Leadless free-cutting copper alloy and method for producing the same

Abstract

Disclosed is a leadless free-cutting copper alloy that exhibits superior machinability, cold workability and dezincification resistance and a method for producing the same. The leadless free-cutting copper alloy comprises 56 to 77% by weight of copper (Cu), 0.1 to 3.0% by weight of manganese (Mn), 1.5 to 3.5% by weight of silicon (Si), and the balance of zinc (Zn) and other inevitable impurities, thus exhibiting superior eco-friendliness, machinability, cold workability and dezincification resistance.

Claims

1. A leadless free-cutting copper alloy comprising: 56 to 77% by weight of copper (Cu); 0.1 to 3.0% by weight of manganese (Mn); 1.5 to 3.5% by weight of silicon (Si); 0.1 to 1.5% by weight of calcium (Ca); and the balance of zinc (Zn) and other inevitable impurities.

2. The leadless free-cutting copper alloy according to claim 1, further comprising: one or more selected from the group consisting of 0.01 to 1.0% by weight of aluminum (Al), 0.01 to 1.0% by weight of tin (Sn), and 0.001 to 0.5% by weight of selenium (Se).

3. The leadless free-cutting copper alloy according to claim 1, further comprising: one or more selected from the group consisting of 0.01 to 1.0% by weight of iron (Fe), 0.001 to 1.0% by weight of zirconium (Zr), and 0.001 to 0.1% by weight of boron (B).

4. A method for producing the leadless free-cutting copper alloy according to claim 1, comprising: hot-rolling and hot-extruding the alloy by heating at a temperature of 570 to 660° C.

5. A method for producing the leadless free-cutting copper alloy according to claim 1, comprising: hot-rolling and hot-extruding the alloy by heating at a temperature of 570 to 660° C.

6. A method for producing the leadless free-cutting copper alloy according to claim 2, comprising: hot-rolling and hot-extruding the alloy by heating at a temperature of 570 to 660° C.

7. The leadless free-cutting copper alloy according to claim 1, wherein the alloy is devoid of a heavy metal.

8. The leadless free-cutting copper alloy according to claim 1, wherein the alloy is devoid of bismuth.

9. The leadless free-cutting copper alloy according to claim 1, wherein the alloy has low speed machinability.

10. The leadless free-cutting copper alloy according to claim 1, wherein the alloy is devoid of phosphorous.

11. The leadless free-cutting copper alloy according to claim 1, consisting essentially of: 56 to 77% by weight of copper (Cu); 0.1 to 3.0% by weight of manganese (Mn); 1.5 to 3.5% by weight of silicon (Si); 0.1 to 1.5% by weight of calcium (Ca); and the balance of zinc (Zn) and other inevitable impurities.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The accompanying drawings, which are included to provide a further understanding of the invention, illustrate embodiments of the invention and together with the description serve to explain the principle of the invention.

(2) In the drawings:

(3) FIG. 1 illustrates a graph showing a component range of a leadless free-cutting copper alloy according to the present invention.

(4) FIG. 2 illustrates a graph showing a maximum cold processability according to the content of manganese.

(5) FIG. 3 illustrates an image of cutting chips sorted based on fineness.

(6) FIG. 4 illustrates an image comparing the shape of chips during low-speed cutting depending on whether or not calcium is contained.

MODE FOR THE INVENTION

(7) The leadless free-cutting copper alloy according to the present invention comprises: 56 to 77% by weight of copper (Cu); 0.1 to 3.0% by weight of manganese (Mn); 1.5 to 3.5% by weight of silicon (Si); and the balance of zinc (Zn) and other inevitable impurities.

(8) When the content of copper (Cu) is lower than 56% by weight, beta-phase is excessively produced and hot processing is advantageous, but cold processability is deteriorated, brittleness is increased, and dezincification corrosion actively occurs, and when the content is higher than 77% by weight, raw material costs increase, formation of beta-phase and gamma-phase is insufficient, and machinability and hot processability cannot be sufficiently secured.

(9) When the content of manganese (Mn) is lower than 0.1% by weight, increase of hardness is insufficient, formation of Mn—Si intermetallic compound is difficult, machinability is little improved, and there is almost no prevention effect of dezincification corrosion. The cold workability caused by addition of manganese is improved, since crystalline-based Cu—Zn—Si compound is dispersed by formation of Mn—Si intermetallic compound. When the content of manganese is lower than 0.1% by weight, there it almost no effect of improvement in cold workability. Also, when the content of manganese is higher than 3.0% by weight, machinability is decreased, oxides are increased during casting, casting is inhibited and formation of normal ingots is thus difficult.

(10) When the content of silicon (Si) is lower than 1.5% by weight, the cutting properties of the Mn—Si intermetallic compound are insufficient, and when the content is higher than 3.5% by weight, a Mn—Si intermetallic compound is grown and present, dispersion by hot processing is relatively difficult and improvement of machinability reaches a critical level.

(11) When the content of zinc (Zn) is lower than 16.5% by weight, the content of copper (Cu), as a raw material, increases, production costs increase, discoloration and corrosion resistance are decreased due to surface oxidation, and when the content of zinc is higher than 42.4% by weight, the hardness and strength of material are excessively increased, brittleness is induced during cold processing and industrial application is difficult.

(12) Also, the leadless free-cutting copper alloy according to the present invention further comprises 0.1 to 1.5% by weight of calcium (Ca) to improve low-speed machinability, in addition to the alloy of the first invention.

(13) When the content of calcium (Ca) is lower than 0.1% by weight, formation of Cu—Ca compound having machinability is insufficient and improvement of machinability is insufficient, and when the content is higher than 1.5% by weight, casting property is deteriorated due to oxides increased during dissolution, it is difficult to obtain a normal ingot, and cracks are generated during hot processing due to production of low-melting point compound such as Ca.sub.2Cu.

(14) Meanwhile, the leadless free-cutting copper alloy according to the present invention is characterized in that at least one of 0.01 to 1.0% by weight of aluminum (Al), 0.01 to 1.0% by weight of tin (Sn), and 0.001 to 0.5% by weight of selenium (Se) to improve machinability is added to the first invention and the second invention, respectively.

(15) When the content of aluminum (Al) is lower than 0.01% by weight, improvement of machinability is insufficient due to addition of aluminum, and when the content is higher than 1.0% by weight, the hardness of the produced copper alloy is excessively increased, brittleness is increased and cracks may thus be induced during cold processing.

(16) When the content of tin (Sn) is lower than 0.01% by weight, improvement of machinability is insufficient due to the addition of tin, and when the content is higher than 1.0% by weight, the cost of raw materials is increased, dispersion of the compound produced in the structure is not effective, relative to the amount of added compound and improvement of machinability is thus limited.

(17) When the content of selenium (Se) is lower than 0.001% by weight, there is no effect of cutting breaker and improvement of machinability is insufficient, and when the content is higher than 0.5% by weight, the cost of raw materials increases, and improvement of machinability, relative to the addition amount is thus limited.

(18) Also, the leadless free-cutting copper alloy according to the present invention is characterized in that at least one of 0.01 to 1.0% by weight of aluminum (Al), 0.01 to 1.0% by weight of tin (Sn), and 0.001 to 0.5% by weight of selenium (Se) is added to the first invention, the second invention and the third invention, respectively, in order to make the alloy structure fine, disperse the intermetallic compound and thereby further improve machinability.

(19) When the content of iron (Fe) is lower than 0.01% by weight, structure fineness effect is low, and when the content is higher than 1.0% by weight, the fineness of the structure is limited and corrosion properties may be deteriorated.

(20) When the content of zirconium (Zr) is lower than 0.001% by weight, the effect of structure fineness is low, and when the content is higher than 1.0% by weight, the cost of raw materials is excessively high, oxides are excessively produced, casting property is deteriorated and production of normal ingot is difficult.

(21) When the content of boron (B) is lower than 0.001% by weight, the effect of structure fineness is low and, when the content is higher than 0.1% by weight, structure fineness is limited.

(22) In the present invention, phosphorous (P) contributes to the fineness of structure, serves as a deoxidizer and thus improves flowability of molten metal. However, when the content is lower than 0.01% by weight, there is almost no effect of structure fineness, and when the content is higher than 0.3% by weight, structure fineness is limited and hot processability is deteriorated. Also, in the copper alloy according to the second invention, preferably, phosphorous (P) is not used since it reacts with calcium (Ca) to form calcium phosphate, which decreases the content of calcium in the base material.

(23) Meanwhile, a method for producing the leadless free-cutting copper alloy according to the present invention, in particular, a method for obtaining a hot-processing material having a fine structure in order to improve machinability of the alloy of the first invention to the fourth invention, respectively, is characterized in that hot rolling and hot extrusion processes are performed at a temperature of 570 to 660° C. More specifically, the method comprises obtaining an ingot from the alloy according to the first invention, the second invention, the third invention or the fourth invention, obtaining a hot-processed material using the obtained ingot, obtaining a cold-processed material using the obtained hot-processed material and optionally hot-forging.

(24) The obtaining the ingot is carried out by melting the alloy component at a temperature of 1,000° C. or less to produce a molten metal, allowing to stand for 20 minutes and casting. Since the component of copper alloy according to the present invention contains a great amount of oxides, it is important to secure a normal ingot using low-speed casting and other casting methods.

(25) The obtaining the hot-processed material is carried out by cutting the ingot into a predetermined length, primarily heating the ingot in a gas furnace at 400 to 600° C. for 1 to 10 hours to homogenize the ingot structure, secondarily heating the ingot in an electric induction furnace at 570 to 660° C. for 5 minutes or shorter, and immediately performing hot extrusion. The hot extrusion speed is controlled to 6 to 20 mpm according to secondary heating temperature and the pressure generated during extrusion. The structure of hot-processed material becomes finer, as hot-processing temperature decreases.

(26) When the temperature of hot extrusion is lower than 570° C., the pressure generated during extrusion is excessively high, extrusion speed cannot be increased and production efficiency is thus deteriorated, and when the temperature exceeds 660° C., it is difficult to obtain fine particles and, disadvantageously, direct extruder-type equipment further induces piping defects.

(27) The obtaining the cold-processed material from the obtained hot-processed material is carried out by cold processing using a drawer to have the desired diameter and tolerance using the obtained hot-processed material and securing straightness using a straightening machine.

(28) The cold-processed material thus obtained is optionally subjected to hot forging. At this time, the heating of the material during hot forging is preferably carried out at a temperature of 600 to 800° C. within 30 minutes. Immediately after heating is completed, hot forging is performed. When heating temperature during hot forging is lower than 600° C., forge property is deteriorated and the desired shape cannot be obtained when the shape is complicated, and when the heating temperature exceeds 800° C., machinability of the forged produced may be inhibited during post processing. The post process may include other processes such as processing and plating that is suitable for the requirement properties of the products.

(29) Hereinafter, the present invention will be described with reference to Examples along with tables and drawings in detail.

(30) Table 1 illustrates Examples of the present invention. The specimens of examples are produced by casting and hot rolling. The characteristics of specimens of respective Examples are expressed based on evaluation of machinability, dezincification depth and cold workability. A detailed method is described with reference to Example 1.

(31) In order to produce a specimen of Example 1, 680 g of copper (Cu), 304 g of zinc (Zn), 15 g of silicon (Si), and 1 g of manganese (Mn) were mixed, and the mixture was added to a graphite crucible, and melted using a high frequency induction furnace. The obtained molten metal was cast into a graphite mold with a thickness of 20 mm, a width 50 mm and a length 150 mm, to obtain an ingot having a length of about 125 mm. The ingot was pre-heated at 650° C. in a box furnace for one hour, and hot-rolled at a draft percentage of about 50% using a two high mill.

(32) Regarding specimen hardness, the specimen hardness was measured by applying a load of 10 kg to the specimen using a Vickers hardness tester.

(33) Regarding alloy machinability, behaviors of cutting chips observed during dipping were compared using a machinability tester, the cutting chips were classified based on fineness, and the hot rolled specimens were expressed as 10 kinds of cutting numbers (Chip No.)

(34) As the cutting chip has a smaller cutting number, it becomes finer. During cutting, the cutting tip has a size of Φ9.5 mm, a rotation speed of 750 RPM, a movement speed of 70 mm/min, a movement distance of 7 mm, and a gravity direction as a movement direction.

(35) The alloy dezincification depth is represented as a dezincification corrosion depth measured in accordance with KSD ISO 6509 (corrosion test of metals and alloys—dezincification corrosion of brass).

(36) The cold workability of alloy was obtained by heating ingot specimens of Examples 1-13 to 1-20 at 650° C. for 90 minutes, hot rolling at a draft percentage of about 50%, water-cooling, and measuring a cold-draft percentage until cracking occurs during cold-rolling. As cold-draft percentage increases, cold workability is improved.

(37) FIG. 1 is a graph showing a component region of copper alloy according to the present invention. The alloy of present invention contains manganese (Mn), calcium (Ca) and other additional alloy elements, in addition to a conventional copper alloy, and is thus different from a component region of the conventional copper alloy.

(38) TABLE-US-00001 TABLE 1 Cold draft Dezincification Alloy components Hardness percentage Depth Chip Cu Zn Si Mn (Hv) (%) (μm) No. Examples 1-1 68 Bal. 1.5 0.1 102 106 9 of the 1-2 68 Bal. 2.5 0.1 128 104 7 first 1-3 68 Bal. 3.5 0.1 149 71 3 invention 1-4 68 Bal. 1.5 1.0 155 62 7 1-5 68 Bal. 2.5 1.0 160 60 5 1-6 68 Bal. 3.5 1.0 182 38 2 1-7 68 Bal. 1.5 2.0 137 44 6 1-8 68 Bal. 2.5 2.0 178 28 4 1-9 68 Bal. 3.5 2.0 194 24 3 1-10 68 Bal. 1.5 3.0 157 21 4 1-11 68 Bal. 2.5 3.0 188 20 2 1-12 68 Bal. 3.5 3.0 196 18 2 1-13 68 Bal. 2.5 0.1 128 14 104 7 1-14 68 Bal. 2.5 0.5 149 21 77 6 1-15 68 Bal. 2.5 1.0 160 28 60 5 1-16 68 Bal. 2.5 1.5 171 30 49 4 1-17 68 Bal. 2.5 2.0 178 33 28 4 1-18 68 Bal. 2.5 2.5 182 36 27 3 1-19 68 Bal. 2.5 3.0 188 37 20 2 1-20 68 Bal. 2.5 3.5 201 38 18 3 Bal.: Balance

(39) As can be seen from Examples 1-13 to 1-20 of Table 1 above, as the content of manganese (Mn) increases from 0.1% by weight to 3.5% by weight, cold draft percentage (%) increases. The results thus obtained are shown in the graph of FIG. 2.

(40) As can be seen from Table 1, as the contents of silicon (Si) and manganese (Mn) in the copper alloy increase, hardness (Hv) increases, and the chip number of cutting chips decreases. The cutting chips of respective Examples are expressed as Chip No. that is classified based on fineness shown in Tables 1 to 4, and the image of cutting chips corresponding to Chip No. is shown in FIG. 3. As the Chip. No. of FIG. 3 becomes smaller, the cutting chips are finer. The segmentation was almost not observed in chips having Chip No. 10 of FIG. 3 containing copper (Cu) and zinc (Zn) alone. Chip No. 9 is a case in which chips are rolled in a longitudinal direction, but segmentation is observed. Chip No. 8 is a case in which chips are rolled in a short section, but segmentation periodically occurs. Chip No. 7 is a case in which rolling of chips is reduced in the form of a funnel and the cycle of segmentation is shortened. Chip No. 6 is a case in which the shape of chips is changed from funnel to fan and the size of chips is thus decreased. Chip No. 5 is a case in which segmented fan-shaped chips are self-rolled. Chip No. 4 is a case in which the fan-shaped chips are more finely segmented in an early stage. Chip No. 3 is a case in which fan-shaped chips are generated along with finely segmented chips. Chip No. 2 is a case in which fan-shaped chips completely disappear and only finer segmented chips are generated. Chip No. 1 is a case in which cutting chips have a linear shape and are considerably fine.

(41) As can be seen from dezincification depths of Examples 1-1 to 1-12 of Table 1 above, as contents of silicon (Si) and manganese (Mn) increase, dezincification depth decreases. This means that silicon and manganese improve dezincification resistance.

(42) TABLE-US-00002 TABLE 2 Dezincification Alloy components Hardness depth Chip Cu Zn Si Mn Ca (Hv) (μm) No. Examples 2-1 68 Bal. 2.5 1.0 0.1 161 68 5 of the second 2-2 68 Bal. 2.5 1.0 0.5 165 72 2 invention 2-3 68 Bal. 2.5 1.0 1.0 168 75 1 2-4 68 Bal. 2.5 1.0 1.5 171 90 1 2-5 68 Bal. 2.5 0.5 0.1 149 78 4 2-6 68 Bal. 2.5 0.5 0.5 152 83 2 2-7 68 Bal. 2.5 0.5 1.0 159 89 1 2-8 68 Bal. 2.5 0.5 1.5 168 101 1 2-9 68 Bal. 2.5 0.1 0.1 112 110 6 2-10 68 Bal. 2.5 0.1 0.5 129 116 3 2-11 68 Bal. 2.5 0.1 1.0 138 123 2 2-12 68 Bal. 2.5 0.1 1.5 144 124 1

(43) Also, as can be seen from Table 2, as calcium (Ca) is added, hardness increases and Chip No. decreases. The addition of calcium improves high-speed cutting properties of copper alloy according to the first invention and enhances low low-speed cutting properties. In Table 2, as a result of comparison of low-speed cutting chip behaviors of copper alloys containing the components shown in Examples 1-5 to 2-3, the cutting chips of copper alloys further containing calcium are finely segmented. That is, machinability is further improved. The compared cutting chip behaviors are shown in FIG. 4. Here, high-speed cutting refers to a cutting process in which a drill tip having a diameter of Φ9.5 mm that rotates at a speed of 750 RPM is cut in a gravity direction at a speed of 70 mm/min. Low-speed cutting refers to a cutting process performed under the same conditions as the high-speed cutting, except that the movement speed of the drill tip in a gravity direction is 8 mm/min.

(44) Also, as can be seen from dezincification depth values of Examples 2-1 to 2-12 of Table 2, as the content of calcium (Ca) increases, dezincification depth increases. Accordingly, this means that calcium decreases dezincification resistance.

(45) TABLE-US-00003 TABLE 3 dezincification Alloy components hardness depth Chip Cu Zn Si Mn Ca Al Sn Se (Hv) (μm) No. Examples 3-1 68 Bal. 2.5 1.0 0.01 162 5 of the 3-2 68 Bal. 2.5 1.0 0.5 171 48 4 third 3-3 68 Bal. 2.5 1.0 1.0 188 3 invention 3-4 68 Bal. 2.5 1.0 0.5 0.5 177 1 3-5 68 Bal. 2.5 1.0 0.01 157 3 3-6 68 Bal. 2.5 1.0 0.5 162 51 2 3-7 68 Bal. 2.5 1.0 1.0 171 2 3-8 68 Bal. 2.5 1.0 0.5 0.5 166 1 3-9 68 Bal. 2.5 1.0 0.001 160 2 3-10 68 Bal. 2.5 1.0 0.1 161 1 3-11 68 Bal. 2.5 1.0 0.5 163 68 1 3-12 68 Bal. 2.5 1.0 0.5 0.1 162 1

(46) TABLE-US-00004 TABLE 4 Dezincification Alloy components Hardness Depth Chip Cu Zn Si Mn Ca Fe P Zr B (Hv) (μm) No. Examples 4-1 68 Bal. 2.5 1.0 0.01 163 4 of the fourth 4-2 68 Bal. 2.5 1.0 0.5 167 64 3 invention 4-3 68 Bal. 2.5 1.0 1.0 176 3 4-4 68 Bal. 2.5 1.0 0.5 0.5 169 1 4-5 68 Bal. 2.5 1.0 0.01 161 4 4-6 68 Bal. 2.5 1.0 0.1 162 61 3 4-7 68 Bal. 2.5 1.0 0.3 166 2 4-8 68 Bal. 2.5 1.0 0.001 159 3 4-9 68 Bal. 2.5 1.0 0.5 168 58 2 4-10 68 Bal. 2.5 1.0 1.0 186 2 4-11 68 Bal. 2.5 1.0 0.5 0.5 171 1 4-12 68 Bal. 2.5 1.0 0.001 162 5 4-13 68 Bal. 2.5 1.0 0.05 165 61 3 4-14 68 Bal. 2.5 1.0 0.1 171 2 4-15 68 Bal. 2.5 1.0 0.5 0.05 170 1

(47) As can be seen from Tables 3 and 4, the copper alloy according to the first invention and the copper alloy according to the second invention further comprise any one of aluminum (Al), tin (Sn) and selenium (Se), or any one of iron (Fe), phosphorous (P), zirconium (Zr) and boron (B), thus improving hardness, decreasing Chip No. of cutting chips and thus making the cutting chips finer.

(48) Also, as can be seen from dezincification depths of Tables 3 and 4, as aluminum (Al) and tin (Sn) are added, dezincification depth is decreased, addition of selenium (Se) and iron (Fe) slightly increases dezincification depth, and phosphorous (P), zirconium (Zr), and boron (B) have almost no influence on dezincification depth.

(49) TABLE-US-00005 TABLE 5 Hardness Hot- of hot pressing Particle Alloy components extrusion temperature size Chip Cu Zn Si Mn (Hv) (° C.) (μm) No. Examples 5-1 68 Bal. 2.5 1.0 168 570 10 3 of the 5-2 68 Bal. 2.5 1.0 160 600 15 4 fifth 5-3 68 Bal. 2.5 1.0 145 630 35 6 invention 5-4 68 Bal. 2.5 1.0 130 660 60 7

(50) As can be seen from Examples 5-1 to 5-4 of Table 5 above, as hot extrusion temperature is increased from 570 to 660° C., hardness of hot extrude material is slightly decreased, particles of structure increase, and Chip No. of cutting chips is also increased. Based on these behaviors, a range of the hot-extrusion temperature required for maintaining machinability of the invented alloy is set to 570 to 660° C.

(51) As apparent from the fore-going, the leadless free-cutting copper alloy according to the present invention exhibits superior machinability and dezincification resistance and excellent cold workability, thus is useful as a leadless free-cutting copper alloy that is harmless to human health and is suitable for various industry applications.

(52) It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.