and the like.

Manufacturing method The molded product made of brass according to the present invention can be manufactured by either die casting or sand casting because of its good castability. You can enjoy it. Moreover, since the brass according to the present invention is also good in its machinability, it may be cut after casting. Further, the brass according to the present invention may be a cutting bar or a forging bar that is formed by extrusion after continuous casting, or a wire that is formed by drawing.
The brass according to the present invention can reduce the β phase inferior in corrosion resistance by maintaining at a temperature of 450 to 550 ° C. for 30 minutes or more and 3 hours or less after casting, and can exhibit excellent corrosion resistance.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.
Evaluation Test Details of each evaluation test in the following examples were as follows.

(1) Cast crackability test Cast crackability was evaluated by a both-end constrained test method. The shape of the mold 1 used was as shown in FIG. In FIG. 1, the heat insulating material 2 is provided in the central portion, the cooling of the central portion is delayed from the both-end constraining portion 3, the constraining end distance (2L) is 100 mm, and the heat insulating material length (2l) is 70 mm. .
In the test, the constrained part is quenched and both ends are constrained, and solidification further proceeds in the central part in that state. It was done by examining.
As a result, the case of no crack was judged as ◎, the case where a partial crack occurred but did not reach the point of rupture was judged as ◯, and the case where a crack was generated and ruptured was judged as ×.

(2) Sink Test FIG. 2 is a cross-sectional view of a test piece showing a sink test. Material is cast into a data mold, and the produced data mold test piece 1 is trimmed at a height of 65 mm from the bottom, and the inner sink part 2 is filled with water 3, and the weight of the water 3 is measured with an electronic balance. The inner sink volume was calculated (the weight of water filled in the inner sink portion = the inner sink volume). After that, the material is halved with a cutting machine as shown in FIG. 2, and the length from the upper surface of the test piece 1, which is aligned at 65 mm, to the lowermost part of the inner sink part 2 is measured by using a caliper to obtain the inner sink depth. 4 out. The internal sink performance of the test material was indexed by setting the internal sink volume and the internal sink depth 4 of three types of brass castings (JIS CAC203) to 100.
Sink depth index = inner sink depth of CAC203 / inner sink depth of test material × 100
Sink volume index = inner sink volume of CAC203 / inner sink volume of test material × 100
As a result, a sink depth index of 85% or more was judged as ８５, 70 or more and less than 85% as ○, and less than 70% as ×. Regarding the sink volume index, the sink volume index was determined as ◎ when 85% or more, ◯ when 70 or more and less than 85%, and × when less than 70%.

(3) Machinability test An ingot having a diameter of 35 mm and a length of 100 mm was produced by die casting, and the outer diameter portion was turned to evaluate the machinability. Specifically, the machinability was evaluated by a cutting resistance index with respect to three types of brass castings (JIS CAC203). Cutting conditions were a peripheral speed of 80 to 175 m / min, a feed amount of 0.07 to 0.14 mm / rev. The cutting depth was 0.25 to 1 mm, and the cutting resistance index was calculated by the following formula.
Cutting resistance index (%) = CAC203 cutting resistance / cutting resistance of test material × 100
As a result, a cutting resistance index of 70% or more was judged as ◎, 50 or more and less than 70% as ○, and less than 50% as ×.

(4) Mechanical property test An ingot having a diameter of 35 mm and a length of 100 mm was produced by die casting, machined into a JIS Z 2201 14A test piece, and subjected to a tensile test. That is, 0.2% yield strength, tensile strength, and elongation at break were measured, and the determination criteria were 0.2% yield strength of 100 N / mm 2 or more, tensile strength of 245 N / mm 2 or more, and elongation of break of 15% or more. A case where all three items were satisfied was judged as ◎, a case where two items were satisfied, ◯, and a case where only one item or less was satisfied was judged as ×.
(5) Corrosion resistance test An ingot with a diameter of 35 mm and a length of 100 mm produced by die casting was obtained, and the air-cooled material held at 530 ° C for 2 hours and then air-cooled was used as a test piece. The test was conducted according to 2007.
A maximum erosion depth of 100 μm or less was evaluated as “◎”, a thickness exceeding 100 μm and not exceeding 300 μm was evaluated as “◯”, and a case where the maximum erosion depth exceeded 300 μm was determined as “×”.
(6) Measurement of crystal phase ratio The crystal structure photograph taken with the optical microscope was image-processed, and the area ratio of α phase and β phase was determined.

Brass having the composition described in the following table was cast. That is, electric Cu, electric Zn, electric Bi, electric Pb, electric Sn, Cu-30% Ni master alloy, electric Al, Cu-15% Si master alloy, Cu-2% B master alloy, Cu-30% Mn mother Alloy, Cu-10% Cr master alloy, Cu-15% P master alloy, Cu-10% Fe master alloy, etc. are used as raw materials and melted while adjusting the components in a high-frequency melting furnace. Then, the casting cracking property was evaluated.
Subsequently, an ingot having a diameter of 35 mm and a length of 100 mm was produced by casting into a cylindrical mold, and the machinability, mechanical properties and corrosion resistance were evaluated and the crystal phase ratio was measured using the ingot as a test material.
The evaluation results were as shown in the following table.

Examples 1-4
In brass with 2% Pb added to brass of Cu / Zn = 60/40, casting cracks do not occur. However, when Bi was added as an alternative to the free-cutting component Pb, casting cracks occurred. Bi, like Pb, improves machinability, but is prone to casting cracks.

Examples 5-9
In this example, Sn, Ni, Sb, P, Al, etc. are added to a base of brass of Cu / Zn = 60/40 to develop excellent corrosion resistance. However, as these elements are added, the castability decreases. Therefore, casting cracks occurred in any of the materials within the range of the examples.

Examples 10-15
Cast cracks in brass to which Bi is added can be prevented by adding B and Si. However, if Cu exceeds 75 wt% as in Example 10, cast cracks are likely to occur. On the other hand, even when Cu was reduced to 60 wt%, no occurrence of casting cracks was observed, but as the amount of Zn increased, the ratio of β phase increased, and a decrease in elongation and a decrease in corrosion resistance were observed. Therefore, to obtain good cast cracking properties and excellent corrosion resistance, Cu is 75 wt% or less, and to obtain good mechanical properties at the same time, Cu is 62 wt% or more.

Examples 16-24
Increasing the amount of B and Si increases the effect of preventing casting cracks. However, if too much B is added, the material becomes hard and brittle, and an intermetallic compound is formed with Fe, Cr, etc., and a hard spot is formed, which may cause problems during surface processing of the molded product after casting. There is. Therefore, as in the present invention, in the case of obtaining smoothness on the surface, it is preferable to reduce the addition amount of B and / or to reduce the content of Fe, Cr and the like. It is preferably 0.0025 wt% or less, more preferably 0.0015 wt% or less, and Fe, Cr, etc. are preferably less than 0.1 wt%.

Examples 25-30
As Bi was added more, the machinability improved, and the effect was obtained with addition of 0.3 wt% or more. However, since it is an expensive element, if it is excessively added, the material cost becomes high, so it is preferable to suppress it to 4 wt% or less. In addition, since Bi is a starting point for occurrence of casting cracks, the ease of occurrence of casting cracks changes depending on the amount of addition. Since the risk of casting cracks increases as the addition amount increases, it is preferable to increase the addition amounts of B and Si in order to prevent cracking. In the present invention, Bi is set to 0.3 wt% or more in order to obtain good machinability. On the other hand, if Bi is excessive, Bi tends to agglomerate, and the agglomerated portion may be a starting point for casting cracks. Moreover, since the casting cracking sensitivity is increased by the addition of the corrosion resistance improving element, the upper limit is set to 1.5 wt%.

Examples 31-35
Examples 31-35 show that good castability and excellent corrosion resistance can be obtained by setting the apparent Zn equivalent to 37.5-40%. When Sn or P is added as an element for improving corrosion resistance, if the Zn equivalent is less than 37.5%, primary crystal α-phase dendrites are generated, and casting cracks are likely to occur. On the other hand, if the Zn equivalent exceeds 40%, the ratio of the β phase increases, and it becomes difficult to maintain excellent corrosion resistance.

Examples 36-37
In order to improve the corrosion resistance by adding Sn, 0.1 wt% or more of Sn is added. On the other hand, excessive Sn may cause casting cracks or sink marks, so the upper limit is 0.5 wt% or less. Preferably there is.

Examples 38-43
P is added to improve the corrosion resistance. However, excessive addition may cause casting cracks and sink marks as well as Sn. In order to effectively improve the corrosion resistance by adding P, 0.15 wt% or more of P is added. On the other hand, excessive addition of P may cause pressure resistance and intergranular corrosion in addition to casting cracks and sink marks. Therefore, the upper limit is preferably 0.5 wt% or less.
When Sn and P coexist, the effect of corrosion resistance is drastically improved, and excellent corrosion resistance can be imparted with a smaller amount of P, so that the casting performance can be improved.

Examples 44-46
In order to effectively improve the corrosion resistance by adding Al, 0.1 wt% or more of Al is added. On the other hand, excessive addition of Al may cause casting cracks or sink marks, or when coexisting with P May form an Al—P compound and impair mechanical properties, so the upper limit is preferably 1.0 wt% or less.

Examples 47-51
In these examples, unavoidable impurities exist, and the addition amount of B and Si that suppresses casting cracks and the addition amount of Sn, P, Al, etc., which improve the corrosion resistance, are optimized to improve the castability, machinability, and corrosion resistance. This is an example in which the mechanical properties can be maintained in a well-balanced manner.

Claims (6)

Cu is 62 wt% or more and 75 wt% or less,
Bi is 0.3 wt% or more and 1.5 wt% or less,
P is 0.15 wt% or more and 0.5 wt% or less Al is 0.1 wt% or more and 1.0 wt% or less B is 0.0005 wt% or more and 0.0035 wt% or less Si is 0.5 wt% or more and 1.0 wt% or less and the balance Is substantially composed of Zn and inevitable impurities. Cu is 62 wt% or more and 75 wt% or less,
Bi is 0.3 wt% or more and 1.5 wt% or less,
Sn 0.1 wt% to 0.5 wt% P 0.15 wt% to 0.5 wt% Al 0.1 wt% to 1.0 wt% B 0.0005 wt% to 0.0035 wt% Si 0.5 wt% or more and 1.0 wt% or less and corrosion-resistant brass characterized in that the balance substantially consists of Zn and inevitable impurities.
Cu is 62 wt% or more and 75 wt% or less,
Bi is 0.3 wt% or more and 1.5 wt% or less,
Sn 0.1 wt% to 0.5 wt% P 0.15 wt% to 0.5 wt% Al 0.1 wt% to 1.0 wt% B 0.0005 wt% to 0.0035 wt% Si 0.5 wt% or more and 1.0 wt% or less An apparent Zn content is 37.5% or more and 40.0% or less, and the corrosion resistance brass characterized by the balance being substantially made of Zn and inevitable impurities.   The brass according to any one of claims 1 to 3, wherein Mn is added in an amount of less than 0.3 wt%.   A faucet fitting made of brass according to any one of claims 1 to 4.   The faucet fitting according to claim 5, which is manufactured by die casting.