KR102334814B1 - Lead-free brass alloy for casting that does not contain lead and bismuth, and method for manufacturing the same - Google Patents

Abstract

The present invention relates to a lead-free brass alloy for casting, particularly not containing lead and bismuth, which are harmful to the human body, and a method for manufacturing the same, and is mainly applied to products accompanied with fluids, such as faucets, valves, and meter components. The lead-free brass alloy for casting according to the present invention comprises 58 to 65 wt% of copper (Cu), 0.1 to 1.5 wt% of silicon (Si), 0.1 to 1.5 wt% of tin (Sn), 0.25 to 0.8 wt% of aluminum (Al), 0.04 to 0.15 wt% of phosphorus (P), and the balance zinc (Zn) and unavoidable impurities, wherein the total of impurities is 0.1 wt% or less.

Description

Lead-free brass alloy for casting that does not contain lead and bismuth, and method for manufacturing the same

The present invention relates to a lead-free brass alloy for casting, specifically, a brass alloy for casting that does not contain lead (Pb) and bismuth (Bi), which are harmful to the human body, and a manufacturing method thereof, and mainly relates to fluids such as faucets, valves, and meter parts. Used for accompanying products.

Brass is an alloy of copper (Cu) and zinc (Zn) and has been used in various ways throughout the industry. However, since brass causes problems such as high cutting load and lowering productivity due to no chip discharge during cutting, 1.0 to 4.5% by weight of lead (Pb) is added to brass to increase the workability of brass. The machinability was ensured. Brass with added lead is called free-cutting brass.

Because free-cutting brass has excellent workability, it is widely used throughout industries that require cutting machinability, but lead (Pb), a component element, is a toxic substance that adversely affects the human body and the environment, and the use of free-cutting brass is limited due to various regulations Moreover, free-cutting brass has weak corrosion resistance, so when used in a product that comes in contact with fluid, corrosion causes a problem of durability of the product itself and a problem of leaching of harmful substances.

In relation to the harmfulness of lead (Pb), specifically, in Europe, RoHS (Restriction of Hazardous Substances) was enacted in 2003 to regulate elements harmful to the human body. Even in the United States, the content of lead (Pb) in copper alloys for faucet fittings is severely restricted. California Bill AB 1953 and NSF 61 standards regulate the allowable amount of lead (Pb) in drinking water products at 0.25% or less, and it is expected that the lead (Pb) content limit will be further strengthened in the future, mainly in developed countries.

In the Republic of Korea, materials and products used in water supply parts (water meters, valves, pumps, etc.) are regulated in accordance with the hygiene and safety standards of the Water Supply Act (Act No. 17178, promulgated March 31, 2020). Among local governments in the Republic of Korea, the Seoul Metropolitan Government announced the first all lead-free water meter introduction plan in February 2020. These regulations will be expanded nationwide, and ultimately, the use of components harmful to the human body, such as lead (Pb), will be restricted not only in water meters, but also in parts for drinking water related to drinking water such as valves and pumps.

As such, due to safety issues and environmental pollution issues for living things, including humans, research on a new type of copper alloy that can replace free-cutting brass has been conducted. As one of the alternatives, bismuth lead-free brass in which bismuth (Bi) is added to copper (Cu) instead of lead (Pb) has been developed. This is being reluctant Furthermore, although bismuth (Bi) has not yet been clearly identified as to whether it is harmful to the human body, it is a heavy metal such as lead (Pb), so it may be selected for the same regulation as lead in the future. Already, the European Copper Institute has recommended avoiding the use of bismuth (Bi) in lead-free brass.

In order to solve the above problems, it is required to develop a lead-free brass alloy for casting that does not use heavy metal elements harmful to the human body, such as lead and bismuth, and has excellent machinability and excellent corrosion resistance at the same time.

In Korean Patent Laid-Open Publication No. 10-2014-0035578, copper (Cu) 60 to 65 wt%, zinc (Zn) 35 to 38 wt%, tin (Sn) 0.7 to 1.5 wt%, aluminum (Al) 0.3 to 0.8 wt% %, phosphorus (P) 0.01 to 0.3 wt%, lead (Pb) 0.1 wt% or less, manganese (Mn) 0.008 wt% or less, iron (Fe) 0.06 wt% or less, nickel (Ni) 0.04 wt% or less, silicon ( Si) 0.02 wt% or less, magnesium (Mg) 0.0007 wt% or less, chromium (Cr) 0.008 wt% or less, arsenic (As) 0.02 wt% or less, antimony (Sb) 0.06 wt% or less, bismuth (Bi) 0.02 wt% Hereinafter, cobalt (Co) 0.008% by weight or less, sulfur (S) 0.009% by weight or less, boron (B) is disclosed a lead-free brass ingot, characterized in that consisting of 0.002% by weight or less. Although the contents of the above patent literature can be considered excellent in terms of metal scrap recycling, lead (Pb) as well as arsenic (As) and antimony (Sb) among the alloying elements included as impurities are toxic substances harmful to the human body, so they are applied as eco-friendly products This is difficult.

In Korean Patent Publication No. 10-2013-0035439, copper (Cu) 56 to 77 wt%, manganese (Mn) 0.1 to 3.0 wt%, silicon (Si) 1.5 to 3.5 wt%, calcium (Ca) 0.1 to 1.5 wt% % and zinc (Zn), a free-machining lead-free copper alloy is disclosed. The free-machining lead-free copper alloy of the above patent document has improved machinability by adding calcium, but due to the high oxidation of calcium, a large amount of oxide is generated during the casting operation, which may cause defects such as winding or cracking in the casting. Since it is difficult to obtain a target component and it is difficult to manufacture a high-quality casting, it can be applied to a rod-shaped product by controlling the characteristics through extrusion, drawing, heat treatment, etc., but it is difficult to apply to a casting product.

Korean Patent Laid-Open No. 10-2018-0165425 discloses a free-machining lead-free copper alloy exhibiting excellent machinability and corrosion resistance and a method for manufacturing the same, but it is a chemical suitable for rod-shaped products manufactured through extrusion, drawing and heat treatment processes. It is difficult to apply for casting because it is very poor in castability as a component and causes defects such as cracks and wrinkles on the surface of the product during casting.

An object of the present invention is to provide a lead-free brass alloy for casting that does not contain lead (Pb) and bismuth (Bi) components, and has excellent castability, machinability and corrosion resistance.

One aspect of the present invention is copper (Cu) 58 to 65% by weight, silicon (Si) 0.1 to 1.5% by weight, tin (Sn) 0.1 to 1.5% by weight, aluminum (Al) 0.25 to 0.8% by weight, phosphorus (P) ) 0.04 to 0.15% by weight, the balance of zinc (Zn) and unavoidable impurities, and the total amount of impurities is 0.1% by weight or less. ), and the lead-free brass alloy for casting provides a lead-free brass alloy for casting that has an average dezincification corrosion depth of 300 μm or less, conducted by the test method of KS D ISO 6509 standard. The lead-free brass alloy includes an α phase, a β phase and an ε phase.

In another aspect of the present invention, copper (Cu) 58 to 65 wt%, silicon (Si) 0.1 to 1.5 wt%, tin (Sn) 0.1 to 1.5 wt%, aluminum (Al) 0.25 to 0.8 wt% , 0.04 to 0.15 wt% of phosphorus (P), and the remainder of zinc (Zn) dissolved at 970 to 1200 ° C. to obtain a molten metal, and stabilizing by maintaining for 10 minutes or more; Casting the stabilized molten metal at 920 ~ 1000 ℃; cooling to 400° C. or less in the mold; And it provides a method for producing the above-described lead-free brass alloy for casting comprising the step of separating the casting and water cooling or air cooling to obtain a casting.

The lead-free brass alloy for casting according to the present invention has excellent castability, machinability and corrosion resistance. In addition, since all the elements added to the lead-free brass alloy of the present invention do not contain lead and bismuth, it is safe for living things including humans and is environmentally friendly because environmental pollution can be avoided.

1 is a view of a mold for measuring molten metal flowability (length) for evaluating the castability of a molten copper alloy.
2 is a graph showing the machinability test conditions and test results of Example 10, Comparative Example 15, and Comparative Example 20;
3 is a photograph showing a criterion for classification of chips generated during a machinability test of a copper alloy.
4 is an SEM photograph of measuring the dezincification corrosion depth of specimens prepared according to Example 10, Comparative Example 18, and Comparative Example 20;
5 is an FE-SEM photograph of observing the microstructure of the specimens prepared according to Example 10, Comparative Example 6, and Comparative Example 20, respectively.

Hereinafter, the present invention will be described in more detail. The following description should be understood only as exemplary embodiments for implementing the present invention, and the scope of the present invention is defined by the content set forth in the claims to be described later.

The present invention is copper (Cu) 58 to 65% by weight, silicon (Si) 0.1 to 1.5% by weight, tin (Sn) 0.1 to 1.5% by weight, aluminum (Al) 0.25 to 0.8% by weight, phosphorus (P) 0.04 to 0.15 Disclosed is a lead-free brass alloy for casting consisting of weight %, the balance of zinc (Zn) and unavoidable impurities. The total of the unavoidable impurities is 0.1% by weight or less.

The specific meaning of the composition and content of the lead-free brass alloy for casting according to the present invention is as follows.

Composition and content of lead-free brass alloy for casting according to the present invention

(1) Copper (Cu): 58 to 65 wt%

In the lead-free brass alloy for casting according to the present invention, copper (Cu) is the main component of the copper alloy and forms α-phase, β-phase and ε-phase structures according to the content of zinc (Zn) and additional elements to improve machinability and machinability. plays a role The content of copper in the lead-free brass alloy for casting according to the present invention is in the range of 58 to 65% by weight. If the content of copper (Cu) is less than 58% by weight, the ε phase and the β phase are excessively generated to reduce cold workability and increase brittleness, and corrosion resistance is also deteriorated. When the copper (Cu) content exceeds 65% by weight, the ε phase formation is insufficient along with an increase in the raw material price, so that the machinability is not sufficiently secured.

(2) Silicon (Si): 0.1 to 1.5 wt%

In the lead-free brass alloy for casting according to the present invention, silicon (Si) helps to form the ε phase, and is dissolved in the Cu matrix to improve machinability and strength. In the case of silicon, although it is not an element constituting the ε phase, it has a high solubility in Cu, so it can be seen that it promotes the formation of the ε phase by being dissolved before Sn.

In the lead-free brass alloy for casting according to the present invention, the content of silicon (Si) is in the range of 0.1 to 1.5% by weight. If the content of silicon (Si) is less than 0.1% by weight, ε phase is not generated and does not contribute to increase in machinability and strength. As the silicon (Si) content increases, the amount of ε phase generated and machinability are improved, but when it exceeds 1.5 wt%, the size of the ε phase is coarsened, and the product is hardened to reduce the machinability improvement effect and adversely affect machinability, especially During the casting operation, the solidification rate of the molten metal is lowered, which lowers the castability and reduces the surface quality.

(3) Tin (Sn): 0.1 to 1.5 wt%

In the lead-free brass alloy for casting according to the present invention, tin (Sn) contributes to the generation of the ε phase to increase the size and fraction of the ε phase and improve machinability, and strengthen the α phase to improve corrosion resistance such as dezincification corrosion resistance plays a role In the brass alloy for casting of the present invention, the content of tin (Sn) is in the range of 0.1 to 1.5% by weight. If the tin content is less than 0.1% by weight, it does not contribute to the generation of the ε phase, and the effect of improving corrosion resistance is not obtained. On the other hand, when the tin content exceeds 1.5% by weight, the raw material price is increased, and the coarsening and the fraction of the ε phase are increased, thereby adversely affecting the machinability.

(4) Zinc (Zn): balance

In the lead-free brass alloy for casting according to the present invention, zinc forms a Cu-Zn-based alloy together with copper (Cu), and contributes to the formation of α-phase, β-phase and ε-phase structures depending on the added content, and the castability and machinability will affect In the present invention, the balance is added. If the content of zinc is too large, the product is hardened and brittleness is increased as well as corrosion resistance is reduced.

(5) Aluminum (Al): 0.25 to 0.8 wt%

In the lead-free brass alloy for casting according to the present invention, aluminum (Al) has the effect of improving corrosion resistance and castability, so that it is possible to obtain improved productivity and excellent quality during the casting operation. If it is less than 0.25% by weight, the effect of improving the castability cannot be expected, and if it is more than 0.8% by weight, the increase in strength and the generation of the ε phase are suppressed to reduce the machinability, and the brittleness increases, resulting in defects in the cast product. In the case of aluminum, the high zinc equivalent promotes the formation of the β phase, thereby preventing the formation of the ε phase similarly to the case of high zinc.

(6) phosphorus (P): 0.04 to 0.15 wt%

In the lead-free brass alloy for casting according to the present invention, phosphorus (P) improves corrosion resistance by stabilizing the α phase and refining the structure, and serves as a deoxidizer during casting to improve the fluidity of the molten metal. If the content of phosphorus (P) is less than 0.04% by weight, there is almost no effect of tissue refinement and corrosion resistance improvement, and when it exceeds 0.15% by weight, there is a limit to tissue refinement, and hot workability is reduced.

(7) unavoidable impurities

In the lead-free brass alloy for casting according to the present invention, unavoidable impurities are elements that are unavoidably added in the manufacturing process, and are mainly contained in unavoidable trace amounts in brass scrap, for example, iron (Fe), nickel (Ni), manganese ( Mn), chromium (Cr), magnesium (Mg), etc., and the total amount is controlled to 0.1% by weight or less and does not affect the properties of the copper alloy in the above content range.

The lead-free brass alloy for casting according to the present invention is copper (Cu)-zinc (Zn) in the basic brass alloy, by the addition of tin (Sn) and silicon (Si), ε phase (Cu ₃ Sn, hereinafter omitted) in the metal structure ) is dispersed, which improves machinability by acting as a chip segment during cutting.

In addition, the lead-free brass alloy for casting according to the present invention sufficiently satisfies the dezincification corrosion depth of 300 μm or less, which is the test standard of the environmental mark certification (EL742) for copper alloys for castings by the Ministry of Environment with excellent corrosion resistance due to the addition of tin. Dezincification corrosion is a phenomenon in which zinc is selectively removed from brass alloys by dealloying or selective leaching corrosion. Dezincification corrosion resistance is essential for KC certification according to the Korean water supply law and application of lead-free water meters. Excellent dezincification corrosion resistance is required for water pipe material applications. Dezincification depth of 300㎛ or less can be evaluated to have excellent corrosion resistance.

On the other hand, the most important casting properties for casting applications are improved by the addition of aluminum (Al), so that good casting surface quality can be obtained without cracks or wrinkles during casting.

Characteristics of the lead-free brass alloy according to the present invention

Since the lead-free brass alloy according to the present invention is for casting, all of the properties described below must be satisfied.

Castability is a very important characteristic of casting products. If the castability is poor, the product may not be filled sufficiently according to the product shape in the sand or mold during injection of molten metal, or the thickness may be distributed depending on the location due to gravity, causing product defects such as cracks or wrinkles. do.

Brass alloy for casting can be used when the cutting torque is 2.0 N·m or less, but if it exceeds 2.0 N·m, it is not suitable for use because it causes tool breakage or reduced productivity in industrial sites due to the cutting load. Therefore, in the lead-free brass alloy according to the present invention, the cutting torque is 2.0 N m should be less than

In addition, when cutting brass alloy for casting, the shape of the generated chip is also important for machinability evaluation. If the shape of the cutting chips is bad, the cutting chips generated during machining cannot be discharged out of the tool or cause damage to the cutting edge. The criterion for determining the shape of the cutting chip is shown in FIG. 3 . Based on the shape of FIG. 3 , the bad (X) shape of the chip is excluded because it damages the cutting surface and the cutting tool and is unsuitable due to low chip evacuation. That is, in the lead-free brass alloy according to the present invention, the cutting chips should be above the average level.

The dezincification corrosion resistance complies with the passing standards for the dezincification corrosion test of lead-free brass in the KC certification according to the domestic waterworks law and the environmental mark certification for casting copper alloys (EL742) of the Ministry of Environment. The standard is 300 µm or less on average, and it can be evaluated that the depth of dezincification corrosion is 300 µm or less to have excellent corrosion resistance. In the lead-free brass alloy according to the present invention, the depth of dezincification should be an average of 300 μm or less.

As described above, the lead-free brass alloy for casting according to the present invention does not contain lead (Pb) and bismuth (Bi). Therefore, it is safe for living things, including humans, and environmental pollution can be avoided.

Method for producing a lead-free brass alloy for casting according to the present invention

The lead-free brass alloy for casting according to the present invention may be manufactured according to the following method.

In order to produce the copper alloy for casting according to the present invention, raw materials of the component elements are dissolved according to the content disclosed herein. Melting is carried out at 970 to 1200 ° C, which is about 100 to 300 ° C higher than the melting point (liquidus temperature) of the alloy of the present invention. When dissolving, it is sufficiently carried out until the charged raw material is completely in liquid form, and after dissolution, it is maintained for at least 10 minutes to homogenize and stabilize the molten metal.

After removing oxides from the surface of the molten metal, casting is performed by setting the temperature of the molten metal to 920 to 1000°C, which is 50 to 100°C higher than the melting point. Molds used for casting are generally applied to molds including sand sand, which is used the most, and casting is completed by pouring molten metal into the mold.

Cool to 400°C or less in the mold. The cooling rate after casting is different depending on the amount of casting and the material of the mold, and a person skilled in the art can determine it appropriately according to the characteristics. For example, in the case of sand casting, which is most often used to obtain brass casting products, it is cooled in the mold at a cooling rate of 0.5~5℃/min, although there is a difference depending on the mold size or design.

After cooling to 400° C. or less in the mold, the mold and the casting are separated and cooled to obtain a casting. Cooling may be water-cooled to improve productivity, or may be air-cooled.

The examples set forth below are for the purpose of illustrating or explaining the present invention, and are not intended to limit the scope of the present invention.

Example

Chemical compositions of Examples 1-22 and Comparative Examples 1-20 of the present invention are disclosed in Table 1. In each of the Examples and Comparative Examples, each specimen was obtained according to the manufacturing method described below by preparing a total weight of 3.5 kg with the chemical composition shown in Table 1. For each obtained specimen, the properties of the alloy were evaluated by measuring or observing the molten metal flow length, cutting torque, chip shape, dezincification depth, and microstructure, respectively, according to a test example to be described later.

Examples 1-22

Specimens according to Examples 1 to 22 were prepared through the above-described lead-free brass manufacturing method with the chemical composition shown in Table 1. Specifically, the raw materials prepared according to Table 1 were dissolved at 1100° C. in a graphite crucible and stabilized for 10 minutes. The stabilized molten metal was cast at 950° C. and cooled in the mold to below 400° C. at a rate of 3° C./min. The mold and the casting were separated, cooled with water to obtain a casting, and 0.5 kg of the shrinkage area was removed and cut by 1 kg, which was used for casting properties, machinability tests, and dezincification corrosion tests, respectively.

Table 1 also shows the results of the characteristic test to be described later of the produced specimen.

Comparative Examples 1 to 20

Specimens according to Comparative Examples 1 to 20 were prepared in the same manner as in the manufacturing method disclosed in Examples, with the chemical compositions shown in Table 1. Table 1 also shows the results of the characteristic test to be described later of the produced specimen.

division Chemical composition (wt%) castability cutting
talk chip
shape Dezincification
depth Cu Zn Si Sn Al P Pb (mm) (Nm) (μm) Example 1 58.1 Bal. 1.49 1.48 0.79 0.15 - 201 1.89 △ 208 Example 2 58.1 Bal. 0.11 1.49 0.79 0.15 - 216 1.92 ○ 191 Example 3 58.2 Bal. 1.48 0.12 0.79 0.15 - 209 1.88 ○ 257 Example 4 58.2 Bal. 1.48 1.48 0.26 0.15 - 169 1.78 △ 250 Example 5 58.1 Bal. 1.48 1.49 0.25 0.04 - 162 1.77 △ 251 Example 6 58.1 Bal. 0.11 0.12 0.25 0.04 - 171 1.93 △ 298 Example 7 58.2 Bal. 0.12 0.11 0.25 0.15 - 178 1.94 △ 286 Example 8 58.1 Bal. 0.12 0.11 0.78 0.04 - 252 1.99 △ 297 Example 9 61.9 Bal. 1.02 0.91 0.52 0.08 - 221 1.56 ◎ 189 Example 10 62.5 Bal. 0.92 0.91 0.61 0.10 - 239 1.59 ◎ 188 Example 11 62.1 Bal. 0.78 1.19 0.49 0.12 - 211 1.64 ◎ 186 Example 12 62.7 Bal. 1.21 1.27 0.56 0.11 - 212 1.51 ◎ 185 Example 13 63.9 Bal. 1.35 0.59 0.31 0.12 - 171 1.49 ◎ 194 Example 14 64.9 Bal. 0.10 0.11 0.25 0.04 - 181 1.89 △ 209 Example 15 64.8 Bal. 1.50 0.11 0.26 0.04 - 171 1.72 ○ 201 Example 16 65.0 Bal. 0.11 1.50 0.25 0.04 - 179 1.77 ○ 38 Example 17 64.9 Bal. 0.11 0.10 0.80 0.04 - 261 1.94 △ 199 Example 18 65.0 Bal. 0.11 0.11 0.25 0.15 - 184 1.91 △ 102 Example 19 64.8 Bal. 1.50 1.49 0.80 0.15 - 238 1.81 △ 159 Example 20 64.6 Bal. 1.49 0.10 0.25 0.11 - 193 1.73 ○ 178 Example 21 64.8 Bal. 0.11 1.48 0.79 0.05 - 246 1.85 △ 74 Example 22 65.0 Bal. 0.12 0.11 0.80 0.15 - 268 1.82 △ 201 Comparative Example 1 58.2 Bal. 0.09 1.48 0.78 0.16 - 215 1.99 △ 321 Comparative Example 2 58.1 Bal. 0.11 1.52 0.79 0.15 - 211 2.02 △ 315 Comparative Example 3 58.1 Bal. 1.53 0.09 0.79 0.15 - 201 1.91 △ 359 Comparative Example 4 58.3 Bal. 0.91 1.02 0.82 0.14 - 214 1.96 △ 329 Comparative Example 5 58.1 Bal. 1.41 1.46 0.24 0.03 - 118 1.81 X 271 Comparative Example 6 58.2 Bal. 0.08 0.09 0.09 0.03 - 91 1.99 X 312 Comparative Example 7 58.1 Bal. 0.55 0.91 0.91 0.16 - 241 2.21 X 198 Comparative Example 8 58.2 Bal. 1.52 1.51 0.82 0.19 - 229 2.04 △ 215 Comparative Example 9 62.4 Bal. 1.52 0.91 0.61 0.09 - 209 2.11 △ 179 Comparative Example 10 62.5 Bal. 0.92 1.55 0.61 0.10 - 218 2.09 △ 159 Comparative Example 11 62.4 Bal. 0.92 0.91 0.09 0.10 - 102 2.04 △ 183 Comparative Example 12 62.7 Bal. 0.91 1.01 0.59 0.03 - 202 2.14 △ 189 Comparative Example 13 62.4 Bal. 0.08 0.92 0.60 0.11 - 216 2.21 △ 201 Comparative Example 14 62.5 Bal. 0.91 0.09 0.23 0.09 - 129 2.09 ○ 279 Comparative Example 15 65.2 Bal. 0.11 0.10 0.23 0.04 - 151 1.95 X 119 Comparative Example 16 65.3 Bal. 1.51 1.52 0.82 0.16 - 261 1.83 X 111 Comparative Example 17 69.1 Bal. 0.91 1.02 0.61 0.11 - 289 2.21 X 45 Comparative Example 18 62.5 Bal. 0.91 0.92 0.51 0.11 2.0 234 1.41 ◎ 912 Comparative Example 19 62.1 Bal. - - 0.51 0.06 2.0 264 1.49 ◎ 1301 Comparative Example 20 61.9 Bal. - - - - 2.0 149 1.45 ◎ 1769

test example

(1) Castability (melt flow) test

Castability is also called molten metal flowability or molten metal fluidity. Castability refers to the ability of the molten metal to fill the mold cavity.

Brass alloys for casting are generally manufactured in the form of ingots (castings) and provided to industrial sites. Then, in the industrial field, the ingot is redissolved and injected into a sand sand or mold, and a final casting product is manufactured. Accordingly, the castability should be evaluated under conditions equivalent to the manufacturing conditions in actual industrial sites. To this end, in the present invention, evaluation was performed using a mold as shown in FIG. 1 .

Specifically, each ingot specimen prepared according to the chemical composition of Table 1 is prepared with the same weight of 1 kg. Then, the ingot-shaped specimen was re-melted at 1000° C., and the molten metal flow length was measured in the mold shown in FIG. 1 . When the molten metal flow length is 160mm or more, it can be considered to have good casting properties, and it can be applied to the production of casting products. The test results are shown in Table 1.

(2) Machinability test (cutting torque and chip shape)

The machinability of the specimen is evaluated by cutting torque and cutting chip shape.

The cutting torque was evaluated by measuring the torque transmitted to the drill tool during drilling using a machinability tester as shown in FIG. 2 . When cutting, the size of the cutting drill is Φ8 mm, the rotation speed is 700 rpm, the movement speed is 80 mm/min, the movement distance is 10 mm, and the movement direction is the direction of gravity. .

The obtained results are shown in Table 1. If the torque is high, it means that the machinability is low, and if the torque is low, even if the same depth is machined, less force is required, so the machinability is high. The lead-free brass alloy of the present invention has a cutting torque of 2.0 in terms of productivity and tool protection. N m should be less than

On the other hand, even if the cutting torque is low and the cutting machinability is good, if the cutting chip shape is bad, the cutting chips generated during machining cannot be discharged out of the tool or cause damage to the cutting edge. Therefore, the shape of the cutting chips should also be evaluated. Therefore, in the present invention, the shape of chips generated during cutting was observed and shown in Table 1. The determination criteria are based on the four criteria of FIG. 3 , very good (◎), excellent (○), average (Δ), and bad (X). The very good (◎), excellent (○), and normal (△) types of cutting chips have excellent dispersibility and chip evacuation, but the bad (X) shape of the chips damages the cutting surface and cutting tool and has excellent chip evacuation properties. This is not good, so it is not suitable for use in industrial fields.

The test results are shown in Table 1.

(3) Dezincification corrosion test

In order to evaluate the dezincification corrosion properties of the manufactured specimens, the average dezincification corrosion depth was measured by the test method of KS D ISO 6509 (Corrosion of metals and alloys - Dezincification corrosion test of brass) and shown in Table 1. The surface of each sample was polished up to abrasive paper #2000, which was then ultrasonically washed with pure water and dried. The washed sample was immersed in a 1% CuCl ₂ aqueous solution, heated to a temperature of 75° C. and maintained for 24 hours, and then the depth of dezincification was measured.

In the KC certification according to the domestic waterworks law and the environmental mark certification (EL742) for copper alloy for castings by the Ministry of Environment, the pass standard for the dezincification corrosion test of lead-free brass is 300㎛ on average, and the depth of dezincification corrosion below 300㎛ has excellent corrosion resistance. can be evaluated

The test results are shown in Table 1.

(4) Microstructure observation

The microstructures of the specimens prepared with the chemical composition according to Table 1 were observed using a scanning electron microscope (Scanning Electron Microscopy). For microstructure observation, the surface of each sample was polished up to abrasive paper #4000, and the grain boundaries were pretreated with an etchant, followed by scanning electron microscopy. The microstructure observation results of the specimens of some Examples and Comparative Examples are disclosed in FIG. 5 , and the content will be described later.

As described above, Table 1 discloses the results of the above-described castability (molten metal flowability) evaluation, machinability test (cutting torque and chip shape), and dezincification corrosion test results together.

As can be seen from the results of Table 1, the specimens prepared according to Examples 1 to 22 satisfies all conditions of cutting torque, chip shape, zinc corrosion resistance, and casting properties.

However, the specimens prepared according to Comparative Examples 1 to 20 did not satisfy all of the above characteristics at the same time. Specifically, Comparative Examples 18 to 20 have a chemical composition in which lead (Pb) is added, and have excellent cutting torque and chip shape, but have very poor dezincification corrosion resistance.

In addition, although the chemical compositions according to Comparative Examples 1 to 17 did not contain lead (Pb), they did not satisfy all of the characteristic conditions required by the present invention. For example, when the cutting torque is good, the dezincification corrosion resistance is insufficient, or even if the cutting torque is excellent, the chip shape is very bad and cannot be used. For example, it can be confirmed that the dezincification corrosion depth of the specimens prepared according to Examples 1 to 22 is 300 μm or less. On the other hand, Comparative Examples 1 to 4, Comparative Examples 6, particularly Comparative Examples 18 to 20, the dezincification corrosion depth was more than 300㎛. In this regard, SEM photographs comparing the corrosion depth of the specimens after the dezincification corrosion test of Example 10 and Comparative Examples 18 and 20 are additionally presented in FIG. 4 .

Meanwhile, FIG. 5 shows microstructures of specimens prepared with the chemical compositions of Example 10, Comparative Example 6, and Comparative Example 20, respectively, as FE-SEM photographs. In the case of the specimen of Example 10, microstructures including α-phase, β-phase and ε-phase were observed. On the other hand, in Comparative Example 6, since the content of additional elements such as silicon (Si), tin (Sn), aluminum (Al), and phosphorus (P) was very trace, it was observed that only the α phase and the β phase existed, and Comparative Example 20 It was confirmed that α-phase, β-phase and undissolved lead (Pb) were distributed in the conventional free-cutting brass chemical composition containing lead (Pb).

In summary, the specimens prepared by Examples 1 to 22 according to the present invention satisfy all of the criteria for castability, machinability, dezincification corrosion resistance and environment-friendliness required in the present invention, while they are prepared by Comparative Examples 1 to 20 The psalms were not like that.

Claims (3)

Copper (Cu) 58 to 65% by weight, silicon (Si) 0.1 to 1.5% by weight, tin (Sn) 0.1 to 1.5% by weight, aluminum (Al) 0.25 to 0.8% by weight, phosphorus (P) 0.04 to 0.15% by weight, It is a lead-free brass alloy for casting that consists of the remainder of zinc (Zn) and unavoidable impurities, and the total amount of impurities is 0.1% by weight or less,
The lead-free brass alloy for casting does not contain lead (Pb) and bismuth (Bi),
The lead-free brass alloy for casting has an average dezincification corrosion depth of 300㎛ or less, conducted by the test method of KS D ISO 6509 standard,
The lead-free brass alloy is a lead-free brass alloy for casting that includes an α phase, a β phase and an ε phase. Copper (Cu) 58 to 65% by weight, silicon (Si) 0.1 to 1.5% by weight, tin (Sn) 0.1 to 1.5% by weight, aluminum (Al) 0.25 to 0.8% by weight, phosphorus (P) 0.04 to 0.15% by weight, and dissolving the remainder of zinc (Zn) at 970 to 1200° C. to obtain a molten metal, and stabilizing it by maintaining it for at least 10 minutes;
Casting the stabilized molten metal at 920 ~ 1000 ℃;
cooling to 400° C. or less in the mold; and
Separating the mold and the casting to obtain a casting by water cooling or air cooling
A method for producing a lead-free brass alloy for casting according to claim 1 comprising a. delete

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