KR20020060018A - Brass alloy for cutting tool with high speed performance - Google Patents

Abstract

PURPOSE: Provided is a brass alloy for free cutting tool with improved machinability by reducing Pb content in the brass alloy while uniformly diffusing bismuth and selenium(Se) through the grain boundary of the brass alloy. Further, cerium(Ce) is added in the brass alloy so that grain size of the brass alloy is reduced and uniformly diffused in the alloy matrix. CONSTITUTION: The brass alloy of Cu-Zn for free cutting tool comprises Cu 56 to 62 wt.%, Pb 0.10 wt.% or less, Fe+Sn 1.0 wt.% or less, Bi 0.5 to 3.0 wt.%, Se 0.5 to 2.0 wt.%, Ce 0.25 wt.% or less, unavoidable impurities 0.5 wt.% or less and a balance of Zn.

Description

Lead-free free-cutting brass alloy with high strength cutting ability {BRASS ALLOY FOR CUTTING TOOL WITH HIGH SPEED PERFORMANCE}

The present invention relates to a lead-free free-cut brass alloy excellent in high-intensity machinability, specifically, in a conventional copper-zinc binary brass alloy, by significantly reducing the amount of lead added and adding cerium, it is harmless to human body and comparable to that of lead-free brass. A lead-free free-cut brass alloy with processing properties.

Free cutting brass, which has been developed and used up to now, has the effect of crushing chips during metal processing by adding 1.0 to 4,5 wt% of lead (Pb), and also has relatively low melting point (Pb) due to heat generated during processing. As a lubricant, it has the effect of reducing the processing resistance, and has the effect of extending the life of the cutting tool, and the need for the addition of lead is very high in parts requiring surface polishing.

However, lead tends to leach out of general supply water, which is now strictly regulated worldwide. Therefore, efforts have been actively made to develop a material having a machinability and mechanical properties comparable to that of free-cutting brass as a substitute for lead-based free-cutting brass.

In general, list the lead-free grinding brass currently under development,

First, heterogeneous particles which are not dissolved in the copper base such as graphite powder or BN powder are uniformly dispersed in the copper alloy by forcibly adding and stirring the copper (Cu) molten metal. It is difficult, and the processing surface by peeling of dissimilar particles becomes rough and there is a problem in plating property.

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

Third, bismuth (Bi) is added to bismuth and alloy elements having low melting point process composition. In this method, the crystallized phase is often crystallized at the grain boundary in the form of a thin film, which impairs cutting processability and inhibits the processing surface. There is a concern.

Fourthly, selenium (Se) is a method of adding selenium to form various intermetallic compounds with fine crystallization at grain boundaries, and it is known to improve processability even at a small amount of less than 1%. It is vaporized, generating poisonous vapor when added alone, and its use is restricted.

Fifth, selenium (Se) is added in the form of bismuth-selenide to prevent the toxicity of selenium and to form bismuth and selenide evenly in the grain boundary and in the mouth to improve processability, but it is known as rod, plate, thin film, etc. Due to the strong tendency to form, it is difficult to obtain the effect of improving the machinability and properties compared to the conventional brazed brass. Due to the above reasons, continued research and development is in progress.

The present invention has been made in consideration of the above circumstances, and an object thereof is to significantly reduce lead content, improve the machinability of copper alloy using bismuth-selenide, and add cerium (Ce) thereto to refine grains of copper alloy and to achieve abnormalities. It is to provide a lead-free brass alloy with high strength and machinability, which is excellent in high machinability and is harmless to the human body, by dispersing particles evenly in the copper alloy base to significantly improve the mechanical properties without degrading the machinability compared to the existing lead-free brass alloy containing Pb. .

In order to achieve the above object, the present invention, in the copper (Cu) -zinc (Zn) brass alloy, copper (Cu) 56 ~ 62wt%, lead (Pb) 0.10wt% or less, iron (Fe) + tin (Sn) It is to provide a lead-free free-cut brass alloy having excellent machinability having a composition of 1.0 wt% or less, bismuth (Bi) 0.5 to 3.0 wt%, selenium (Se) 0.5 to 2.0 wt%, and selium (Ce) 0.25 wt% or less.

1 is a cast optical micrograph of the lead-free free-cut brass of the present invention,

Figure 2 is an extruded structure optical micrograph of the lead-free free-cut brass alloy of the present invention.

The present invention improves the machinability of copper alloy using bismuth-selenite in copper-zinc binary brass alloy, and adds selium to refine the grains of copper alloy, and disperses abnormal particles evenly in the copper alloy material. The present invention relates to a brass alloy that can prevent leaching of lead and significantly improve mechanical properties without deteriorating machinability, compared to conventional free cutting brass alloys containing copper 56-62wt%, lead 0.1wt% or less, and iron + tin. A lead-free free-cut brass alloy having a selium composition of 1.0 wt% or less, impurity 0.5 wt% or less, bismuth 0.5-3.0 wt% in the remaining zinc brass alloy, and 0.5-2.0 wt% selenium in an amount of 0.25 wt% or less.

Hereinafter will be described an embodiment of the present invention.

The present invention is based on the composition of 56-62wt% Cu-0.5-3.0wt% Bi-0.5-2.0wt% Se-0.25wt% or less of Cerium (Ce) 0.1% or less of Pb, 1.0% or less of Sn + Fe, the rest In order to check the mechanical properties of the lead-free free grinding brass, Zn% was dissolved and cast so as to have a composition as shown in the following table.

Tables 1-3 are used as comparative examples, in which sample No. 1 is a conventional 6: 4 brass and Nos. 2 and 3 are conventional lead free grinding brass C3604 and C3771. The chemical composition of the specimen was added to or subtracted from the bismuth and selenium contents according to the copper content, and the cerium was changed from 0 to 0.21%.

Examples and comparative examples of the lead-free free-cut brass alloy of the present invention was dissolved and cast in the air.

As shown in FIG. 1, in the second cast structure, bismuth-selenide is distributed at the grain boundary, and cerium is evenly distributed in the grain boundary and the mouth. The molded tissue is subjected to the process of extrusion and drawing, as shown in FIG. 2, to promote particle miniaturization, to have no segregation in the tissue, and to be dispersed evenly throughout the structure, thereby improving brittleness due to grain boundary segregation of bismuth-selenide-based materials. It can prevent grain boundary cracking and improve mechanical properties without degrading machinability.

To evaluate the machinability, the shape of the drill and cutting chips were examined using a tool dynamometer.

In Table 2, drill cutting data using a tool dynamometer are shown to show the machinability.

In Table 2, the cutting resistance at the time of drill cutting of the lead-free free-cut brass alloy of the present invention is shown as a torque value.

The test condition was a high speed steel (HSS) drill of 3.5 ψ, which was tested at a depth of 10 mm at a cutting speed of 1100 rpm.

As can be seen from the experiment, Comparative 1 sample without addition of bismuth, selenium, and selium has a torque value of 8.25, and in tests 1,2,3,4 where the bismuth-selenide is similar, 0.02 wt. % Added torque value 2.70kgf / cm, 0.10wt%, torque number 2.77kgf / cm, 0.15wt% added, # 4 torque value 2.89kgf / cm, 0.21wt% added, torque number 2.92 The lower the addition of a small amount of cerium at kgf / cm is shown to be higher machinability. In particular, Example 2 having a bismuth-selenium-celium of 2.60wt% -0.90wt% -0.06wt% shows that the cutting ability of 98% is comparable to that of the conventional free cutting brass C3604.

When the cutting property of the conventional braze-containing brass (free-cut brass) was 100%, Comparative No. 1 containing no alloying elements other than lead (Pb) was found to have a very low machinability of 32.1%, and the bismuth- Alloys using selenium-celium exhibited a machinability of at least 90% to 98%.

90% machinability can be classified as free cutting brass as the material comparable to the existing forging forging brass C3771, and the alloy with 98% cutting property of Example 2 can be classified as a material to replace the existing free cutting brass C3604. .

In the present invention, the mechanical properties obtained by the addition of celium (Ce) are as shown in Table 3 below.

In Examples 1, 2, 3, and 4, the content of bismuth-selenide remains unchanged, but hardness is 65.0 at 0.06 wt% of cerium (Ce), hardness is 66.2 at 0.10 wt% Ce, and 0.15 wt% Ce. When the hardness is 69.2 and 0.21 wt% Ce, the hardness is increased to 70.1, and the increase in hardness is proportionally increased with the increase in the amount of cerium.

It can be seen that the addition of selium maintains the machinability comparable to that of free-cut brass and the mechanical properties are significantly improved compared to the existing brazed brass.

Examples of lead leaching tests of the present invention are shown in Table 4 below.

The alloys prepared according to the examples and comparative examples in Table 1 were sampled from the casting according to the Ministry of Health and Welfare Notice No. 98-60, "Tools and Containers. Distilled water and 4% acetic acid solution were used as the leaching solution at a rate of 2 ml with respect to the surface area of 1 cm2, and the samples were immersed in the leaching solution, covered with a glass plate, and leached for 30 minutes while maintaining 95 ° C. The content was measured and the results are shown in the table.

As shown in the above table, lead (Pb) of about 0.07% used in the present invention is eluted at less than 1 ppm, which is based on the Ministry of Health and Welfare, even in distilled water and 4% acetic acid. The leaching is 3.4 ppm in distilled water and 30 ppm in 4% acetic acid solution, which is lower than the Ministry of Health and Welfare.

As described above, Pb 0.10% or less based on lead-free sulfur copper alloy 57-62wt%, Cu-0.5-3.0wt%, Bi-0.5-2.0wt%, Se-0.0-0.25wt%, Ce as basic composition Alloys with less than 1.0% Sn, Fe and Zn% remain harmless to humans due to less leaching of lead, and can be classified as lead-free copper alloys that can replace conventional copper-containing copper alloys due to their excellent machinability and mechanical properties. .

The above-mentioned brass alloy is added with cerium in the brass alloy to evenly disperse bismuth and selenium at grain boundaries to suppress bismuth selenium segregation and promote micronization of particles so that the processing surface is dense and the plating property is excellent. Leachability can be greatly reduced, and it is a lead-free free-cut brass alloy excellent in harmless high strength cutting property.

Claims (1)

From copper (Cu) -zinc (Zn) brass alloy, copper (Cu) 56-62 wt%, lead (Pb) 0.10 wt% or less, iron (Fe) + tin (Sn) 1.0 wt% secondary, bismuth (Bi) 0.5- A high strength lead-free free-cut brass alloy having a chemical composition of 3.0 wt%, selenium (Se) 0.5-2.0 wt%, and celium (Ce) 0.25 wt% or less.