KR100592369B1 - Bismuth Inclusion Sphericals Lead-Free Brass Alloy - Google Patents

Abstract

In the present invention, lead (Pb) is not added to the copper (Cu) -zinc (Zn) brass alloy, and a small amount of bismuth (Bi), misch metal (Misch metal), phosphorus (P), and sulfur (S) is added. A bismuth (Bi) inclusion spherical shaped lead-free brass alloy configured to suppress sphericalization and formation of interfaces of bismuth (Bi) inclusions. Bismuth (Bi) inclusions spherical shaped lead-free brass alloy according to the present invention, copper (Cu)-zinc (Zn) brass alloy copper (Cu) 50 ~ 70wt%, bismuth (Bi) 0.5 ~ 3.5wt%, Mish metal ( Misch metal) has a chemical composition of 0.01 to 0.3wt%, phosphorus (P) 0.01 to 0.3wt%, the remainder is zinc (Zn) content (wt%), and the copper (Cu) -zinc (Zn) brass alloy contains sulfur ( S) is added at 0.1 wt% or less, and the sum of iron (Fe) and tin (Sn) is added at 1.0 wt% or less to the copper (Cu) -zinc (Zn) brass alloy. According to the present invention as described above, there is no lead (Pb) elution is harmless to the human body has the advantage of excellent machinability.

Brass Alloy, Lead-free, Spherical, Mish Metal (Ms), Phosphorous (P), Sulfur (S), Bismuth (Bi)

Description

Global shaped Bismuth inclusion in Lead-free copper based alloy materials

1 is a graph showing the hardness change of phosphorus (P) -mesh metal (Ms) addition bismuth (Bi) lead-free brass.

Figure 2 is a graph showing the mechanical properties of phosphorus (P) -mesh metal (Ms) addition bismuth (Bi) lead-free brass.

Figure 3 is a scanning electron microscope (SEM) photograph showing the shape and distribution of bismuth (Bi) inclusions according to the addition composition after heat treatment in 65-35 brass.

Figure 4 is a graph showing the back angle distribution of bismuth (Bi) inclusions present in the grain boundary according to the addition composition after heat treatment in 65-35 brass.

5 is a scanning electron microscope (SEM) photograph showing the shape and distribution of bismuth (Bi) inclusions according to the addition composition after heat treatment in 50-50 brass.

6 is a graph showing the back angle distribution of bismuth (Bi) inclusions present in grain boundaries according to the addition composition after heat treatment in 50-50 brass.

7 is a scanning electron microscope (SEM) photograph showing the shape of the interface inclusion after the main structure of 66Cu-33.1Zn-1.5Bi-0.1P-0.3Ms-0.1S brass.

Explanation of symbols on the main parts of the drawings

100. Grain 100a. Grain boundary

120. Bismuth (Bi) inclusions 140. Phosphorus (P) -mesh metal (Ms)-sulfur (S) compounds

The present invention relates to a brass alloy, and more particularly, lead (Pb) is not added to a copper (Cu) -zinc (Zn) brass alloy, and a small amount of bismuth (Bi), Misch metal, phosphorus ( P), sulfur (S) is added to the bismuth (Bi) inclusions spherical lead-free brass alloy harmless to the human body and showing excellent cutting properties.

In general, brass (Pb) -containing brass alloys have excellent free-cutting properties and are widely used as constituents of various products (for example, water stoppers, water supply and drainage valves, valves, etc.) for water supply pipes.

Free cutting brass, which has been developed and used up to now, has 1.0 to 4.5wt% of lead (Pb) to crush chips during metal processing and also has a relatively low melting point due to heat generated during processing. ) Acts as a lubricant to reduce the processing resistance.

Therefore, since there is an effect of extending the life of the cutting tool, the necessity of adding lead (Pb) was very high in parts requiring surface polishing.

However, recently, when used as a plumbing facility or a faucet for a beverage connection part made of such a Pb-based free cutting brass material, the harmful lead (Pb) component dispersed in the brass alloy is eluted into the beverage. Serious health problems have been raised.

Therefore, attention has been drawn to the development of a new free cutting brass material which is harmless to the human body as an alternative material of the lead-based free cutting brass and exhibits satisfactory machinability.

The lead-free free-cut brass currently under development is listed. First, heterogeneous particles which are not dissolved in the copper (Cu) base such as graphite powder or BN powder are uniformly dispersed in the copper alloy by forced addition and stirring in the copper (Cu) molten metal. Since the density difference between Cu) and the dissimilar particles is large, it is difficult to uniformly distribute the dissimilar particles, and the surface of the dissociation of the dissimilar particles becomes rough, which causes problems in plating property.

Secondly, bismuth (Bi) is added to Pb and the adjacent elements on the periodic table. Bismuth (Bi) is used as an element that has no solid solution in the copper base and is not harmful to the human body. Since it forms coarse grains and tends to cause shrinkage pores and severe grain boundary segregation, it causes brittleness of copper alloys. Therefore, it has a drawback that the grains have to be refined and spheroidized by heat treatment.

Third, a method of adding an alloying element having a low melting point process composition together with bismuth (Bi) is added to the bismuth (Bi) system. There is a danger of inhibiting the processed surface.

Fourthly, selenium (Se) is a method of adding selenium (Se) to form various intermetallic compounds with copper, and has a characteristic of fine crystallization at grain boundaries, and is known to improve workability even with a small amount of less than 1%. , The price of selenium (Se) is expensive, the use of it is restricted by the vaporization at 650 ℃ to generate toxic vapor when added alone.

Fifth, selenium (Se) is added in the form of bismuth-selenide to prevent the toxicity of selenium (Se), and it is known that bismuth (Bi) and selenide can be formed evenly in grain boundaries and grains to improve workability. It is hard to obtain the effect of improving the machinability and properties compared to the conventional brazed brass because it has a tendency to be formed into a plate, a thin film, or the like.

Looking at the microstructure of lead (Pb) -containing free-cutting brass and bismuth (Bi) substituted alloys during the research and development proceeding as described above, first, in order to easily analyze the backside angle of the interface inclusions in the lead-containing free-cut brass. Casting and heat treatment at 760 ° C. for 16 hours.

The role of lead (Pb) in copper alloy is to create spherical inclusions in grains and grain boundaries with very low solid solubility in copper (Cu) bases, reducing the continuity of the matrix during cutting to improve cutting processability, The lubricity not only has abrasion resistance but also maintains the conductivity and mechanical properties peculiar to copper alloys even in the presence of small inclusions.

In addition, when the bismuth (Bi) substituted brass is cast and subjected to heat treatment at 760 ° C. for 16 hours, bismuth (Bi) has a similar chemical property to that of lead (Pb), and thus has a very low solubility in the copper base. It exhibits 70-80% machinability of Pb) -containing copper alloy, and has a feature that the amount of elution is about 10% of lead (Pb), which is harmless to humans and the environment.

However, the formation of a bismuth (Bi) interface at grain boundaries causes a decrease in machinability and hot workability, in particular, since the melting point of lead (Pb) is 327.46 ° C and the melting point of bismuth (Bi) is 271.4 ° C, which is higher than the melting point of the inclusions. Processing and casting at temperature will cause cracking.

In addition, since the volume occupied by the film is small, but the specific area is large, the possibility of microcracks due to shrinkage during liquid-solid transformation is very high.

Therefore, in the development of bismuth (Bi) substituted lead-free (Pb-free) brass, the inhibition of formation of the bismuth (Bi) inclusions in grains and spheronization are important requirements.

An object of the present invention for solving the problems as described above, lead (Pb) is not added to the copper (Cu) -zinc (Zn) brass alloy, a small amount of bismuth (Bi), Misch metal (Misch metal), It is to provide a bismuth (Bi) inclusions spheroidized lead-free brass alloy that is configured to suppress the sphericalization of the bismuth (Bi) inclusions and the formation of the interface (Film) by adding phosphorus (P), sulfur (S).
Another object of the present invention is to spherical lead-free brass alloy bismuth (Bi) inclusions to reduce the manufacturing cost by using as it is, without extracting a specific rare earth element from the Misch Metal consisting of rare earth (稀土 類) element To provide.

Bismuth (Bi) inclusions spheronized lead-free brass alloy according to the present invention for achieving the above object, 50 ~ 70wt% copper (Cu) in the copper (Cu) -zinc (Zn) brass alloy, bismuth (Bi) 1 to 3.5 wt%, Misch metal 0.01 to 0.30 wt%, phosphorus (P) 0.05 to 0.3 wt%, sulfur (S) 0.1 wt% or less, sum of iron (Fe) and tin (Sn) 1.0 wt It is characterized by having a chemical composition which is% or less and the remainder is zinc (Zn) content (wt%).

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According to the bismuth (Bi) inclusions spheroidized lead-free brass alloy of the present invention having such a composition, there is no lead (Pb) elution is harmless to the human body and has excellent cutting properties.

Hereinafter, a preferred embodiment of the bismuth (Bi) inclusion spherical shaped lead-free brass alloy according to the present invention having the composition as described above will be described in detail with reference to the accompanying drawings.

1 is a graph showing the hardness change of phosphorus (P) -michmetal (Ms) -added bismuth (Bi) lead-free brass, and FIG. 2 is a lead-free bismuth (Bi) -added phosphorus (P) -michmetal (Ms) A graph showing the mechanical properties of brass is shown, and FIG. 3 is a scanning electron microscope (SEM) photograph showing the shape and distribution of bismuth (Bi) inclusions according to the addition composition after heat treatment in 65-35 brass.

And, Figure 4 is a graph showing the back angle distribution of the bismuth (Bi) inclusions present in the grain boundary according to the addition composition after heat treatment in 65-35 brass, Figure 5 shows the addition composition after heat treatment in 50-50 brass A scanning electron microscope (SEM) photograph showing the shape and distribution of the bismuth (Bi) inclusions is shown, and FIG. 6 shows the back surface of the bismuth (Bi) inclusions present at grain boundaries according to the addition composition after heat treatment in 50-50 brass. A graph showing the angular distribution is shown.

7 shows a scanning electron microscope (SEM) photograph showing the shape of the interface inclusion after the main structure of 66Cu-33.1Zn-1.5Bi-0.1P-0.3Ms-0.1S brass.

In general, the brass alloy is a brass alloy with a α- (Fully-α structure), a brass alloy with a β-phase (Fully-β structure) and α + β phase (α + β dual phase) according to the content of zinc (Zn). There is a brass alloy consisting of.

α phase is soft in its physical properties, so it is excellent in room temperature processing and corrosion resistance, but has low mechanical strength. It is mainly used for products requiring malleability or processability.

β phase is hard in physical properties, has excellent hot workability, but has too high mechanical strength and is weak, and has a problem of being corroded better than α phase. In particular, β single phase tissue is used when high hardness and abrasion resistance are required. Sometimes.

Brass alloy composed of two phases of α + β has low ductility at room temperature, but has high strength and high zinc content. It is the cheapest among brass, and the price is the lowest among brass. It is widely used in various parts such as connecting parts of piping materials, pipes and valves for water and beverages.

In addition, when bismuth (Bi) is added to such a brass alloy, bismuth (Bi) is known to act as a cause of brittleness by being biased at grain boundaries, but when a predetermined amount of zinc (Zn) is added, the surface tension of the brass alloy decreases. Bismuth (Bi) is not biased at the grain boundary or triple point of the grain boundary, of course, the shape is also present in a round or oval shape.

In contrast to the above advantages, bismuth (Bi) forms coarse grains and tends to cause shrinkage pores and severe grain boundary segregation, which causes brittleness of copper alloys. There is a drawback to doing this.

Therefore, for suppressing spherical formation and spheronization of inclusions in grains, bismuth (Bi) -misch metal compounds are formed to form bismuth (Bi) traps on the interface (Milm). (Misch metal) and copper (Cu) -bismuth (Bi) increase in the interfacial energy to increase the dihedral angle, the experimental data carried out by the addition of phosphorus (P) having the effect of inhibiting the expansion of the interface (Film) is shown in Table 1 below have.

             <Table 1. Chemical composition of P and Ms-added Bi lead-free brass

Mechanical properties and machinability of the bismuth (Bi) substituted alloy according to the addition of phosphorus (P) -mesh metal (Ms) based on the data in Table 1, as shown in Figures 1 and 2, conventional commercial lead (Pb) It shows mechanical properties similar to that of brass, and it can be seen that the elongation increases in the α + β phase and the β phase.

And, compared with the conventional alloy (MB12), as shown in Table 2 below, in the 6-4 brass Ms 0.1 ~ 0.3, P 0.1 ~ 0.3, when the S 0.1 or less added, the cutting performance is nearly 80%.

<Table 2. Changes in Machinability in 6-4 Brass by Adding Ms0.1 ~ 0.3, P0.1 ~ 0.3, and S0.1 or Less>

Dimensions (mm) Strength (Kgf / ㎡) Elongation (%) Hardness (Hv, 10) Machinability (Rotational Resistance) Ms P S addition φ3.16 56.1 7.2 172 80.5 φ4.50 52.2 8.1 158 79.7 φ31.75 42.6 25.5 138 86.9 Existing Alloy φ4.5 56.8 9.0 177 67.9

Meanwhile, the shapes of the bismuth (Bi) inclusions in the bismuth (Bi) -michmetal (Ms) -added bismuth (Bi) substituted alloys are shown in FIGS. 3, 5, and 7. That is, the shape and distribution of bismuth (Bi) inclusions according to the addition composition after heat treatment in 65-35 brass (α phase) and 50-50 brass (β phase), and the interface inclusions after the main structure of 65-35 brass (α phase) The shape of is shown.

As shown therein, the bismuth (Bi) inclusions 120 are uniformly distributed within the grain boundaries 100a and grains 100. At this time, the shape of the bismuth (Bi) inclusions 120 after the main structure is circular or rod-shaped, but the shape is uniform, but is not ubiquitous in the grain boundary (100a) or grains (100), but within the grain boundaries (100a) and grains (100) Evenly distributed throughout.

When the casting structure is subjected to a process of extrusion and drawing, the shape of the bismuth (Bi) inclusions 120 may be uniformly distributed in the grain boundaries 100a and grains 100 as a shape that is close to a circular or elliptical shape.

The Misch metal (60Ce-23La-12Nd-4Pr) is a mixture of 15 elements of rare earths. Among the 15 elements of rare earths, in particular, cerium (Ce), lanthanum (La), praseodymium (Pr), and neodymium (Nd) It contains a large amount of metal elements such as these, and is used as an additive element to form a ignition alloy.
In addition, the misch metal (Ms) is known as grain refiners such as aluminum (Al) and copper (Cu), and is mainly distributed in the grain boundary 100a so that bismuth (Bi) and misch metal (Ms) react.
In addition, phosphorus (P) is added as an element that is dissolved in copper (Cu) and improves the interfacial energy of bismuth (Bi) -copper (Cu), and as shown in FIGS. 4 and 6, 65-35 brass (α phase) ) And 50-50 brass (β phase), the back angle is similar to that of conventional lead (Pb) brass.

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Therefore, as the back angle, which is important for spheronization, increases, the expansion of the interface is suppressed, and the formation of the phosphorus (P) -mesh metal (Ms) -sulfur (S) compound 140 results in the formation of bismuth on the interface (Film). Bi) By the trap effect, the expansion of the interface is further suppressed.

In addition, the sum of iron (Fe) and tin (Sn) may be added in an amount of 1.0 wt% or less to the bismuth (Bi) inclusion spherical lead-free brass alloy having the chemical composition as described above.

The scope of the present invention is not limited to the above-exemplified embodiments, and many other modifications based on the present invention may be made by those skilled in the art within the above technical scope.

In the bismuth (Bi) inclusion spherical lead-free brass alloy according to the present invention as described in detail above, lead (Pb) is not added to the copper (Cu) -zinc (Zn) brass alloy, and a small amount of bismuth (Bi) By adding a metal (Misch metal), phosphorus (P), sulfur (S) to constitute a brass alloy that is harmless to the human body and exhibits excellent machinability.

Accordingly, it is expected that the lead-free brass alloy can be produced without maintaining the mechanical properties and machinability as in the conventional lead-based brass alloy without adding lead (Pb).

Subsequently, small amounts of bismuth (Bi), misch metal (Misch metal), phosphorus (P), and sulfur (S) are added to replace lead (Pb), which is harmful to the human body, and phosphorus (P) -bismuth (Bi) in grain boundaries and grains. -Formation of sulfur (S) compound is expected to effect spherical formation of bismuth (Bi) inclusions.

In addition, it is possible to suppress the expansion of the interface at the grain boundary due to the increase of the backside angle due to the increase of the interfacial energy between copper (Cu) and bismuth (Bi), and to form a bismuth (Bi) -michmetal (Ms) compound. The effect of spheronization of bismuth (Bi) inclusions is also expected under the influence of the bismuth (Ti) trap effect on the interface.
In addition, there is an advantage that the manufacturing cost is significantly reduced by using as it is instead of extracting a specific element from the mesh metal.

Claims (3)

Copper (Cu) -Zn Brass 50-70 wt% Cu, Bismuth 1-3.5 wt%, Misch metal 0.01-0.30 wt%, Phosphorus 0.05-0.3 Bismuth characterized by having a chemical composition of wt%, sulfur (S) of 0.1 wt% or less, the sum of iron (Fe) and tin (Sn) of 1.0 wt% or less, and the remainder of which is zinc (Zn) content (wt%). Bi) Inclusion spherical lead-free brass alloy. delete delete

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