US20110056591A1 - Brass alloy powder, brass alloy extruded material, and method for producing the brass alloy extruded material - Google Patents

Brass alloy powder, brass alloy extruded material, and method for producing the brass alloy extruded material Download PDF

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US20110056591A1
US20110056591A1 US12/991,259 US99125909A US2011056591A1 US 20110056591 A1 US20110056591 A1 US 20110056591A1 US 99125909 A US99125909 A US 99125909A US 2011056591 A1 US2011056591 A1 US 2011056591A1
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brass
brass alloy
phase
chromium
powder
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Katsuyoshi Kondoh
Gen Katano
Hisashi Imai
Yoshiharu Kosaka
Akimichi Kojima
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SAN-ETSU METALS Co Ltd
Japan Science and Technology Agency
Osaka University NUC
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Japan Science and Technology Agency
Osaka University NUC
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
    • B21C23/00—Extruding metal; Impact extrusion
    • B21C23/002—Extruding materials of special alloys so far as the composition of the alloy requires or permits special extruding methods of sequences
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/04—Making non-ferrous alloys by powder metallurgy
    • C22C1/0425—Copper-based alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C9/00—Alloys based on copper
    • C22C9/04—Alloys based on copper with zinc as the next major constituent
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/08—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of copper or alloys based thereon
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
    • B22F2998/10—Processes characterised by the sequence of their steps

Definitions

  • the present invention relates to high strength brass alloys, and more particularly to brass alloy powder and brass alloy extruded materials that are free of lead that is harmful to the environment and the human body.
  • 6/4 brass is not only used as mechanical parts, but also used in a wide range of applications such as gas pipes, water pipes, and valves, due to its reasonable strength, satisfactory mechanical characteristics, and nonmagnetic property.
  • the alloy composition typically includes several percent of lead in order to increase workability of 6/4 brass members. If such lead-containing brass members are used in water pipes, lead can dissolve into the water supply.
  • Leadless brass materials have been developed or under development in order to solve this problem.
  • Conventional development examples include: brass materials containing bismuth instead of lead; brass materials having y-phase precipitated by adding tin, as disclosed in Japanese Patent Publication No. 2000-309835 of unexamined applications (Patent Document 1) and International Patent Publication No. WO98/10106 (Patent Document 2); and brass materials having fine silicon particles dispersed therein.
  • the strength obtained by adding bismuth is about the same as that obtained by adding lead.
  • Bismuth and lead are both elements that reduce the strength of brass when added to brass materials, and thus do not contribute to an increase in strength of brass members.
  • the method for precipitating ⁇ -phase by adding tin as disclosed in Japanese Patent Publication No. 2000-309835 of unexamined applications (Patent Document 1) and International Patent Publication No. WO98/10106 (Patent Document 2), increases the proof stress, tensile strength, and the like of brass members, but significantly reduces deformability thereof, thereby reducing workability.
  • the method causes brittle fractures originating from the ⁇ -phase.
  • the method for dispersing fine silicon particles contributes to an increase in mechanical strength of brass alloy members, but is disadvantageous in that the machinability of the members is reduced.
  • a method for producing, based on a powder metallurgy method, a free-cutting brass alloy with graphite particles dispersed therein is disclosed in Katsuyoshi Kondoh et al., “Characteristics of Completely Leadless Free-Cutting Brass Alloy by Powder Process,” Collected Abstracts of 46th Technology Conference of Japan Copper and Brass Association (2006), pp 153-154 (Non-Patent Document 1).
  • Advantages of adding graphite are that completely leadless brass alloys can be obtained, and that graphite can be easily separated upon recycling as graphite floats on molten brass.
  • adding graphite is not expected to increase the strength of brass members.
  • techniques that improve the strength of brass members by using a powder metallurgy method should also be considered when adding graphite.
  • the low melting point metal In general, when melting a low melting point metal in a high melting point metal by heating, the low melting point metal rapidly evaporates while being melted due to its high vapor pressure, and it is difficult to control the alloy to a desired alloy composition.
  • Brass is an alloy of copper and zinc. Adding a high melting point metal to brass can be expected to increase strength. However, the boiling point of zinc is as low as 907° C., and it is not easy to add chromium having a melting point of 1,907° C., vanadium having a melting point of 1,902° C., or the like to brass. Increasing the temperature of liquid-phase brass necessarily increases the amount of evaporation of zinc, and the alloy composition rapidly changes toward a copper-rich composition.
  • Examples of a method for melting a high melting point metal include an electron beam melting method, a hydrogen plasma arc melting method, and the like. However, these methods are not suitable for mass production, and are used in small batch processing of rare metals. Moreover, these methods cannot prevent evaporation of low melting point metals.
  • Patent Document 3 discloses a method for adding an alloy component to zinc.
  • this patent publication describes that a mother alloy was used to add chromium, the Zn—Cr thermal equilibrium diagram shows that chromium is hardly solid-solved in zinc.
  • Zn 17 Cr or Zn l3 Cr as a compound is dispersed in a zinc matrix.
  • Adding this mother alloy to zinc merely increases the ratio of the zinc component, and does not cause any change in the chromium compound.
  • Techniques of adding chromium to copper are more advanced as compared to techniques of zinc-containing alloys.
  • Representative methods include methods disclosed in Japanese Patent Publications Nos. H11-209835 (Patent Document 4) and 2006-124835 (Patent Document 5) of unexamined applications.
  • chromium, zirconium, tellurium, sulfur, iron, silicon, titanium, or phosphorus is contained in copper.
  • the alloys obtained by each method are precipitation-type copper alloys, and a copper-zirconium compound or the like is precipitated as a strengthening phase.
  • these alloys can be produced even at high temperatures, which facilitates fabrication of these materials.
  • Patent Document 1 Japanese Patent Publication No. 2000-309835 of unexamined applications
  • Patent Document 2 International Patent Publication No.
  • Patent Document 3 Japanese Patent Publication No. H10-168533 of unexamined applications
  • Patent Document 4 Japanese Patent Publication No. H11-209835 of unexamined applications
  • Patent Document 5 Japanese Patent Publication No. 2006-124835 of unexamined applications
  • Non-Patent Document 1 Katsuyoshi Kondoh et al., Collected Abstracts of 46th Technology Conference of Japan Copper and Brass Association (2006), pp 153-154
  • the inventors of the present application have been developing graphite-containing brass as part of development of leadless brass alloys.
  • leadless free-cutting brass alloys having graphite particles dispersed therein have about the same strength as that of lead-containing free-cutting brass alloys, and the strength of such leadless free-cutting brass alloys is not dramatically increased.
  • Brass alloy powder according to the present invention has a brass composition formed by a mixed phase of ⁇ -phase and ( ⁇ -phase, and contains 0.5 to 5.0 mass % of chromium.
  • the chromium includes a component that is solid-solved in a mother phase of brass, and a component that is precipitated at crystal grain boundaries.
  • a brass alloy extruded material having high mechanical strength is obtained by extruding an aggregate of the brass alloy powder.
  • the chromium content needs to be 0.5 mass % or more to obtain desired mechanical strength.
  • the chromium content in the brass alloy powder can be increased in order to further increase the mechanical strength of the final brass alloy extruded material.
  • the upper limit of the chromium content is 5.0 mass % due to manufacturing reasons.
  • a more preferred chromium content is 1.0 to 2.4 mass %.
  • the chromium component forcibly solid-solved in the mother phase reduces dislocation motion in crystal, and contributes to an increase in proof stress.
  • the chromium component precipitated at the crystal grain boundaries reduces grain boundary sliding to cause extreme work hardening, and contributes to an increase in tensile strength.
  • the component that is solid-solved in the mother phase of the brass includes a component that is solid-solved and dispersed in the mother phase, and a component that is dispersed in the mother phase as precipitates.
  • the brass alloy powder may contain at least one element selected from the group consisting of nickel, manganese, zirconium, vanadium, titanium, silicon, aluminum, and tin.
  • the brass alloy powder is rapidly solidified powder, and more preferably, is powder rapidly solidified by a water atomizing method.
  • a brass alloy extruded material according to the present invention is produced by extruding an aggregate of brass alloy powder having a brass composition formed by a mixed phase of ⁇ -phase and ⁇ -phase, and containing 0.5 to 5.0 mass % of chromium, wherein the chromium includes a component that is solid-solved in a mother phase of brass, and a component that is precipitated at crystal grain boundaries.
  • the brass alloy extruded material has a 0.2% proof stress of 300 MPa or more.
  • the brass alloy extruded material has a tensile strength of 500 MPa or more.
  • the brass alloy extruded material in order to increase machinability of the brass alloy extruded material, is produced by adding 0.2 to 2.0 wt % of graphite particles to the brass alloy powder and mixing them together, and extruding the resultant mixed powder aggregate.
  • the graphite particles Preferably, have a particle size of 1 ⁇ m to 100 ⁇ m.
  • a brass alloy member according to the present invention has a brass composition formed by a mixed phase of ⁇ -phase and ⁇ -phase, contains 0.5 to 5.0 mass % of chromium, and contains at least one element selected from the group consisting of nickel, manganese, zirconium, vanadium, titanium, silicon, aluminum, and tin.
  • the chromium includes a component that is solid-solved in a mother phase of brass, and a component that is precipitated at crystal grain boundaries.
  • the brass alloy member in order to increase machinability of the brass alloy member, the brass alloy member further contains graphite particles.
  • a method for producing a brass alloy extruded material according to the present invention includes the steps of; producing, by using a rapid solidification method, brass alloy powder having a brass composition formed by a mixed phase of ⁇ -phase and ⁇ -phase, and containing 0.5 to 5.0 mass % of chromium; and extruding an aggregate of the rapidly solidified brass alloy powder.
  • the rapid solidification method is a water atomizing method.
  • a heating temperature of the extrusion process is 650° C. or less.
  • the method further includes the step of; before the extrusion process, adding 0.2 to 2.0 wt % of graphite particles to the brass alloy powder and mixing them together.
  • FIG. 1 shows scanning electron microscope (SEM) images of powders produced by a water atomizing method, where FIG. 1( a ) shows Cr-free 6/4 brass alloy powder, FIG. 1( b ) shows 6/4 brass alloy powder containing 0.5 mass % of Cr, and FIG. 1( c ) shows 6/4 brass alloy powder containing 1.0 mass % of Cr.
  • SEM scanning electron microscope
  • FIG. 2 is a graph showing the result of X-ray diffraction of the produced water atomized powders.
  • FIG. 3 is a graph showing stress-strain curves of extruded materials.
  • FIG. 4 shows optical microscope images showing the structures of extruded materials, where FIG. 4( a ) shows an extruded material formed from a compact billet of a brass alloy containing 1 mass % of Cr, FIG. 4( b ) shows an extruded material formed from a compact billet of a brass alloy containing 0.5 mass % of Cr, FIG. 4( c ) shows an extruded material formed from a compact billet of a Cr-free brass alloy, and FIG. 4( d ) shows an extruded material formed from an ingot billet of a Cr-free brass alloy.
  • FIG. 5 is an SEM image of an extruded material formed from a compact billet of a brass alloy containing 1.0 mass % of Cr.
  • FIG. 6 is a graph showing the relation between the concentration of a chromium component that is solid-solved in a mother phase of brass, and the proof stress.
  • FIG. 7 is a graph showing the relation between the amount of graphite particles added, and machinability.
  • the inventors of the present application studied methods for producing a novel high strength free-cutting brass member by increasing the strength of brass itself as a base material.
  • various additives are added as a method for increasing the strength of brass.
  • high strength brass is obtained by adding iron, aluminum, manganese, or the like to a copper-zinc alloy, and is used for ship propellers and the like due to its tensile strength as high as 460 MPa and its satisfactory corrosion resistance.
  • the high strength brass does not necessarily have high workability as its guaranteed elongation is only about 15%.
  • a water atomizing method as one of rapid solidification methods is a method for very rapidly solidifying a molten metal to produce powder, and thus is characterized not only in that a non-equilibrium phase is formed in the powder, but also in that fine crystal grains are obtained.
  • the inventors added a small amount of chromium (Cr) as a third element to a brass alloy formed by a mixed phase of ⁇ -phase and ⁇ -phase, to produce powder having different properties from those of conventional brass powder, and obtained a new material by extruding and solidifying an aggregate of this powder by a hot extrusion method.
  • Cr chromium
  • the inventors propose a new method for adding chromium as a high melting point metal to 6/4 brass.
  • the molten metal needs to be heated to the melting point of chromium, but this temperature is higher than the boiling point of zinc.
  • this temperature is higher than the boiling point of zinc.
  • Another possible method for adding chromium to brass is to use a mother alloy containing chromium.
  • a method for adding brass to a molten copper-chromium mother alloy cannot maintain a predetermined composition due to evaporation of zinc.
  • the inventors developed a method for producing a brass alloy by using a commercially available Cu-10% Cr mother alloy.
  • the mother alloy chromium is dispersed as particles with a particle size of about 10 to 50 ⁇ m, and is not solid-solved in copper.
  • This mother alloy is first melted at about 1,200° C. At this temperature, chromium contained in the mother alloy does not melt, and floats as a solid phase in a liquid phase of copper. In this state, copper is gradually added to reduce the chromium concentration.
  • the chromium concentration reaches about 4%, a single-phase state, namely a liquid phase, is established beyond the solidus and liquidus lines on the phase diagram.
  • a mixed liquid phase of chromium as a high melting point metal with copper was able to be formed in this manner.
  • a predetermined amount of zinc is added, and the mixture is rapidly solidified by a water atomizing method.
  • alloy composition control can be appropriately performed while reducing evaporation of added zinc as much as possible. It is known that, in 6/4 brass, a slight change in the amount of zinc component changes the ratio of ⁇ -phase to ⁇ -phase. It is also known that the difference in the ratio of ⁇ -phase to ⁇ -phase affects the mechanical properties of brass alloys.
  • the above powder producing method developed by the inventors is an advantageous method for adding a high melting point metal to brass, even in view of composition control of brass alloys. Further adding nickel and manganese having relatively low melting points makes the resultant powder more useful, as this powder can further increase strength.
  • a leadless free-cutting brass alloy having a high strength and an excellent free cutting property can be obtained by adding graphite to the brass alloy powder thus obtained, and extruding the graphite-containing brass alloy powder.
  • the present invention can be used in a wide range of applications, it can be said that the inventors have opened the way to development of various kinds of leadless brass having various mechanical characteristics.
  • the crystal grain size can be typically reduced by repeatedly performing plastic working and heat treatment on the workpiece.
  • the use of a powder metallurgy method as in the present invention eliminates the need for a special process for reducing the crystal grain size, as powder having a fine crystal structure is already prepared as a starting material.
  • the material composition is already determined in the powder state, the composition of a final product can be known in this stage.
  • the material of the present invention has several excellent characteristics as described below.
  • chromium is hardly solid-solved in brass.
  • a rapid solidification method such as a water atomizing method
  • chromium melted in a liquid phase state is forcibly solid-solved in a mother phase of brass only by a fixed amount.
  • the component that is solid-solved in the mother phase of brass includes a component that is solid-solved and dispersed in the mother phase, and a component that is dispersed in the mother phase as precipitates.
  • the chromium component forcibly solid-solved in the mother phase and the chromium component precipitated at the crystal grain boundaries act differently on the applied stress. That is, the chromium component forcibly solid-solved in the mother phase reduces dislocation motion in crystal, and contributes to an increase in proof stress of brass alloy members. On the other hand, the chromium component precipitated at the crystal grain boundaries reduces grain boundary sliding to cause extreme work hardening, and contributes to an increase in tensile strength.
  • manganese is basically solid-solved in brass.
  • manganese produces no grain boundary precipitate, and causes no extreme work hardening, but acts to increase the proof stress and the tensile strength in a balanced manner.
  • a possible reason for this is that manganese solid-solved in the mother phase causes dislocation pinning.
  • Nickel is also completely solid-solved in brass, but facilitates transformation from ⁇ -phase to ⁇ -phase during hot extrusion of brass alloys to form a fine ⁇ -phase in crystal, and thus greatly contributes to an increase in proof stress.
  • nickel does not contribute to work hardening, the maximum tensile stress of a nickel-containing powder extruded material is not much different than that of a nickel-free powder extruded material.
  • Chromium, manganese, and nickel are transition elements in the fourth period of the periodic table, but have different effects when added to brass as described above, and exhibit completely different behaviors. This is because these transition elements strengthen brass by different mechanisms. Thus, adding two or more kinds of elements can produce the respective effects of the elements.
  • Vanadium as a transition element in the fourth period of the periodic table has an equilibrium diagram similar to that of chromium.
  • vanadium component that is forcibly solid-solved in a mother phase
  • vanadium component that is precipitated at crystal grain boundaries
  • titanium, silicon, aluminum, tin, and the like which are commonly known as elements that strengthen brass, are also expected to effectively strengthen brass containing chromium, when added as auxiliary elements.
  • the effects of the present invention are significantly produced because producing brass alloy powder by a rapid solidification method not only produces the non-equilibrium phase and fine crystal grains, but also causes work hardening using grain boundary precipitation of chromium.
  • the inventors used a water atomizing method as an example of the rapid solidification method.
  • Water atomized powder having a 6/4 brass composition is characterized in that ⁇ -phase as a non-equilibrium phase is formed. This will be described in more detail below.
  • powder is solidified as ⁇ -phase as the region beyond the solidus and liquidus lines is a ⁇ -phase region.
  • the powder should have a mixed phase of ⁇ -phase and ⁇ -phase due to phase transformation.
  • this phase transformation hardly occurs due to a high degree of rapid solidification.
  • phase transformation from ⁇ -phase to ⁇ -phase occurs, and the powder has a mixed phase.
  • Chromium and manganese are recognized to have an effect of delaying transformation to ⁇ -phase. This is an effect of reducing atomic diffusion in crystal grains, and is highly effective in retaining a non-equilibrium phase formed by rapid solidification.
  • the grain boundary precipitates that are produced during the solidification process reduce grain boundary sliding, thereby causing a remarkable work hardening phenomenon.
  • the size of the grain boundary precipitates is controlled to about 100 nm to 500 nm (the maximum length).
  • the dispersed state of the precipitates is also an important factor, and ideally, the precipitates are uniformly dispersed in the structure.
  • base powder be homogeneous.
  • the use of an atomizing method to produce powder facilitates control of the solidification speed and the powder particle size.
  • the extrusion temperature is a very important factor to increase the strength of a brass alloy extruded material.
  • the lower the extrusion temperature the more desirable. Powder needs to be heated in order to extrude a powder aggregate. Heating the powder to a high temperature facilitates atomic diffusion, whereby the non-equilibrium phase produced by rapid solidification becomes close to a thermal equilibrium state. Thus, it is important to extrude a brass alloy powder aggregate at the lowest possible temperature for the extrusion process.
  • a preferable extrusion temperature is 650° C. or less. It is difficult to determine the lower limit of the extrusion temperature, because the lower limit temperature is determined by the size of an extrusion billet, the extrusion ratio, the maximum extrusion load of an apparatus, and the like. If extrusion at 500° C. is possible, 500° C. is an appropriate temperature for the extrusion process. In fact, however, a temperature of 550° C. or higher appears to be required to perform the extrusion process.
  • an actual extrusion temperature is determined by two factors, namely a temperature drop due to heat dissipation of the billet, and a temperature rise due to the extrusion pressure.
  • a temperature drop due to heat dissipation of the billet and a temperature rise due to the extrusion pressure.
  • it is impractical to define the extrusion temperature and it is practical to manage the heating temperature of the billet.
  • it took 48 seconds until the extrusion was started when the heating temperature of the billets was controlled to 650° C. In view of data obtained by simulation, the extrusion was started at 577° C. in this case.
  • the particle size of the graphite particles is preferably in the range of 1 ⁇ m to 100 ⁇ m.
  • the amount of chromium is preferably 0.5 mass % or more, and more preferably 1.0 mass % or more.
  • the upper limit of the chromium content is 5.0 mass %. Due to the limitations in the process of producing powder, the upper limit of the chromium concentration is 4% in a copper-chromium liquid phase state.
  • the chromium content becomes 2.4 mass % by adding zinc. It is possible to increase the chromium content by increasing the melting temperature of copper-chromium. For example, if the melting temperature is increased to 1,300° C., chromium can be melted at a concentration of up to 8%, and the chromium content becomes 5.0 mass % by adding zinc. At this temperature, however, the vapor pressure of zinc becomes too high, making composition control difficult. Thus, a more preferable upper limit of the chromium content is 2.4 mass %.
  • Vanadium is precipitated at crystal grain boundaries even if the amount thereof is very small.
  • the amount of vanadium that is added should be close to the upper limit in order to make the most of the effects of vanadium.
  • the vanadium concentration becomes 0.3 mass % by adding zinc.
  • the melting temperature needs to be increased in order to increase the vanadium concentration to a value higher than 0.3 mass %.
  • the melting temperature is increased to 1,200° C. or higher, the vapor pressure of zinc is too high, making it difficult to produce powder with an optimal composition.
  • the effect of adding vanadium is necessarily limited, and strengthening needs to be implemented by combination with other elements.
  • the strength of brass alloys can further be increased by adding manganese as an auxiliary element in combination with addition of chromium or addition of chromium and vanadium. It was verified that adding 0.5 mass % of manganese is effective enough. In conventional study examples, it is also recognized that increasing the amount of manganese significantly reduces material workability. Thus, a preferred upper limit of the amount of manganese is 7 mass % or less, which is a range in which no compound is produced. A more preferred amount of manganese is 1 to 3 mass %. If the amount of manganese exceeds this range, elongation can be reduced, and workability of brass can be reduced.
  • nickel is completely solid-solved in copper, it is possible to add any amount of nickel to a Cu—Zn—Ni material to make an alloy. Thus, in the present invention, there is no specific upper limit for the amount of nickel. Adding nickel produces a special effect of increasing only the proof stress, and the proof stress exceeding 300 Mpa can be implemented by adding 1 mass % of nickel.
  • the proof stress is more important than the tensile strength.
  • the most significant effect of the present invention is that a predetermined amount of chromium is contained in 6/4 brass, more advantages can be obtained by further adding nickel. Since chromium has a high melting point, it is not easy to add chromium even by a small amount. As described above, the thermal equilibrium state in metallurgy is used to overcome this disadvantage. Naturally, both chromium and nickel should be added in order to simultaneously produce the effects of both elements. In this case, there is an easier way to add chromium and nickel. That is, although the process as described above is performed in order to add only chromium, it is preferable that chromium and nickel be contained in a mother alloy from the beginning in order to add chromium and nickel at the same time.
  • Nickel chromium alloys are commercially available, and their melting point is 1,345° C., which is lower than the melting points of nickel and chromium. It is possible to melt this alloy and copper in a high-frequency furnace.
  • the mixing ratio of nickel to chromium is 1:1, but producing a molten metal by using the nickel-chromium mother alloy is much more easier than producing a molten metal by using a copper-chromium mother alloy.
  • a preferred upper limit of the amount of nickel is 2.4 mass % like chromium.
  • the amount of nickel can be increased by changing the mixing ratio of nickel to chromium in the mother alloy. Increasing the amount of chromium in the mother alloy sharply increases the melting point, thereby making production of powder more difficult. However, increasing the ratio of nickel does not significantly increase the melting point, and the melting point does not exceed that of nickel. Thus, it is possible to produce nickel-rich powder, and to increase the amount of nickel.
  • the upper limit of the amount of nickel is not specifically limited, but adding 5 mass % or less of nickel is desirable as this range does not degrade characteristics as brass. With the nickel content in this range, alloys having desired mechanical characteristics can be produced, and such alloys can be used in a wide range of applications.
  • the effect of adding the element is produced by adding about several percent, and at least 0.1%, of the element.
  • Appropriate amounts of the elements and combinations thereof vary depending on the desired mechanical characteristics.
  • zirconium has an effect of reducing the crystal grain size, and the effect is sufficiently recognized even if 0.1% of zirconium is added.
  • zirconium can be definitely said to be a strengthening element according to the Hall-Petch law.
  • titanium, aluminum, or the like increases the strength of the mother phase by solid solution strengthening, this effect can be produced by adding even a small amount, as small as 1% or less, of the element.
  • Silicon is an element that is commonly used for dispersion strengthening, and an appropriate amount of silicon is about 3%.
  • adding silicon does not necessarily result in strengthening, depending on other elements that are added.
  • no strengthening effect can be obtained if the precipitation sites of chromium are located at the same positions as the dispersion sites of silicon.
  • the amount of silicon to be added is limited by the amount of chromium to be added, and it is preferable that the total content of chromium and silicon is 3% or less.
  • Tin is solid-solved at about 0.3%, and has an effect as a strengthening element.
  • y-phase is formed, which causes embrittlement.
  • FIG. 1( a ) shows Cr-free 6/4 brass alloy powder
  • FIG. 1( b ) shows 6/4 brass alloy powder containing 0.5 mass % of Cr
  • FIG. 1( c ) shows 6/4 brass alloy powder having 1.0 mass % of Cr.
  • FIG. 2 shows the result of X-ray diffraction of the produced powders. Only ⁇ -phase was detected in the Cr-free brass alloy powder and the brass alloy powder containing 0.5 mass % of Cr. Two phases, namely ⁇ -phase and ⁇ -phase, were detected in the brass alloy powder containing 1.0 mass % of Cr. In the 6/4 brass composition, ⁇ -phase is formed when the brass alloy powder goes beyond the solidus and liquidus lines from the liquid phase, and the rapidly solidified powder is commonly cooled without a transformation. Detailed examination of the brass alloy powder containing 1.0 mass % of Cr showed that this brass alloy powder was in a mixed state of ⁇ -phase powder and ⁇ -phase powder.
  • the billets were extruded by heating in an electric furnace.
  • the heating electric furnace was set to four different temperatures, 650° C., 700° C., 750° C., and 780° C.
  • the billets were extruded into bars by an extruder at an extrusion speed of 3 mm/s and an extrusion ratio of 37.
  • the billets were extruded by heating in an electric furnace.
  • the heating electric furnace was set to four different temperatures, 650° C., 700° C., 750° C., and 780° C.
  • the billets were extruded into bars by an extruder at an extrusion speed of 3 mm/s and an extrusion ratio of 37.
  • the billets were extruded by heating in an electric furnace.
  • the heating electric furnace was set to four different temperatures, 650° C., 700° C., 750° C., and 780° C.
  • the billets were extruded into bars by an extruder at an extrusion speed of 3 mm/s and an extrusion ratio of 37.
  • the billets were extruded by heating in an electric furnace.
  • the heating electric furnace was set to four different temperatures, 650° C., 700° C., 750° C., and 780° C.
  • the billets were extruded into bars by an extruder at an extrusion speed of 3 mm/s and an extrusion ratio of 37.
  • Powder having a composition of 60% of Cu and 40% of Zn which was produced by a water atomizing method, was compacted at 600 MPa into extrusion billets.
  • the billets were extruded by heating in an electric furnace.
  • the heating electric furnace was set to four different temperatures, 650° C., 700° C., 750° C., and 780° C.
  • the billets were extruded into bars by an extruder at an extrusion speed of 3 mm/s and an extrusion ratio of 37.
  • Brass alloy extruded materials which were produced by extruding various billets by heating to 650° C., were compared in terms of the maximum tensile strength and the 0.2% proof stress. Table 5 shows the comparison result.
  • FIG. 3 shows stress-strain curves of the extruded materials. The following four types of billets were compared: ingot billets of Cr-free brass alloy; compact billets of Cr-free brass alloy; compact billets of brass alloy containing 0.5% of Cr; and compact billets of brass alloy containing 1.0% of Cr.
  • FIG. 4 shows the result of observing, with an optical microscope, the structures of extruded materials produced by heating billets to 650° C.
  • FIG. 4( a ) shows an extruded material formed from a compact billet of a brass alloy containing 1 mass % of Cr.
  • FIG. 4( b ) shows an extruded material formed from a compact billet of a brass alloy containing 0.5 mass % of Cr.
  • FIG. 4( c ) shows an extruded material formed from a compact billet of a Cr-free brass alloy.
  • FIG. 4( d ) shows an extruded material formed from an ingot billet of a Cr-free brass alloy.
  • the comparative observation of the images of FIG. 4 shows that the extruded materials of the compact billets have finer crystal grains than those of the extruded material of the ingot billet.
  • the extruded material of the brass alloy ingot billet has a crystal grain size of 3 to 10 ⁇ M, while the extruded material of the Cr-free brass alloy compact billet has a crystal grain size as small as 1 to 6 ⁇ m.
  • the extruded materials of the Cr-containing brass alloy compact billets have a crystal grain size of submicron to 5 ⁇ m, and thus it is recognized that the crystal grain size is further reduced in the extruded materials of the Cr-containing brass alloy compact billets.
  • FIG. 5 shows a SEM image of a compact billet of a brass alloy containing 1 mass % of Cr.
  • the present invention is also applicable to brass alloy members. That is, the brass alloy members have a brass composition formed by a mixed phase of ⁇ -phase and ⁇ -phase, contain 0.5 to 5.0 mass % of chromium, and contain at least one element selected from the group consisting of nickel, manganese, zirconium, vanadium, titanium, silicon, aluminum, and tin.
  • chromium increases the yield stress of brass alloy members.
  • a chromium component that is solid-solved and dispersed in a mother phase of brass especially contributes to the increase in yield stress.
  • Precipitates were quantified by using the result of structure analysis, and the amount of chromium solid-solved in the mother phase was calculated from the amount of chromium added.
  • FIG. 6 is a graph in which the ordinate represents the difference in yield stress between Cr-free brass alloy members, and Cr-containing brass alloy members, and the abscissa represents the concentration (%) of the chromium component solid-solved in the mother phase.
  • the yield stress increased by 34 MPa when the solid-solution amount of chromium was 0.22%, and increased by 54 MPa when the solid-solution amount of chromium was 0.35%.
  • the yield stress increases in proportion to the concentration of chromium that is solid-solved in the mother phase of brass.
  • Graphite particles used have an average particle size of 5 ⁇ m. Chromium-containing brass powder produced by a water atomizing method was mixed with the graphite particles by a mechanical stirring method. The mixed powder thus obtained was formed into compact billets by a method similar to that described above, and the compact billets were extruded into bars by a hot extrusion process. Three different amounts of graphite particles, namely 0.5 wt %, 0.75 wt %, and 1.0 wt % of graphite particles, were added to the chromium-containing brass alloy powder.
  • FIG. 7 is a graph showing the relation between the amount of graphite particles and machinability. It is recognized that the machinability is dramatically increased by adding graphite particles to the chromium-containing brass alloy powder and extruding the resultant brass alloy powder.
  • the machinability was evaluated by measuring the test time of a drilling test. Test pieces were round bars cut with a length of 5 cm, and the drilling test was conducted with a drill diameter of 4.5 mm. A load of 1.3 kgf was applied to the drill, and the rotating speed of the spindle was 900 rpm. The test was conducted ten times, and an average value of the times required for the drill to penetrate the extruded material is shown in the graph of FIG. 7 .
  • the drill did not penetrate the test pieces containing no graphite, even if the cutting process was performed for 180 seconds or longer. Since the cutting progress seemed to be stopping, the test was stopped if the drill didn't penetrate the test piece within 180 seconds.
  • the relation between the amount of graphite added and the time required for the drill to penetrate the test piece was examined.
  • the brass alloys containing 0.5% of chromium it took 180 seconds or more for the drill to penetrate the test piece when no graphite was added, but the drill penetrated the test piece in an average of 28 seconds when 0.5% of graphite was added.
  • the time required for the drill to penetrate the test piece was reduced to 20 second or less by adding 0.75% or more of graphite, and a dramatic increase in machinability was recognized.
  • adding 0.75% or more of graphite is preferable in order to significantly increase the machinability.
  • the actual measurement values are as follows. Regarding the brass alloys containing 1.0% of chromium, the proof stress was 317 MPa and the maximum tensile strength was 565 MPa when the extrusion process was performed at a normal speed (ram speed: 3 mm/s). However, the proof stress was increased to 467 MPa and the maximum tensile strength was increased to 632 MPa when the extrusion process was performed at one tenth the normal extrusion speed (ram speed: 0.3 mm/s).
  • the present invention can be advantageously used to manufacture 6/4 brass alloy members having excellent mechanical characteristics.

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US20130104349A1 (en) * 2010-07-05 2013-05-02 Yasuharu Yoshimura Copper-Zinc Alloy Product and Process for Producing Copper-Zinc Alloy Product
US20140339200A1 (en) * 2011-04-29 2014-11-20 Ki-Chul Seong Electrode wire for electro-discharge machining and method for manufacturing the same
US9803264B2 (en) * 2013-11-25 2017-10-31 Ningbo Powerway Alloy Material Co., Ltd. High-plasticity free-cutting zinc alloy
US11077495B2 (en) 2015-05-13 2021-08-03 Daihen Corporation Metal powder, method of producing additively-manufactured article, and additively-manufactured article
EP3765643A4 (fr) * 2018-03-13 2021-12-01 Mueller Industries, Inc. Procédé de métallurgie des poudres destiné à la fabrication d'alliages de laiton sans plomb
US11351607B2 (en) 2016-05-18 2022-06-07 Almag S.P.A. Method for manufacturing a lead-free or low lead content bass billet and billet thus obtained
US11459639B2 (en) 2018-03-13 2022-10-04 Mueller Industries, Inc. Powder metallurgy process for making lead free brass alloys

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IT202000004480A1 (it) * 2020-03-03 2021-09-03 A L M A G S P A Azienda Lavorazioni Metallurgiche E Affini Gnutti Processo per l’ottenimento di una billetta di ottone a ridotto tenore di piombo e billetta così ottenuta
CN111621667A (zh) * 2020-06-30 2020-09-04 兰州理工大学 一种铜钛合金及其制备方法
CN112458334A (zh) * 2020-11-27 2021-03-09 台州正兴阀门有限公司 水龙头本体铸造用低铅易切削铜合金及其制造方法

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US20130104349A1 (en) * 2010-07-05 2013-05-02 Yasuharu Yoshimura Copper-Zinc Alloy Product and Process for Producing Copper-Zinc Alloy Product
US9023272B2 (en) * 2010-07-05 2015-05-05 Ykk Corporation Copper-zinc alloy product and process for producing copper-zinc alloy product
US20140339200A1 (en) * 2011-04-29 2014-11-20 Ki-Chul Seong Electrode wire for electro-discharge machining and method for manufacturing the same
US9803264B2 (en) * 2013-11-25 2017-10-31 Ningbo Powerway Alloy Material Co., Ltd. High-plasticity free-cutting zinc alloy
US11077495B2 (en) 2015-05-13 2021-08-03 Daihen Corporation Metal powder, method of producing additively-manufactured article, and additively-manufactured article
US11351607B2 (en) 2016-05-18 2022-06-07 Almag S.P.A. Method for manufacturing a lead-free or low lead content bass billet and billet thus obtained
US11679436B2 (en) 2016-05-18 2023-06-20 Almag S.P.A. Method for manufacturing a lead-free or low lead content brass billet and billet thus obtained
EP3765643A4 (fr) * 2018-03-13 2021-12-01 Mueller Industries, Inc. Procédé de métallurgie des poudres destiné à la fabrication d'alliages de laiton sans plomb
US11440094B2 (en) 2018-03-13 2022-09-13 Mueller Industries, Inc. Powder metallurgy process for making lead free brass alloys
US11459639B2 (en) 2018-03-13 2022-10-04 Mueller Industries, Inc. Powder metallurgy process for making lead free brass alloys

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JPWO2009136552A1 (ja) 2011-09-08
CN102016089B (zh) 2012-08-22
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EP2275582A1 (fr) 2011-01-19
EP2275582A4 (fr) 2014-08-20
CN102016089A (zh) 2011-04-13

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